wdiff draft-ietf-masque-h3-datagram-04.txt draft-ietf-masque-h3-datagram-05.txt

MASQUE D. Schinazi
Internet-Draft Google LLC
Intended status: Standards Track L. Pardue
Expires: 10 28 April 2022 Cloudflare
7
25 October 2021

Using Datagrams with HTTP
draft-ietf-masque-h3-datagram-04
draft-ietf-masque-h3-datagram-05

Abstract

The QUIC DATAGRAM extension provides application protocols running
over QUIC with a mechanism to send unreliable data while leveraging
the security and congestion-control properties of QUIC. However,
QUIC DATAGRAM frames do not provide a means to demultiplex
application contexts. This document describes how to use QUIC
DATAGRAM frames when the application protocol running over QUIC is
HTTP/3. It associates datagrams with client-initiated bidirectional
streams and defines an optional additional demultiplexing layer.
Additionally, this document defines how to convey datagrams over
prior versions of HTTP.

Discussion Venues

This note is to be removed before publishing as an RFC.

Discussion of this document takes place on the MASQUE WG mailing list
(masque@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/masque/.

Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-masque/draft-ietf-masque-h3-datagram.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on 10 28 April 2022.

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Please review these documents carefully, as they describe your rights
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 4
2. Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Datagram Contexts . . . . . . . . . . . . . . . . . . . . 4
2.2. Datagram Formats . . . . . . . . . . . . . . . . . . . . 5
2.3. Context ID Allocation . . . . . . . . . . . . . . . . . . 5
3. HTTP/3 DATAGRAM Format . . . . . . . . . . . . . . . . . . . 6
4. Capsules . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Capsule Protocol . . . . . . . . . . . . . . . . . . . . 8
4.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 9
4.3. Intermediary Processing . . . . . . . . . . . . . . . . . 9
4.4. Capsule Types . . . . . . . . . . . . . . . . . . . . . . 10
4.4.1. The REGISTER_DATAGRAM_CONTEXT Capsule Datagram Registration Capsules . . . . . . . . . 10
4.4.2. The REGISTER_DATAGRAM_NO_CONTEXT Datagram Close Capsule . . . . . . 11
4.4.3. The CLOSE_DATAGRAM_CONTEXT Capsule . . . . . . . . . 12
4.4.4. 11
4.4.3. The DATAGRAM Capsule Datagram Capsules . . . . . . . . . . . . . . . . 14 13
5. The H3_DATAGRAM HTTP/3 SETTINGS Parameter . . . . . . . . . . 16 14
5.1. Note About Draft Versions . . . . . . . . . . . . . . . . 16 15
6. The Sec-Use-Datagram-Contexts HTTP Header . . . . . . . . . . 15
7. Prioritization . . . . . . . . . . . . . . . . . . . . . . . 16
7.
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8.
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1.
9.1. HTTP/3 SETTINGS Parameter . . . . . . . . . . . . . . . . 17
8.2.
9.2. HTTP Header Field Name . . . . . . . . . . . . . . . . . 17
9.3. Capsule Types . . . . . . . . . . . . . . . . . . . . . . 17
8.3. 18
9.4. Datagram Format Types . . . . . . . . . . . . . . . . . . 18
8.4.
9.5. Context Close Codes . . . . . . . . . . . . . . . . . . . 19
9.
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. 20
10.1. Normative References . . . . . . . . . . . . . . . . . . 19
9.2. 20
10.2. Informative References . . . . . . . . . . . . . . . . . 20 21
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 21
A.1. CONNECT-UDP . . . . . . . . . . . . . . . . . . . . . . . 21
A.2. CONNECT-UDP with Delayed Timestamp Extension . . . . . . 22
A.2.1. With Delay . . . . . . 21 . . . . . . . . . . . . . . . 22
A.3. Successful Optimistic . . . . . . . . . . . . . . . . . . 23
A.4. Optimistic but Unsupported . . . . . . . . . . . . . . . 24
A.5. CONNECT-IP with IP compression . . . . . . . . . . . . . 22
A.4. 25
A.6. WebTransport . . . . . . . . . . . . . . . . . . . . . . 24 26
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 24 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 27

1. Introduction

The QUIC DATAGRAM extension [DGRAM] provides application protocols
running over QUIC [QUIC] with a mechanism to send unreliable data
while leveraging the security and congestion-control properties of
QUIC. However, QUIC DATAGRAM frames do not provide a means to
demultiplex application contexts. This document describes how to use
QUIC DATAGRAM frames when the application protocol running over QUIC
is HTTP/3 [H3]. It associates datagrams with client-initiated
bidirectional streams and defines an optional additional
demultiplexing layer. Additionally, this document defines how to
convey datagrams over prior versions of HTTP.

