MASQUE D. Schinazi Internet-Draft Google LLC Intended status: Standards Track L. Pardue Expires: 5 September 2022 Cloudflare 4 March 2022 Using Datagrams with HTTP draft-ietf-masque-h3-datagram-06 Abstract The QUIC DATAGRAM extension provides application protocols running over QUIC with a mechanism to send unreliable data while leveraging the security and congestion-control properties of QUIC. However, QUIC DATAGRAM frames do not provide a means to demultiplex application contexts. This document describes how to use QUIC DATAGRAM frames with HTTP/3 by association with HTTP requests. Additionally, this document defines the Capsule Protocol that can convey datagrams over prior versions of HTTP. Discussion Venues This note is to be removed before publishing as an RFC. Discussion of this document takes place on the MASQUE WG mailing list (masque@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/masque/. Source for this draft and an issue tracker can be found at https://github.com/ietf-wg-masque/draft-ietf-masque-h3-datagram. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 5 September 2022. Schinazi & Pardue Expires 5 September 2022 [Page 1] Internet-Draft HTTP Datagrams March 2022 Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3 2. Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . 3 3. HTTP/3 Datagram Format . . . . . . . . . . . . . . . . . . . 4 3.1. The H3_DATAGRAM HTTP/3 SETTINGS Parameter . . . . . . . . 5 3.1.1. Note About Draft Versions . . . . . . . . . . . . . . 6 4. Capsules . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Capsule Protocol . . . . . . . . . . . . . . . . . . . . 7 4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . 8 4.3. The Capsule-Protocol Header Field . . . . . . . . . . . . 8 4.4. The DATAGRAM Capsule . . . . . . . . . . . . . . . . . . 9 5. Prioritization . . . . . . . . . . . . . . . . . . . . . . . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7.1. HTTP/3 SETTINGS Parameter . . . . . . . . . . . . . . . . 11 7.2. HTTP/3 Error Code . . . . . . . . . . . . . . . . . . . . 11 7.3. HTTP Header Field Name . . . . . . . . . . . . . . . . . 12 7.4. Capsule Types . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.1. Normative References . . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . 14 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 14 A.1. CONNECT-UDP . . . . . . . . . . . . . . . . . . . . . . . 14 A.2. WebTransport . . . . . . . . . . . . . . . . . . . . . . 15 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Schinazi & Pardue Expires 5 September 2022 [Page 2] Internet-Draft HTTP Datagrams March 2022 1. Introduction The QUIC DATAGRAM extension [DGRAM] provides application protocols running over QUIC [QUIC] with a mechanism to send unreliable data while leveraging the security and congestion-control properties of QUIC. However, QUIC DATAGRAM frames do not provide a means to demultiplex application contexts. This document describes how to use QUIC DATAGRAM frames with HTTP/3 [H3] by association with HTTP requests. Additionally, this document defines the Capsule Protocol that can convey datagrams over prior versions of HTTP. This document is structured as follows: * Section 2 presents core concepts for multiplexing across HTTP versions. * Section 3 defines how QUIC DATAGRAM frames are used with HTTP/3. - Section 3.1 defines an HTTP/3 setting that endpoints can use to advertise support of the frame. * Section 4 introduces the Capsule Protocol and the "data stream" concept. Data streams are initiated using special-purpose HTTP requests, after which Capsules, an end-to-end message, can be sent. - Section 4.4 defines Datagram Capsule types, along with guidance for specifying new capsule types. 1.1. Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Multiplexing All HTTP Datagrams are associated with an HTTP request. When running over HTTP/3, multiple exchanges of datagrams need the ability to coexist on a given QUIC connection. To allow this, the QUIC DATAGRAM frame payload starts with an encoded stream identifier that associates the datagram with a request stream. Schinazi & Pardue Expires 5 September 2022 [Page 3] Internet-Draft HTTP Datagrams March 2022 When running over HTTP/2, demultiplexing is provided by the HTTP/2 framing layer. When running over HTTP/1, requests are strictly serialized in the connection, therefore demultiplexing is not needed. 