--- 1/draft-ietf-masque-h3-datagram-04.txt 2021-10-25 15:15:31.941675817 -0700 +++ 2/draft-ietf-masque-h3-datagram-05.txt 2021-10-25 15:15:31.997677216 -0700 @@ -1,19 +1,19 @@ MASQUE D. Schinazi Internet-Draft Google LLC Intended status: Standards Track L. Pardue -Expires: 10 April 2022 Cloudflare - 7 October 2021 +Expires: 28 April 2022 Cloudflare + 25 October 2021 Using Datagrams with HTTP - draft-ietf-masque-h3-datagram-04 + draft-ietf-masque-h3-datagram-05 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 when the application protocol running over QUIC is HTTP/3. It associates datagrams with client-initiated bidirectional @@ -39,21 +39,21 @@ 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 10 April 2022. + This Internet-Draft will expire on 28 April 2022. Copyright Notice Copyright (c) 2021 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 @@ -69,64 +69,69 @@ 2. Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Datagram Contexts . . . . . . . . . . . . . . . . . . . . 4 2.2. Datagram Formats . . . . . . . . . . . . . . . . . . . . 5 2.3. Context ID Allocation . . . . . . . . . . . . . . . . . . 5 3. HTTP/3 DATAGRAM Format . . . . . . . . . . . . . . . . . . . 6 4. Capsules . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Capsule Protocol . . . . . . . . . . . . . . . . . . . . 8 4.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 9 4.3. Intermediary Processing . . . . . . . . . . . . . . . . . 9 4.4. Capsule Types . . . . . . . . . . . . . . . . . . . . . . 10 - 4.4.1. The REGISTER_DATAGRAM_CONTEXT Capsule . . . . . . . . 10 - 4.4.2. The REGISTER_DATAGRAM_NO_CONTEXT Capsule . . . . . . 11 - 4.4.3. The CLOSE_DATAGRAM_CONTEXT Capsule . . . . . . . . . 12 - 4.4.4. The DATAGRAM Capsule . . . . . . . . . . . . . . . . 14 - 5. The H3_DATAGRAM HTTP/3 SETTINGS Parameter . . . . . . . . . . 16 - 5.1. Note About Draft Versions . . . . . . . . . . . . . . . . 16 - 6. Prioritization . . . . . . . . . . . . . . . . . . . . . . . 16 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 - 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 - 8.1. HTTP/3 SETTINGS Parameter . . . . . . . . . . . . . . . . 17 - 8.2. Capsule Types . . . . . . . . . . . . . . . . . . . . . . 17 - 8.3. Datagram Format Types . . . . . . . . . . . . . . . . . . 18 - 8.4. Context Close Codes . . . . . . . . . . . . . . . . . . . 19 - 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 - 9.1. Normative References . . . . . . . . . . . . . . . . . . 19 - 9.2. Informative References . . . . . . . . . . . . . . . . . 20 + 4.4.1. The Datagram Registration Capsules . . . . . . . . . 10 + 4.4.2. The Datagram Close Capsule . . . . . . . . . . . . . 11 + 4.4.3. The Datagram Capsules . . . . . . . . . . . . . . . . 13 + 5. The H3_DATAGRAM HTTP/3 SETTINGS Parameter . . . . . . . . . . 14 + 5.1. Note About Draft Versions . . . . . . . . . . . . . . . . 15 + 6. The Sec-Use-Datagram-Contexts HTTP Header . . . . . . . . . . 15 + 7. Prioritization . . . . . . . . . . . . . . . . . . . . . . . 16 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 + 9.1. HTTP/3 SETTINGS Parameter . . . . . . . . . . . . . . . . 17 + 9.2. HTTP Header Field Name . . . . . . . . . . . . . . . . . 17 + 9.3. Capsule Types . . . . . . . . . . . . . . . . . . . . . . 18 + 9.4. Datagram Format Types . . . . . . . . . . . . . . . . . . 18 + 9.5. Context Close Codes . . . . . . . . . . . . . . . . . . . 19 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 20 + 10.2. Informative References . . . . . . . . . . . . . . . . . 21 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 21 A.1. CONNECT-UDP . . . . . . . . . . . . . . . . . . . . . . . 21 - A.2. CONNECT-UDP with Timestamp Extension . . . . . . . . . . 21 - A.3. CONNECT-IP with IP compression . . . . . . . . . . . . . 22 - A.4. WebTransport . . . . . . . . . . . . . . . . . . . . . . 24 - Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 24 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 + A.2. CONNECT-UDP with Delayed Timestamp Extension . . . . . . 22 + A.2.1. With Delay . . . . . . . . . . . . . . . . . . . . . 22 + A.3. Successful Optimistic . . . . . . . . . . . . . . . . . . 23 + A.4. Optimistic but Unsupported . . . . . . . . . . . . . . . 24 + A.5. CONNECT-IP with IP compression . . . . . . . . . . . . . 25 + A.6. WebTransport . . . . . . . . . . . . . . . . . . . . . . 26 + Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 27 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 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 when the application protocol running over QUIC is HTTP/3 [H3]. It associates datagrams with client-initiated bidirectional streams and defines an optional additional demultiplexing layer. Additionally, this document defines how to convey datagrams over prior versions of HTTP. This document is structured as follows: * Section 2 presents core concepts for multiplexing across HTTP versions. - Section 2.1 defines datagram contexts, an optional end-to-end - multiplexing concept scoped to each HTTP request. + multiplexing concept scoped to each HTTP request. Whether + contexts are in use is defined in Section 6. - Section 2.2 defines datagram formats, which are scoped to contexts. Formats communicate the format and encoding of datagrams sent using the associated context. - Contexts are identified using a variable-length integer. Requirements for allocating identifier values are detailed in Section 2.3. * Section 3 defines how QUIC DATAGRAM frames are used with HTTP/3. @@ -134,26 +139,25 @@ 