This document is structured as follows:

* Section 2 presents core concepts for multiplexing across HTTP
versions.

- Section 2.1 defines datagram contexts, an optional end-to-end
multiplexing concept scoped to each HTTP request. 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 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 Capsule types are defined, together with guidance
for defining new types:

o REGISTER_DATAGRAM_CONTEXT Datagram registration capsules Section 4.4.1

o REGISTER_DATAGRAM_NO_CONTEXT Datagram close capsule Section 4.4.2

o CLOSE_DATAGRAM_CONTEXT Datagram capsules Section 4.4.3

o DATAGRAM Section 4.4.4

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

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 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.

Contexts are optional, whether to use them or not is decided by the
client on each request stream using registration capsules, see
Section 4.4.1 and Section 4.4.2. When contexts are used, they are
identified within the scope of a given request by a numeric value,
referred to as the context ID. A context ID is a 62-bit integer (0
to 2^62-1).

While stream IDs are a per-hop concept, context IDs are an end-to-end
concept. In other words, if a datagram travels through one or more
intermediaries on its way from client to server, the stream ID will
most likely change from hop to hop, but the context ID will remain
the same. Context IDs are opaque to intermediaries.

2.2. Datagram Formats

Contexts are OPTIONAL to implement for both endpoints.
Intermediaries do not require any context-specific software to enable
contexts. When an endpoint registers a datagram context (or the lack of
contexts), it communicates 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 and Section 4.4.2. 4.4.1. This type
identifier is registered with IANA (see Section 8.3) 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 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. Receipt of a frame that includes a larger value MUST be
treated as a connection error of type FRAME_ENCODING_ERROR.

Context ID: A variable-length integer indicating the context ID of
the datagram (see Section 2.1). Whether or not this field is
present depends on which registration capsules were exchanged on
the associated stream: if a REGISTER_DATAGRAM_CONTEXT capsule (see
Section 4.4.1) has been sent or received whether datagram contexts are in use on this
stream, then the
field is present; if a REGISTER_DATAGRAM_NO_CONTEXT capsule (see see Section 4.4.2) has been sent or received, then 6. If this field QUIC DATAGRAM frame is
absent; if neither has been sent or received, reordered
and arrives before the receiver knows whether datagram contexts
are in use on this stream, then it is not yet
possible to the receiver cannot parse this
datagram and the receiver MUST either drop that datagram silently
or buffer it temporarily while awaiting the
registration capsule. temporarily.

HTTP Datagram Payload: The payload of the datagram, whose semantics
are defined by individual applications. Note that this field can
be empty.

Intermediaries parse the Quarter Stream ID field in order to
associate the QUIC DATAGRAM frame with a stream. If an intermediary
receives a QUIC DATAGRAM frame whose payload is too short to allow
parsing the Quarter Stream ID field, the intermediary MUST treat it
as an HTTP/3 connection error of type H3_GENERAL_PROTOCOL_ERROR. The
Context ID field is optional and whether it is present or not is
decided end-to-end by the client, endpoints, see Section 4.4.2. 6. Therefore
intermediaries cannot know whether the Context ID field is present or
absent and they MUST ignore any HTTP/3 Datagram fields after the
Quarter Stream ID.

Endpoints parse both the Quarter Stream ID field and the Context ID
field in order to associate the QUIC DATAGRAM frame with a stream and
context within that stream. If an endpoint receives a QUIC DATAGRAM
frame whose payload is too short to allow parsing the Quarter Stream
ID field, the endpoint MUST treat it as an HTTP/3 connection error of
type H3_GENERAL_PROTOCOL_ERROR. If an endpoint receives a QUIC
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. Capsules

This specification introduces the Capsule Protocol. The Capsule
Protocol is a sequence of type-length-value tuples that allows
endpoints to reliably communicate request-related information end-to-
end, even in the presence of HTTP intermediaries.

4.1. Capsule Protocol

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. 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 of new HTTP Methods or 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 or HTTP Upgrade Token states that
it uses the 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 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 this mode, the intermediary forwards the data
stream between two associated streams without any modification of
the data stream.

Participant mode: In this mode, the intermediary terminates 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, or removed by
intermediaries. Intermediaries MAY modify the contents of the
Capsule Data field of transparent capsule types.