3. HTTP/3 Datagram Format When used with HTTP/3, the Datagram Data field of QUIC DATAGRAM frames uses the following format (using the notation from the "Notational Conventions" section of [QUIC]): HTTP/3 Datagram { Quarter Stream ID (i), HTTP Datagram Payload (..), } Figure 1: HTTP/3 DATAGRAM Format Quarter Stream ID: A variable-length integer that contains the value of the client-initiated bidirectional stream that this datagram is associated with, divided by four (the division by four stems from the fact that HTTP requests are sent on client-initiated bidirectional streams, and those have stream IDs that are divisible by four). The largest legal QUIC stream ID value is 2^62-1, so the largest legal value of Quarter Stream ID is 2^60-1. Receipt of a frame that includes a larger value MUST be treated as an HTTP/3 connection error of type H3_DATAGRAM_ERROR. HTTP Datagram Payload: The payload of the datagram, whose semantics are defined by individual applications. Note that this field can be empty. Receipt of a QUIC DATAGRAM frame whose payload is too short to allow parsing the Quarter Stream ID field MUST be treated as an HTTP/3 connection error of type H3_DATAGRAM_ERROR. Endpoints MUST NOT send HTTP/3 datagrams unless the corresponding stream's send side is open. On a given endpoint, once the receive side of a stream is closed, incoming datagrams for this stream are no longer expected so the endpoint can release related state. Endpoints MAY keep state for a short time to account for reordering. Once the state is released, the endpoint MUST silently drop received associated datagrams. If an HTTP/3 datagram is received and its Quarter Stream ID maps to a stream that has not yet been created, the receiver SHALL either drop that datagram silently or buffer it temporarily (on the order of a round trip) while awaiting the creation of the corresponding stream. Schinazi & Pardue Expires 5 September 2022 [Page 4] Internet-Draft HTTP Datagrams March 2022 If an HTTP/3 datagram is received and its Quarter Stream ID maps to a stream that cannot be created due to client-initiated bidirectional stream limits, it SHOULD be treated as an HTTP/3 connection error of type H3_ID_ERROR. Generating an error is not mandatory in this case because HTTP/3 implementations might have practical barriers to determining the active stream concurrency limit that is applied by the QUIC layer. HTTP/3 datagrams MUST only be sent with an association to a stream that supports semantics for HTTP Datagrams. For example, existing HTTP methods GET and POST do not define semantics for associated HTTP Datagrams; therefore, HTTP/3 datagrams cannot be sent associated with GET or POST request streams. If an endpoint receives an HTTP/3 datagram associated with a method that has no known semantics for HTTP Datagrams, it MUST abort the corresponding stream with H3_DATAGRAM_ERROR. Future extensions MAY remove these requirements if they define semantics for such HTTP Datagrams and negotiate mutual support. 3.1. The H3_DATAGRAM HTTP/3 SETTINGS Parameter Implementations of HTTP/3 that support HTTP Datagrams can indicate that to their peer by sending the H3_DATAGRAM SETTINGS parameter with a value of 1. The value of the H3_DATAGRAM SETTINGS parameter MUST be either 0 or 1. A value of 0 indicates that HTTP Datagrams are not supported. An endpoint that receives the H3_DATAGRAM SETTINGS parameter with a value that is neither 0 or 1 MUST terminate the connection with error H3_SETTINGS_ERROR. Endpoints MUST NOT send QUIC DATAGRAM frames until they have both sent and received the H3_DATAGRAM SETTINGS parameter with a value of 1. When clients use 0-RTT, they MAY store the value of the server's H3_DATAGRAM SETTINGS parameter. Doing so allows the client to send QUIC DATAGRAM frames in 0-RTT packets. When servers decide to accept 0-RTT data, they MUST send a H3_DATAGRAM SETTINGS parameter greater than or equal to the value they sent to the client in the connection where they sent them the NewSessionTicket message. If a client stores the value of the H3_DATAGRAM SETTINGS parameter with their 0-RTT state, they MUST validate that the new value of the H3_DATAGRAM SETTINGS parameter sent by the server in the handshake is greater than or equal to the stored value; if not, the client MUST terminate the connection with error H3_SETTINGS_ERROR. In all cases, the maximum permitted value of the H3_DATAGRAM SETTINGS parameter is 1. Schinazi & Pardue Expires 5 September 2022 [Page 5] Internet-Draft HTTP Datagrams March 2022 It is RECOMMENDED that implementations that support receiving HTTP Datagrams using QUIC always send the H3_DATAGRAM SETTINGS parameter with a value of 1, even if the application does not intend to use HTTP Datagrams. This helps to avoid "sticking out"; see Section 6. 