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Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-21) exists of draft-ietf-quic-qpack-12 == Outdated reference: draft-ietf-quic-transport has been published as RFC 9000 -- Duplicate reference: RFC7838, mentioned in 'RFC7838', was also mentioned in 'ALTSVC'. ** Downref: Normative reference to an Historic RFC: RFC 8164 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 QUIC M. Bishop, Ed. 3 Internet-Draft Akamai 4 Intended status: Standards Track 22 January 2020 5 Expires: 25 July 2020 7 Hypertext Transfer Protocol Version 3 (HTTP/3) 8 draft-ietf-quic-http-25 10 Abstract 12 The QUIC transport protocol has several features that are desirable 13 in a transport for HTTP, such as stream multiplexing, per-stream flow 14 control, and low-latency connection establishment. This document 15 describes a mapping of HTTP semantics over QUIC. This document also 16 identifies HTTP/2 features that are subsumed by QUIC, and describes 17 how HTTP/2 extensions can be ported to HTTP/3. 19 Note to Readers 21 Discussion of this draft takes place on the QUIC working group 22 mailing list (quic@ietf.org), which is archived at 23 https://mailarchive.ietf.org/arch/search/?email_list=quic 24 (https://mailarchive.ietf.org/arch/search/?email_list=quic). 26 Working Group information can be found at https://github.com/quicwg 27 (https://github.com/quicwg); source code and issues list for this 28 draft can be found at https://github.com/quicwg/base-drafts/labels/- 29 http (https://github.com/quicwg/base-drafts/labels/-http). 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on 25 July 2020. 48 Copyright Notice 50 Copyright (c) 2020 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 55 license-info) in effect on the date of publication of this document. 56 Please review these documents carefully, as they describe your rights 57 and restrictions with respect to this document. Code Components 58 extracted from this document must include Simplified BSD License text 59 as described in Section 4.e of the Trust Legal Provisions and are 60 provided without warranty as described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 65 1.1. Prior versions of HTTP . . . . . . . . . . . . . . . . . 4 66 1.2. Delegation to QUIC . . . . . . . . . . . . . . . . . . . 5 67 2. HTTP/3 Protocol Overview . . . . . . . . . . . . . . . . . . 5 68 2.1. Document Organization . . . . . . . . . . . . . . . . . . 6 69 2.2. Conventions and Terminology . . . . . . . . . . . . . . . 7 70 3. Connection Setup and Management . . . . . . . . . . . . . . . 8 71 3.1. Draft Version Identification . . . . . . . . . . . . . . 8 72 3.2. Discovering an HTTP/3 Endpoint . . . . . . . . . . . . . 8 73 3.3. Connection Establishment . . . . . . . . . . . . . . . . 9 74 3.4. Connection Reuse . . . . . . . . . . . . . . . . . . . . 9 75 4. HTTP Request Lifecycle . . . . . . . . . . . . . . . . . . . 10 76 4.1. HTTP Message Exchanges . . . . . . . . . . . . . . . . . 10 77 4.1.1. Header Formatting and Compression . . . . . . . . . . 12 78 4.1.2. Request Cancellation and Rejection . . . . . . . . . 13 79 4.1.3. Malformed Requests and Responses . . . . . . . . . . 14 80 4.2. The CONNECT Method . . . . . . . . . . . . . . . . . . . 14 81 4.3. HTTP Upgrade . . . . . . . . . . . . . . . . . . . . . . 15 82 4.4. Server Push . . . . . . . . . . . . . . . . . . . . . . . 15 83 5. Connection Closure . . . . . . . . . . . . . . . . . . . . . 17 84 5.1. Idle Connections . . . . . . . . . . . . . . . . . . . . 17 85 5.2. Connection Shutdown . . . . . . . . . . . . . . . . . . . 17 86 5.3. Immediate Application Closure . . . . . . . . . . . . . . 19 87 5.4. Transport Closure . . . . . . . . . . . . . . . . . . . . 19 88 6. Stream Mapping and Usage . . . . . . . . . . . . . . . . . . 19 89 6.1. Bidirectional Streams . . . . . . . . . . . . . . . . . . 20 90 6.2. Unidirectional Streams . . . . . . . . . . . . . . . . . 20 91 6.2.1. Control Streams . . . . . . . . . . . . . . . . . . . 22 92 6.2.2. Push Streams . . . . . . . . . . . . . . . . . . . . 22 93 6.2.3. Reserved Stream Types . . . . . . . . . . . . . . . . 23 94 7. HTTP Framing Layer . . . . . . . . . . . . . . . . . . . . . 23 95 7.1. Frame Layout . . . . . . . . . . . . . . . . . . . . . . 24 96 7.2. Frame Definitions . . . . . . . . . . . . . . . . . . . . 25 97 7.2.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . 25 98 7.2.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . 26 99 7.2.3. CANCEL_PUSH . . . . . . . . . . . . . . . . . . . . . 26 100 7.2.4. SETTINGS . . . . . . . . . . . . . . . . . . . . . . 27 101 7.2.5. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . 30 102 7.2.6. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . 31 103 7.2.7. MAX_PUSH_ID . . . . . . . . . . . . . . . . . . . . . 32 104 7.2.8. DUPLICATE_PUSH . . . . . . . . . . . . . . . . . . . 32 105 7.2.9. Reserved Frame Types . . . . . . . . . . . . . . . . 33 106 8. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 34 107 8.1. HTTP/3 Error Codes . . . . . . . . . . . . . . . . . . . 34 108 9. Extensions to HTTP/3 . . . . . . . . . . . . . . . . . . . . 35 109 10. Security Considerations . . . . . . . . . . . . . . . . . . . 36 110 10.1. Traffic Analysis . . . . . . . . . . . . . . . . . . . . 37 111 10.2. Frame Parsing . . . . . . . . . . . . . . . . . . . . . 37 112 10.3. Early Data . . . . . . . . . . . . . . . . . . . . . . . 37 113 10.4. Migration . . . . . . . . . . . . . . . . . . . . . . . 37 114 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 115 11.1. Registration of HTTP/3 Identification String . . . . . . 37 116 11.2. New Registries . . . . . . . . . . . . . . . . . . . . . 38 117 11.2.1. Frame Types . . . . . . . . . . . . . . . . . . . . 38 118 11.2.2. Settings Parameters . . . . . . . . . . . . . . . . 39 119 11.2.3. Error Codes . . . . . . . . . . . . . . . . . . . . 40 120 11.2.4. Stream Types . . . . . . . . . . . . . . . . . . . . 43 121 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 122 12.1. Normative References . . . . . . . . . . . . . . . . . . 43 123 12.2. Informative References . . . . . . . . . . . . . . . . . 45 124 Appendix A. Considerations for Transitioning from HTTP/2 . . . . 46 125 A.1. Streams . . . . . . . . . . . . . . . . . . . . . . . . . 46 126 A.2. HTTP Frame Types . . . . . . . . . . . . . . . . . . . . 47 127 A.2.1. Prioritization Differences . . . . . . . . . . . . . 47 128 A.2.2. Header Compression Differences . . . . . . . . . . . 47 129 A.2.3. Guidance for New Frame Type Definitions . . . . . . . 48 130 A.2.4. Mapping Between HTTP/2 and HTTP/3 Frame Types . . . . 48 131 A.3. HTTP/2 SETTINGS Parameters . . . . . . . . . . . . . . . 49 132 A.4. HTTP/2 Error Codes . . . . . . . . . . . . . . . . . . . 50 133 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 51 134 B.1. Since draft-ietf-quic-http-24 . . . . . . . . . . . . . . 51 135 B.2. Since draft-ietf-quic-http-23 . . . . . . . . . . . . . . 51 136 B.3. Since draft-ietf-quic-http-22 . . . . . . . . . . . . . . 52 137 B.4. Since draft-ietf-quic-http-21 . . . . . . . . . . . . . . 53 138 B.5. Since draft-ietf-quic-http-20 . . . . . . . . . . . . . . 53 139 B.6. Since draft-ietf-quic-http-19 . . . . . . . . . . . . . . 54 140 B.7. Since draft-ietf-quic-http-18 . . . . . . . . . . . . . . 54 141 B.8. Since draft-ietf-quic-http-17 . . . . . . . . . . . . . . 54 142 B.9. Since draft-ietf-quic-http-16 . . . . . . . . . . . . . . 54 143 B.10. Since draft-ietf-quic-http-15 . . . . . . . . . . . . . . 55 144 B.11. Since draft-ietf-quic-http-14 . . . . . . . . . . . . . . 55 145 B.12. Since draft-ietf-quic-http-13 . . . . . . . . . . . . . . 55 146 B.13. Since draft-ietf-quic-http-12 . . . . . . . . . . . . . . 55 147 B.14. Since draft-ietf-quic-http-11 . . . . . . . . . . . . . . 56 148 B.15. Since draft-ietf-quic-http-10 . . . . . . . . . . . . . . 56 149 B.16. Since draft-ietf-quic-http-09 . . . . . . . . . . . . . . 56 150 B.17. Since draft-ietf-quic-http-08 . . . . . . . . . . . . . . 56 151 B.18. Since draft-ietf-quic-http-07 . . . . . . . . . . . . . . 56 152 B.19. Since draft-ietf-quic-http-06 . . . . . . . . . . . . . . 56 153 B.20. Since draft-ietf-quic-http-05 . . . . . . . . . . . . . . 57 154 B.21. Since draft-ietf-quic-http-04 . . . . . . . . . . . . . . 57 155 B.22. Since draft-ietf-quic-http-03 . . . . . . . . . . . . . . 57 156 B.23. Since draft-ietf-quic-http-02 . . . . . . . . . . . . . . 57 157 B.24. Since draft-ietf-quic-http-01 . . . . . . . . . . . . . . 57 158 B.25. Since draft-ietf-quic-http-00 . . . . . . . . . . . . . . 58 159 B.26. Since draft-shade-quic-http2-mapping-00 . . . . . . . . . 58 160 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 58 161 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 58 163 1. Introduction 165 HTTP semantics are used for a broad range of services on the 166 Internet. These semantics have commonly been used with two different 167 TCP mappings, HTTP/1.1 and HTTP/2. HTTP/3 supports the same 168 semantics over a new transport protocol, QUIC. 170 1.1. Prior versions of HTTP 172 HTTP/1.1 is a TCP mapping which uses whitespace-delimited text fields 173 to convey HTTP messages. While these exchanges are human-readable, 174 using whitespace for message formatting leads to parsing difficulties 175 and workarounds to be tolerant of variant behavior. Because each 176 connection can transfer only a single HTTP request or response at a 177 time in each direction, multiple parallel TCP connections are often 178 used, reducing the ability of the congestion controller to accurately 179 manage traffic between endpoints. 181 HTTP/2 introduced a binary framing and multiplexing layer to improve 182 latency without modifying the transport layer. However, because the 183 parallel nature of HTTP/2's multiplexing is not visible to TCP's loss 184 recovery mechanisms, a lost or reordered packet causes all active 185 transactions to experience a stall regardless of whether that 186 transaction was impacted by the lost packet. 188 1.2. Delegation to QUIC 190 The QUIC transport protocol incorporates stream multiplexing and per- 191 stream flow control, similar to that provided by the HTTP/2 framing 192 layer. By providing reliability at the stream level and congestion 193 control across the entire connection, it has the capability to 194 improve the performance of HTTP compared to a TCP mapping. QUIC also 195 incorporates TLS 1.3 at the transport layer, offering comparable 196 security to running TLS over TCP, with the improved connection setup 197 latency of TCP Fast Open [RFC7413]. 199 This document defines a mapping of HTTP semantics over the QUIC 200 transport protocol, drawing heavily on the design of HTTP/2. While 201 delegating stream lifetime and flow control issues to QUIC, a similar 202 binary framing is used on each stream. Some HTTP/2 features are 203 subsumed by QUIC, while other features are implemented atop QUIC. 205 QUIC is described in [QUIC-TRANSPORT]. For a full description of 206 HTTP/2, see [HTTP2]. 208 2. HTTP/3 Protocol Overview 210 HTTP/3 provides a transport for HTTP semantics using the QUIC 211 transport protocol and an internal framing layer similar to HTTP/2. 213 Once a client knows that an HTTP/3 server exists at a certain 214 endpoint, it opens a QUIC connection. QUIC provides protocol 215 negotiation, stream-based multiplexing, and flow control. An HTTP/3 216 endpoint can be discovered using HTTP Alternative Services; this 217 process is described in greater detail in Section 3.2. 219 Within each stream, the basic unit of HTTP/3 communication is a frame 220 (Section 7.2). Each frame type serves a different purpose. For 221 example, HEADERS and DATA frames form the basis of HTTP requests and 222 responses (Section 4.1). 224 Multiplexing of requests is performed using the QUIC stream 225 abstraction, described in Section 2 of [QUIC-TRANSPORT]. Each 226 request-response pair consumes a single QUIC stream. Streams are 227 independent of each other, so one stream that is blocked or suffers 228 packet loss does not prevent progress on other streams. 230 Server push is an interaction mode introduced in HTTP/2 [HTTP2] which 231 permits a server to push a request-response exchange to a client in 232 anticipation of the client making the indicated request. This trades 233 off network usage against a potential latency gain. Several HTTP/3 234 frames are used to manage server push, such as PUSH_PROMISE, 235 DUPLICATE_PUSH, MAX_PUSH_ID, and CANCEL_PUSH. 237 As in HTTP/2, request and response headers are compressed for 238 transmission. Because HPACK [HPACK] relies on in-order transmission 239 of compressed header blocks (a guarantee not provided by QUIC), 240 HTTP/3 replaces HPACK with QPACK [QPACK]. QPACK uses separate 241 unidirectional streams to modify and track header table state, while 242 header blocks refer to the state of the table without modifying it. 244 2.1. Document Organization 246 The following sections provide a detailed overview of the connection 247 lifecycle and key concepts: 249 * Connection Setup and Management (Section 3) covers how an HTTP/3 250 endpoint is discovered and a connection is established. 252 * HTTP Request Lifecycle (Section 4) describes how HTTP semantics 253 are expressed using frames. 255 * Connection Closure (Section 5) describes how connections are 256 terminated, either gracefully or abruptly. 258 The details of the wire protocol and interactions with the transport 259 are described in subsequent sections: 261 * Stream Mapping and Usage (Section 6) describes the way QUIC 262 streams are used. 264 * HTTP Framing Layer (Section 7) describes the frames used on most 265 streams. 267 * Error Handling (Section 8) describes how error conditions are 268 handled and expressed, either on a particular stream or for the 269 connection as a whole. 271 Additional resources are provided in the final sections: 273 * Extensions to HTTP/3 (Section 9) describes how new capabilities 274 can be added in future documents. 276 * A more detailed comparison between HTTP/2 and HTTP/3 can be found 277 in Appendix A. 279 2.2. Conventions and Terminology 281 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 282 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 283 "OPTIONAL" in this document are to be interpreted as described in BCP 284 14 [RFC2119] [RFC8174] when, and only when, they appear in all 285 capitals, as shown here. 287 Field definitions are given in Augmented Backus-Naur Form (ABNF), as 288 defined in [RFC5234]. 290 This document uses the variable-length integer encoding from 291 [QUIC-TRANSPORT]. 293 The following terms are used: 295 abort: An abrupt termination of a connection or stream, possibly due 296 to an error condition. 298 client: The endpoint that initiates an HTTP/3 connection. Clients 299 send HTTP requests and receive HTTP responses. 301 connection: A transport-layer connection between two endpoints, 302 using QUIC as the transport protocol. 304 connection error: An error that affects the entire HTTP/3 305 connection. 307 endpoint: Either the client or server of the connection. 