Internet-Draft HTTP/3 Datagrams May 2021
Schinazi & Pardue Expires 28 November 2021 [Page]
Workgroup:
MASQUE
Internet-Draft:
draft-ietf-masque-h3-datagram-02
Published:
Intended Status:
Standards Track
Expires:
Authors:
D. Schinazi
Google LLC
L. Pardue
Cloudflare

Using QUIC Datagrams with HTTP/3

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 streams and defines an optional additional demultiplexing layer.

Discussion of this work is encouraged to happen on the MASQUE IETF mailing list (masque@ietf.org) or on the GitHub repository which contains the draft: 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 28 November 2021.

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.

Discussion of this work is encouraged to happen on the MASQUE IETF mailing list (masque@ietf.org) or on the GitHub repository which contains the draft: https://github.com/ietf-wg-masque/draft-ietf-masque-h3-datagram.

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

In order to allow multiple exchanges of datagrams to coexist on a given QUIC connection, HTTP datagrams contain two layers of multiplexing. First, the QUIC DATAGRAM frame payload starts with an encoded stream identifier that associates the datagram with a given QUIC stream. Second, datagrams optionally carry a context identifier (see Section 2.1) that allows multiplexing multiple datagram contexts related to a given HTTP request. Conceptually, the first layer of multiplexing is per-hop, while the second is end-to-end.

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, their use is negotiated on each request stream using registration capsules, see Section 4.1 and Section 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.

2.2. Context ID Allocation

Implementations of HTTP/3 that support the DATAGRAM extension MUST provide a context ID allocation service. That service will allow applications co-located with HTTP/3 to request a unique context ID that they can subsequently use for their own purposes. The HTTP/3 implementation will then parse the context ID of incoming DATAGRAM frames 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/3 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 distinct requests.

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),
  [Context ID (i)],
  HTTP/3 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.)

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 4.1) has been sent or received on this stream, then the field is present; if a REGISTER_DATAGRAM_NO_CONTEXT capsule (see Section 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.

HTTP/3 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 its use is negotiated end-to-end, see Section 4.2. 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 DATAGRAM frame whose payload is long enough to allow parsing the Quarter Stream ID field but too short to allow parsing the Context ID field, the endpoint MUST abruptly terminate the corresponding stream with a stream error of type H3_GENERAL_PROTOCOL_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 while awaiting the creation of the corresponding stream.

4. CAPSULE HTTP/3 Frame Definition

CAPSULE allows reliably sending request-related information end-to-end, even in the presence of HTTP intermediaries.

CAPSULE is an HTTP/3 Frame (as opposed to a QUIC frame) which SHALL only be sent in client-initiated bidirectional streams. Intermediaries forward received CAPSULE frames on the same stream where it would forward DATA frames. Each Capsule Type determines whether it is opaque or transparent to intermediaries: opaque capsules are forwarded unmodified while transparent ones can be parsed, added, or removed by intermediaries.

This specification of CAPSULE currently uses HTTP/3 frame type 0xffcab5. If this document is approved, a lower number will be requested from IANA.

CAPSULE HTTP/3 Frame {
  Type (i) = 0xffcab5,
  Length (i),
  Capsule Type (i),
  Capsule Data (..),
}
Figure 2: CAPSULE HTTP/3 Frame Format

The Type and Length fields follows the definition of HTTP/3 frames from [H3]. The payload consists of:

Capsule Type:

The type of this capsule.

Capsule Data:

Data whose semantics depends on the Capsule Type.

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. 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.

Receipt of a CAPSULE HTTP/3 Frame on a stream that is not a client-initiated bidirectional stream MUST be treated as a connection error of type H3_FRAME_UNEXPECTED.

4.1. The REGISTER_DATAGRAM_CONTEXT Capsule

The REGISTER_DATAGRAM_CONTEXT capsule (type=0x00) allows an endpoint to inform its peer of the encoding and semantics of datagrams associated with a given context ID. Its Capsule Data field consists of:

REGISTER_DATAGRAM_CONTEXT Capsule {
  Context ID (i),
  Context Extensions (..),
}
Figure 3: REGISTER_DATAGRAM_CONTEXT Capsule Format
Context ID:

The context ID to register.

Context Extensions:

See Section 5.

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.