Unless otherwise specified, all Capsule Types are defined as opaque
to intermediaries. Intermediaries MUST forward all received opaque
CAPSULE frames in their unmodified entirety. Intermediaries MUST NOT
send any opaque CAPSULE frames other than the ones it is forwarding.
All Capsule Types defined in this document are opaque, with the
exception of the DATAGRAM Capsule, datagram capsules, see Section 4.4.4. 4.4.3. Definitions
of new Capsule Types MAY specify that the newly introduced type is
transparent. Intermediaries MUST treat unknown Capsule Types as
opaque.

Intermediaries respect the order of opaque CAPSULE frames: if an
intermediary receives two opaque CAPSULE frames in a given order, it
MUST forward them in the same order.

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

4.4. Capsule Types

4.4.1. The Datagram Registration Capsules

This document defines the REGISTER_DATAGRAM and
REGISTER_DATAGRAM_CONTEXT Capsule

The REGISTER_DATAGRAM_CONTEXT capsule capsules types, known collectively as the
datagram registration capsules (see Section 8.2 9.3 for the value of the
capsule type) allows an endpoint types). The REGISTER_DATAGRAM capsule is used by endpoints
to inform its their peer of the encoding and semantics of all datagrams
associated with a stream. The REGISTER_DATAGRAM_CONTEXT capsule is
used by endpoints to inform their peer of the encoding and semantics
of all datagrams associated with a given context
ID.

REGISTER_DATAGRAM_CONTEXT ID on this stream.

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

Figure 4: REGISTER_DATAGRAM_CONTEXT Capsule Format

Context ID: The context ID to register.

Datagram Format Type: A variable-length integer that defines indicating the
semantics and encoding of context ID to
register (see Section 2.1). This field is present in
REGISTER_DATAGRAM_CONTEXT capsules but not in REGISTER_DATAGRAM
capsules. If a REGISTER_DATAGRAM capsule is used on a stream
where datagram contexts are in use, it is associated with context
ID 0. REGISTER_DATAGRAM_CONTEXT capsules MUST NOT carry context
ID 0 as that context ID is conveyed using the REGISTER_DATAGRAM
capsule.

Datagram Format Type: A variable-length integer that defines the
semantics and encoding of the HTTP Datagram Payload field of
datagrams with this context ID, see Section 2.2.

Datagram Format Additional Data: This field carries additional
information that impact the format of datagrams with this context
ID, see Section 2.2.

Note that these registrations are unilateral and bidirectional: the
sender of the frame capsule unilaterally defines the semantics it will
apply to the datagrams it sends and receives using this context ID.
Once a context ID is registered, it can be used in both directions.

Endpoints MUST NOT send DATAGRAM frames using a Context ID HTTP Datagrams until they have either sent or
received a REGISTER_DATAGRAM_CONTEXT Capsule datagram registration capsule with the same Context ID.
However, reordering can cause DATAGRAM frames HTTP Datagrams to be received with an
unknown Context ID. Receipt of such frames HTTP datagrams MUST NOT be
treated as an error. Endpoints SHALL drop the DATAGRAM
frame HTTP Datagram
silently, or buffer it temporarily while awaiting the corresponding REGISTER_DATAGRAM_CONTEXT Capsule.
datagram registration capsule. Intermediaries SHALL drop the DATAGRAM frame HTTP
Datagram silently, MAY buffer it, or forward it on immediately.

Endpoints MUST NOT register the same Context ID twice on the same
stream. This also applies to Context IDs that have been closed using
a CLOSE_DATAGRAM_CONTEXT capsule. Clients MUST NOT register server-
initiated Context IDs and servers MUST NOT register client-initiated
Context IDs. If an endpoint receives a REGISTER_DATAGRAM_CONTEXT
capsule that violates one or more of these requirements, the endpoint
MUST abruptly terminate the corresponding stream with a stream error
of type H3_GENERAL_PROTOCOL_ERROR.

Servers MUST NOT send a REGISTER_DATAGRAM_CONTEXT capsule on a stream
before they have received at least one REGISTER_DATAGRAM_CONTEXT
capsule or one REGISTER_DATAGRAM_NO_CONTEXT capsule from the client
on that stream. This ensures that clients control whether

If datagrams contexts 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, in use, the client MUST
abruptly terminate is responsible for
choosing the corresponding stream with datagram format and informing the server via a stream error of
type H3_GENERAL_PROTOCOL_ERROR.
REGISTER_DATAGRAM capsule. Servers MUST NOT send a REGISTER_DATAGRAM_CONTEXT capsule on a stream
where it has received a REGISTER_DATAGRAM_NO_CONTEXT the
REGISTER_DATAGRAM capsule. If a client receives a REGISTER_DATAGRAM_CONTEXT capsule on a stream where
the client has sent a REGISTER_DATAGRAM_NO_CONTEXT REGISTER_DATAGRAM
capsule, the client MUST abruptly terminate the corresponding stream
with a stream error of type H3_GENERAL_PROTOCOL_ERROR.

