wdiff draft-ietf-masque-h3-datagram-05.txt draft-ietf-masque-h3-datagram-06.txt

MASQUE D. Schinazi
Internet-Draft Google LLC
Intended status: Standards Track L. Pardue
Expires: 28 April 5 September 2022 Cloudflare
25 October 2021
4 March 2022

Using Datagrams with HTTP
draft-ietf-masque-h3-datagram-05
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 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. HTTP/3 by association with HTTP requests.
Additionally, this document defines how to 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

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provisions of BCP 78 and BCP 79.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 4 3
2. Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. 3
3. HTTP/3 Datagram Contexts . Format . . . . . . . . . . . . . . . . . . . 4
2.2. Datagram Formats . . . . . . . . . . . . . . . . . . . . 5
2.3. Context ID Allocation . . . . . . . . . .
3.1. The H3_DATAGRAM HTTP/3 SETTINGS Parameter . . . . . . . . 5
3. HTTP/3 DATAGRAM Format . . . . .
3.1.1. Note About Draft Versions . . . . . . . . . . . . . . 6
4. Capsules . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6
4.1. Capsule Protocol . . . . . . . . . . . . . . . . . . . . 8 7
4.2. Requirements . Error Handling . . . . . . . . . . . . . . . . . . . . . 9 8
4.3. Intermediary Processing . . . . . The Capsule-Protocol Header Field . . . . . . . . . . . . 9 8
4.4. Capsule Types . . . . . . . . . . . . . . . . . . . . . . 10
4.4.1. The Datagram Registration Capsules . . . . . . . . . 10
4.4.2. The Datagram Close DATAGRAM Capsule . . . . . . . . . . . . . 11
4.4.3. The Datagram Capsules . . . . . . . . . . . . . . . . 13 9
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. 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9. 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9.1. 11
7.1. HTTP/3 SETTINGS Parameter . . . . . . . . . . . . . . . . 17
9.2. HTTP Header Field Name . . 11
7.2. HTTP/3 Error Code . . . . . . . . . . . . . . . 17
9.3. Capsule Types . . . . . 11
7.3. HTTP Header Field Name . . . . . . . . . . . . . . . . . 18
9.4. Datagram Format 12
7.4. Capsule Types . . . . . . . . . . . . . . . . . . 18
9.5. Context Close Codes . . . . . . . . . . . . . . . . . . . 19
10. 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 20
10.2. 13
8.2. Informative References . . . . . . . . . . . . . . . . . 21 14
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 21 14
A.1. CONNECT-UDP . . . . . . . . . . . . . . . . . . . . . . . 21 14
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 15
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 27 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 16

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 with HTTP/3 [H3]. It associates datagrams [H3] by association with client-initiated
bidirectional streams and defines an optional additional
demultiplexing layer. HTTP
requests. Additionally, this document defines how to 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 2.1 defines datagram contexts, an optional end-to-end
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.

- Section 5 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.

- The following Section 4.4 defines Datagram Capsule types are defined, together types, along with guidance
for defining specifying new types:

o Datagram registration capsules Section 4.4.1

o Datagram close capsule Section 4.4.2

o Datagram capsules Section 4.4.3 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, 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 request 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.

When running over HTTP/2, the first level of demultiplexing is provided by the HTTP/2
framing layer. When running over HTTP/1, requests are strictly
serialized in the connection, therefore the
first layer of demultiplexing is not needed.

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.

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
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 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
distinct requests.

3. HTTP/3 DATAGRAM 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 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 2^62-1
/ 4. 2^60-1.
Receipt of a frame that includes a larger value MUST be treated as a
an HTTP/3 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 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. 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.

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

Receipt 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 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 field MUST treat it be treated 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. 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.

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.

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,
end-to-end on HTTP request streams, even in the presence of HTTP
intermediaries.

4.1. 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.

Definitions

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 Methods or Upgrade
Tokens can use HTTP Datagrams with their own data stream protocol.

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.

4.2. Requirements

If the definition of an HTTP Method

Because new protocols or HTTP Upgrade Token states that
it uses the extensions may involve defining new capsule protocol, its implementations MUST follow the
following requirements:

* A server MUST NOT send any Transfer-Encoding or Content-Length
header fields in a 2xx (Successful) response. If a client
receives a Content-Length or Transfer-Encoding header fields in a
successful response, it MUST treat
types, intermediaries that response as malformed.