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. - The following Capsule types are defined, together with guidance for defining new types: - o REGISTER_DATAGRAM_CONTEXT Section 4.4.1 - o REGISTER_DATAGRAM_NO_CONTEXT Section 4.4.2 + o Datagram registration capsules Section 4.4.1 - o CLOSE_DATAGRAM_CONTEXT Section 4.4.3 + o Datagram close capsule Section 4.4.2 - o DATAGRAM Section 4.4.4 + o Datagram capsules Section 4.4.3 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 @@ -175,63 +179,68 @@ 2.1. Datagram Contexts Within the scope of a given HTTP request, contexts provide an additional demultiplexing layer. Contexts determine the encoding of datagrams, and can be used to implicitly convey metadata. For example, contexts can be used for compression to elide some parts of the datagram: the context identifier then maps to a compression context that the receiver can use to reconstruct the elided data. - Contexts are optional, whether to use them or not is decided by the - client on each request stream using registration capsules, see - Section 4.4.1 and Section 4.4.2. When contexts are used, they are - identified within the scope of a given request by a numeric value, - referred to as the context ID. A context ID is a 62-bit integer (0 - to 2^62-1). - While stream IDs are a per-hop concept, context IDs are an end-to-end concept. In other words, if a datagram travels through one or more intermediaries on its way from client to server, the stream ID will most likely change from hop to hop, but the context ID will remain the same. Context IDs are opaque to intermediaries. + Contexts are OPTIONAL to implement for both endpoints. + Intermediaries do not require any context-specific software to enable + contexts. When contexts are supported by the implementation, their + use is optional and can be selected on each stream. Endpoints inform + their peer of whether they wish to use contexts via the Sec-Use- + Datagram-Contexts HTTP header, see Section 6. + + When contexts are used, they are identified within the scope of a + given request by a numeric value, referred to as the context ID. A + context ID is a 62-bit integer (0 to 2^62-1). + 2.2. Datagram Formats When an endpoint registers a datagram context (or the lack of contexts), it communicates the format (i.e., the semantics and encoding) of datagrams sent using this context. This is acccomplished by sending a Datagram Format Type as part of the - registration capsule, see Section 4.4.1 and Section 4.4.2. This type - identifier is registered with IANA (see Section 8.3) and allows + datagram registration capsule, see Section 4.4.1. This type + identifier is registered with IANA (see Section 9.4) and allows applications that use HTTP Datagrams to indicate what the content of datagrams are. Registration capsules carry a Datagram Format Additional Data field which allows sending some additional information that would impact the format of datagrams. For example, a protocol which proxies IP packets can define a Datagram Format Type which represents an IP packet. The corresponding Datagram Format Additional Data field would be empty. An extension to such a protocol that wishes to compress IP addresses could define a distinct Datagram Format Type and exchange two IP addresses via the Datagram Format Additional Data field. Then any datagrams with that type would contain the IP packet with addresses elided. 2.3. Context ID Allocation - Implementations of HTTP Datagrams MUST provide a context ID - allocation service. That service will allow applications co-located - with HTTP to request a unique context ID that they can subsequently - use for their own purposes. The HTTP implementation will then parse - the context ID of incoming HTTP Datagrams and use it to deliver the - frame to the appropriate application context. + Implementations of HTTP Datagrams that support datagram contexts MUST + provide a context ID allocation service. That service will allow + applications co-located with HTTP to request a unique context ID that + they can subsequently use for their own purposes. The HTTP + implementation will then parse the context ID of incoming HTTP + Datagrams and use it to deliver the frame to the appropriate + application context. Even-numbered context IDs are client-initiated, while odd-numbered context IDs are server-initiated. This means that an HTTP client implementation of the context ID allocation service MUST only provide even-numbered IDs, while a server implementation MUST only provide odd-numbered IDs. Note that, once allocated, any context ID can be used by both client and server - only allocation carries separate namespaces to avoid requiring synchronization. Additionally, note that the context ID namespace is tied to a given HTTP request: it is possible for the same numeral context ID to be used simultaneously in @@ -256,41 +265,38 @@ 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 2^62-1 / 4. Receipt of a frame that includes a larger value MUST be treated as a connection error of type FRAME_ENCODING_ERROR. Context ID: A variable-length integer indicating the context ID of the datagram (see Section 2.1). Whether or not this field is - present depends on which registration capsules were exchanged on - the associated stream: if a REGISTER_DATAGRAM_CONTEXT capsule (see - Section 4.4.1) has been sent or received on this stream, then the - field is present; if a REGISTER_DATAGRAM_NO_CONTEXT capsule (see - Section 4.4.2) has been sent or received, then this field is - absent; if neither has been sent