309 frame: The smallest unit of communication on a stream in HTTP/3, 310 consisting of a header and a variable-length sequence of bytes 311 structured according to the frame type. Protocol elements called 312 "frames" exist in both this document and [QUIC-TRANSPORT]. Where 313 frames from [QUIC-TRANSPORT] are referenced, the frame name will 314 be prefaced with "QUIC." For example, "QUIC CONNECTION_CLOSE 315 frames." References without this preface refer to frames defined 316 in Section 7.2. 318 peer: An endpoint. When discussing a particular endpoint, "peer" 319 refers to the endpoint that is remote to the primary subject of 320 discussion. 322 receiver: An endpoint that is receiving frames. 324 sender: An endpoint that is transmitting frames. 326 server: The endpoint that accepts an HTTP/3 connection. Servers 327 receive HTTP requests and send HTTP responses. 329 stream: A bidirectional or unidirectional bytestream provided by the 330 QUIC transport. 332 stream error: An error on the individual HTTP/3 stream. 334 The term "payload body" is defined in Section 3.3 of [RFC7230]. 336 Finally, the terms "gateway", "intermediary", "proxy", and "tunnel" 337 are defined in Section 2.3 of [RFC7230]. Intermediaries act as both 338 client and server at different times. 340 3. Connection Setup and Management 342 3.1. Draft Version Identification 344 *RFC Editor's Note:* Please remove this section prior to 345 publication of a final version of this document. 347 HTTP/3 uses the token "h3" to identify itself in ALPN and Alt-Svc. 348 Only implementations of the final, published RFC can identify 349 themselves as "h3". Until such an RFC exists, implementations MUST 350 NOT identify themselves using this string. 352 Implementations of draft versions of the protocol MUST add the string 353 "-" and the corresponding draft number to the identifier. For 354 example, draft-ietf-quic-http-01 is identified using the string 355 "h3-01". 357 Non-compatible experiments that are based on these draft versions 358 MUST append the string "-" and an experiment name to the identifier. 359 For example, an experimental implementation based on draft-ietf-quic- 360 http-09 which reserves an extra stream for unsolicited transmission 361 of 1980s pop music might identify itself as "h3-09-rickroll". Note 362 that any label MUST conform to the "token" syntax defined in 363 Section 3.2.6 of [RFC7230]. Experimenters are encouraged to 364 coordinate their experiments on the quic@ietf.org mailing list. 366 3.2. Discovering an HTTP/3 Endpoint 368 An HTTP origin advertises the availability of an equivalent HTTP/3 369 endpoint via the Alt-Svc HTTP response header field or the HTTP/2 370 ALTSVC frame ([ALTSVC]), using the ALPN token defined in Section 3.3. 372 For example, an origin could indicate in an HTTP response that HTTP/3 373 was available on UDP port 50781 at the same hostname by including the 374 following header field: 376 Alt-Svc: h3=":50781" 378 On receipt of an Alt-Svc record indicating HTTP/3 support, a client 379 MAY attempt to establish a QUIC connection to the indicated host and 380 port and, if successful, send HTTP requests using the mapping 381 described in this document. 383 Connectivity problems (e.g. firewall blocking UDP) can result in QUIC 384 connection establishment failure, in which case the client SHOULD 385 continue using the existing connection or try another alternative 386 endpoint offered by the origin. 388 Servers MAY serve HTTP/3 on any UDP port, since an alternative always 389 includes an explicit port. 391 3.3. Connection Establishment 393 HTTP/3 relies on QUIC as the underlying transport. The QUIC version 394 being used MUST use TLS version 1.3 or greater as its handshake 395 protocol. HTTP/3 clients MUST indicate the target domain name during 396 the TLS handshake. This may be done using the Server Name Indication 397 (SNI) [RFC6066] extension to TLS or using some other mechanism. 399 QUIC connections are established as described in [QUIC-TRANSPORT]. 400 During connection establishment, HTTP/3 support is indicated by 401 selecting the ALPN token "h3" in the TLS handshake. Support for 402 other application-layer protocols MAY be offered in the same 403 handshake. 405 While connection-level options pertaining to the core QUIC protocol 406 are set in the initial crypto handshake, HTTP/3-specific settings are 407 conveyed in the SETTINGS frame. After the QUIC connection is 408 established, a SETTINGS frame (Section 7.2.4) MUST be sent by each 409 endpoint as the initial frame of their respective HTTP control stream 410 (see Section 6.2.1). 412 3.4. Connection Reuse 414 Once a connection exists to a server endpoint, this connection MAY be 415 reused for requests with multiple different URI authority components. 416 The client MAY send any requests for which the client considers the 417 server authoritative. 419 An authoritative HTTP/3 endpoint is typically discovered because the 420 client has received an Alt-Svc record from the request's origin which 421 nominates the endpoint as a valid HTTP Alternative Service for that 422 origin. As required by [RFC7838], clients MUST check that the 423 nominated server can present a valid certificate for the origin 424 before considering it authoritative. Clients MUST NOT assume that an 425 HTTP/3 endpoint is authoritative for other origins without an 426 explicit signal. 428 Prior to making requests for an origin whose scheme is not "https," 429 the client MUST ensure the server is willing to serve that scheme. 430 If the client intends to make requests for an origin whose scheme is 431 "http", this means that it MUST obtain a valid "http-opportunistic" 432 response for the origin as described in [RFC8164] prior to making any 433 such requests. Other schemes might define other mechanisms. 435 A server that does not wish clients to reuse connections for a 436 particular origin can indicate that it is not authoritative for a 437 request by sending a 421 (Misdirected Request) status code in 438 response to the request (see Section 9.1.2 of [HTTP2]). 440 The considerations discussed in Section 9.1 of [HTTP2] also apply to 441 the management of HTTP/3 connections. 443 4. HTTP Request Lifecycle 445 4.1. HTTP Message Exchanges 447 A client sends an HTTP request on a client-initiated bidirectional 448 QUIC stream. A client MUST send only a single request on a given 449 stream. A server sends zero or more non-final HTTP responses on the 450 same stream as the request, followed by a single final HTTP response, 451 as detailed below. 453 An HTTP message (request or response) consists of: 455 1. the message header (see Section 3.2 of [RFC7230]), sent as a 456 single HEADERS frame (see Section 7.2.2), 458 2. optionally, the payload body, if present (see Section 3.3 of 459 [RFC7230]), sent as a series of DATA frames (see Section 7.2.1), 461 3. optionally, trailing headers, if present (see Section 4.1.2 of 462 [RFC7230]), sent as a single HEADERS frame. 464 A server MAY send one or more PUSH_PROMISE (see Section 7.2.5) or 465 DUPLICATE_PUSH (see Section 7.2.8) frames before, after, or 466 interleaved with the frames of a response message. These 467 PUSH_PROMISE and DUPLICATE_PUSH frames are not part of the response; 468 see Section 4.4 for more details. 470 Frames of unknown types (Section 9), including reserved frames 471 (Section 7.2.9) MAY be sent on a request or push stream before, 472 after, or interleaved with other frames described in this section. 474 The HEADERS and PUSH_PROMISE frames might reference updates to the 475 QPACK dynamic table. While these updates are not directly part of 476 the message exchange, they must be received and processed before the 477 message can be consumed. See Section 4.1.1 for more details. 479 The "chunked" transfer encoding defined in Section 4.1 of [RFC7230] 480 MUST NOT be used. 482 A response MAY consist of multiple messages when and only when one or 483 more informational responses (1xx; see Section 6.2 of [RFC7231]) 484 precede a final response to the same request. Non-final responses do 485 not contain a payload body or trailers. 487 If an endpoint receives an invalid sequence of frames on either a 488 request or a push stream, it MUST respond with a connection error of 489 type H3_FRAME_UNEXPECTED (Section 8). In particular, a DATA frame 490 before any HEADERS frame, or a HEADERS or DATA frame after the 491 trailing HEADERS frame is considered invalid. 493 An HTTP request/response exchange fully consumes a bidirectional QUIC 494 stream. After sending a request, a client MUST close the stream for 495 sending. Unless using the CONNECT method (see Section 4.2), clients 496 MUST NOT make stream closure dependent on receiving a response to 497 their request. After sending a final response, the server MUST close 498 the stream for sending. At this point, the QUIC stream is fully 499 closed. 501 When a stream is closed, this indicates the end of an HTTP message. 502 Because some messages are large or unbounded, endpoints SHOULD begin 503 processing partial HTTP messages once enough of the message has been 504 received to make progress. If a client stream terminates without 505 enough of the HTTP message to provide a complete response, the server 506 SHOULD abort its response with the error code H3_REQUEST_INCOMPLETE. 508 A server can send a complete response prior to the client sending an 509 entire request if the response does not depend on any portion of the 510 request that has not been sent and received. When the server does 511 not need to receive the remainder of the request, it MAY abort 512 reading the request stream, send a complete response, and cleanly 513 close the sending part of the stream. The error code H3_NO_ERROR 514 SHOULD be used when requesting that the client stop sending on the 515 request stream. Clients MUST NOT discard complete responses as a 516 result of having their request terminated abruptly, though clients 517 can always discard responses at their discretion for other reasons. 519 If the server sends a partial or complete response but does not abort 520 reading, clients SHOULD continue sending the body of the request and 521 close the stream normally. 523 4.1.1. Header Formatting and Compression 525 HTTP message headers carry information as a series of key-value 526 pairs, called header fields. For a listing of registered HTTP header 527 fields, see the "Message Header Field" registry maintained at 528 https://www.iana.org/assignments/message-headers 529 (https://www.iana.org/assignments/message-headers). 531 Just as in previous versions of HTTP, header field names are strings 532 of ASCII characters that are compared in a case-insensitive fashion. 533 Properties of HTTP header field names and values are discussed in 534 more detail in Section 3.2 of [RFC7230], though the wire rendering in 535 HTTP/3 differs. As in HTTP/2, header field names MUST be converted 536 to lowercase prior to their encoding. A request or response 537 containing uppercase header field names MUST be treated as malformed 538 (Section 4.1.3). 540 As in HTTP/2, HTTP/3 uses special pseudo-header fields beginning with 541 the ':' character (ASCII 0x3a) to convey the target URI, the method 542 of the request, and the status code for the response. These pseudo- 543 header fields are defined in Section 8.1.2.3 and 8.1.2.4 of [HTTP2]. 544 Pseudo-header fields are not HTTP header fields. Endpoints MUST NOT 545 generate pseudo-header fields other than those defined in [HTTP2]. 546 The restrictions on the use of pseudo-header fields in Section 8.1.2 547 of [HTTP2] also apply to HTTP/3. Messages which are considered 548 malformed under these restrictions are handled as described in 549 Section 4.1.3. 551 HTTP/3 uses QPACK header compression as described in [QPACK], a 552 variation of HPACK which allows the flexibility to avoid header- 553 compression-induced head-of-line blocking. See that document for 554 additional details. 556 To allow for better compression efficiency, the cookie header field 557 [RFC6265] MAY be split into separate header fields, each with one or 558 more cookie-pairs, before compression. If a decompressed header list 559 contains multiple cookie header fields, these MUST be concatenated 560 before being passed into a non-HTTP/2, non-HTTP/3 context, as 561 described in Section 8.1.2.5 of [HTTP2]. 563 An HTTP/3 implementation MAY impose a limit on the maximum size of 564 the message header it will accept on an individual HTTP message. A 565 server that receives a larger header field list than it is willing to 566 handle can send an HTTP 431 (Request Header Fields Too Large) status 567 code [RFC6585]. A client can discard responses that it cannot 568 process. The size of a header field list is calculated based on the 569 uncompressed size of header fields, including the length of the name 570 and value in bytes plus an overhead of 32 bytes for each header 571 field. 573 If an implementation wishes to advise its peer of this limit, it can 574 be conveyed as a number of bytes in the 575 "SETTINGS_MAX_HEADER_LIST_SIZE" parameter. An implementation which 576 has received this parameter SHOULD NOT send an HTTP message header 577 which exceeds the indicated size, as the peer will likely refuse to 578 process it. However, because this limit is applied at each hop, 579 messages below this limit are not guaranteed to be accepted. 581 4.1.2. Request Cancellation and Rejection 583 Clients can cancel requests by resetting and aborting the request 584 stream with an error code of H3_REQUEST_CANCELLED (Section 8.1). 585 When the client aborts reading a response, it indicates that this 586 response is no longer of interest. Implementations SHOULD cancel 587 requests by abruptly terminating any directions of a stream that are 588 still open. 590 When the server rejects a request without performing any application 591 processing, it SHOULD abort its response stream with the error code 592 H3_REQUEST_REJECTED. In this context, "processed" means that some 593 data from the stream was passed to some higher layer of software that 594 might have taken some action as a result. The client can treat 595 requests rejected by the server as though they had never been sent at 596 all, thereby allowing them to be retried later on a new connection. 597 Servers MUST NOT use the H3_REQUEST_REJECTED error code for requests 598 which were partially or fully processed. When a server abandons a 599 response after partial processing, it SHOULD abort its response 600 stream with the error code H3_REQUEST_CANCELLED. 602 When a client resets a request with the error code 603 H3_REQUEST_CANCELLED, a server MAY abruptly terminate the response 604 using the error code H3_REQUEST_REJECTED if no processing was 605 performed. Clients MUST NOT use the H3_REQUEST_REJECTED error code, 606 except when a server has requested closure of the request stream with 607 this error code. 609 If a stream is cancelled after receiving a complete response, the 610 client MAY ignore the cancellation and use the response. However, if 611 a stream is cancelled after receiving a partial response, the 612 response SHOULD NOT be used. Automatically retrying such requests is 613 not possible, unless this is otherwise permitted (e.g., idempotent 614 actions like GET, PUT, or DELETE). 