* A request message does not have content.

* A successful response message does not have content.

* Responses are not cacheable.

4.3. Intermediary Processing

Intermediaries MUST operate in one of the two following modes:

Pass-through mode: In wish to allow for future extensibility
SHOULD forward capsules unmodified. One exception to this mode, rule is
the DATAGRAM capsule; see Section 4.4. An intermediary forwards can identify
the data
stream between two associated streams without any modification use of the data stream.

Participant mode: In this mode, capsule protocol either through the intermediary terminates presence of the data
stream and parses all Capsule Type and Capsule Length fields it
receives.

Each Capsule Type determines whether it is opaque or transparent to
intermediaries in participant mode: opaque capsules are forwarded
unmodified while transparent ones can be parsed, added,
Capsule-Protocol header field (Section 4.3) or removed by
intermediaries. Intermediaries MAY modify understanding the contents of
chosen HTTP Upgrade token. An intermediary that identifies the
Capsule Data field use
of transparent the 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 protocol MAY convert between DATAGRAM capsules and
QUIC DATAGRAM frames other than the ones it is when forwarding.
All Capsule Types defined in this document are opaque, with the
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 optional custom intermediary receives two opaque CAPSULE frames in a given order, it
MUST forward them in the same order. processing.

Endpoints which receive a Capsule with an unknown Capsule Type MUST
silently drop that Capsule.

4.4. Capsule Types

4.4.1. The Datagram Registration Capsules

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

By virtue of the
capsule types). The REGISTER_DATAGRAM capsule is used by endpoints
to inform their peer definition 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 data stream, the encoding and semantics
of all datagrams associated with a given context ID on this stream.

Datagram Registration Capsule {
Type (i) = REGISTER_DATAGRAM or REGISTER_DATAGRAM_CONTEXT,
Length (i),
[Context ID (i)],
Datagram Format Type (i),
Datagram Format Additional Data (..),
}

Figure 4: REGISTER_DATAGRAM_CONTEXT Capsule Format

Context ID: A variable-length integer indicating the context ID to
register (see Section 2.1). This field Protocol
is present in
REGISTER_DATAGRAM_CONTEXT capsules but not in REGISTER_DATAGRAM
capsules. If a REGISTER_DATAGRAM capsule is used use on responses unless the response includes a stream
where datagram contexts are in use, it is associated 2xx
(Successful) status code.

The Capsule Protocol MUST NOT be used with context
ID 0. REGISTER_DATAGRAM_CONTEXT capsules 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 carry context
ID 0 as be sent on responses
that context ID is conveyed using use the REGISTER_DATAGRAM
capsule.

Datagram Format Type: A variable-length integer that defines Capsule Protocol.

4.2. Error Handling

When an error occurs processing the
semantics and encoding of capsule protocol, the HTTP Datagram Payload field receiver
MUST treat the message as malformed or incomplete, according to the
underlying transport protocol. For HTTP/3, the handling of
datagrams with this context ID, see malformed
messages is described in Section 2.2.

Datagram Format Additional Data: This field carries additional
information that impact 4.1.3 of [H3]. For HTTP/2, the format
handling of datagrams with this context
ID, see malformed messages is described in Section 2.2.

Note that these registrations are unilateral and bidirectional: the
sender 8.1.1 of [H2].
For HTTP/1.1, the capsule unilaterally defines the semantics it will
apply to the datagrams it sends and receives using this context ID.
Once a context ID handling of incomplete messages is registered, it can be used described in both directions.

Endpoints
Section 8 of [H1].

Each capsule's payload MUST NOT send HTTP Datagrams until they have either sent contain exactly the fields identified in
its description. A capsule payload that contains additional bytes
after the identified fields or
received a datagram registration capsule with payload that terminates
before the same Context ID.
However, reordering can cause HTTP Datagrams to be received with an
unknown Context ID. Receipt end of such HTTP datagrams the identified fields 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, a
malformed or forward it on immediately.

Endpoints incomplete message. In particular, redundant length
encodings MUST NOT register the same Context ID twice on the same
stream. This also applies be verified 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 be self-consistent.

When a REGISTER_DATAGRAM_CONTEXT
capsule that violates one or more of these requirements, stream carrying capsules terminates cleanly, if the endpoint
MUST abruptly terminate last
capsule on the corresponding stream with was truncated, this MUST be treated as a stream error
of type H3_GENERAL_PROTOCOL_ERROR.