or received, then it is not yet - possible to parse this datagram and the receiver MUST either drop - that datagram silently or buffer it temporarily while awaiting the - registration capsule. + present depends on whether datagram contexts are in use on this + stream, see Section 6. If this QUIC DATAGRAM frame is reordered + and arrives before the receiver knows whether datagram contexts + are in use on this stream, then the receiver cannot parse this + datagram and the receiver MUST either drop that datagram silently + or buffer it temporarily. HTTP Datagram Payload: The payload of the datagram, whose semantics are defined by individual applications. Note that this field can be empty. Intermediaries parse the Quarter Stream ID field in order to associate the QUIC DATAGRAM frame with a stream. If an intermediary receives a QUIC DATAGRAM frame whose payload is too short to allow parsing the Quarter Stream ID field, the intermediary MUST treat it as an HTTP/3 connection error of type H3_GENERAL_PROTOCOL_ERROR. The Context ID field is optional and whether it is present or not is - decided end-to-end by the client, see Section 4.4.2. Therefore + decided end-to-end by the endpoints, see Section 6. Therefore intermediaries cannot know whether the Context ID field is present or absent and they MUST ignore any HTTP/3 Datagram fields after the Quarter Stream ID. Endpoints parse both the Quarter Stream ID field and the Context ID field in order to associate the QUIC DATAGRAM frame with a stream and context within that stream. If an endpoint receives a QUIC DATAGRAM frame whose payload is too short to allow parsing the Quarter Stream ID field, the endpoint MUST treat it as an HTTP/3 connection error of type H3_GENERAL_PROTOCOL_ERROR. If an endpoint receives a QUIC @@ -396,219 +402,160 @@ intermediaries in participant mode: opaque capsules are forwarded unmodified while transparent ones can be parsed, added, or removed by intermediaries. Intermediaries MAY modify the contents of the Capsule Data field of transparent capsule types. Unless otherwise specified, all Capsule Types are defined as opaque to intermediaries. Intermediaries MUST forward all received opaque CAPSULE frames in their unmodified entirety. Intermediaries MUST NOT send any opaque CAPSULE frames other than the ones it is forwarding. All Capsule Types defined in this document are opaque, with the - exception of the DATAGRAM Capsule, see Section 4.4.4. Definitions of - new Capsule Types MAY specify that the newly introduced type is + exception of the datagram capsules, see Section 4.4.3. Definitions + of new Capsule Types MAY specify that the newly introduced type is transparent. Intermediaries MUST treat unknown Capsule Types as opaque. Intermediaries respect the order of opaque CAPSULE frames: if an intermediary receives two opaque CAPSULE frames in a given order, it MUST forward them in the same order. Endpoints which receive a Capsule with an unknown Capsule Type MUST silently drop that Capsule. 4.4. Capsule Types -4.4.1. The REGISTER_DATAGRAM_CONTEXT Capsule +4.4.1. The Datagram Registration Capsules - The REGISTER_DATAGRAM_CONTEXT capsule (see Section 8.2 for the value - of the capsule type) allows an endpoint to inform its peer of the - encoding and semantics of datagrams associated with a given context - ID. + This document defines the REGISTER_DATAGRAM and + REGISTER_DATAGRAM_CONTEXT capsules types, known collectively as the + datagram registration capsules (see Section 9.3 for the value of the + capsule types). The REGISTER_DATAGRAM capsule is used by endpoints + to inform their peer of the encoding and semantics of all datagrams + associated with a stream. The REGISTER_DATAGRAM_CONTEXT capsule is + used by endpoints to inform their peer of the encoding and semantics + of all datagrams associated with a given context ID on this stream. - REGISTER_DATAGRAM_CONTEXT Capsule { - Type (i) = REGISTER_DATAGRAM_CONTEXT, + Datagram Registration Capsule { + Type (i) = REGISTER_DATAGRAM or REGISTER_DATAGRAM_CONTEXT, Length (i), - Context ID (i), + [Context ID (i)], Datagram Format Type (i), Datagram Format Additional Data (..), } Figure 4: REGISTER_DATAGRAM_CONTEXT Capsule Format - Context ID: The context ID to register. + Context ID: A variable-length integer indicating the context ID to + register (see Section 2.1). This field is present in + REGISTER_DATAGRAM_CONTEXT capsules but not in REGISTER_DATAGRAM + capsules. If a REGISTER_DATAGRAM capsule is used on a stream + where datagram contexts are in use, it is associated with context + ID 0. REGISTER_DATAGRAM_CONTEXT capsules MUST NOT carry context + ID 0 as that context ID is conveyed using the REGISTER_DATAGRAM + capsule. Datagram Format Type: A variable-length integer that defines the semantics and encoding of the HTTP Datagram Payload field of datagrams with this context ID, see Section 2.2. Datagram Format Additional Data: This field carries additional information that impact the format of datagrams with this context ID, see Section 2.2. Note that these registrations are unilateral and bidirectional: the - sender of the frame unilaterally defines the semantics it will apply - to the datagrams it sends and receives using this context ID. Once a - context ID is registered, it can be used in both directions. + sender of the capsule unilaterally defines the semantics it will + apply to the datagrams it sends and receives using this context ID. + Once a context ID is registered, it can be used in both directions. - Endpoints MUST NOT send DATAGRAM