4.4.2. The REGISTER_DATAGRAM_NO_CONTEXT Datagram Close Capsule

The REGISTER_DATAGRAM_NO_CONTEXT CLOSE_DATAGRAM_CONTEXT capsule (see Section 8.2 9.3 for the value of
the capsule type) allows a client an endpoint to inform the server its peer that
datagram contexts it will not be used with this stream. It also informs
the server of the encoding and semantics of
no longer send or parse received datagrams associated with
this stream.

REGISTER_DATAGRAM_NO_CONTEXT a given
context ID.

CLOSE_DATAGRAM_CONTEXT Capsule {
Type (i) = REGISTER_DATAGRAM_NO_CONTEXT, CLOSE_DATAGRAM_CONTEXT,
Length (i),
Datagram Format Type
Context ID (i),
Datagram Format Additional Data
Close Code (i),
Close Details (..),
}

Figure 5: REGISTER_DATAGRAM_NO_CONTEXT CLOSE_DATAGRAM_CONTEXT Capsule Format

Datagram Format Type: A variable-length integer that

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 the
semantics and encoding a set of codes, the HTTP Datagram Payload field of
datagrams, see Section 2.2.

Datagram Format Additional Data: circumstances under
which an implementation sends them, and how receivers react.

Close Details: This field carries additional
information that impact the format is meant for debugging purposes. It consists of datagrams, see Section 2.2.
a human-readable string encoded in UTF-8.

Note that this registration close is unilateral and bidirectional: the
client sender of
the frame unilaterally defines informs its peer of the semantics it will apply closure. Endpoints
can use CLOSE_DATAGRAM_CONTEXT capsules to the
datagrams it sends and receives with this stream. close a context that was
initially registered by either themselves, or by their peer.
Endpoints MUST NOT send DATAGRAM frames without MAY use the CLOSE_DATAGRAM_CONTEXT capsule to immediately
reject a Context ID until context that was just registered using a
REGISTER_DATAGRAM_CONTEXT capsule if they have find its Datagram Format
Type field to be unacceptable.

After an endpoint has either sent or received a REGISTER_DATAGRAM_NO_CONTEXT
Capsule.
CLOSE_DATAGRAM_CONTEXT frame, it MUST NOT send any HTTP Datagrams
with that Context ID. However, due to reordering, an endpoint that
receives an HTTP Datagram with a
DATAGRAM frame before receiving either a REGISTER_DATAGRAM_CONTEXT
capsule or a REGISTER_DATAGRAM_NO_CONTEXT capsule closed Context ID MUST NOT treat it
as an error, it SHALL instead drop the DATAGRAM frame silently, or
buffer it temporarily while awaiting HTTP Datagram silently.

Endpoints MUST NOT close a REGISTER_DATAGRAM_NO_CONTEXT
capsule or the corresponding REGISTER_DATAGRAM_CONTEXT capsule.

Servers Context ID that was not previously
registered. Endpoints MUST NOT send the REGISTER_DATAGRAM_NO_CONTEXT capsule. If close 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. Context ID that has already
been closed. If a server an endpoint receives a second
REGISTER_DATAGRAM_NO_CONTEXT CLOSE_DATAGRAM_CONTEXT
capsule on the same stream, that violates one or more of these requirements, the server endpoint
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,

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 server
MUST abruptly terminate receiver to not open another context under certain
conditions.

This specification defines the corresponding stream with a stream error
of type H3_GENERAL_PROTOCOL_ERROR. close codes below. Their numeric
values are in Section 9.5. Extensions to this mechanism MAY define a different mechanism to communicate whether
contexts are in use,
new close codes and they MAY do so in a way which is opaque SHOULD state how receivers react to
intermediaries.

4.4.3. The CLOSE_DATAGRAM_CONTEXT Capsule

The CLOSE_DATAGRAM_CONTEXT capsule (see Section 8.2 them.

NO_ERROR: This indicates that a context was closed without any
action specified for the value of receiver.