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, due to reordering, an endpoint that receives a DATAGRAM frame with an unknown Context ID MUST NOT treat it as an error, it SHALL instead drop the DATAGRAM frame silently, or buffer it temporarily while awaiting the corresponding REGISTER_DATAGRAM_CONTEXT Capsule.

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.

Endpoints MUST NOT send a REGISTER_DATAGRAM_CONTEXT capsule on a stream before they have sent at least one HEADERS frame on that stream. This removes the need to buffer REGISTER_DATAGRAM_CONTEXT capsules when the endpoint needs information from headers to determine how to react to the capsule. If an endpoint receives a REGISTER_DATAGRAM_CONTEXT capsule on a stream that hasn't yet received a HEADERS frame, 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.

4.2. The REGISTER_DATAGRAM_NO_CONTEXT Capsule

The REGISTER_DATAGRAM_NO_CONTEXT capsule (type=0x03) 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. Its Capsule Data field consists of:

REGISTER_DATAGRAM_NO_CONTEXT Capsule {
  Context Extensions (..),
}
Figure 4: REGISTER_DATAGRAM_NO_CONTEXT Capsule Format
Context Extensions:

See Section 5.

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 a REGISTER_DATAGRAM_NO_CONTEXT capsule on a stream before they have sent at least one HEADERS frame on that stream. This removes the need to buffer REGISTER_DATAGRAM_CONTEXT capsules when the server needs information from headers to determine how to react to the capsule. If a server receives a REGISTER_DATAGRAM_NO_CONTEXT capsule on a stream that hasn't yet received a HEADERS frame, 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 negotiate the presence of contexts, and they MAY do so in a way which is opaque to intermediaries.

4.3. The CLOSE_DATAGRAM_CONTEXT Capsule

The CLOSE_DATAGRAM_CONTEXT capsule (type=0x01) allows an endpoint to inform its peer that it will no longer send or parse received datagrams associated with a given context ID. Its Capsule Data field consists of:

CLOSE_DATAGRAM_CONTEXT Capsule {
  Context ID (i),
  Context Extensions (..),
}
Figure 5: CLOSE_DATAGRAM_CONTEXT Capsule Format
Context ID:

The context ID to close.

Context Extensions:

See Section 5.

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 Context Extensions field to be unacceptable.

After an endpoint has either sent or received a CLOSE_DATAGRAM_CONTEXT frame, it MUST NOT send any DATAGRAM frames 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.

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.

All CLOSE_DATAGRAM_CONTEXT capsules MUST contain a CLOSE_CODE context extension, see Section 5.1. If an endpoint receives a CLOSE_DATAGRAM_CONTEXT capsule without a CLOSE_CODE context extension, the endpoint MUST abruptly terminate the corresponding stream with a stream error of type H3_GENERAL_PROTOCOL_ERROR.

4.4. The DATAGRAM Capsule

The DATAGRAM capsule (type=0x02) 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. Its Capsule Data field consists of:

DATAGRAM Capsule {
  [Context ID (i)],
  HTTP/3 Datagram Payload (..),
}
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 4.1) has been sent or received on this stream, then the field is present; if a REGISTER_DATAGRAM_NO_CONTEXT capsule (see Section 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.

HTTP/3 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 semantics as datagrams sent in QUIC DATAGRAM frames. In particular, the restrictions on when it is allowed to send an HTTP/3 datagram and how to process them from Section 3 also apply to HTTP/3 datagrams sent and received using the DATAGRAM capsule.

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/3 Datagrams as it forwards them: in other words, an intermediary MAY send a DATAGRAM Capsule to forward an HTTP/3 Datagram which was received in a QUIC DATAGRAM frame, and vice versa.

Note that while DATAGRAM capsules are sent on a stream, intermediaries can reencode HTTP/3 datagrams into QUIC DATAGRAM frames over the next hop, and those could be dropped. Because of this, applications have to always consider HTTP/3 datagrams to be unreliable, even if they were initially sent in a capsule.