frames using a Context ID until they - have either sent or received a REGISTER_DATAGRAM_CONTEXT Capsule with - the same Context ID. However, reordering can cause DATAGRAM frames - to be received with an unknown Context ID. Receipt of such frames - MUST NOT be treated as an error. Endpoints SHALL drop the DATAGRAM - frame silently, or buffer it temporarily while awaiting the - corresponding REGISTER_DATAGRAM_CONTEXT Capsule. Intermediaries - SHALL drop the DATAGRAM frame silently, MAY buffer it, or forward it - on immediately. + Endpoints MUST NOT send HTTP Datagrams until they have either sent or + received a datagram registration capsule with the same Context ID. + However, reordering can cause HTTP Datagrams to be received with an + unknown Context ID. Receipt of such HTTP datagrams MUST NOT be + treated as an error. Endpoints SHALL drop the HTTP Datagram + silently, or buffer it temporarily while awaiting the corresponding + datagram registration capsule. Intermediaries SHALL drop the HTTP + Datagram silently, MAY buffer it, or forward it on immediately. Endpoints MUST NOT register the same Context ID twice on the same stream. This also applies to Context IDs that have been closed using a CLOSE_DATAGRAM_CONTEXT capsule. Clients MUST NOT register server- initiated Context IDs and servers MUST NOT register client-initiated Context IDs. If an endpoint receives a REGISTER_DATAGRAM_CONTEXT capsule that violates one or more of these requirements, the endpoint MUST abruptly terminate the corresponding stream with a stream error of type H3_GENERAL_PROTOCOL_ERROR. - Servers MUST NOT send a REGISTER_DATAGRAM_CONTEXT capsule on a stream - before they have received at least one REGISTER_DATAGRAM_CONTEXT - capsule or one REGISTER_DATAGRAM_NO_CONTEXT capsule from the client - on that stream. This ensures that clients control whether datagrams - are allowed for a given request. If a client receives a - REGISTER_DATAGRAM_CONTEXT capsule on a stream where the client has - not yet sent a REGISTER_DATAGRAM_CONTEXT capsule, the client MUST - abruptly terminate the corresponding stream with a stream error of - type H3_GENERAL_PROTOCOL_ERROR. - - Servers MUST NOT send a REGISTER_DATAGRAM_CONTEXT capsule on a stream - where it has received a REGISTER_DATAGRAM_NO_CONTEXT capsule. If a - client receives a REGISTER_DATAGRAM_CONTEXT capsule on a stream where - the client has sent a REGISTER_DATAGRAM_NO_CONTEXT capsule, the - client MUST abruptly terminate the corresponding stream with a stream - error of type H3_GENERAL_PROTOCOL_ERROR. - -4.4.2. The REGISTER_DATAGRAM_NO_CONTEXT Capsule - - The REGISTER_DATAGRAM_NO_CONTEXT capsule (see Section 8.2 for the - value of the capsule type) allows a client to inform the server that - datagram contexts will not be used with this stream. It also informs - the server of the encoding and semantics of datagrams associated with - this stream. - - REGISTER_DATAGRAM_NO_CONTEXT Capsule { - Type (i) = REGISTER_DATAGRAM_NO_CONTEXT, - Length (i), - Datagram Format Type (i), - Datagram Format Additional Data (..), - } - - Figure 5: REGISTER_DATAGRAM_NO_CONTEXT Capsule Format - - Datagram Format Type: A variable-length integer that defines the - semantics and encoding of the HTTP Datagram Payload field of - datagrams, see Section 2.2. - - Datagram Format Additional Data: This field carries additional - information that impact the format of datagrams, see Section 2.2. - - Note that this registration is unilateral and bidirectional: the - client unilaterally defines the semantics it will apply to the - datagrams it sends and receives with this stream. - - Endpoints MUST NOT send DATAGRAM frames without a Context ID until - they have either sent or received a REGISTER_DATAGRAM_NO_CONTEXT - Capsule. However, due to reordering, an endpoint that receives a - DATAGRAM frame before receiving either a REGISTER_DATAGRAM_CONTEXT - capsule or a REGISTER_DATAGRAM_NO_CONTEXT capsule MUST NOT treat it - as an error, it SHALL instead drop the DATAGRAM frame silently, or - buffer it temporarily while awaiting a REGISTER_DATAGRAM_NO_CONTEXT - capsule or the corresponding REGISTER_DATAGRAM_CONTEXT capsule. - - Servers MUST NOT send the REGISTER_DATAGRAM_NO_CONTEXT capsule. If a - client receives a REGISTER_DATAGRAM_NO_CONTEXT capsule, the client - MUST abruptly terminate the corresponding stream with a stream error - of type H3_GENERAL_PROTOCOL_ERROR. - - Clients MUST NOT send more than one REGISTER_DATAGRAM_NO_CONTEXT - capsule on a stream. If a server receives a second - REGISTER_DATAGRAM_NO_CONTEXT capsule on the same stream, the server - MUST abruptly terminate the corresponding stream with a stream error - of type H3_GENERAL_PROTOCOL_ERROR. - - Clients MUST NOT send both REGISTER_DATAGRAM_CONTEXT capsules and - REGISTER_DATAGRAM_NO_CONTEXT capsules on the same stream. If a - server receives both a REGISTER_DATAGRAM_CONTEXT capsule and a - REGISTER_DATAGRAM_NO_CONTEXT capsule on the same stream, the server - MUST abruptly terminate the corresponding stream with a stream error - of type H3_GENERAL_PROTOCOL_ERROR. - - Extensions MAY define a different mechanism to communicate whether - contexts are in use, and they MAY do so in a way which is opaque to - intermediaries. + If datagrams contexts are not in use, the client is responsible for + choosing the datagram format and informing the server via a + REGISTER_DATAGRAM capsule. Servers MUST NOT send the + REGISTER_DATAGRAM capsule. If a client receives a REGISTER_DATAGRAM + capsule, the client MUST abruptly