3.1.1. Note About Draft Versions [[RFC editor: please remove this section before publication.]] Some revisions of this draft specification use a different value (the Identifier field of a Setting in the HTTP/3 SETTINGS frame) for the H3_DATAGRAM Settings Parameter. This allows new draft revisions to make incompatible changes. Multiple draft versions MAY be supported by either endpoint in a connection. Such endpoints MUST send multiple values for H3_DATAGRAM. Once an endpoint has sent and received SETTINGS, it MUST compute the intersection of the values it has sent and received, and then it MUST select and use the most recent draft version from the intersection set. This ensures that both endpoints negotiate the same draft version. 4. Capsules This specification introduces the Capsule Protocol. The Capsule Protocol is a sequence of type-length-value tuples that new HTTP Upgrade Tokens (see Section 16.7 of [HTTP]) can choose to use. It allows endpoints to reliably communicate request-related information end-to-end on HTTP request streams, even in the presence of HTTP intermediaries. The Capsule Protocol can be used to exchange HTTP Datagrams when HTTP is running over a transport that does not support the QUIC DATAGRAM frame. This specification defines the "data stream" of an HTTP request as the bidirectional stream of bytes that follow the headers in both directions. In HTTP/1.x, the data stream consists of all bytes on the connection that follow the blank line that concludes either the request header section, or the 2xx (Successful) response header section. (Note that only a single HTTP request starting the capsule protocol can be sent on HTTP/1.x connections.) In HTTP/2 and HTTP/3, the data stream of a given HTTP request consists of all bytes sent in DATA frames with the corresponding stream ID. The concept of a data stream is particularly relevant for methods such as CONNECT where there is no HTTP message content after the headers. Note that use of the Capsule Protocol is not required to use HTTP Datagrams. If a new HTTP Upgrade Token is only defined over transports that support QUIC DATAGRAM frames, they might not need a stream encoding. Additionally, definitions of new HTTP Upgrade Tokens can use HTTP Datagrams with their own data stream protocol. Schinazi & Pardue Expires 5 September 2022 [Page 6] Internet-Draft HTTP Datagrams March 2022 However, new HTTP Upgrade Tokens that wish to use HTTP Datagrams SHOULD use the Capsule Protocol unless they have a good reason not to. 4.1. Capsule Protocol Definitions of new HTTP Upgrade Tokens can state that their data stream uses the Capsule Protocol. If they do so, that means that the contents of their data stream uses the following format (using the notation from the "Notational Conventions" section of [QUIC]): Capsule Protocol { Capsule (..) ..., } Figure 2: Capsule Protocol Stream Format Capsule { Capsule Type (i), Capsule Length (i), Capsule Value (..), } Figure 3: Capsule Format Capsule Type: A variable-length integer indicating the Type of the capsule. Endpoints that receive a capsule with an unknown Capsule Type MUST silently skip over that capsule. Capsule Length: The length of the Capsule Value field following this field, encoded as a variable-length integer. Note that this field can have a value of zero. Capsule Value: The payload of this capsule. Its semantics are determined by the value of the Capsule Type field. Because new protocols or extensions may involve defining new capsule types, intermediaries that wish to allow for future extensibility SHOULD forward capsules unmodified. One exception to this rule is the DATAGRAM capsule; see Section 4.4. An intermediary can identify the use of the capsule protocol either through the presence of the Capsule-Protocol header field (Section 4.3) or by understanding the chosen HTTP Upgrade token. An intermediary that identifies the use of the capsule protocol MAY convert between DATAGRAM capsules and