5. Context Extensibility

In order to facilitate extensibility of contexts, the REGISTER_DATAGRAM_CONTEXT, REGISTER_DATAGRAM_NO_CONTEXT, and the CLOSE_DATAGRAM_CONTEXT capsules carry a Context Extensions field. That field contains a sequence of context extensions:

  Context Extensions {
    Context Extension (..) ...,
  }

Each context extension is encoded as a (type, length, value) tuple:

  Context Extension {
    Context Extension Type (i),
    Context Extension Length (i),
    Context Extension Value (..),
  }

Context Extension Types are registered with IANA, see Section 10.4. The Context Extension Length field contains the length of the Context Extension Value field in bytes. The semantics of the Context Extension Value field are defined by the corresponding Context Extension Type.

5.1. The CLOSE_CODE Context Extension Type

The CLOSE_CODE context extension type (type=0x00) allows an endpoint to provide additional information as to why a datagram context was closed. This type SHALL only be sent in CLOSE_DATAGRAM_CONTEXT capsules. Its Context Extension Value field consists of a single variable-length integer which contains the close code. The following codes are defined:

NO_ERROR (code=0x00):

This indicates that the registration was closed without any additional information.

DENIED (code=0x01):

This indicates that the sender has rejected the context registration based on its local policy. The endpoint that had originally registered this context MUST NOT try to register another context with the same context extensions on this stream.

RESOURCE_LIMIT (code=0x02):

This indicates that the context was closed to save resources. The recipient SHOULD limit its future registration of resource-incentive 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 10.5.

5.2. The DETAILS Context Extension Type

The DETAILS context extension type (type=0x01) allows an endpoint to provide additional details to context capsules. It is meant for debugging purposes. Its Context Extension Value field consists of a human-readable string encoded in UTF-8.

6. The H3_DATAGRAM HTTP/3 SETTINGS Parameter

Implementations of HTTP/3 that support this mechanism 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 this mechanism is 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.

An endpoint that sends the H3_DATAGRAM SETTINGS parameter with a value of 1 MUST send the max_datagram_frame_size QUIC Transport Parameter [DGRAM]. An endpoint that receives the H3_DATAGRAM SETTINGS parameter with a value of 1 on a QUIC connection that did not also receive the max_datagram_frame_size QUIC Transport Parameter MUST terminate the connection with error H3_SETTINGS_ERROR.

When clients use 0-RTT, they MAY store the value of the server's H3_DATAGRAM SETTINGS parameter. Doing so allows the client to use HTTP/3 datagrams 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.

7. Prioritization

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.

8. HTTP/1.x and HTTP/2 Support

We can provide DATAGRAM support in HTTP/2 by defining the CAPSULE frame in HTTP/2.

We can provide DATAGRAM support in HTTP/1.x by defining its data stream format to a sequence of length-value capsules.

TODO: Refactor this document into "HTTP Datagrams" with definitions for HTTP/1.x, HTTP/2, and HTTP/3.

9. 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.

10. IANA Considerations

10.1. HTTP/3 CAPSULE Frame

This document will request IANA to register the following entry in the "HTTP/3 Frames" registry:

  +------------+----------+---------------+
  | Frame Type |   Value  | Specification |
  +============+==========+===============+
  |  CAPSULE   | 0xffcab5 | This Document |
  +------------+----------+---------------+

10.2. HTTP 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  | 0xffd276 | This Document |    0    |
  +--------------+----------+---------------+---------+

10.3. Capsule Types

This document establishes a registry for HTTP/3 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) is a 62bit 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 |
+------------------------------+-------+---------------+
| REGISTER_DATAGRAM_CONTEXT    | 0x00  | This Document |
+------------------------------+-------+---------------+
| CLOSE_DATAGRAM_CONTEXT       | 0x01  | This Document |
+------------------------------+-------+---------------+
| DATAGRAM                     | 0x02  | This Document |
+------------------------------+-------+---------------+
| REGISTER_DATAGRAM_NO_CONTEXT | 0x03  | This Document |
+------------------------------+-------+---------------+

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.

10.4. Context Extension Types

This document establishes a registry for HTTP/3 datagram context extension type codes. The "HTTP Context Extension Types" registry governs a 62-bit space. Registrations in this registry MUST include the following fields:

Type:

A name or label for the context extension type.

Value:

The value of the Context Extension Type field (see Section 5) is a 62bit 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:

+------------------------------+-------+---------------+
| Context Extension Type       | Value | Specification |
+------------------------------+-------+---------------+
| CLOSE_CODE                   | 0x00  | This Document |
+------------------------------+-------+---------------+
| DETAILS                      | 0x01  | This Document |
+------------------------------+-------+---------------+

Context extension types with a value of the form 41 * N + 17 for integer values of N are reserved to exercise the requirement that unknown context extension types be ignored. These extensions 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.