terminate the corresponding stream + with a stream error of type H3_GENERAL_PROTOCOL_ERROR. -4.4.3. The CLOSE_DATAGRAM_CONTEXT Capsule +4.4.2. The Datagram Close Capsule - The CLOSE_DATAGRAM_CONTEXT capsule (see Section 8.2 for the value of + The CLOSE_DATAGRAM_CONTEXT capsule (see Section 9.3 for the value of the capsule type) allows an endpoint to inform its peer that it will no longer send or parse received datagrams associated with a given context ID. CLOSE_DATAGRAM_CONTEXT Capsule { Type (i) = CLOSE_DATAGRAM_CONTEXT, Length (i), Context ID (i), Close Code (i), Close Details (..), } - Figure 6: CLOSE_DATAGRAM_CONTEXT Capsule Format + Figure 5: CLOSE_DATAGRAM_CONTEXT Capsule Format Context ID: The context ID to close. Close Code: The close code allows an endpoint to provide additional information as to why a datagram context was closed. - Section 4.4.3.1 defines a set of codes, the circumstances under + Section 4.4.2.1 defines a set of codes, the circumstances under which an implementation sends them, and how receivers react. Close Details: This is meant for debugging purposes. It consists of a human-readable string encoded in UTF-8. Note that this close is unilateral and bidirectional: the sender of the frame unilaterally informs its peer of the closure. Endpoints can use CLOSE_DATAGRAM_CONTEXT capsules to close a context that was initially registered by either themselves, or by their peer. Endpoints MAY use the CLOSE_DATAGRAM_CONTEXT capsule to immediately reject a context that was just registered using a REGISTER_DATAGRAM_CONTEXT capsule if they find its Datagram Format Type field to be unacceptable. After an endpoint has either sent or received a - CLOSE_DATAGRAM_CONTEXT frame, it MUST NOT send any DATAGRAM frames + CLOSE_DATAGRAM_CONTEXT frame, it MUST NOT send any HTTP Datagrams with that Context ID. However, due to reordering, an endpoint that - receives a DATAGRAM frame with a closed Context ID MUST NOT treat it - as an error, it SHALL instead drop the DATAGRAM frame silently. + receives an HTTP Datagram with a closed Context ID MUST NOT treat it + as an error, it SHALL instead drop the HTTP Datagram silently. Endpoints MUST NOT close a Context ID that was not previously registered. Endpoints MUST NOT close a Context ID that has already been closed. If an endpoint receives a CLOSE_DATAGRAM_CONTEXT capsule that violates one or more of these requirements, the endpoint MUST abruptly terminate the corresponding stream with a stream error of type H3_GENERAL_PROTOCOL_ERROR. -4.4.3.1. Close Codes +4.4.2.1. Close Codes Close codes are intended to allow implementations to react differently when they receive them - for example, some close codes require the receiver to not open another context under certain conditions. This specification defines the close codes below. Their numeric - values are in Section 8.4. Extensions to this mechanism MAY define + values are in Section 9.5. Extensions to this mechanism MAY define new close codes and they SHOULD state how receivers react to them. NO_ERROR: This indicates that a context was closed without any action specified for the receiver. UNKNOWN_FORMAT: This indicates that the sender does not know how to interpret the datagram format type associated with this context. The endpoint that had originally registered this context MUST NOT try to register another context with the same datagram format type on this stream. @@ -618,85 +565,83 @@ originally registered this context MUST NOT try to register another context with the same datagram format type and datagram format data on this stream. RESOURCE_LIMIT: This indicates that the context was closed to save resources. The recipient SHOULD limit its future registration of resource-intensive contexts. Receipt of an unknown close code MUST be treated as if the NO_ERROR code was present. Close codes are registered with IANA, see - Section 8.4. + Section 9.5. -4.4.4. The DATAGRAM Capsule +4.4.3. The Datagram Capsules - The DATAGRAM capsule (see Section 8.2 for the value of the capsule - type) allows an endpoint to send a datagram frame over an HTTP - stream. This is particularly useful when using a version of HTTP - that does not support QUIC DATAGRAM frames. + This document defines the DATAGRAM and DATAGRAM_WITH_CONTEXT capsules + types, known collectively as the datagram capsules (see Section 9.3 + for the value of the capsule types). These capsules allow an + endpoint to send a datagram frame over an HTTP stream. This is + particularly useful when using a version of HTTP that does not + support QUIC DATAGRAM frames. - DATAGRAM Capsule { - Type (i) = DATAGRAM, + Datagram Capsule { + Type (i) = DATAGRAM or DATAGRAM_WITH_CONTEXT, Length (i), [Context ID (i)], HTTP Datagram Payload (..), } - Figure 7: DATAGRAM Capsule Format + Figure 6: DATAGRAM Capsule Format Context ID: A variable-length integer indicating the context ID of - the datagram (see Section 2.1). Whether or not this field is - present depends on which registration capsules were exchanged on - the associated stream: if a REGISTER_DATAGRAM_CONTEXT capsule (see - Section 4.4.1) has been sent or received on this stream, then the - field is present; if a REGISTER_DATAGRAM_NO_CONTEXT capsule (see - Section 4.4.2) has been sent or received, then this field is - absent; if neither has been sent or received, then it is not yet - possible to parse this datagram and the receiver MUST either drop - that datagram silently or buffer it temporarily while awaiting the - registration capsule. + the datagram (see Section 2.1). This field is present in + DATAGRAM_WITH_CONTEXT capsules but not in DATAGRAM capsules. If a + DATAGRAM capsule is used on a stream where datagram contexts are + in use, it is associated with context ID 0. DATAGRAM_WITH_CONTEXT + capsules MUST NOT carry context ID 0 as that context ID is + conveyed using the DATAGRAM capsule. 