If datagrams contexts are not in use,
malformed or incomplete message.

4.3. The Capsule-Protocol Header Field

This document defines the client "Capsule-Protocol" header field. It is responsible for
choosing the datagram format and informing the server via a
REGISTER_DATAGRAM capsule. Servers an
Item Structured Field, see Section 3.3 of [STRUCT-FIELD]; its value
MUST NOT send the
REGISTER_DATAGRAM capsule. If a client receives be a REGISTER_DATAGRAM
capsule, Boolean. Its ABNF is:

Capsule-Protocol = sf-item
Endpoints indicate that the client MUST abruptly terminate Capsule Protocol is in use on the corresponding data
stream by sending the Capsule-Protocol header field with a stream error of type H3_GENERAL_PROTOCOL_ERROR.

4.4.2. The Datagram Close Capsule

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
?1. A Capsule-Protocol header field 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 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 4.4.2.1 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 value of ?0 has the frame unilaterally informs its peer of same
semantics as when 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 header is not present. Intermediaries 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
this header field to be unacceptable.

After an endpoint has either sent or received a
CLOSE_DATAGRAM_CONTEXT frame, it MUST NOT send any allow processing of HTTP Datagrams
with that Context ID. However, due to reordering, an endpoint that
receives an for unknown
HTTP Datagram with a closed Context ID MUST NOT treat it
as an error, it SHALL instead drop the Upgrade Tokens; note that this is only possible for HTTP Datagram silently.

Endpoints Upgrade
or Extended CONNECT.

The Capsule-Protocol header field MUST NOT close be sent multiple times on
a Context ID that was not previously
registered. Endpoints message. The Capsule-Protocol header field 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 be used on
HTTP responses with a stream error
of type H3_GENERAL_PROTOCOL_ERROR.

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. status code different from 2xx (Successful).
This specification defines the close codes below. Their numeric
values are in Section 9.5. Extensions to this mechanism MAY does not 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 parameters 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 Capsule-
Protocol header field value, but future documents MAY define
parameters. Receivers MUST NOT
try to register another context with the same datagram format type
on this stream.

DENIED: This indicates that the sender has rejected the context
registration based on its local policy. The endpoint ignore unknown parameters.

Definitions of new HTTP Upgrade Tokens that had
originally registered this context MUST NOT try to register
another context with use the same datagram format type and datagram
format data on this stream.

RESOURCE_LIMIT: This indicates that Capsule Protocol
MAY use the context was closed Capsule-Protocol header field 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 9.5.

4.4.3. simplify intermediary
processing.

4.4. The Datagram Capsules DATAGRAM Capsule

This document defines the DATAGRAM and DATAGRAM_WITH_CONTEXT capsules
types, known collectively as the datagram capsules capsule type (see Section 9.3 7.4 for
the value of the capsule types). These capsules allow type). This capsule allows an endpoint to
send a datagram frame over an HTTP stream. Datagram on a stream using the Capsule Protocol. This
is particularly useful when using a version of HTTP is running over a transport that
does not support the QUIC DATAGRAM frames. frame.

Datagram Capsule {
Type (i) = DATAGRAM or DATAGRAM_WITH_CONTEXT, DATAGRAM,
Length (i),
[Context ID (i)],
HTTP Datagram Payload (..),
}

Figure 6: 4: DATAGRAM Capsule Format

Context ID: A variable-length integer indicating the context ID of
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 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 capsules.

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 DATAGRAM capsule.

An intermediary to can reencode HTTP Datagrams as it forwards them: in them. In
other words, an intermediary MAY send a datagram DATAGRAM capsule to forward
an HTTP Datagram which was received in a QUIC DATAGRAM frame, and
vice versa.

Note that while datagram DATAGRAM capsules that are sent on a stream, stream are
reliably delivered in order, intermediaries can reencode HTTP Datagrams DATAGRAM
capsules into QUIC DATAGRAM frames
over the next hop, and those when forwarding messages, which
could be dropped. Because of this,
applications have to always consider HTTP Datagrams to be unreliable,
even if they were initially sent result in a capsule. 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 [RFC8899]. [DPLPMTUD]. An intermediary that converts QUIC DATAGRAM
frames to datagram DATAGRAM capsules allows HTTP Datagrams to be arbitrarily
large without suffering any loss; this can misrepresent the true path
properties, defeating methods such a as DPLPMTUD.