QUIC DATAGRAM frames when forwarding. Definitions of new Capsule Types MAY specify optional custom intermediary processing. Schinazi & Pardue Expires 5 September 2022 [Page 7] Internet-Draft HTTP Datagrams March 2022 Endpoints which receive a Capsule with an unknown Capsule Type MUST silently drop that Capsule. By virtue of the definition of the data stream, the Capsule Protocol is not in use on responses unless the response includes a 2xx (Successful) status code. The Capsule Protocol MUST NOT be used with messages that contain Content-Length, Content-Type, or Transfer-Encoding header fields. Additionally, HTTP status codes 204 (No Content), 205 (Reset Content), and 206 (Partial Content) MUST NOT be sent on responses that use the Capsule Protocol. 4.2. Error Handling When an error occurs processing the capsule protocol, the receiver MUST treat the message as malformed or incomplete, according to the underlying transport protocol. For HTTP/3, the handling of malformed messages is described in Section 4.1.3 of [H3]. For HTTP/2, the handling of malformed messages is described in Section 8.1.1 of [H2]. For HTTP/1.1, the handling of incomplete messages is described in Section 8 of [H1]. Each capsule's payload MUST contain exactly the fields identified in its description. A capsule payload that contains additional bytes after the identified fields or a capsule payload that terminates before the end of the identified fields MUST be treated as a malformed or incomplete message. In particular, redundant length encodings MUST be verified to be self-consistent. When a stream carrying capsules terminates cleanly, if the last capsule on the stream was truncated, this MUST be treated as a malformed or incomplete message. 4.3. The Capsule-Protocol Header Field This document defines the "Capsule-Protocol" header field. It is an Item Structured Field, see Section 3.3 of [STRUCT-FIELD]; its value MUST be a Boolean. Its ABNF is: Capsule-Protocol = sf-item Schinazi & Pardue Expires 5 September 2022 [Page 8] Internet-Draft HTTP Datagrams March 2022 Endpoints indicate that the Capsule Protocol is in use on the data stream by sending the Capsule-Protocol header field with a value of ?1. A Capsule-Protocol header field with a value of ?0 has the same semantics as when the header is not present. Intermediaries MAY use this header field to allow processing of HTTP Datagrams for unknown HTTP Upgrade Tokens; note that this is only possible for HTTP Upgrade or Extended CONNECT. The Capsule-Protocol header field MUST NOT be sent multiple times on a message. The Capsule-Protocol header field MUST NOT be used on HTTP responses with a status code different from 2xx (Successful). This specification does not define any parameters for the Capsule- Protocol header field value, but future documents MAY define parameters. Receivers MUST ignore unknown parameters. Definitions of new HTTP Upgrade Tokens that use the Capsule Protocol MAY use the Capsule-Protocol header field to simplify intermediary processing. 4.4. The DATAGRAM Capsule This document defines the DATAGRAM capsule type (see Section 7.4 for the value of the capsule type). This capsule allows an endpoint to send an HTTP Datagram on a stream using the Capsule Protocol. This is particularly useful when HTTP is running over a transport that does not support the QUIC DATAGRAM frame. Datagram Capsule { Type (i) = DATAGRAM, Length (i), HTTP Datagram Payload (..), } Figure 4: DATAGRAM Capsule Format HTTP Datagram Payload: The payload of the datagram, whose semantics are defined by individual applications. Note that this field can be empty. Datagrams sent using the DATAGRAM capsule have the same semantics as datagrams sent in QUIC DATAGRAM frames. In particular, the restrictions on when it is allowed to send an HTTP Datagram and how to process them from Section 3 also apply to HTTP Datagrams sent and received using the DATAGRAM capsule. Schinazi & Pardue Expires 5 September 2022 [Page 9] Internet-Draft HTTP Datagrams March 2022 An intermediary can reencode HTTP Datagrams as it forwards them. In other words, an intermediary MAY send a DATAGRAM capsule to forward an HTTP Datagram which was received in a QUIC DATAGRAM frame, and vice versa. Note that while DATAGRAM capsules that are sent on a stream are reliably delivered in order, intermediaries can reencode DATAGRAM capsules into QUIC DATAGRAM