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 exact same + Datagrams sent using the datagram capsule have the exact 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. + and received using the datagram capsules. - The DATAGRAM Capsule is transparent to intermediaries, meaning that - intermediaries MAY parse it and send DATAGRAM Capsules that they did - not receive. This allows an intermediary to 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. + The datagram capsules are transparent to intermediaries, meaning that + intermediaries MAY parse them and send datagram capsules that they + did not receive. This allows an intermediary to 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 are sent on a stream, + Note that while datagram capsules are sent on a stream, intermediaries can reencode HTTP Datagrams into QUIC DATAGRAM frames over the next hop, and those could be dropped. Because of this, applications have to always consider HTTP Datagrams to be unreliable, even if they were initially sent in a capsule. 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 [RFC8899]. An intermediary that converts QUIC DATAGRAM - frames to DATAGRAM capsules allows HTTP Datagrams to be arbitrarily + 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 a DPLPMTUD. 5. 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 @@ -728,96 +673,181 @@ 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. -6. Prioritization +6. The Sec-Use-Datagram-Contexts HTTP Header + + Endpoints indicate their support for datagram contexts by sending the + Sec-Use-Datagram-Contexts header with a value of ?1. If the header + is missing or has a value different from ?1, that indicates that its + sender does not wish to use datagram contexts. Endpoints that wish + to use datagram contexts SHALL send the Sec-Use-Datagram-Contexts + header with a value of ?1 on requests and responses that use the + capsule protocol. + + "Sec-Use-Datagram-Contexts" is an Item Structured Header [RFC8941]. + Its value MUST be a Boolean, its ABNF is: + + Sec-Use-Datagram-Contexts = sf-boolean + + The REGISTER_DATAGRAM_CONTEXT, DATAGRAM_WITH_CONTEXT, and + CLOSE_DATAGRAM_CONTEXT capsules as refered to as context-related + capsules. Endpoints which do not wish to use contexts MUST NOT send + context-related capsules, and MUST silently ignore any received + context-related capsules. + + Both endpoints unilaterally decide whether they wish to use datagram + contexts on a given stream. Contexts are used on a given stream if + and only if both endpoints indicate they wish to use them on this + stream. Once an endpoint has received the HTTP request or response, + it knows whether datagram contexts are in use on this stream or not. + + Conceptually, when datagram contexts are not in use on a stream, all + datagrams use context ID 0, which is client-initiated. This means + that the client chooses the datagram format for all datagrams when + datagram contexts are not in use. + + If datagram contexts are not in use on a stream, endpoints MUST NOT + send context-related capsules to the peer on that stream. Clients + MAY optimistically send context-related capsules before learning + whether the server wishes to support datagram contexts or not. + + This allows a client to optimistically use extensions that rely on + datagram contexts without knowing a priori whether the server + supports them, and without incurring a latency cost to negotiate + extension support. In this scenario, the client would send its + request with the Sec-Use-Datagram-Contexts header set to ?1, and + register two datagram contexts: the main context would use context ID + 0 and the extension context would use context ID 2. The client then + sends a REGISTER_DATAGRAM capsule to register the main context, and a + REGISTER_DATAGRAM_CONTEXT to register the extension context. The + client can then immediately send DATAGRAM capsules to send main + datagrams and DATAGRAM_WITH_CONTEXT capsules to send extension + datagrams. + + * If the server wishes to use datagram contexts, it will set Sec- + Use-Datagram-Contexts to ?1 on its response and correctly parse + all the received capsules. + + * If the server does not wish to use datagram contexts (for example + if the server implementation does not support them), it will not + set Sec-Use-Datagram-Contexts to ?1 on its response. It will then + parse the REGISTER_DATAGRAM and DATAGRAM capsules without datagram + contexts being in use on this stream, and parse the main datagrams + correctly while silently dropping the extension datagrams. Once + the client receives the server's response, it will know datagram + contexts are not in use, and then will be able to send HTTP + Datagrams via the QUIC DATAGRAM frame. + + Extensions MAY define a different mechanism to communicate whether + contexts are in use, and they MAY do so in a way which is opaque to + intermediaries. + +7. 