616 4.1.3. Malformed Requests and Responses 618 A malformed request or response is one that is an otherwise valid 619 sequence of frames but is invalid due to the presence of extraneous 620 frames, prohibited header fields, the absence of mandatory header 621 fields, or the inclusion of uppercase header field names. 623 A request or response that includes a payload body can include a 624 "content-length" header field. A request or response is also 625 malformed if the value of a content-length header field does not 626 equal the sum of the DATA frame payload lengths that form the body. 627 A response that is defined to have no payload, as described in 628 Section 3.3.2 of [RFC7230] can have a non-zero content-length header 629 field, even though no content is included in DATA frames. 631 Intermediaries that process HTTP requests or responses (i.e., any 632 intermediary not acting as a tunnel) MUST NOT forward a malformed 633 request or response. Malformed requests or responses that are 634 detected MUST be treated as a stream error (Section 8) of type 635 H3_GENERAL_PROTOCOL_ERROR. 637 For malformed requests, a server MAY send an HTTP response prior to 638 closing or resetting the stream. Clients MUST NOT accept a malformed 639 response. Note that these requirements are intended to protect 640 against several types of common attacks against HTTP; they are 641 deliberately strict because being permissive can expose 642 implementations to these vulnerabilities. 644 4.2. The CONNECT Method 646 The pseudo-method CONNECT (Section 4.3.6 of [RFC7231]) is primarily 647 used with HTTP proxies to establish a TLS session with an origin 648 server for the purposes of interacting with "https" resources. In 649 HTTP/1.x, CONNECT is used to convert an entire HTTP connection into a 650 tunnel to a remote host. In HTTP/2, the CONNECT method is used to 651 establish a tunnel over a single HTTP/2 stream to a remote host for 652 similar purposes. 654 A CONNECT request in HTTP/3 functions in the same manner as in 655 HTTP/2. The request MUST be formatted as described in Section 8.3 of 656 [HTTP2]. A CONNECT request that does not conform to these 657 restrictions is malformed (see Section 4.1.3). The request stream 658 MUST NOT be closed at the end of the request. 660 A proxy that supports CONNECT establishes a TCP connection 661 ([RFC0793]) to the server identified in the ":authority" pseudo- 662 header field. Once this connection is successfully established, the 663 proxy sends a HEADERS frame containing a 2xx series status code to 664 the client, as defined in Section 4.3.6 of [RFC7231]. 666 All DATA frames on the stream correspond to data sent or received on 667 the TCP connection. Any DATA frame sent by the client is transmitted 668 by the proxy to the TCP server; data received from the TCP server is 669 packaged into DATA frames by the proxy. Note that the size and 670 number of TCP segments is not guaranteed to map predictably to the 671 size and number of HTTP DATA or QUIC STREAM frames. 673 Once the CONNECT method has completed, only DATA frames are permitted 674 to be sent on the stream. Extension frames MAY be used if 675 specifically permitted by the definition of the extension. Receipt 676 of any other frame type MUST be treated as a connection error of type 677 H3_FRAME_UNEXPECTED. 679 The TCP connection can be closed by either peer. When the client 680 ends the request stream (that is, the receive stream at the proxy 681 enters the "Data Recvd" state), the proxy will set the FIN bit on its 682 connection to the TCP server. When the proxy receives a packet with 683 the FIN bit set, it will terminate the send stream that it sends to 684 the client. TCP connections which remain half-closed in a single 685 direction are not invalid, but are often handled poorly by servers, 686 so clients SHOULD NOT close a stream for sending while they still 687 expect to receive data from the target of the CONNECT. 689 A TCP connection error is signaled by abruptly terminating the 690 stream. A proxy treats any error in the TCP connection, which 691 includes receiving a TCP segment with the RST bit set, as a stream 692 error of type H3_CONNECT_ERROR (Section 8.1). Correspondingly, if a 693 proxy detects an error with the stream or the QUIC connection, it 694 MUST close the TCP connection. If the underlying TCP implementation 695 permits it, the proxy SHOULD send a TCP segment with the RST bit set. 697 4.3. HTTP Upgrade 699 HTTP/3 does not support the HTTP Upgrade mechanism (Section 6.7 of 700 [RFC7230]) or 101 (Switching Protocols) informational status code 701 (Section 6.2.2 of [RFC7231]). 703 4.4. Server Push 705 Server push is an interaction mode introduced in HTTP/2 [HTTP2] which 706 permits a server to push a request-response exchange to a client in 707 anticipation of the client making the indicated request. This trades 708 off network usage against a potential latency gain. HTTP/3 server 709 push is similar to what is described in HTTP/2 [HTTP2], but uses 710 different mechanisms. 712 Each server push is identified by a unique Push ID. This Push ID is 713 used in a single PUSH_PROMISE frame (see Section 7.2.5) which carries 714 the request headers, possibly included in one or more DUPLICATE_PUSH 715 frames (see Section 7.2.8), then included with the push stream which 716 ultimately fulfills those promises. 718 Server push is only enabled on a connection when a client sends a 719 MAX_PUSH_ID frame (see Section 7.2.7). A server cannot use server 720 push until it receives a MAX_PUSH_ID frame. A client sends 721 additional MAX_PUSH_ID frames to control the number of pushes that a 722 server can promise. A server SHOULD use Push IDs sequentially, 723 starting at 0. A client MUST treat receipt of a push stream with a 724 Push ID that is greater than the maximum Push ID as a connection 725 error of type H3_ID_ERROR. 727 The header of the request message is carried by a PUSH_PROMISE frame 728 (see Section 7.2.5) on the request stream which generated the push. 729 Promised requests MUST conform to the requirements in Section 8.2 of 730 [HTTP2]. 732 Each pushed response is associated with one or more client requests. 733 The push is associated with the request stream on which the 734 PUSH_PROMISE frame was received. The same server push can be 735 associated with additional client requests using a DUPLICATE_PUSH 736 frame (see Section 7.2.8). These associations do not affect the 737 operation of the protocol, but MAY be used by user agents when 738 deciding how to use pushed resources. 740 Ordering of a PUSH_PROMISE or DUPLICATE_PUSH in relation to certain 741 parts of the response is important. The server SHOULD send 742 PUSH_PROMISE or DUPLICATE_PUSH frames prior to sending HEADERS or 743 DATA frames that reference the promised responses. This reduces the 744 chance that a client requests a resource that will be pushed by the 745 server. 747 When a server later fulfills a promise, the server push response is 748 conveyed on a push stream (see Section 6.2.2). The push stream 749 identifies the Push ID of the promise that it fulfills, then contains 750 a response to the promised request using the same format described 751 for responses in Section 4.1. 753 Due to reordering, DUPLICATE_PUSH frames or push stream data can 754 arrive before the corresponding PUSH_PROMISE frame. When a client 755 receives a DUPLICATE_PUSH frame for an as-yet-unknown Push ID, the 756 request headers of the push are not immediately available. The 757 client can either delay generating new requests for content 758 referenced following the DUPLICATE_PUSH frame until the request 759 headers become available, or can initiate requests for discovered 760 resources and cancel the requests if the requested resource is 761 already being pushed. When a client receives a new push stream with 762 an as-yet-unknown Push ID, both the associated client request and the 763 pushed request headers are unknown. The client can buffer the stream 764 data in expectation of the matching PUSH_PROMISE. The client can use 765 stream flow control (see section 4.1 of [QUIC-TRANSPORT]) to limit 766 the amount of data a server may commit to the pushed stream. 768 If a promised server push is not needed by the client, the client 769 SHOULD send a CANCEL_PUSH frame. If the push stream is already open 770 or opens after sending the CANCEL_PUSH frame, the client can abort 771 reading the stream with an error code of H3_REQUEST_CANCELLED. This 772 asks the server not to transfer additional data and indicates that it 773 will be discarded upon receipt. 775 5. Connection Closure 777 Once established, an HTTP/3 connection can be used for many requests 778 and responses over time until the connection is closed. Connection 779 closure can happen in any of several different ways. 781 5.1. Idle Connections 783 Each QUIC endpoint declares an idle timeout during the handshake. If 784 the connection remains idle (no packets received) for longer than 785 this duration, the peer will assume that the connection has been 786 closed. HTTP/3 implementations will need to open a new connection 787 for new requests if the existing connection has been idle for longer 788 than the server's advertised idle timeout, and SHOULD do so if 789 approaching the idle timeout. 791 HTTP clients are expected to request that the transport keep 792 connections open while there are responses outstanding for requests 793 or server pushes, as described in Section 19.2 of [QUIC-TRANSPORT]. 794 If the client is not expecting a response from the server, allowing 795 an idle connection to time out is preferred over expending effort 796 maintaining a connection that might not be needed. A gateway MAY 797 maintain connections in anticipation of need rather than incur the 798 latency cost of connection establishment to servers. Servers SHOULD 799 NOT actively keep connections open. 801 5.2. Connection Shutdown 803 Even when a connection is not idle, either endpoint can decide to 804 stop using the connection and let the connection close gracefully. 805 Since clients drive request generation, clients perform a connection 806 shutdown by not sending additional requests on the connection; 807 responses and pushed responses associated to previous requests will 808 continue to completion. Servers perform the same function by 809 communicating with clients. 811 Servers initiate the shutdown of a connection by sending a GOAWAY 812 frame (Section 7.2.6). The GOAWAY frame indicates that client- 813 initiated requests on lower stream IDs were or might be processed in 814 this connection, while requests on the indicated stream ID and 815 greater were rejected. This enables client and server to agree on 816 which requests were accepted prior to the connection shutdown. This 817 identifier MAY be zero if no requests were processed. Servers SHOULD 818 NOT permit additional QUIC streams after sending a GOAWAY frame. 820 Clients MUST NOT send new requests on the connection after receiving 821 GOAWAY; a new connection MAY be established to send additional 822 requests. 824 Some requests might already be in transit. If the client has already 825 sent requests on streams with a Stream ID greater than or equal to 826 that indicated in the GOAWAY frame, those requests will not be 827 processed and MAY be retried by the client on a different connection. 828 The client MAY cancel these requests. It is RECOMMENDED that the 829 server explicitly reject such requests (see Section 4.1.2) in order 830 to clean up transport state for the affected streams. 832 Requests on Stream IDs less than the Stream ID in the GOAWAY frame 833 might have been processed; their status cannot be known until a 834 response is received, the stream is reset individually, or the 835 connection terminates. Servers MAY reject individual requests on 836 streams below the indicated ID if these requests were not processed. 838 Servers SHOULD send a GOAWAY frame when the closing of a connection 839 is known in advance, even if the advance notice is small, so that the 840 remote peer can know whether a request has been partially processed 841 or not. For example, if an HTTP client sends a POST at the same time 842 that a server closes a QUIC connection, the client cannot know if the 843 server started to process that POST request if the server does not 844 send a GOAWAY frame to indicate what streams it might have acted on. 846 A client that is unable to retry requests loses all requests that are 847 in flight when the server closes the connection. A server MAY send 848 multiple GOAWAY frames indicating different stream IDs, but MUST NOT 849 increase the value they send in the last Stream ID, since clients 850 might already have retried unprocessed requests on another 851 connection. 853 A server that is attempting to gracefully shut down a connection can 854 send an initial GOAWAY frame with the last Stream ID set to the 855 maximum possible value for a client-initiated, bidirectional stream 856 (i.e. 2^62-4 in case of QUIC version 1). This GOAWAY frame signals 857 to the client that shutdown is imminent and that initiating further 858 requests is prohibited. After allowing time for any in-flight 859 requests to reach the server, the server can send another GOAWAY 860 frame indicating which requests it will accept before the end of the 861 connection. This ensures that a connection can be cleanly shut down 862 without causing requests to fail. 864 Once all accepted requests have been processed, the server can permit 865 the connection to become idle, or MAY initiate an immediate closure 866 of the connection. An endpoint that completes a graceful shutdown 867 SHOULD use the H3_NO_ERROR code when closing the connection. 869 If a client has consumed all available bidirectional stream IDs with 870 requests, the server need not send a GOAWAY frame, since the client 871 is unable to make further requests. 873 5.3. Immediate Application Closure 875 An HTTP/3 implementation can immediately close the QUIC connection at 876 any time. This results in sending a QUIC CONNECTION_CLOSE frame to 877 the peer; the error code in this frame indicates to the peer why the 878 connection is being closed. See Section 8 for error codes which can 879 be used when closing a connection. 881 Before closing the connection, a GOAWAY MAY be sent to allow the 882 client to retry some requests. Including the GOAWAY frame in the 883 same packet as the QUIC CONNECTION_CLOSE frame improves the chances 884 of the frame being received by clients. 886 5.4. Transport Closure 888 For various reasons, the QUIC transport could indicate to the 889 application layer that the connection has terminated. This might be 890 due to an explicit closure by the peer, a transport-level error, or a 891 change in network topology which interrupts connectivity. 