5. The H3_DATAGRAM HTTP/3 SETTINGS Parameter

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

While 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.

5.1. 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 capsules can theoretically carry a connection. Such endpoints MUST send
multiple values for H3_DATAGRAM. Once an endpoint has sent and
received SETTINGS, it MUST compute the intersection payload of the values it
has sent and received, and then it MUST select and use the length
2^62-1, most
recent draft version from the intersection set. This ensures that
both endpoints negotiate the same draft version.

6. The Sec-Use-Datagram-Contexts HTTP Header

Endpoints indicate applications will have 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 own limits on a given stream. Contexts what datagran
payload sizes are used on a given stream if
and only practical. Implementations SHOULD take those
limits into account when parsing DATAGRAM capsules: if both endpoints indicate they wish to use them on this
stream. Once an endpoint incoming
DATAGRAM capsule 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 length 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 is known to use datagram contexts, it will set Sec-
Use-Datagram-Contexts be so large as 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
be usable, the server implementation does not support them), it will not
set Sec-Use-Datagram-Contexts to ?1 on its response. It will then
parse SHOULD discard the REGISTER_DATAGRAM and DATAGRAM capsules capsule 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.
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.

6. Security Considerations

Since this feature 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 this feature. Implementations 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 SHOULD to always send this Settings parameter to avoid leaking parameter, see Section 3.1.

Since use of the fact that there are applications using HTTP/3 datagrams enabled
on this endpoint.

9. 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

9.1.

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)

Default: 0

Status: provisional (permanent if this document is approved)

Specification: This Document | 0 |
+--------------+----------+---------------+---------+

Table 1: New

Change Controller: IETF

Contact: HTTP_WG; HTTP working group; ietf-http-wg@w3.org

7.2. HTTP/3 Settings

9.2. 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
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: Sec-Use-Datagram-Contexts Capsule-Protocol

Template: None

Status: provisional (permanent if this document is approved)

Reference: This document

Comments: None

9.3.

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 entries:

+===========================+==========+===============+ entry:

Table 2: 1: 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.

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.

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 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.

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 4.4.2) 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:

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.

10.

8. References

10.1.

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-06, 5 October 2021, draft-ietf-quic-datagram-10, 4 February 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
datagram-06>.
datagram-10>.

[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,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
messaging-19>.

[H2] Thomson, M. and C. Benfield, "HTTP/2", Work in Progress,
Internet-Draft, draft-ietf-httpbis-http2bis-07, 24 January
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
httpbis-http2bis-07>.

[H3] Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-34, 2 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
http-34>.

[HTTP] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-19>.

[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,
<https://www.rfc-editor.org/rfc/rfc8126>.

[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<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,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

[RFC8941]

[STRUCT-FIELD]
Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.

10.2.

8.2. Informative References

[PRIORITY] Oku, K. and L. Pardue, "Extensible Prioritization Scheme
for HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-priority-07, 25 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
priority-07>.

[RFC8899]

[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, <https://www.rfc-editor.org/rfc/rfc8899>.

[PRIORITY] Oku, K. and L. Pardue, "Extensible Prioritization Scheme
for HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-priority-12, 17 January 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
priority-12>.

Appendix A. Examples

A.1. CONNECT-UDP

[[RFC editor: please remove this example, the client does not support any appendix before publication.]]

A.1. CONNECT-UDP nor HTTP
Datagram extensions, and therefore has no use for datagram contexts
on this stream.
Client Server

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

STREAM(44): DATA -------->
Capsule Type
capsule-protocol = REGISTER_DATAGRAM
Datagram Format Type = UDP_PAYLOAD
Datagram Format Additional Data = "" ?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. 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
:protocol = connect-udp
:scheme = https
: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

/* 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.4. Optimistic but Unsupported

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

/* 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 -------->
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 2-tuple. */

STREAM(44): DATA -------->
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.6. WebTransport

Client Server

STREAM(44): HEADERS -------->
:method = CONNECT
:scheme = https
:method
:protocol = webtransport
:path = /hello
:authority = webtransport.example.org:443
Origin
origin = https://www.example.org:443

STREAM(44): DATA -------->
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

The DATAGRAM context identifier was

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