frames when forwarding messages, which could result in loss or reordering. If an intermediary receives an HTTP Datagram in a QUIC DATAGRAM frame and is forwarding it on a connection that supports QUIC DATAGRAM frames, the intermediary SHOULD NOT convert that HTTP Datagram to a DATAGRAM capsule. If the HTTP Datagram is too large to fit in a DATAGRAM frame (for example because the path MTU of that QUIC connection is too low or if the maximum UDP payload size advertised on that connection is too low), the intermediary SHOULD drop the HTTP Datagram instead of converting it to a DATAGRAM capsule. This preserves the end-to-end unreliability characteristic that methods such as Datagram Packetization Layer Path MTU Discovery (DPLPMTUD) depend on [DPLPMTUD]. An intermediary that converts QUIC DATAGRAM frames to DATAGRAM capsules allows HTTP Datagrams to be arbitrarily large without suffering any loss; this can misrepresent the true path properties, defeating methods such as DPLPMTUD. While DATAGRAM capsules can theoretically carry a payload of length 2^62-1, most applications will have their own limits on what datagran payload sizes are practical. Implementations SHOULD take those limits into account when parsing DATAGRAM capsules: if an incoming DATAGRAM capsule has a length that is known to be so large as to not be usable, the implementation SHOULD discard the capsule without buffering its contents into memory. 5. Prioritization Data streams (see Section 4.1) can be prioritized using any means suited to stream or request prioritization. For example, see Section 11 of [PRIORITY]. Prioritization of HTTP/3 datagrams is not defined in this document. Future extensions MAY define how to prioritize datagrams, and MAY define signaling to allow endpoints to communicate their prioritization preferences. Schinazi & Pardue Expires 5 September 2022 [Page 10] Internet-Draft HTTP Datagrams March 2022 6. Security Considerations Since transmitting HTTP Datagrams using QUIC DATAGRAM frames requires sending an HTTP/3 Settings parameter, it "sticks out". In other words, probing clients can learn whether a server supports HTTP Datagrams over QUIC DATAGRAM frames. As some servers might wish to obfuscate the fact that they offer application services that use HTTP datagrams, it's best for all implementations that support this feature to always send this Settings parameter, see Section 3.1. Since use of the Capsule Protocol is restricted to new HTTP Upgrade Tokens, it is not accessible from Web Platform APIs (such as those commonly accessed via JavaScript in web browsers). 7. IANA Considerations 7.1. HTTP/3 SETTINGS Parameter This document will request IANA to register the following entry in the "HTTP/3 Settings" registry: Value: 0xffd277 (note that this will switch to a lower value before publication) Setting Name: H3_DATAGRAM Default: 0 Status: provisional (permanent if this document is approved) Specification: This Document Change Controller: IETF Contact: HTTP_WG; HTTP working group; ietf-http-wg@w3.org 7.2. HTTP/3 Error Code This document will request IANA to register the following entry in the "HTTP/3 Error Codes" registry: Value: 0x4A1268 (note that this will switch to a lower value before publication) Name: H3_DATAGRAM_ERROR Description: Datagram or capsule protocol parse error Schinazi & Pardue Expires 5 September 2022 [Page 11] Internet-Draft HTTP Datagrams March 2022 Status: provisional (permanent if this document is approved) Specification: This Document Change Controller: IETF Contact: HTTP_WG; HTTP working group; ietf-http-wg@w3.org 7.3. HTTP Header Field Name This document will request IANA to register the following entry in the "HTTP Field Name" registry: Field Name: Capsule-Protocol Template: None Status: provisional (permanent if this document is approved) Reference: This document Comments: None 7.4. Capsule Types This document establishes a registry for HTTP capsule type codes. The "HTTP Capsule Types" registry governs a 62-bit space. Registrations in this registry MUST include the following fields: Type: A name or label for the capsule type. Value: The value of the Capsule Type field (see Section 4.1) is a 62-bit integer. Reference: An optional reference to a specification for the type. This field MAY be empty. Registrations follow the "First Come First Served" policy (see Section 4.4 of [IANA-POLICY]) where two registrations