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. -7. Security Considerations +8. Security Considerations Since this feature requires sending an HTTP/3 Settings parameter, it "sticks out". In other words, probing clients can learn whether a server supports this feature. Implementations that support this feature SHOULD always send this Settings parameter to avoid leaking the fact that there are applications using HTTP/3 datagrams enabled on this endpoint. -8. IANA Considerations +9. IANA Considerations -8.1. HTTP/3 SETTINGS Parameter +9.1. HTTP/3 SETTINGS Parameter This document will request IANA to register the following entry in the "HTTP/3 Settings" registry: +==============+==========+===============+=========+ | Setting Name | Value | Specification | Default | +==============+==========+===============+=========+ | H3_DATAGRAM | 0xffd277 | This Document | 0 | +--------------+----------+---------------+---------+ Table 1: New HTTP/3 Settings -8.2. Capsule Types +9.2. HTTP Header Field Name + + This document will request IANA to register the following entry in + the "HTTP Field Name" registry: + + Field Name: Sec-Use-Datagram-Contexts + + Template: None + + Status: provisional (permanent if this document is approved) + + Reference: This document + + Comments: None + +9.3. 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 entries: - +==============================+==========+===============+ + +===========================+==========+===============+ | Capsule Type | Value | Specification | - +==============================+==========+===============+ - | DATAGRAM | 0xff37a0 | This Document | - +------------------------------+----------+---------------+ + +===========================+==========+===============+ | REGISTER_DATAGRAM_CONTEXT | 0xff37a1 | This Document | - +------------------------------+----------+---------------+ - | REGISTER_DATAGRAM_NO_CONTEXT | 0xff37a2 | This Document | - +------------------------------+----------+---------------+ + +---------------------------+----------+---------------+ + | REGISTER_DATAGRAM | 0xff37a2 | This Document | + +---------------------------+----------+---------------+ | CLOSE_DATAGRAM_CONTEXT | 0xff37a3 | This Document | - +------------------------------+----------+---------------+ + +---------------------------+----------+---------------+ + | DATAGRAM_WITH_CONTEXT | 0xff37a4 | This Document | + +---------------------------+----------+---------------+ + | DATAGRAM | 0xff37a5 | This Document | + +---------------------------+----------+---------------+ Table 2: Initial Capsule Types Registry Entries 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. -8.3. Datagram Format Types +9.4. Datagram Format Types This document establishes a registry for HTTP datagram format type codes. The "HTTP Datagram Format Types" registry governs a 62-bit space. Registrations in this registry MUST include the following fields: Type: A name or label for the datagram format type. Value: The value of the Datagram Format Type field (see Section 2.2) is a 62-bit integer. @@ -831,29 +861,29 @@ This registry is initially empty. Datagram format types with a value of the form 41 * N + 17 for integer values of N are reserved to exercise the requirement that unknown datagram format types be ignored. These format types 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. -8.4. Context Close Codes +9.5. Context Close Codes This document establishes a registry for HTTP context close codes. The "HTTP Context Close Codes" registry governs a 62-bit space. Registrations in this registry MUST include the following fields: Type: A name or label for the close code. - Value: The value of the Close Code field (see Section 4.4.3) is a + Value: The value of the Close Code field (see Section 4.4.2) is a 62-bit integer. Reference: An optional reference to a specification for the parameter. 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 nor Value. This registry initially contains the following entries: @@ -872,23 +902,23 @@ Table 3: Initial Context Close Code Registry Entries Context close codes with a value of the form 41 * N + 19 for integer values of N are reserved to exercise the requirement that unknown context close codes be treated as NO_ERROR. These values MUST NOT be assigned by IANA and MUST NOT appear in the listing of assigned values. -9. References +10. References -9.1. Normative References +10.1. 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-06, 5 October 2021, . [H3] Bishop, M., "Hypertext Transfer Protocol Version 3 (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf- quic-http-34, 2 February 2021, @@ -908,118 +938,228 @@ [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, . -9.2. Informative References + [RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for + HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, + . + +10.2. Informative References [PRIORITY] Oku, K. and L. Pardue, "Extensible Prioritization Scheme for HTTP", Work in Progress, Internet-Draft, draft-ietf- - httpbis-priority-06, 30 September 2021, + httpbis-priority-07, 25 October 2021, . + priority-07>. [RFC8899] 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, . Appendix A. Examples A.1. CONNECT-UDP + In this example, the client does not support any CONNECT-UDP nor HTTP + Datagram extensions, and therefore has no use for datagram contexts + on this stream. + Client Server STREAM(44): HEADERS --------> - :method = CONNECT-UDP + :method = CONNECT + :protocol = connect-udp :scheme = https - :path = / - :authority = target.example.org:443 + :path = /target.example.org/443/ + :authority = proxy.example.org:443 STREAM(44): DATA --------> - Capsule Type = REGISTER_DATAGRAM_CONTEXT - Context ID = 0 + Capsule Type = REGISTER_DATAGRAM Datagram Format Type = UDP_PAYLOAD Datagram Format Additional Data = "" DATAGRAM --------> Quarter Stream