893 If a connection terminates without a GOAWAY frame, clients MUST 894 assume that any request which was sent, whether in whole or in part, 895 might have been processed. 897 6. Stream Mapping and Usage 899 A QUIC stream provides reliable in-order delivery of bytes, but makes 900 no guarantees about order of delivery with regard to bytes on other 901 streams. On the wire, data is framed into QUIC STREAM frames, but 902 this framing is invisible to the HTTP framing layer. The transport 903 layer buffers and orders received QUIC STREAM frames, exposing the 904 data contained within as a reliable byte stream to the application. 905 Although QUIC permits out-of-order delivery within a stream, HTTP/3 906 does not make use of this feature. 908 QUIC streams can be either unidirectional, carrying data only from 909 initiator to receiver, or bidirectional. Streams can be initiated by 910 either the client or the server. For more detail on QUIC streams, 911 see Section 2 of [QUIC-TRANSPORT]. 913 When HTTP headers and data are sent over QUIC, the QUIC layer handles 914 most of the stream management. HTTP does not need to do any separate 915 multiplexing when using QUIC - data sent over a QUIC stream always 916 maps to a particular HTTP transaction or connection context. 918 6.1. Bidirectional Streams 920 All client-initiated bidirectional streams are used for HTTP requests 921 and responses. A bidirectional stream ensures that the response can 922 be readily correlated with the request. This means that the client's 923 first request occurs on QUIC stream 0, with subsequent requests on 924 stream 4, 8, and so on. In order to permit these streams to open, an 925 HTTP/3 server SHOULD configure non-zero minimum values for the number 926 of permitted streams and the initial stream flow control window. So 927 as to not unnecessarily limit parallelism, at least 100 requests 928 SHOULD be permitted at a time. 930 HTTP/3 does not use server-initiated bidirectional streams, though an 931 extension could define a use for these streams. Clients MUST treat 932 receipt of a server-initiated bidirectional stream as a connection 933 error of type H3_STREAM_CREATION_ERROR unless such an extension has 934 been negotiated. 936 6.2. Unidirectional Streams 938 Unidirectional streams, in either direction, are used for a range of 939 purposes. The purpose is indicated by a stream type, which is sent 940 as a variable-length integer at the start of the stream. The format 941 and structure of data that follows this integer is determined by the 942 stream type. 944 0 1 2 3 945 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 946 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 947 | Stream Type (i) ... 948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 950 Figure 1: Unidirectional Stream Header 952 Some stream types are reserved (Section 6.2.3). Two stream types are 953 defined in this document: control streams (Section 6.2.1) and push 954 streams (Section 6.2.2). [QPACK] defines two additional stream 955 types. Other stream types can be defined by extensions to HTTP/3; 956 see Section 9 for more details. 958 The performance of HTTP/3 connections in the early phase of their 959 lifetime is sensitive to the creation and exchange of data on 960 unidirectional streams. Endpoints that excessively restrict the 961 number of streams or the flow control window of these streams will 962 increase the chance that the remote peer reaches the limit early and 963 becomes blocked. In particular, implementations should consider that 964 remote peers may wish to exercise reserved stream behavior 965 (Section 6.2.3) with some of the unidirectional streams they are 966 permitted to use. To avoid blocking, the transport parameters sent 967 by both clients and servers MUST allow the peer to create at least 968 one unidirectional stream for the HTTP control stream plus the number 969 of unidirectional streams required by mandatory extensions (three 970 being the minimum number required for the base HTTP/3 protocol and 971 QPACK), and SHOULD provide at least 1,024 bytes of flow control 972 credit to each stream. 974 Note that an endpoint is not required to grant additional credits to 975 create more unidirectional streams if its peer consumes all the 976 initial credits before creating the critical unidirectional streams. 977 Endpoints SHOULD create the HTTP control stream as well as the 978 unidirectional streams required by mandatory extensions (such as the 979 QPACK encoder and decoder streams) first, and then create additional 980 streams as allowed by their peer. 982 If the stream header indicates a stream type which is not supported 983 by the recipient, the remainder of the stream cannot be consumed as 984 the semantics are unknown. Recipients of unknown stream types MAY 985 abort reading of the stream with an error code of 986 H3_STREAM_CREATION_ERROR, but MUST NOT consider such streams to be a 987 connection error of any kind. 989 Implementations MAY send stream types before knowing whether the peer 990 supports them. However, stream types which could modify the state or 991 semantics of existing protocol components, including QPACK or other 992 extensions, MUST NOT be sent until the peer is known to support them. 994 A sender can close or reset a unidirectional stream unless otherwise 995 specified. A receiver MUST tolerate unidirectional streams being 996 closed or reset prior to the reception of the unidirectional stream 997 header. 999 6.2.1. Control Streams 1001 A control stream is indicated by a stream type of "0x00". Data on 1002 this stream consists of HTTP/3 frames, as defined in Section 7.2. 1004 Each side MUST initiate a single control stream at the beginning of 1005 the connection and send its SETTINGS frame as the first frame on this 1006 stream. If the first frame of the control stream is any other frame 1007 type, this MUST be treated as a connection error of type 1008 H3_MISSING_SETTINGS. Only one control stream per peer is permitted; 1009 receipt of a second stream which claims to be a control stream MUST 1010 be treated as a connection error of type H3_STREAM_CREATION_ERROR. 1011 The sender MUST NOT close the control stream, and the receiver MUST 1012 NOT request that the sender close the control stream. If either 1013 control stream is closed at any point, this MUST be treated as a 1014 connection error of type H3_CLOSED_CRITICAL_STREAM. 1016 A pair of unidirectional streams is used rather than a single 1017 bidirectional stream. This allows either peer to send data as soon 1018 as it is able. Depending on whether 0-RTT is enabled on the 1019 connection, either client or server might be able to send stream data 1020 first after the cryptographic handshake completes. 1022 6.2.2. Push Streams 1024 Server push is an optional feature introduced in HTTP/2 that allows a 1025 server to initiate a response before a request has been made. See 1026 Section 4.4 for more details. 1028 A push stream is indicated by a stream type of "0x01", followed by 1029 the Push ID of the promise that it fulfills, encoded as a variable- 1030 length integer. The remaining data on this stream consists of HTTP/3 1031 frames, as defined in Section 7.2, and fulfills a promised server 1032 push by zero or more non-final HTTP responses followed by a single 1033 final HTTP response, as defined in Section 4.1. Server push and Push 1034 IDs are described in Section 4.4. 1036 Only servers can push; if a server receives a client-initiated push 1037 stream, this MUST be treated as a connection error of type 1038 H3_STREAM_CREATION_ERROR. 1040 0 1 2 3 1041 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1042 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1043 | 0x01 (i) ... 1044 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1045 | Push ID (i) ... 1046 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1047 Figure 2: Push Stream Header 1049 Each Push ID MUST only be used once in a push stream header. If a 1050 push stream header includes a Push ID that was used in another push 1051 stream header, the client MUST treat this as a connection error of 1052 type H3_ID_ERROR. 1054 6.2.3. Reserved Stream Types 1056 Stream types of the format "0x1f * N + 0x21" for integer values of N 1057 are reserved to exercise the requirement that unknown types be 1058 ignored. These streams have no semantics, and can be sent when 1059 application-layer padding is desired. They MAY also be sent on 1060 connections where no data is currently being transferred. Endpoints 1061 MUST NOT consider these streams to have any meaning upon receipt. 1063 The payload and length of the stream are selected in any manner the 1064 implementation chooses. Implementations MAY terminate these streams 1065 cleanly, or MAY abruptly terminate them. When terminating abruptly, 1066 the error code H3_NO_ERROR or a reserved error code (Section 8.1) 1067 SHOULD be used. 1069 7. HTTP Framing Layer 1071 HTTP frames are carried on QUIC streams, as described in Section 6. 1072 HTTP/3 defines three stream types: control stream, request stream, 1073 and push stream. This section describes HTTP/3 frame formats and the 1074 streams types on which they are permitted; see Table 1 for an 1075 overview. A comparison between HTTP/2 and HTTP/3 frames is provided 1076 in Appendix A.2. 1078 +----------------+----------------+---------+--------+---------+ 1079 | Frame | Control Stream | Request | Push | Section | 1080 | | | Stream | Stream | | 1081 +================+================+=========+========+=========+ 1082 | DATA | No | Yes | Yes | Section | 1083 | | | | | 7.2.1 | 1084 +----------------+----------------+---------+--------+---------+ 1085 | HEADERS | No | Yes | Yes | Section | 1086 | | | | | 7.2.2 | 1087 +----------------+----------------+---------+--------+---------+ 1088 | CANCEL_PUSH | Yes | No | No | Section | 1089 | | | | | 7.2.3 | 1090 +----------------+----------------+---------+--------+---------+ 1091 | SETTINGS | Yes (1) | No | No | Section | 1092 | | | | | 7.2.4 | 1093 +----------------+----------------+---------+--------+---------+ 1094 | PUSH_PROMISE | No | Yes | No | Section | 1095 | | | | | 7.2.5 | 1096 +----------------+----------------+---------+--------+---------+ 1097 | GOAWAY | Yes | No | No | Section | 1098 | | | | | 7.2.6 | 1099 +----------------+----------------+---------+--------+---------+ 1100 | MAX_PUSH_ID | Yes | No | No | Section | 1101 | | | | | 7.2.7 | 1102 +----------------+----------------+---------+--------+---------+ 1103 | DUPLICATE_PUSH | No | Yes | No | Section | 1104 | | | | | 7.2.8 | 1105 +----------------+----------------+---------+--------+---------+ 1106 | Reserved | Yes | Yes | Yes | Section | 1107 | | | | | 7.2.9 | 1108 +----------------+----------------+---------+--------+---------+ 1110 Table 1: HTTP/3 Frames and Stream Type Overview 1112 Certain frames can only occur as the first frame of a particular 1113 stream type; these are indicated in Table 1 with a (1). Specific 1114 guidance is provided in the relevant section. 1116 Note that, unlike QUIC frames, HTTP/3 frames can span multiple 1117 packets. 1119 7.1. Frame Layout 1121 All frames have the following format: 1123 0 1 2 3 1124 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1126 | Type (i) ... 1127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1128 | Length (i) ... 1129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1130 | Frame Payload (*) ... 1131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1133 Figure 3: HTTP/3 Frame Format 1135 A frame includes the following fields: 1137 Type: A variable-length integer that identifies the frame type. 1139 Length: A variable-length integer that describes the length in bytes 1140 of the Frame Payload. 1142 Frame Payload: A payload, the semantics of which are determined by 1143 the Type field. 1145 Each frame's payload MUST contain exactly the fields identified in 1146 its description. A frame payload that contains additional bytes 1147 after the identified fields or a frame payload that terminates before 1148 the end of the identified fields MUST be treated as a connection 1149 error of type H3_FRAME_ERROR. 1151 When a stream terminates cleanly, if the last frame on the stream was 1152 truncated, this MUST be treated as a connection error (Section 8) of 1153 type H3_FRAME_ERROR. Streams which terminate abruptly may be reset 1154 at any point in a frame. 1156 7.2. Frame Definitions 1158 7.2.1. DATA 1160 DATA frames (type=0x0) convey arbitrary, variable-length sequences of 1161 bytes associated with an HTTP request or response payload. 1163 DATA frames MUST be associated with an HTTP request or response. If 1164 a DATA frame is received on a control stream, the recipient MUST 1165 respond with a connection error (Section 8) of type 1166 H3_FRAME_UNEXPECTED. 1168 0 1 2 3 1169 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1171 | Payload (*) ... 1172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1174 Figure 4: DATA Frame Payload 1176 7.2.2. HEADERS 1178 The HEADERS frame (type=0x1) is used to carry a header block, 1179 compressed using QPACK. See [QPACK] for more details. 1181 0 1 2 3 1182 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1184 | Header Block (*) ... 1185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1187 Figure 5: HEADERS Frame Payload 1189 HEADERS frames can only be sent on request / push streams. If a 1190 HEADERS frame is received on a control stream, the recipient MUST 1191 respond with a connection error (Section 8) of type 1192 H3_FRAME_UNEXPECTED. 1194 7.2.3. CANCEL_PUSH 1196 The CANCEL_PUSH frame (type=0x3) is used to request cancellation of a 1197 server push prior to the push stream being received. The CANCEL_PUSH 1198 frame identifies a server push by Push ID (see Section 7.2.5), 1199 encoded as a variable-length integer. 1201 When a client sends CANCEL_PUSH, it is indicating that it does not 1202 wish to receive the promised resource. The server SHOULD abort 1203 sending the resource, but the mechanism to do so depends on the state 1204 of the corresponding push stream. If the server has not yet created 1205 a push stream, it does not create one. If the push stream is open, 1206 the server SHOULD abruptly terminate that stream. If the push stream 1207 has already ended, the server MAY still abruptly terminate the stream 1208 or MAY take no action. 1210 When a server sends CANCEL_PUSH, it is indicating that it will not be 1211 fulfilling a promise and has not created a push stream. The client 1212 should not expect the corresponding promise to be fulfilled. 1214 Sending CANCEL_PUSH has no direct effect on the state of existing 1215 push streams. A server SHOULD NOT send a CANCEL_PUSH when it has 1216 already created a corresponding push stream, and a client SHOULD NOT 1217 send a CANCEL_PUSH when it has already received a corresponding push 1218 stream. 1220 A CANCEL_PUSH frame is sent on the control stream. Receiving a 1221 CANCEL_PUSH frame on a stream other than the control stream MUST be 1222 treated as a connection error of type H3_FRAME_UNEXPECTED. 1224 0 1 2 3 1225 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1227 | Push ID (i) ... 