MUST NOT have the same Type. This registry initially contains the following entry: Schinazi & Pardue Expires 5 September 2022 [Page 12] Internet-Draft HTTP Datagrams March 2022 +==============+==========+===============+ | Capsule Type | Value | Specification | +==============+==========+===============+ | DATAGRAM | 0xff37a5 | This Document | +--------------+----------+---------------+ Table 1: Initial Capsule Types Registry Capsule types with a value of the form 41 * N + 23 for integer values of N are reserved to exercise the requirement that unknown capsule types be ignored. These capsules have no semantics and can carry arbitrary values. These values MUST NOT be assigned by IANA and MUST NOT appear in the listing of assigned values. 8. References 8.1. Normative References [DGRAM] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable Datagram Extension to QUIC", Work in Progress, Internet- Draft, draft-ietf-quic-datagram-10, 4 February 2022, . [H1] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP/1.1", Work in Progress, Internet-Draft, draft-ietf- httpbis-messaging-19, 12 September 2021, . [H2] Thomson, M. and C. Benfield, "HTTP/2", Work in Progress, Internet-Draft, draft-ietf-httpbis-http2bis-07, 24 January 2022, . [H3] Bishop, M., "Hypertext Transfer Protocol Version 3 (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf- quic-http-34, 2 February 2021, . [HTTP] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP Semantics", Work in Progress, Internet-Draft, draft-ietf- httpbis-semantics-19, 12 September 2021, . Schinazi & Pardue Expires 5 September 2022 [Page 13] Internet-Draft HTTP Datagrams March 2022 [IANA-POLICY] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . [QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [STRUCT-FIELD] Nottingham, M. and P-H. Kamp, "Structured Field Values for HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, . 8.2. Informative References [DPLPMTUD] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T. Völker, "Packetization Layer Path MTU Discovery for Datagram Transports", RFC 8899, DOI 10.17487/RFC8899, September 2020, . [PRIORITY] Oku, K. and L. Pardue, "Extensible Prioritization Scheme for HTTP", Work in Progress, Internet-Draft, draft-ietf- httpbis-priority-12, 17 January 2022, . Appendix A. Examples [[RFC editor: please remove this appendix before publication.]] A.1. CONNECT-UDP Schinazi & Pardue Expires 5 September 2022 [Page 14] Internet-Draft HTTP Datagrams March 2022 Client Server STREAM(44): HEADERS --------> :method = CONNECT :protocol = connect-udp :scheme = https :path = /target.example.org/443/ :authority = proxy.example.org:443 capsule-protocol = ?1 DATAGRAM --------> Quarter Stream ID = 11 Payload = Encapsulated UDP Payload <-------- STREAM(44): HEADERS :status = 200 capsule-protocol = ?1 /* Wait for target server to respond to UDP packet. */ <-------- DATAGRAM Quarter Stream ID = 11 Payload = Encapsulated UDP Payload A.2. WebTransport Client Server STREAM(44): HEADERS --------> :method = CONNECT :scheme = https :protocol = webtransport :path = /hello :authority = webtransport.example.org:443 origin = https://www.example.org:443 <-------- STREAM(44): HEADERS :status = 200 /* Both endpoints can now send WebTransport datagrams. */ Schinazi & Pardue Expires 5 September 2022 [Page 15] Internet-Draft HTTP Datagrams March 2022 Acknowledgments Portions of this document were previously part of the QUIC DATAGRAM frame definition itself, the authors would like to acknowledge the authors of that document and the members of the IETF MASQUE working group for their suggestions. Additionally, the authors would like to thank Martin Thomson for suggesting the use of an HTTP/3 SETTINGS parameter. Furthermore, the authors would like to thank Ben Schwartz for writing the first proposal that used two layers of indirection. The final design in this document came out of the HTTP Datagrams Design Team, whose members were Alan Frindell, Alex Chernyakhovsky, Ben Schwartz, Eric Rescorla, Marcus Ihlar, Martin Thomson, Mike Bishop, Tommy Pauly, Victor Vasiliev, and the authors of this document. Authors' Addresses David Schinazi Google LLC 1600 Amphitheatre Parkway Mountain View, California 94043, United States of America Email: dschinazi.ietf@gmail.com Lucas Pardue Cloudflare Email: lucaspardue.24.7@gmail.com Schinazi & Pardue Expires 5 September 2022 [Page 16]