ID = 11 - Context ID = 0 Payload = Encapsulated UDP Payload <-------- STREAM(44): HEADERS :status = 200 /* Wait for target server to respond to UDP packet. */ <-------- DATAGRAM Quarter Stream ID = 11 - Context ID = 0 Payload = Encapsulated UDP Payload -A.2. CONNECT-UDP with Timestamp Extension +A.2. CONNECT-UDP with Delayed Timestamp Extension + + In these examples, the client supports a CONNECT-UDP Timestamp + Extension, which uses a different Datagram Format Type that carries a + timestamp followed by the encapsulated UDP payload. + +A.2.1. With Delay + + In this instance, the client prefers to wait a round trip to learn + whether the server supports datagram contexts. + Client Server STREAM(44): HEADERS --------> - :method = CONNECT-UDP + :method = CONNECT + :protocol = connect-udp :scheme = https - :path = / - :authority = target.example.org:443 + :path = /target.example.org/443/ + :authority = proxy.example.org:443 + Sec-Use-Datagram-Contexts = ?1 + + <-------- STREAM(44): HEADERS + :status = 200 + Sec-Use-Datagram-Contexts = ?1 STREAM(44): DATA --------> Capsule Type = REGISTER_DATAGRAM_CONTEXT Context ID = 0 Datagram Format Type = UDP_PAYLOAD Datagram Format Additional Data = "" DATAGRAM --------> Quarter Stream ID = 11 Context ID = 0 Payload = Encapsulated UDP Payload + <-------- DATAGRAM + Quarter Stream ID = 11 + Context ID = 0 + Payload = Encapsulated UDP Payload + + STREAM(44): DATA --------> + Capsule Type = REGISTER_DATAGRAM_CONTEXT + Context ID = 2 + Datagram Format Type = UDP_PAYLOAD_WITH_TIMESTAMP + Datagram Format Additional Data = "" + + DATAGRAM --------> + Quarter Stream ID = 11 + Context ID = 2 + Payload = Encapsulated UDP Payload With Timestamp + +A.3. Successful Optimistic + + In this instance, the client does not wish to spend a round trip + waiting to learn whether the server supports datagram contexts. It + registers its context optimistically in such a way that the server + will react well whether it supports contexts or not. In this case, + the server does support datagram contexts. + + Client Server + + STREAM(44): HEADERS --------> + :method = CONNECT + :protocol = connect-udp + :scheme = https + :path = /target.example.org/443/ + :authority = proxy.example.org:443 + Sec-Use-Datagram-Contexts = ?1 + + STREAM(44): DATA --------> + Capsule Type = REGISTER_DATAGRAM + Datagram Format Type = UDP_PAYLOAD + Datagram Format Additional Data = "" + + STREAM(44): DATA --------> + Capsule Type = DATAGRAM + Payload = Encapsulated UDP Payload + <-------- STREAM(44): HEADERS :status = 200 + Sec-Use-Datagram-Contexts = ?1 - /* Wait for target server to respond to UDP packet. */ + /* Datagram contexts are in use on this stream */ <-------- DATAGRAM Quarter Stream ID = 11 Context ID = 0 Payload = Encapsulated UDP Payload STREAM(44): DATA --------> Capsule Type = REGISTER_DATAGRAM_CONTEXT Context ID = 2 Datagram Format Type = UDP_PAYLOAD_WITH_TIMESTAMP Datagram Format Additional Data = "" DATAGRAM --------> Quarter Stream ID = 11 Context ID = 2 Payload = Encapsulated UDP Payload With Timestamp -A.3. CONNECT-IP with IP compression +A.4. Optimistic but Unsupported + + In this instance, the client does not wish to spend a round trip + waiting to learn whether the server supports datagram contexts. It + registers its context optimistically in such a way that the server + will react well whether it supports contexts or not. In this case, + the server does not support datagram contexts. + Client Server STREAM(44): HEADERS --------> - :method = CONNECT-IP + :method = CONNECT + :protocol = connect-udp + :scheme = https + :path = /target.example.org/443/ + :authority = proxy.example.org:443 + Sec-Use-Datagram-Contexts = ?1 + + STREAM(44): DATA --------> + Capsule Type = REGISTER_DATAGRAM + Datagram Format Type = UDP_PAYLOAD + Datagram Format Additional Data = "" + + STREAM(44): DATA --------> + Capsule Type = DATAGRAM + Payload = Encapsulated UDP Payload + + <-------- STREAM(44): HEADERS + :status = 200 + + /* Datagram contexts are not in use on this stream */ + + <-------- DATAGRAM + Quarter Stream ID = 11 + Payload = Encapsulated UDP Payload + + DATAGRAM --------> + Quarter Stream ID = 11 + Payload = Encapsulated UDP Payload + +A.5. CONNECT-IP with IP compression + + Client Server + + STREAM(44): HEADERS --------> + :method = CONNECT + :protocol = connect-ip :scheme = https :path = / :authority = proxy.example.org:443 + Sec-Use-Datagram-Contexts = ?1 <-------- STREAM(44): HEADERS :status = 200 + Sec-Use-Datagram-Contexts = ?1 /* Exchange CONNECT-IP configuration information. */ STREAM(44): DATA --------> Capsule Type = REGISTER_DATAGRAM_CONTEXT Context ID = 0 Datagram Format Type = IP_PACKET Datagram Format Additional Data = "" DATAGRAM --------> @@ -1042,34 +1182,33 @@ Capsule Type = REGISTER_DATAGRAM_CONTEXT Context ID = 2 Datagram Format Type = COMPRESSED_IP_PACKET Datagram Format Additional Data = "192.0.2.6,192.0.2.7" DATAGRAM --------> Quarter Stream ID = 11 Context ID = 2 Payload = Compressed IP Packet -A.4. WebTransport - +A.6. WebTransport Client Server STREAM(44): HEADERS --------> :method = CONNECT :scheme = https :method = webtransport :path = /hello :authority = webtransport.example.org:443 Origin = https://www.example.org:443 STREAM(44): DATA --------> - Capsule Type = REGISTER_DATAGRAM_NO_CONTEXT + Capsule Type = REGISTER_DATAGRAM Datagram Format Type = WEBTRANSPORT_DATAGRAM Datagram Format Additional Data = "" <-------- STREAM(44): HEADERS :status = 200 /* Both endpoints can now send WebTransport datagrams. */ Acknowledgments