1228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1230 Figure 6: CANCEL_PUSH Frame Payload 1232 The CANCEL_PUSH frame carries a Push ID encoded as a variable-length 1233 integer. The Push ID identifies the server push that is being 1234 cancelled (see Section 7.2.5). If a CANCEL_PUSH frame is received 1235 which references a Push ID greater than currently allowed on the 1236 connection, this MUST be treated as a connection error of type 1237 H3_ID_ERROR. 1239 If the client receives a CANCEL_PUSH frame, that frame might identify 1240 a Push ID that has not yet been mentioned by a PUSH_PROMISE frame due 1241 to reordering. If a server receives a CANCEL_PUSH frame for a Push 1242 ID that has not yet been mentioned by a PUSH_PROMISE frame, this MUST 1243 be treated as a connection error of type H3_ID_ERROR. 1245 7.2.4. SETTINGS 1247 The SETTINGS frame (type=0x4) conveys configuration parameters that 1248 affect how endpoints communicate, such as preferences and constraints 1249 on peer behavior. Individually, a SETTINGS parameter can also be 1250 referred to as a "setting"; the identifier and value of each setting 1251 parameter can be referred to as a "setting identifier" and a "setting 1252 value". 1254 SETTINGS frames always apply to a connection, never a single stream. 1255 A SETTINGS frame MUST be sent as the first frame of each control 1256 stream (see Section 6.2.1) by each peer, and MUST NOT be sent 1257 subsequently. If an endpoint receives a second SETTINGS frame on the 1258 control stream, the endpoint MUST respond with a connection error of 1259 type H3_FRAME_UNEXPECTED. 1261 SETTINGS frames MUST NOT be sent on any stream other than the control 1262 stream. If an endpoint receives a SETTINGS frame on a different 1263 stream, the endpoint MUST respond with a connection error of type 1264 H3_FRAME_UNEXPECTED. 1266 SETTINGS parameters are not negotiated; they describe characteristics 1267 of the sending peer, which can be used by the receiving peer. 1268 However, a negotiation can be implied by the use of SETTINGS - each 1269 peer uses SETTINGS to advertise a set of supported values. The 1270 definition of the setting would describe how each peer combines the 1271 two sets to conclude which choice will be used. SETTINGS does not 1272 provide a mechanism to identify when the choice takes effect. 1274 Different values for the same parameter can be advertised by each 1275 peer. For example, a client might be willing to consume a very large 1276 response header, while servers are more cautious about request size. 1278 The same setting identifier MUST NOT occur more than once in the 1279 SETTINGS frame. A receiver MAY treat the presence of duplicate 1280 setting identifiers as a connection error of type H3_SETTINGS_ERROR. 1282 The payload of a SETTINGS frame consists of zero or more parameters. 1283 Each parameter consists of a setting identifier and a value, both 1284 encoded as QUIC variable-length integers. 1286 0 1 2 3 1287 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1289 | Identifier (i) ... 1290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1291 | Value (i) ... 1292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1294 Figure 7: SETTINGS Parameter Format 1296 An implementation MUST ignore the contents for any SETTINGS 1297 identifier it does not understand. 1299 7.2.4.1. Defined SETTINGS Parameters 1301 The following settings are defined in HTTP/3: 1303 SETTINGS_MAX_HEADER_LIST_SIZE (0x6): The default value is unlimited. 1304 See Section 4.1.1 for usage. 1306 Setting identifiers of the format "0x1f * N + 0x21" for integer 1307 values of N are reserved to exercise the requirement that unknown 1308 identifiers be ignored. Such settings have no defined meaning. 1309 Endpoints SHOULD include at least one such setting in their SETTINGS 1310 frame. Endpoints MUST NOT consider such settings to have any meaning 1311 upon receipt. 1313 Because the setting has no defined meaning, the value of the setting 1314 can be any value the implementation selects. 1316 Additional settings can be defined by extensions to HTTP/3; see 1317 Section 9 for more details. 1319 7.2.4.2. Initialization 1321 An HTTP implementation MUST NOT send frames or requests which would 1322 be invalid based on its current understanding of the peer's settings. 1324 All settings begin at an initial value. Each endpoint SHOULD use 1325 these initial values to send messages before the peer's SETTINGS 1326 frame has arrived, as packets carrying the settings can be lost or 1327 delayed. When the SETTINGS frame arrives, any settings are changed 1328 to their new values. 1330 This removes the need to wait for the SETTINGS frame before sending 1331 messages. Endpoints MUST NOT require any data to be received from 1332 the peer prior to sending the SETTINGS frame; settings MUST be sent 1333 as soon as the transport is ready to send data. 1335 For servers, the initial value of each client setting is the default 1336 value. 1338 For clients using a 1-RTT QUIC connection, the initial value of each 1339 server setting is the default value. 1-RTT keys will always become 1340 available prior to SETTINGS arriving, even if the server sends 1341 SETTINGS immediately. Clients SHOULD NOT wait indefinitely for 1342 SETTINGS to arrive before sending requests, but SHOULD process 1343 received datagrams in order to increase the likelihood of processing 1344 SETTINGS before sending the first request. 1346 When a 0-RTT QUIC connection is being used, the initial value of each 1347 server setting is the value used in the previous session. Clients 1348 SHOULD store the settings the server provided in the connection where 1349 resumption information was provided, but MAY opt not to store 1350 settings in certain cases (e.g., if the session ticket is received 1351 before the SETTINGS frame). A client MUST comply with stored 1352 settings - or default values, if no values are stored - when 1353 attempting 0-RTT. Once a server has provided new settings, clients 1354 MUST comply with those values. 1356 A server can remember the settings that it advertised, or store an 1357 integrity-protected copy of the values in the ticket and recover the 1358 information when accepting 0-RTT data. A server uses the HTTP/3 1359 settings values in determining whether to accept 0-RTT data. If the 1360 server cannot determine that the settings remembered by a client are 1361 compatible with its current settings, it MUST NOT accept 0-RTT data. 1362 Remembered settings are compatible if a client complying with those 1363 settings would not violate the server's current settings. 1365 A server MAY accept 0-RTT and subsequently provide different settings 1366 in its SETTINGS frame. If 0-RTT data is accepted by the server, its 1367 SETTINGS frame MUST NOT reduce any limits or alter any values that 1368 might be violated by the client with its 0-RTT data. The server MUST 1369 include all settings which differ from their default values. If a 1370 server accepts 0-RTT but then sends settings that are not compatible 1371 with the previously specified settings, this MUST be treated as a 1372 connection error of type H3_SETTINGS_ERROR. If a server accepts 1373 0-RTT but then sends a SETTINGS frame that omits a setting value that 1374 the client understands (apart from reserved setting identifiers) that 1375 was previously specified to have a non-default value, this MUST be 1376 treated as a connection error of type H3_SETTINGS_ERROR. 1378 7.2.5. PUSH_PROMISE 1380 The PUSH_PROMISE frame (type=0x5) is used to carry a promised request 1381 header set from server to client on a request stream, as in HTTP/2. 1383 0 1 2 3 1384 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1385 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1386 | Push ID (i) ... 1387 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1388 | Header Block (*) ... 1389 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1391 Figure 8: PUSH_PROMISE Frame Payload 1393 The payload consists of: 1395 Push ID: A variable-length integer that identifies the server push 1396 operation. A Push ID is used in push stream headers 1397 (Section 4.4), CANCEL_PUSH frames (Section 7.2.3), and 1398 DUPLICATE_PUSH frames (Section 7.2.8). 1400 Header Block: QPACK-compressed request header fields for the 1401 promised response. See [QPACK] for more details. 1403 A server MUST NOT use a Push ID that is larger than the client has 1404 provided in a MAX_PUSH_ID frame (Section 7.2.7). A client MUST treat 1405 receipt of a PUSH_PROMISE frame that contains a larger Push ID than 1406 the client has advertised as a connection error of H3_ID_ERROR. 1408 A server MUST NOT use the same Push ID in multiple PUSH_PROMISE 1409 frames. A client MUST treat receipt of a Push ID which has already 1410 been promised as a connection error of type H3_ID_ERROR. 1412 If a PUSH_PROMISE frame is received on the control stream, the client 1413 MUST respond with a connection error (Section 8) of type 1414 H3_FRAME_UNEXPECTED. 1416 A client MUST NOT send a PUSH_PROMISE frame. A server MUST treat the 1417 receipt of a PUSH_PROMISE frame as a connection error of type 1418 H3_FRAME_UNEXPECTED. 1420 See Section 4.4 for a description of the overall server push 1421 mechanism. 1423 7.2.6. GOAWAY 1425 The GOAWAY frame (type=0x7) is used to initiate graceful shutdown of 1426 a connection by a server. GOAWAY allows a server to stop accepting 1427 new requests while still finishing processing of previously received 1428 requests. This enables administrative actions, like server 1429 maintenance. GOAWAY by itself does not close a connection. 1431 0 1 2 3 1432 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1434 | Stream ID (i) ... 1435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1437 Figure 9: GOAWAY Frame Payload 1439 The GOAWAY frame is always sent on the control stream. It carries a 1440 QUIC Stream ID for a client-initiated bidirectional stream encoded as 1441 a variable-length integer. A client MUST treat receipt of a GOAWAY 1442 frame containing a Stream ID of any other type as a connection error 1443 of type H3_ID_ERROR. 1445 Clients do not need to send GOAWAY to initiate a graceful shutdown; 1446 they simply stop making new requests. A server MUST treat receipt of 1447 a GOAWAY frame on any stream as a connection error (Section 8) of 1448 type H3_FRAME_UNEXPECTED. 1450 The GOAWAY frame applies to the connection, not a specific stream. A 1451 client MUST treat a GOAWAY frame on a stream other than the control 1452 stream as a connection error (Section 8) of type H3_FRAME_UNEXPECTED. 1454 See Section 5.2 for more information on the use of the GOAWAY frame. 1456 7.2.7. MAX_PUSH_ID 1458 The MAX_PUSH_ID frame (type=0xD) is used by clients to control the 1459 number of server pushes that the server can initiate. This sets the 1460 maximum value for a Push ID that the server can use in PUSH_PROMISE 1461 and CANCEL_PUSH frames. Consequently, this also limits the number of 1462 push streams that the server can initiate in addition to the limit 1463 maintained by the QUIC transport. 1465 The MAX_PUSH_ID frame is always sent on the control stream. Receipt 1466 of a MAX_PUSH_ID frame on any other stream MUST be treated as a 1467 connection error of type H3_FRAME_UNEXPECTED. 1469 A server MUST NOT send a MAX_PUSH_ID frame. A client MUST treat the 1470 receipt of a MAX_PUSH_ID frame as a connection error of type 1471 H3_FRAME_UNEXPECTED. 1473 The maximum Push ID is unset when a connection is created, meaning 1474 that a server cannot push until it receives a MAX_PUSH_ID frame. A 1475 client that wishes to manage the number of promised server pushes can 1476 increase the maximum Push ID by sending MAX_PUSH_ID frames as the 1477 server fulfills or cancels server pushes. 1479 0 1 2 3 1480 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1482 | Push ID (i) ... 1483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1485 Figure 10: MAX_PUSH_ID Frame Payload 1487 The MAX_PUSH_ID frame carries a single variable-length integer that 1488 identifies the maximum value for a Push ID that the server can use 1489 (see Section 7.2.5). A MAX_PUSH_ID frame cannot reduce the maximum 1490 Push ID; receipt of a MAX_PUSH_ID that contains a smaller value than 1491 previously received MUST be treated as a connection error of type 1492 H3_ID_ERROR. 1494 7.2.8. DUPLICATE_PUSH 1496 The DUPLICATE_PUSH frame (type=0xE) is used by servers to indicate 1497 that an existing pushed resource is related to multiple client 1498 requests. 1500 The DUPLICATE_PUSH frame is always sent on a request stream. Receipt 1501 of a DUPLICATE_PUSH frame on any other stream MUST be treated as a 1502 connection error of type H3_FRAME_UNEXPECTED. 1504 A client MUST NOT send a DUPLICATE_PUSH frame. A server MUST treat 1505 the receipt of a DUPLICATE_PUSH frame as a connection error of type 1506 H3_FRAME_UNEXPECTED. 1508 0 1 2 3 1509 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1511 | Push ID (i) ... 1512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1514 Figure 11: DUPLICATE_PUSH Frame Payload 1516 The DUPLICATE_PUSH frame carries a single variable-length integer 1517 that identifies the Push ID of a resource that the server has 1518 previously promised (see Section 7.2.5), though that promise might 1519 not be received before this frame. A server MUST NOT use a Push ID 1520 that is larger than the client has provided in a MAX_PUSH_ID frame 1521 (Section 7.2.7). A client MUST treat receipt of a DUPLICATE_PUSH 1522 that contains a larger Push ID than the client has advertised as a 1523 connection error of type H3_ID_ERROR. 1525 This frame allows the server to use the same server push in response 1526 to multiple concurrent requests. Referencing the same server push 1527 ensures that a promise can be made in relation to every response in 1528 which server push might be needed without duplicating request headers 1529 or pushed responses. 1531 Allowing duplicate references to the same Push ID is primarily to 1532 reduce duplication caused by concurrent requests. A server SHOULD 1533 avoid reusing a Push ID over a long period. Clients are likely to 1534 consume server push responses and not retain them for reuse over 1535 time. Clients that see a DUPLICATE_PUSH that uses a Push ID that 1536 they have since consumed and discarded are forced to ignore the 1537 DUPLICATE_PUSH. 1539 7.2.9. Reserved Frame Types 1541 Frame types of the format "0x1f * N + 0x21" for integer values of N 1542 are reserved to exercise the requirement that unknown types be 1543 ignored (Section 9). These frames have no semantics, and can be sent 1544 on any open stream when application-layer padding is desired. They 1545 MAY also be sent on connections where no data is currently being 1546 transferred. Endpoints MUST NOT consider these frames to have any 1547 meaning upon receipt. 1549 The payload and length of the frames are selected in any manner the 1550 implementation chooses. 