10.5. Context Close Codes

This document establishes a registry for HTTP/3 context extension type 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 Context Extension Value field (see Section 5.1) is a 62bit 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:

+------------------------------+-------+---------------+
| Context Close Code           | Value | Specification |
+------------------------------+-------+---------------+
| NO_ERROR                     | 0x00  | This Document |
+------------------------------+-------+---------------+
| DENIED                       | 0x01  | This Document |
+------------------------------+-------+---------------+
| RESOURCE_LIMIT               | 0x02  | This Document |
+------------------------------+-------+---------------+

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.

11. 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-02, , <https://tools.ietf.org/html/draft-ietf-quic-datagram-02>.
[H3]
Bishop, M., "Hypertext Transfer Protocol Version 3 (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-quic-http-34, , <https://tools.ietf.org/html/draft-ietf-quic-http-34>.
[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, , <https://www.rfc-editor.org/rfc/rfc8126>.
[QUIC]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed and Secure Transport", Work in Progress, Internet-Draft, draft-ietf-quic-transport-34, , <https://tools.ietf.org/html/draft-ietf-quic-transport-34>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.

Appendix A. Examples

A.1. CONNECT-UDP

Client                                             Server

STREAM(44): HEADERS             -------->
  :method = CONNECT-UDP
  :scheme = https
  :path = /
  :authority = target.example.org:443

STREAM(44): CAPSULE             -------->
  Capsule Type = REGISTER_DATAGRAM_CONTEXT
  Context ID = 0
  Context Extension = {}

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

Client                                             Server

STREAM(44): HEADERS            -------->
  :method = CONNECT-UDP
  :scheme = https
  :path = /
  :authority = target.example.org:443

STREAM(44): CAPSULE            -------->
  Capsule Type = REGISTER_DATAGRAM_CONTEXT
  Context ID = 0
  Context Extension = {}

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


STREAM(44): CAPSULE            -------->
  Capsule Type = REGISTER_DATAGRAM_CONTEXT
  Context ID = 2
  Context Extension = {TIMESTAMP=""}

DATAGRAM                       -------->
  Quarter Stream ID = 11
  Context ID = 2
  Payload = Encapsulated UDP Payload With Timestamp

A.3. CONNECT-IP with IP compression

Client                                             Server

STREAM(44): HEADERS            -------->
  :method = CONNECT-IP
  :scheme = https
  :path = /
  :authority = proxy.example.org:443

           <--------  STREAM(44): HEADERS
                        :status = 200

/* Exchange CONNECT-IP configuration information. */

STREAM(44): CAPSULE             -------->
  Capsule Type = REGISTER_DATAGRAM_CONTEXT
  Context ID = 0
  Context Extension = {}

DATAGRAM                       -------->
  Quarter Stream ID = 11
  Context ID = 0
  Payload = Encapsulated IP Packet

/* Endpoint happily exchange encapsulated IP packets */
/* using Quarter Stream ID 11 and Context ID 0.      */

DATAGRAM                       -------->
  Quarter Stream ID = 11
  Context ID = 0
  Payload = Encapsulated IP Packet

/* After performing some analysis on traffic patterns, */
/* the client decides it wants to compress a 5-tuple.  */


STREAM(44): CAPSULE             -------->
  Capsule Type = REGISTER_DATAGRAM_CONTEXT
  Context ID = 2
  Context Extension = {IP_COMPRESSION=tcp,192.0.2.6:9876,192.0.2.7:443}

DATAGRAM                       -------->
  Quarter Stream ID = 11
  Context ID = 2
  Payload = Compressed IP Packet

A.4. 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): CAPSULE             -------->
  Capsule Type = REGISTER_DATAGRAM_NO_CONTEXT
  Context Extension = {}

           <--------  STREAM(44): HEADERS
                        :status = 200

/* Both endpoints can now send WebTransport datagrams. */

Acknowledgments

The DATAGRAM context identifier was previously part of the 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.

Authors' Addresses

David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 94043,
United States of America
Lucas Pardue
Cloudflare