1552 Frame types which were used in HTTP/2 where there is no corresponding 1553 HTTP/3 frame have also been reserved (Section 11.2.1). These frame 1554 types MUST NOT be sent, and receipt MAY be treated as an error of 1555 type H3_FRAME_UNEXPECTED. 1557 8. Error Handling 1559 QUIC allows the application to abruptly terminate (reset) individual 1560 streams or the entire connection when an error is encountered. These 1561 are referred to as "stream errors" or "connection errors" and are 1562 described in more detail in [QUIC-TRANSPORT]. 1564 An endpoint MAY choose to treat a stream error as a connection error 1565 under certain circumstances. Implementations need to consider the 1566 impact on outstanding requests before making this choice. 1568 Because new error codes can be defined without negotiation (see 1569 Section 9), use of an error code in an unexpected context or receipt 1570 of an unknown error code MUST be treated as equivalent to 1571 H3_NO_ERROR. However, closing a stream can have other effects 1572 regardless of the error code (see Section 4.1). 1574 This section describes HTTP/3-specific error codes which can be used 1575 to express the cause of a connection or stream error. 1577 8.1. HTTP/3 Error Codes 1579 The following error codes are defined for use when abruptly 1580 terminating streams, aborting reading of streams, or immediately 1581 closing connections. 1583 H3_NO_ERROR (0x100): No error. This is used when the connection or 1584 stream needs to be closed, but there is no error to signal. 1586 H3_GENERAL_PROTOCOL_ERROR (0x101): Peer violated protocol 1587 requirements in a way which doesn't match a more specific error 1588 code, or endpoint declines to use the more specific error code. 1590 H3_INTERNAL_ERROR (0x102): An internal error has occurred in the 1591 HTTP stack. 1593 H3_STREAM_CREATION_ERROR (0x103): The endpoint detected that its 1594 peer created a stream that it will not accept. 1596 H3_CLOSED_CRITICAL_STREAM (0x104): A stream required by the 1597 connection was closed or reset. 1599 H3_FRAME_UNEXPECTED (0x105): A frame was received which was not 1600 permitted in the current state or on the current stream. 1602 H3_FRAME_ERROR (0x106): A frame that fails to satisfy layout 1603 requirements or with an invalid size was received. 1605 H3_EXCESSIVE_LOAD (0x107): The endpoint detected that its peer is 1606 exhibiting a behavior that might be generating excessive load. 1608 H3_ID_ERROR (0x108): A Stream ID or Push ID was used incorrectly, 1609 such as exceeding a limit, reducing a limit, or being reused. 1611 H3_SETTINGS_ERROR (0x109): An endpoint detected an error in the 1612 payload of a SETTINGS frame. 1614 H3_MISSING_SETTINGS (0x10A): No SETTINGS frame was received at the 1615 beginning of the control stream. 1617 H3_REQUEST_REJECTED (0x10B): A server rejected a request without 1618 performing any application processing. 1620 H3_REQUEST_CANCELLED (0x10C): The request or its response (including 1621 pushed response) is cancelled. 1623 H3_REQUEST_INCOMPLETE (0x10D): The client's stream terminated 1624 without containing a fully-formed request. 1626 H3_CONNECT_ERROR (0x10F): The connection established in response to 1627 a CONNECT request was reset or abnormally closed. 1629 H3_VERSION_FALLBACK (0x110): The requested operation cannot be 1630 served over HTTP/3. The peer should retry over HTTP/1.1. 1632 Error codes of the format "0x1f * N + 0x21" for integer values of N 1633 are reserved to exercise the requirement that unknown error codes be 1634 treated as equivalent to H3_NO_ERROR (Section 9). Implementations 1635 SHOULD select an error code from this space with some probability 1636 when they would have sent H3_NO_ERROR. 1638 9. Extensions to HTTP/3 1640 HTTP/3 permits extension of the protocol. Within the limitations 1641 described in this section, protocol extensions can be used to provide 1642 additional services or alter any aspect of the protocol. Extensions 1643 are effective only within the scope of a single HTTP/3 connection. 1645 This applies to the protocol elements defined in this document. This 1646 does not affect the existing options for extending HTTP, such as 1647 defining new methods, status codes, or header fields. 1649 Extensions are permitted to use new frame types (Section 7.2), new 1650 settings (Section 7.2.4.1), new error codes (Section 8), or new 1651 unidirectional stream types (Section 6.2). Registries are 1652 established for managing these extension points: frame types 1653 (Section 11.2.1), settings (Section 11.2.2), error codes 1654 (Section 11.2.3), and stream types (Section 11.2.4). 1656 Implementations MUST ignore unknown or unsupported values in all 1657 extensible protocol elements. Implementations MUST discard frames 1658 and unidirectional streams that have unknown or unsupported types. 1659 This means that any of these extension points can be safely used by 1660 extensions without prior arrangement or negotiation. However, where 1661 a known frame type is required to be in a specific location, such as 1662 the SETTINGS frame as the first frame of the control stream (see 1663 Section 6.2.1), an unknown frame type does not satisfy that 1664 requirement and SHOULD be treated as an error. 1666 Extensions that could change the semantics of existing protocol 1667 components MUST be negotiated before being used. For example, an 1668 extension that changes the layout of the HEADERS frame cannot be used 1669 until the peer has given a positive signal that this is acceptable. 1670 Coordinating when such a revised layout comes into effect could prove 1671 complex. As such, allocating new identifiers for new definitions of 1672 existing protocol elements is likely to be more effective. 1674 This document doesn't mandate a specific method for negotiating the 1675 use of an extension but notes that a setting (Section 7.2.4.1) could 1676 be used for that purpose. If both peers set a value that indicates 1677 willingness to use the extension, then the extension can be used. If 1678 a setting is used for extension negotiation, the default value MUST 1679 be defined in such a fashion that the extension is disabled if the 1680 setting is omitted. 1682 10. Security Considerations 1684 The security considerations of HTTP/3 should be comparable to those 1685 of HTTP/2 with TLS; the considerations from Section 10 of [HTTP2] 1686 apply in addition to those listed here. 1688 When HTTP Alternative Services is used for discovery for HTTP/3 1689 endpoints, the security considerations of [ALTSVC] also apply. 1691 10.1. Traffic Analysis 1693 Where HTTP/2 employs PADDING frames and Padding fields in other 1694 frames to make a connection more resistant to traffic analysis, 1695 HTTP/3 can either rely on transport-layer padding or employ the 1696 reserved frame and stream types discussed in Section 7.2.9 and 1697 Section 6.2.3. These methods of padding produce different results in 1698 terms of the granularity of padding, the effect of packet loss and 1699 recovery, and how an implementation might control padding. 1701 10.2. Frame Parsing 1703 Several protocol elements contain nested length elements, typically 1704 in the form of frames with an explicit length containing variable- 1705 length integers. This could pose a security risk to an incautious 1706 implementer. An implementation MUST ensure that the length of a 1707 frame exactly matches the length of the fields it contains. 1709 10.3. Early Data 1711 The use of 0-RTT with HTTP/3 creates an exposure to replay attack. 1712 The anti-replay mitigations in [HTTP-REPLAY] MUST be applied when 1713 using HTTP/3 with 0-RTT. 1715 10.4. Migration 1717 Certain HTTP implementations use the client address for logging or 1718 access-control purposes. Since a QUIC client's address might change 1719 during a connection (and future versions might support simultaneous 1720 use of multiple addresses), such implementations will need to either 1721 actively retrieve the client's current address or addresses when they 1722 are relevant or explicitly accept that the original address might 1723 change. 1725 11. IANA Considerations 1727 This document registers a new ALPN protocol ID (Section 11.1) and 1728 creates new registries that manage the assignment of codepoints in 1729 HTTP/3. 1731 11.1. Registration of HTTP/3 Identification String 1733 This document creates a new registration for the identification of 1734 HTTP/3 in the "Application Layer Protocol Negotiation (ALPN) Protocol 1735 IDs" registry established in [RFC7301]. 1737 The "h3" string identifies HTTP/3: 1739 Protocol: HTTP/3 1741 Identification Sequence: 0x68 0x33 ("h3") 1743 Specification: This document 1745 11.2. New Registries 1747 New registries created in this document operate under the QUIC 1748 registration policy documented in Section 22.1 of [QUIC-TRANSPORT]. 1749 These registries all include the common set of fields listed in 1750 Section 22.1.1 of [QUIC-TRANSPORT]. 1752 The initial allocations in these registries created in this document 1753 are all assigned permanent status and list as contact both the IESG 1754 (iesg@ietf.org) and the HTTP working group (ietf-http-wg@w3.org). 1756 11.2.1. Frame Types 1758 This document establishes a registry for HTTP/3 frame type codes. 1759 The "HTTP/3 Frame Type" registry governs a 62-bit space. This 1760 registry follows the QUIC registry policy; see Section 11.2. 1761 Permanent registrations in this registry are assigned using the 1762 Specification Required policy [RFC8126], except for values between 1763 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned using 1764 Standards Action or IESG Approval as defined in Section 4.9 and 4.10 1765 of [RFC8126]. 1767 While this registry is separate from the "HTTP/2 Frame Type" registry 1768 defined in [HTTP2], it is preferable that the assignments parallel 1769 each other where the code spaces overlap. If an entry is present in 1770 only one registry, every effort SHOULD be made to avoid assigning the 1771 corresponding value to an unrelated operation. 1773 In addition to common fields as described in Section 11.2, permanent 1774 registrations in this registry MUST include the following field: 1776 Frame Type: A name or label for the frame type. 1778 Specifications of frame types MUST include a description of the frame 1779 layout and its semantics, including any parts of the frame that are 1780 conditionally present. 1782 The entries in Table 2 are registered by this document. 1784 +----------------+-------+---------------+ 1785 | Frame Type | Value | Specification | 1786 +================+=======+===============+ 1787 | DATA | 0x0 | Section 7.2.1 | 1788 +----------------+-------+---------------+ 1789 | HEADERS | 0x1 | Section 7.2.2 | 1790 +----------------+-------+---------------+ 1791 | Reserved | 0x2 | N/A | 1792 +----------------+-------+---------------+ 1793 | CANCEL_PUSH | 0x3 | Section 7.2.3 | 1794 +----------------+-------+---------------+ 1795 | SETTINGS | 0x4 | Section 7.2.4 | 1796 +----------------+-------+---------------+ 1797 | PUSH_PROMISE | 0x5 | Section 7.2.5 | 1798 +----------------+-------+---------------+ 1799 | Reserved | 0x6 | N/A | 1800 +----------------+-------+---------------+ 1801 | GOAWAY | 0x7 | Section 7.2.6 | 1802 +----------------+-------+---------------+ 1803 | Reserved | 0x8 | N/A | 1804 +----------------+-------+---------------+ 1805 | Reserved | 0x9 | N/A | 1806 +----------------+-------+---------------+ 1807 | MAX_PUSH_ID | 0xD | Section 7.2.7 | 1808 +----------------+-------+---------------+ 1809 | DUPLICATE_PUSH | 0xE | Section 7.2.8 | 1810 +----------------+-------+---------------+ 1812 Table 2: Initial HTTP/3 Frame Types 1814 Additionally, each code of the format "0x1f * N + 0x21" for integer 1815 values of N (that is, "0x21", "0x40", ..., through 1816 "0x3FFFFFFFFFFFFFFE") MUST NOT be assigned by IANA. 1818 11.2.2. Settings Parameters 1820 This document establishes a registry for HTTP/3 settings. The 1821 "HTTP/3 Settings" registry governs a 62-bit space. This registry 1822 follows the QUIC registry policy; see Section 11.2. Permanent 1823 registrations in this registry are assigned using the Specification 1824 Required policy [RFC8126], except for values between 0x00 and 0x3f 1825 (in hexadecimal; inclusive), which are assigned using Standards 1826 Action or IESG Approval as defined in Section 4.9 and 4.10 of 1827 [RFC8126]. 1829 While this registry is separate from the "HTTP/2 Settings" registry 1830 defined in [HTTP2], it is preferable that the assignments parallel 1831 each other. If an entry is present in only one registry, every 1832 effort SHOULD be made to avoid assigning the corresponding value to 1833 an unrelated operation. 1835 In addition to common fields as described in Section 11.2, permanent 1836 registrations in this registry MUST include the following fields: 1838 Setting Name: A symbolic name for the setting. Specifying a setting 1839 name is optional. 1841 Default: The value of the setting unless otherwise indicated. A 1842 default SHOULD be the most restrictive possible value. 1844 The entries in Table 3 are registered by this document. 1846 +----------------------+-------+-----------------+-----------+ 1847 | Setting Name | Value | Specification | Default | 1848 +======================+=======+=================+===========+ 1849 | Reserved | 0x2 | N/A | N/A | 1850 +----------------------+-------+-----------------+-----------+ 1851 | Reserved | 0x3 | N/A | N/A | 1852 +----------------------+-------+-----------------+-----------+ 1853 | Reserved | 0x4 | N/A | N/A | 1854 +----------------------+-------+-----------------+-----------+ 1855 | Reserved | 0x5 | N/A | N/A | 1856 +----------------------+-------+-----------------+-----------+ 1857 | MAX_HEADER_LIST_SIZE | 0x6 | Section 7.2.4.1 | Unlimited | 1858 +----------------------+-------+-----------------+-----------+ 1860 Table 3: Initial HTTP/3 Settings 1862 Additionally, each code of the format "0x1f * N + 0x21" for integer 1863 values of N (that is, "0x21", "0x40", ..., through 1864 "0x3FFFFFFFFFFFFFFE") MUST NOT be assigned by IANA. 1866 11.2.3. Error Codes 1868 This document establishes a registry for HTTP/3 error codes. The 1869 "HTTP/3 Error Code" registry manages a 62-bit space. This registry 1870 follows the QUIC registry policy; see Section 11.2. Permanent 1871 registrations in this registry are assigned using the Specification 1872 Required policy [RFC8126], except for values between 0x00 and 0x3f 1873 (in hexadecimal; inclusive), which are assigned using Standards 1874 Action or IESG Approval as defined in Section 4.9 and 4.10 of 1875 [RFC8126]. 1877 Registrations for error codes are required to include a description 1878 of the error code. An expert reviewer is advised to examine new 1879 registrations for possible duplication with existing error codes. 1880 Use of existing registrations is to be encouraged, but not mandated. 1882 In addition to common fields as described in Section 11.2, permanent 1883 registrations in this registry MUST include the following fields: 1885 Name: A name for the error code. Specifying an error code name is 1886 optional. 1888 Description: A brief description of the error code semantics. 1890 The entries in the Table 4 are registered by this document. 1892 +---------------------------+--------+--------------+---------------+ 1893 | Name | Value | Description | Specification | 1894 +===========================+========+==============+===============+ 1895 | H3_NO_ERROR | 0x0100 | No error | Section 8.1 | 1896 +---------------------------+--------+--------------+---------------+ 1897 | H3_GENERAL_PROTOCOL_ERROR | 0x0101 | General | Section 8.1 | 1898 | | | protocol | | 1899 | | | error | | 1900 +---------------------------+--------+--------------+---------------+ 1901 | H3_INTERNAL_ERROR | 0x0102 | Internal | Section 8.1 | 1902 | | | error | | 1903 +---------------------------+--------+--------------+---------------+ 1904 | H3_STREAM_CREATION_ERROR | 0x0103 | Stream | Section 8.1 | 1905 | | | creation | | 1906 | | | error | | 1907 +---------------------------+--------+--------------+---------------+ 1908 | H3_CLOSED_CRITICAL_STREAM | 0x0104 | Critical | Section 8.1 | 1909 | | | stream was | | 1910 | | | closed | | 1911 +---------------------------+--------+--------------+---------------+ 1912 | H3_FRAME_UNEXPECTED | 0x0105 | Frame not | Section 8.1 | 1913 | | | permitted | | 1914 | | | in the | | 1915 | | | current | | 1916 | | | state | | 1917 +---------------------------+--------+--------------+---------------+ 1918 | H3_FRAME_ERROR | 0x0106 | Frame | Section 8.1 | 1919 | | | violated | | 1920 | | | layout or | | 1921 | | | size rules | | 1922 +---------------------------+--------+--------------+---------------+ 1923 | H3_EXCESSIVE_LOAD | 0x0107 | Peer | Section 8.1 | 1924 | | | generating | | 1925 | | | excessive | | 1926 | | | load | | 1927 +---------------------------+--------+--------------+---------------+ 1928 | H3_ID_ERROR | 0x0108 | An | Section 8.1 | 1929 | | | identifier | | 1930 | | | was used | | 1931 | | | incorrectly | | 1932 +---------------------------+--------+--------------+---------------+ 1933 | H3_SETTINGS_ERROR | 0x0109 | SETTINGS | Section 8.1 | 1934 | | | frame | | 1935 | | | contained | | 1936 | | | invalid | | 1937 | | | values | | 1938 +---------------------------+--------+--------------+---------------+ 1939 | H3_MISSING_SETTINGS | 0x010A | No SETTINGS | Section 8.1 | 1940 | | | frame | | 1941 | | | received | | 1942 +---------------------------+--------+--------------+---------------+ 1943 | H3_REQUEST_REJECTED | 0x010B | Request not | Section 8.1 | 1944 | | | processed | | 1945 +---------------------------+--------+--------------+---------------+ 1946 | H3_REQUEST_CANCELLED | 0x010C | Data no | Section 8.1 | 1947 | | | longer | | 1948 | | | needed | | 1949 +---------------------------+--------+--------------+---------------+ 1950 | H3_REQUEST_INCOMPLETE | 0x010D | Stream | Section 8.1 | 1951 | | | terminated | | 1952 | | | early | | 1953 +---------------------------+--------+--------------+---------------+ 1954 | H3_CONNECT_ERROR | 0x010F | TCP reset | Section 8.1 | 1955 | | | or error on | | 1956 | | | CONNECT | | 1957 | | | request | | 1958 +---------------------------+--------+--------------+---------------+ 1959 | H3_VERSION_FALLBACK | 0x0110 | Retry over | Section 8.1 | 1960 | | | HTTP/1.1 | | 1961 +---------------------------+--------+--------------+---------------+ 1963 Table 4: Initial HTTP/3 Error Codes 1965 Additionally, each code of the format "0x1f * N + 0x21" for integer 1966 values of N (that is, "0x21", "0x40", ..., through 1967 "0x3FFFFFFFFFFFFFFE") MUST NOT be assigned by IANA. 1969 11.2.4. Stream Types 1971 This document establishes a registry for HTTP/3 unidirectional stream 1972 types. The "HTTP/3 Stream Type" registry governs a 62-bit space. 1973 This registry follows the QUIC registry policy; see Section 11.2. 1974 Permanent registrations in this registry are assigned using the 1975 Specification Required policy [RFC8126], except for values between 1976 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned using 1977 Standards Action or IESG Approval as defined in Section 4.9 and 4.10 1978 of [RFC8126]. 1980 In addition to common fields as described in Section 11.2, permanent 1981 registrations in this registry MUST include the following fields: 1983 Stream Type: A name or label for the stream type. 1985 Sender: Which endpoint on a connection may initiate a stream of this 1986 type. Values are "Client", "Server", or "Both". 1988 Specifications for permanent registrations MUST include a description 1989 of the stream type, including the layout semantics of the stream 1990 contents. 1992 The entries in the following table are registered by this document. 1994 +----------------+-------+---------------+--------+ 1995 | Stream Type | Value | Specification | Sender | 1996 +================+=======+===============+========+ 1997 | Control Stream | 0x00 | Section 6.2.1 | Both | 1998 +----------------+-------+---------------+--------+ 1999 | Push Stream | 0x01 | Section 4.4 | Server | 2000 +----------------+-------+---------------+--------+ 2002 Table 5 2004 Additionally, each code of the format "0x1f * N + 0x21" for integer 2005 values of N (that is, "0x21", "0x40", ..., through 2006 "0x3FFFFFFFFFFFFFFE") MUST NOT be assigned by IANA. 2008 12. References 2010 12.1. Normative References 2012 [ALTSVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP 2013 Alternative Services", RFC 7838, DOI 10.17487/RFC7838, 2014 April 2016, . 2016 [HTTP-REPLAY] 2017 Thomson, M., Nottingham, M., and W. Tarreau, "Using Early 2018 Data in HTTP", RFC 8470, DOI 10.17487/RFC8470, September 2019 2018, . 2021 [HTTP2] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext 2022 Transfer Protocol Version 2 (HTTP/2)", RFC 7540, 2023 DOI 10.17487/RFC7540, May 2015, 2024 . 2026 [QPACK] Krasic, C., Bishop, M., and A. Frindell, Ed., "QPACK: 2027 Header Compression for HTTP over QUIC", Work in Progress, 2028 Internet-Draft, draft-ietf-quic-qpack-12, 22 January 2020, 2029 . 2031 [QUIC-TRANSPORT] 2032 Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based 2033 Multiplexed and Secure Transport", Work in Progress, 2034 Internet-Draft, draft-ietf-quic-transport-25, 22 January 2035 2020, . 2038 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 2039 RFC 793, DOI 10.17487/RFC0793, September 1981, 2040 . 2042 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2043 Requirement Levels", BCP 14, RFC 2119, 2044 DOI 10.17487/RFC2119, March 1997, 2045 . 2047 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 2048 Specifications: ABNF", STD 68, RFC 5234, 2049 DOI 10.17487/RFC5234, January 2008, 2050 . 2052 [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) 2053 Extensions: Extension Definitions", RFC 6066, 2054 DOI 10.17487/RFC6066, January 2011, 2055 . 2057 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 2058 DOI 10.17487/RFC6265, April 2011, 2059 . 2061 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 2062 Protocol (HTTP/1.1): Message Syntax and Routing", 2063 RFC 7230, DOI 10.17487/RFC7230, June 2014, 2064 . 2066 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 2067 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 2068 DOI 10.17487/RFC7231, June 2014, 2069 . 2071 [RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP 2072 Alternative Services", RFC 7838, DOI 10.17487/RFC7838, 2073 April 2016, . 2075 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2076 Writing an IANA Considerations Section in RFCs", BCP 26, 2077 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2078 . 2080 [RFC8164] Nottingham, M. and M. Thomson, "Opportunistic Security for 2081 HTTP/2", RFC 8164, DOI 10.17487/RFC8164, May 2017, 2082 . 2084 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2085 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2086 May 2017, . 2088 12.2. Informative References 2090 [HPACK] Peon, R. and H. Ruellan, "HPACK: Header Compression for 2091 HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, 2092 . 2094 [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status 2095 Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012, 2096 . 2098 [RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan, 2099 "Transport Layer Security (TLS) Application-Layer Protocol 2100 Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, 2101 July 2014, . 2103 [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP 2104 Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, 2105 . 2107 Appendix A. Considerations for Transitioning from HTTP/2 2109 HTTP/3 is strongly informed by HTTP/2, and bears many similarities. 2110 This section describes the approach taken to design HTTP/3, points 2111 out important differences from HTTP/2, and describes how to map 2112 HTTP/2 extensions into HTTP/3. 2114 HTTP/3 begins from the premise that similarity to HTTP/2 is 2115 preferable, but not a hard requirement. HTTP/3 departs from HTTP/2 2116 where QUIC differs from TCP, either to take advantage of QUIC 2117 features (like streams) or to accommodate important shortcomings 2118 (such as a lack of total ordering). These differences make HTTP/3 2119 similar to HTTP/2 in key aspects, such as the relationship of 2120 requests and responses to streams. However, the details of the 2121 HTTP/3 design are substantially different than HTTP/2. 2123 These departures are noted in this section. 2125 A.1. Streams 2127 HTTP/3 permits use of a larger number of streams (2^62-1) than 2128 HTTP/2. The considerations about exhaustion of stream identifier 2129 space apply, though the space is significantly larger such that it is 2130 likely that other limits in QUIC are reached first, such as the limit 2131 on the connection flow control window. 2133 In contrast to HTTP/2, stream concurrency in HTTP/3 is managed by 2134 QUIC. QUIC considers a stream closed when all data has been received 2135 and sent data has been acknowledged by the peer. HTTP/2 considers a 2136 stream closed when the frame containing the END_STREAM bit has been 2137 committed to the transport. As a result, the stream for an 2138 equivalent exchange could remain "active" for a longer period of 2139 time. HTTP/3 servers might choose to permit a larger number of 2140 concurrent client-initiated bidirectional streams to achieve 2141 equivalent concurrency to HTTP/2, depending on the expected usage 2142 patterns. 2144 Due to the presence of other unidirectional stream types, HTTP/3 does 2145 not rely exclusively on the number of concurrent unidirectional 2146 streams to control the number of concurrent in-flight pushes. 2147 Instead, HTTP/3 clients use the MAX_PUSH_ID frame to control the 2148 number of pushes received from an HTTP/3 server. 2150 A.2. HTTP Frame Types 2152 Many framing concepts from HTTP/2 can be elided on QUIC, because the 2153 transport deals with them. Because frames are already on a stream, 2154 they can omit the stream number. Because frames do not block 2155 multiplexing (QUIC's multiplexing occurs below this layer), the 2156 support for variable-maximum-length packets can be removed. Because 2157 stream termination is handled by QUIC, an END_STREAM flag is not 2158 required. This permits the removal of the Flags field from the 2159 generic frame layout. 2161 Frame payloads are largely drawn from [HTTP2]. However, QUIC 2162 includes many features (e.g., flow control) which are also present in 2163 HTTP/2. In these cases, the HTTP mapping does not re-implement them. 2164 As a result, several HTTP/2 frame types are not required in HTTP/3. 2165 Where an HTTP/2-defined frame is no longer used, the frame ID has 2166 been reserved in order to maximize portability between HTTP/2 and 2167 HTTP/3 implementations. However, even equivalent frames between the 2168 two mappings are not identical. 2170 Many of the differences arise from the fact that HTTP/2 provides an 2171 absolute ordering between frames across all streams, while QUIC 2172 provides this guarantee on each stream only. As a result, if a frame 2173 type makes assumptions that frames from different streams will still 2174 be received in the order sent, HTTP/3 will break them. 2176 Some examples of feature adaptations are described below, as well as 2177 general guidance to extension frame implementors converting an HTTP/2 2178 extension to HTTP/3. 2180 A.2.1. Prioritization Differences 2182 HTTP/2 specifies priority assignments in PRIORITY frames and 2183 (optionally) in HEADERS frames. HTTP/3 does not provide a means of 2184 signaling priority. 2186 Note that while there is no explicit signaling for priority, this 2187 does not mean that prioritization is not important for achieving good 2188 performance. 2190 A.2.2. Header Compression Differences 2192 HPACK was designed with the assumption of in-order delivery. A 2193 sequence of encoded header blocks must arrive (and be decoded) at an 2194 endpoint in the same order in which they were encoded. This ensures 2195 that the dynamic state at the two endpoints remains in sync. 2197 Because this total ordering is not provided by QUIC, HTTP/3 uses a 2198 modified version of HPACK, called QPACK. QPACK uses a single 2199 unidirectional stream to make all modifications to the dynamic table, 2200 ensuring a total order of updates. All frames which contain encoded 2201 headers merely reference the table state at a given time without 2202 modifying it. 2204 [QPACK] provides additional details. 2206 A.2.3. Guidance for New Frame Type Definitions 2208 Frame type definitions in HTTP/3 often use the QUIC variable-length 2209 integer encoding. In particular, Stream IDs use this encoding, which 2210 allows for a larger range of possible values than the encoding used 2211 in HTTP/2. Some frames in HTTP/3 use an identifier rather than a 2212 Stream ID (e.g., Push IDs). Redefinition of the encoding of 2213 extension frame types might be necessary if the encoding includes a 2214 Stream ID. 2216 Because the Flags field is not present in generic HTTP/3 frames, 2217 those frames which depend on the presence of flags need to allocate 2218 space for flags as part of their frame payload. 2220 Other than this issue, frame type HTTP/2 extensions are typically 2221 portable to QUIC simply by replacing Stream 0 in HTTP/2 with a 2222 control stream in HTTP/3. HTTP/3 extensions will not assume 2223 ordering, but would not be harmed by ordering, and would be portable 2224 to HTTP/2 in the same manner. 2226 A.2.4. Mapping Between HTTP/2 and HTTP/3 Frame Types 2228 DATA (0x0): Padding is not defined in HTTP/3 frames. See 2229 Section 7.2.1. 2231 HEADERS (0x1): The PRIORITY region of HEADERS is not defined in 2232 HTTP/3 frames. Padding is not defined in HTTP/3 frames. See 2233 Section 7.2.2. 2235 PRIORITY (0x2): As described in Appendix A.2.1, HTTP/3 does not 2236 provide a means of signaling priority. 2238 RST_STREAM (0x3): RST_STREAM frames do not exist, since QUIC 2239 provides stream lifecycle management. The same code point is used 2240 for the CANCEL_PUSH frame (Section 7.2.3). 2242 SETTINGS (0x4): SETTINGS frames are sent only at the beginning of 2243 the connection. See Section 7.2.4 and Appendix A.3. 2245 PUSH_PROMISE (0x5): The PUSH_PROMISE does not reference a stream; 2246 instead the push stream references the PUSH_PROMISE frame using a 2247 Push ID. See Section 7.2.5. 2249 PING (0x6): PING frames do not exist, since QUIC provides equivalent 2250 functionality. 2252 GOAWAY (0x7): GOAWAY is sent only from server to client and does not 2253 contain an error code. See Section 7.2.6. 2255 WINDOW_UPDATE (0x8): WINDOW_UPDATE frames do not exist, since QUIC 2256 provides flow control. 2258 CONTINUATION (0x9): CONTINUATION frames do not exist; instead, 2259 larger HEADERS/PUSH_PROMISE frames than HTTP/2 are permitted. 2261 Frame types defined by extensions to HTTP/2 need to be separately 2262 registered for HTTP/3 if still applicable. The IDs of frames defined 2263 in [HTTP2] have been reserved for simplicity. Note that the frame 2264 type space in HTTP/3 is substantially larger (62 bits versus 8 bits), 2265 so many HTTP/3 frame types have no equivalent HTTP/2 code points. 2266 See Section 11.2.1. 2268 A.3. HTTP/2 SETTINGS Parameters 2270 An important difference from HTTP/2 is that settings are sent once, 2271 as the first frame of the control stream, and thereafter cannot 2272 change. This eliminates many corner cases around synchronization of 2273 changes. 2275 Some transport-level options that HTTP/2 specifies via the SETTINGS 2276 frame are superseded by QUIC transport parameters in HTTP/3. The 2277 HTTP-level options that are retained in HTTP/3 have the same value as 2278 in HTTP/2. 2280 Below is a listing of how each HTTP/2 SETTINGS parameter is mapped: 2282 SETTINGS_HEADER_TABLE_SIZE: See [QPACK]. 2284 SETTINGS_ENABLE_PUSH: This is removed in favor of the MAX_PUSH_ID 2285 which provides a more granular control over server push. 2287 SETTINGS_MAX_CONCURRENT_STREAMS: QUIC controls the largest open 2288 Stream ID as part of its flow control logic. Specifying 2289 SETTINGS_MAX_CONCURRENT_STREAMS in the SETTINGS frame is an error. 2291 SETTINGS_INITIAL_WINDOW_SIZE: QUIC requires both stream and 2292 connection flow control window sizes to be specified in the 2293 initial transport handshake. Specifying 2294 SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame is an error. 2296 SETTINGS_MAX_FRAME_SIZE: This setting has no equivalent in HTTP/3. 2297 Specifying it in the SETTINGS frame is an error. 2299 SETTINGS_MAX_HEADER_LIST_SIZE: See Section 7.2.4.1. 2301 In HTTP/3, setting values are variable-length integers (6, 14, 30, or 2302 62 bits long) rather than fixed-length 32-bit fields as in HTTP/2. 2303 This will often produce a shorter encoding, but can produce a longer 2304 encoding for settings which use the full 32-bit space. Settings 2305 ported from HTTP/2 might choose to redefine their value to limit it 2306 to 30 bits for more efficient encoding, or to make use of the 62-bit 2307 space if more than 30 bits are required. 2309 Settings need to be defined separately for HTTP/2 and HTTP/3. The 2310 IDs of settings defined in [HTTP2] have been reserved for simplicity. 2311 Note that the settings identifier space in HTTP/3 is substantially 2312 larger (62 bits versus 16 bits), so many HTTP/3 settings have no 2313 equivalent HTTP/2 code point. See Section 11.2.2. 2315 As QUIC streams might arrive out-of-order, endpoints are advised to 2316 not wait for the peers' settings to arrive before responding to other 2317 streams. See Section 7.2.4.2. 2319 A.4. HTTP/2 Error Codes 2321 QUIC has the same concepts of "stream" and "connection" errors that 2322 HTTP/2 provides. However, there is no direct portability of HTTP/2 2323 error codes to HTTP/3 error codes; the values are shifted in order to 2324 prevent accidental or implicit conversion. 2326 The HTTP/2 error codes defined in Section 7 of [HTTP2] logically map 2327 to the HTTP/3 error codes as follows: 2329 NO_ERROR (0x0): H3_NO_ERROR in Section 8.1. 2331 PROTOCOL_ERROR (0x1): This is mapped to H3_GENERAL_PROTOCOL_ERROR 2332 except in cases where more specific error codes have been defined. 2333 This includes H3_FRAME_UNEXPECTED and H3_CLOSED_CRITICAL_STREAM 2334 defined in Section 8.1. 2336 INTERNAL_ERROR (0x2): H3_INTERNAL_ERROR in Section 8.1. 2338 FLOW_CONTROL_ERROR (0x3): Not applicable, since QUIC handles flow 2339 control. 2341 SETTINGS_TIMEOUT (0x4): Not applicable, since no acknowledgement of 2342 SETTINGS is defined. 2344 STREAM_CLOSED (0x5): Not applicable, since QUIC handles stream 2345 management. 2347 FRAME_SIZE_ERROR (0x6): H3_FRAME_ERROR error code defined in 2348 Section 8.1. 2350 REFUSED_STREAM (0x7): H3_REQUEST_REJECTED (in Section 8.1) is used 2351 to indicate that a request was not processed. Otherwise, not 2352 applicable because QUIC handles stream management. 2354 CANCEL (0x8): H3_REQUEST_CANCELLED in Section 8.1. 2356 COMPRESSION_ERROR (0x9): Multiple error codes are defined in 2357 [QPACK]. 2359 CONNECT_ERROR (0xa): H3_CONNECT_ERROR in Section 8.1. 2361 ENHANCE_YOUR_CALM (0xb): H3_EXCESSIVE_LOAD in Section 8.1. 2363 INADEQUATE_SECURITY (0xc): Not applicable, since QUIC is assumed to 2364 provide sufficient security on all connections. 2366 H3_1_1_REQUIRED (0xd): H3_VERSION_FALLBACK in Section 8.1. 2368 Error codes need to be defined for HTTP/2 and HTTP/3 separately. See 2369 Section 11.2.3. 2371 Appendix B. Change Log 2373 *RFC Editor's Note:* Please remove this section prior to 2374 publication of a final version of this document. 2376 B.1. Since draft-ietf-quic-http-24 2378 * Removed H3_EARLY_RESPONSE error code; H3_NO_ERROR is recommended 2379 instead (#3130,#3208) 2381 * Unknown error codes are equivalent to H3_NO_ERROR (#3276,#3331) 2383 * Some error codes are reserved for greasing (#3325,#3360) 2385 B.2. Since draft-ietf-quic-http-23 2387 * Removed "quic" Alt-Svc parameter (#3061,#3118) 2388 * Clients need not persist unknown settings for use in 0-RTT 2389 (#3110,#3113) 2391 * Clarify error cases around CANCEL_PUSH (#2819,#3083) 2393 B.3. Since draft-ietf-quic-http-22 2395 * Removed priority signaling (#2922,#2924) 2397 * Further changes to error codes (#2662,#2551): 2399 - Error codes renumbered 2401 - HTTP_MALFORMED_FRAME replaced by HTTP_FRAME_ERROR, 2402 HTTP_ID_ERROR, and others 2404 * Clarify how unknown frame types interact with required frame 2405 sequence (#2867,#2858) 2407 * Describe interactions with the transport in terms of defined 2408 interface terms (#2857,#2805) 2410 * Require the use of the "http-opportunistic" resource (RFC 8164) 2411 when scheme is "http" (#2439,#2973) 2413 * Settings identifiers cannot be duplicated (#2979) 2415 * Changes to SETTINGS frames in 0-RTT (#2972,#2790,#2945): 2417 - Servers must send all settings with non-default values in their 2418 SETTINGS frame, even when resuming 2420 - If a client doesn't have settings associated with a 0-RTT 2421 ticket, it uses the defaults 2423 - Servers can't accept early data if they cannot recover the 2424 settings the client will have remembered 2426 * Clarify that Upgrade and the 101 status code are prohibited 2427 (#2898,#2889) 2429 * Clarify that frame types reserved for greasing can occur on any 2430 stream, but frame types reserved due to HTTP/2 correspondence are 2431 prohibited (#2997,#2692,#2693) 2433 * Unknown error codes cannot be treated as errors (#2998,#2816) 2435 B.4. Since draft-ietf-quic-http-21 2437 No changes 2439 B.5. Since draft-ietf-quic-http-20 2441 * Prohibit closing the control stream (#2509, #2666) 2443 * Change default priority to use an orphan node (#2502, #2690) 2445 * Exclusive priorities are restored (#2754, #2781) 2447 * Restrict use of frames when using CONNECT (#2229, #2702) 2449 * Close and maybe reset streams if a connection error occurs for 2450 CONNECT (#2228, #2703) 2452 * Encourage provision of sufficient unidirectional streams for QPACK 2453 (#2100, #2529, #2762) 2455 * Allow extensions to use server-initiated bidirectional streams 2456 (#2711, #2773) 2458 * Clarify use of maximum header list size setting (#2516, #2774) 2460 * Extensive changes to error codes and conditions of their sending 2462 - Require connection errors for more error conditions (#2511, 2463 #2510) 2465 - Updated the error codes for illegal GOAWAY frames (#2714, 2466 #2707) 2468 - Specified error code for HEADERS on control stream (#2708) 2470 - Specified error code for servers receiving PUSH_PROMISE (#2709) 2472 - Specified error code for receiving DATA before HEADERS (#2715) 2474 - Describe malformed messages and their handling (#2410, #2764) 2476 - Remove HTTP_PUSH_ALREADY_IN_CACHE error (#2812, #2813) 2478 - Refactor Push ID related errors (#2818, #2820) 2480 - Rationalize HTTP/3 stream creation errors (#2821, #2822) 2482 B.6. Since draft-ietf-quic-http-19 2484 * SETTINGS_NUM_PLACEHOLDERS is 0x9 (#2443,#2530) 2486 * Non-zero bits in the Empty field of the PRIORITY frame MAY be 2487 treated as an error (#2501) 2489 B.7. Since draft-ietf-quic-http-18 2491 * Resetting streams following a GOAWAY is recommended, but not 2492 required (#2256,#2457) 2494 * Use variable-length integers throughout (#2437,#2233,#2253,#2275) 2496 - Variable-length frame types, stream types, and settings 2497 identifiers 2499 - Renumbered stream type assignments 2501 - Modified associated reserved values 2503 * Frame layout switched from Length-Type-Value to Type-Length-Value 2504 (#2395,#2235) 2506 * Specified error code for servers receiving DUPLICATE_PUSH (#2497) 2508 * Use connection error for invalid PRIORITY (#2507, #2508) 2510 B.8. Since draft-ietf-quic-http-17 2512 * HTTP_REQUEST_REJECTED is used to indicate a request can be retried 2513 (#2106, #2325) 2515 * Changed error code for GOAWAY on the wrong stream (#2231, #2343) 2517 B.9. Since draft-ietf-quic-http-16 2519 * Rename "HTTP/QUIC" to "HTTP/3" (#1973) 2521 * Changes to PRIORITY frame (#1865, #2075) 2523 - Permitted as first frame of request streams 2525 - Remove exclusive reprioritization 2527 - Changes to Prioritized Element Type bits 2529 * Define DUPLICATE_PUSH frame to refer to another PUSH_PROMISE 2530 (#2072) 2532 * Set defaults for settings, allow request before receiving SETTINGS 2533 (#1809, #1846, #2038) 2535 * Clarify message processing rules for streams that aren't closed 2536 (#1972, #2003) 2538 * Removed reservation of error code 0 and moved HTTP_NO_ERROR to 2539 this value (#1922) 2541 * Removed prohibition of zero-length DATA frames (#2098) 2543 B.10. Since draft-ietf-quic-http-15 2545 Substantial editorial reorganization; no technical changes. 2547 B.11. Since draft-ietf-quic-http-14 2549 * Recommend sensible values for QUIC transport parameters 2550 (#1720,#1806) 2552 * Define error for missing SETTINGS frame (#1697,#1808) 2554 * Setting values are variable-length integers (#1556,#1807) and do 2555 not have separate maximum values (#1820) 2557 * Expanded discussion of connection closure (#1599,#1717,#1712) 2559 * HTTP_VERSION_FALLBACK falls back to HTTP/1.1 (#1677,#1685) 2561 B.12. Since draft-ietf-quic-http-13 2563 * Reserved some frame types for grease (#1333, #1446) 2565 * Unknown unidirectional stream types are tolerated, not errors; 2566 some reserved for grease (#1490, #1525) 2568 * Require settings to be remembered for 0-RTT, prohibit reductions 2569 (#1541, #1641) 2571 * Specify behavior for truncated requests (#1596, #1643) 2573 B.13. Since draft-ietf-quic-http-12 2575 * TLS SNI extension isn't mandatory if an alternative method is used 2576 (#1459, #1462, #1466) 2578 * Removed flags from HTTP/3 frames (#1388, #1398) 2580 * Reserved frame types and settings for use in preserving 2581 extensibility (#1333, #1446) 2583 * Added general error code (#1391, #1397) 2585 * Unidirectional streams carry a type byte and are extensible 2586 (#910,#1359) 2588 * Priority mechanism now uses explicit placeholders to enable 2589 persistent structure in the tree (#441,#1421,#1422) 2591 B.14. Since draft-ietf-quic-http-11 2593 * Moved QPACK table updates and acknowledgments to dedicated streams 2594 (#1121, #1122, #1238) 2596 B.15. Since draft-ietf-quic-http-10 2598 * Settings need to be remembered when attempting and accepting 0-RTT 2599 (#1157, #1207) 2601 B.16. Since draft-ietf-quic-http-09 2603 * Selected QCRAM for header compression (#228, #1117) 2605 * The server_name TLS extension is now mandatory (#296, #495) 2607 * Specified handling of unsupported versions in Alt-Svc (#1093, 2608 #1097) 2610 B.17. Since draft-ietf-quic-http-08 2612 * Clarified connection coalescing rules (#940, #1024) 2614 B.18. Since draft-ietf-quic-http-07 2616 * Changes for integer encodings in QUIC (#595,#905) 2618 * Use unidirectional streams as appropriate (#515, #240, #281, #886) 2620 * Improvement to the description of GOAWAY (#604, #898) 2622 * Improve description of server push usage (#947, #950, #957) 2624 B.19. Since draft-ietf-quic-http-06 2625 * Track changes in QUIC error code usage (#485) 2627 B.20. Since draft-ietf-quic-http-05 2629 * Made push ID sequential, add MAX_PUSH_ID, remove 2630 SETTINGS_ENABLE_PUSH (#709) 2632 * Guidance about keep-alive and QUIC PINGs (#729) 2634 * Expanded text on GOAWAY and cancellation (#757) 2636 B.21. Since draft-ietf-quic-http-04 2638 * Cite RFC 5234 (#404) 2640 * Return to a single stream per request (#245,#557) 2642 * Use separate frame type and settings registries from HTTP/2 (#81) 2644 * SETTINGS_ENABLE_PUSH instead of SETTINGS_DISABLE_PUSH (#477) 2646 * Restored GOAWAY (#696) 2648 * Identify server push using Push ID rather than a stream ID 2649 (#702,#281) 2651 * DATA frames cannot be empty (#700) 2653 B.22. Since draft-ietf-quic-http-03 2655 None. 2657 B.23. Since draft-ietf-quic-http-02 2659 * Track changes in transport draft 2661 B.24. Since draft-ietf-quic-http-01 2663 * SETTINGS changes (#181): 2665 - SETTINGS can be sent only once at the start of a connection; no 2666 changes thereafter 2668 - SETTINGS_ACK removed 2670 - Settings can only occur in the SETTINGS frame a single time 2672 - Boolean format updated 2674 * Alt-Svc parameter changed from "v" to "quic"; format updated 2675 (#229) 2677 * Closing the connection control stream or any message control 2678 stream is a fatal error (#176) 2680 * HPACK Sequence counter can wrap (#173) 2682 * 0-RTT guidance added 2684 * Guide to differences from HTTP/2 and porting HTTP/2 extensions 2685 added (#127,#242) 2687 B.25. Since draft-ietf-quic-http-00 2689 * Changed "HTTP/2-over-QUIC" to "HTTP/QUIC" throughout (#11,#29) 2691 * Changed from using HTTP/2 framing within Stream 3 to new framing 2692 format and two-stream-per-request model (#71,#72,#73) 2694 * Adopted SETTINGS format from draft-bishop-httpbis-extended- 2695 settings-01 2697 * Reworked SETTINGS_ACK to account for indeterminate inter-stream 2698 order (#75) 2700 * Described CONNECT pseudo-method (#95) 2702 * Updated ALPN token and Alt-Svc guidance (#13,#87) 2704 * Application-layer-defined error codes (#19,#74) 2706 B.26. Since draft-shade-quic-http2-mapping-00 2708 * Adopted as base for draft-ietf-quic-http 2710 * Updated authors/editors list 2712 Acknowledgements 2714 The original authors of this specification were Robbie Shade and Mike 2715 Warres. 2717 A substantial portion of Mike's contribution was supported by 2718 Microsoft during his employment there. 2720 Author's Address 2721 Mike Bishop (editor) 2722 Akamai 2724 Email: mbishop@evequefou.be