UNKNOWN_FORMAT: This indicates that the capsule type) allows an endpoint sender does not know how to inform its peer that it will
no longer send or parse received datagrams
interpret the datagram format type associated with a given this context.
The endpoint that had originally registered this context ID.

CLOSE_DATAGRAM_CONTEXT Capsule {
Type (i) = CLOSE_DATAGRAM_CONTEXT,
Length (i),
Context ID (i),
Close Code (i),
Close Details (..),
}

Figure 6: CLOSE_DATAGRAM_CONTEXT Capsule Format

Context ID: The context ID MUST NOT
try to close.

Close Code: 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 close code allows an endpoint that had
originally registered this context MUST NOT try to provide additional
information as to why a datagram register
another context was closed.
Section 4.4.3.1 defines a set of codes, with the circumstances under
which an implementation sends them, same datagram format type and how receivers react.

Close Details: datagram
format data on this stream.

RESOURCE_LIMIT: This is meant for debugging purposes. It consists of
a human-readable string encoded in UTF-8.

Note indicates that this close is unilateral and bidirectional: the sender of the frame unilaterally informs context was closed to save
resources. The recipient SHOULD limit its peer future registration of the closure. Endpoints
can use CLOSE_DATAGRAM_CONTEXT capsules to
resource-intensive contexts.

Receipt of an unknown close a context that code MUST be treated as if the NO_ERROR
code was
initially present. Close codes are registered by either themselves, or by their peer.
Endpoints MAY use with IANA, see
Section 9.5.

4.4.3. The Datagram Capsules

This document defines the DATAGRAM and DATAGRAM_WITH_CONTEXT capsules
types, known collectively as the datagram capsules (see Section 9.3
for the value of the CLOSE_DATAGRAM_CONTEXT capsule types). These capsules allow an
endpoint to immediately
reject send a context that was just registered datagram frame over an HTTP stream. This is
particularly useful when using a
REGISTER_DATAGRAM_CONTEXT capsule if they find its version of HTTP that does not
support QUIC DATAGRAM frames.

Datagram Format Capsule {
Type field to be unacceptable.

After an endpoint has either sent (i) = DATAGRAM or received a
CLOSE_DATAGRAM_CONTEXT frame, it MUST NOT send any DATAGRAM_WITH_CONTEXT,
Length (i),
[Context ID (i)],
HTTP Datagram Payload (..),
}

Figure 6: DATAGRAM frames
with that Capsule Format

Context ID. However, due to reordering, an endpoint that
receives 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 frame with capsule is used on a closed Context ID MUST NOT treat it
as an error, stream where datagram contexts are
in use, it SHALL instead drop the DATAGRAM frame silently.

Endpoints is associated with context ID 0. DATAGRAM_WITH_CONTEXT
capsules MUST NOT close a Context carry context ID 0 as that was not previously
registered. Endpoints MUST NOT close a Context 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 has already
been closed. If an endpoint receives a CLOSE_DATAGRAM_CONTEXT this field can
be empty.

Datagrams sent using the datagram capsule that violates one or more of these requirements, have the endpoint
MUST abruptly terminate exact same
semantics as datagrams sent in QUIC DATAGRAM frames. In particular,
the corresponding stream with a stream error
of type H3_GENERAL_PROTOCOL_ERROR.

4.4.3.1. Close Codes

Close codes are intended restrictions on when it is allowed to allow implementations send an HTTP Datagram and
how to react
differently when they receive process them - for example, some close codes
require from Section 3 also apply to HTTP Datagrams sent
and received using the receiver datagram capsules.

The datagram capsules are transparent to not open another context under certain
conditions.

This specification defines the close codes below. Their numeric
values are in Section 8.4. Extensions to this mechanism intermediaries, meaning that
intermediaries MAY define
new close codes parse them and send datagram capsules that they SHOULD state how receivers react to them.

NO_ERROR:
did not receive. This indicates that allows an intermediary to reencode HTTP
Datagrams as it forwards them: in other words, an intermediary MAY
send a context datagram capsule to forward an HTTP Datagram which was closed without any
action specified for the receiver.

UNKNOWN_FORMAT: This indicates
received in a QUIC DATAGRAM frame, and vice versa.

Note that while datagram capsules are sent on a stream,
intermediaries can reencode HTTP Datagrams into QUIC DATAGRAM frames
over the sender does not know how next hop, and those could be dropped. Because of this,
applications have to
interpret the datagram format type associated with this context.
The endpoint always consider HTTP Datagrams to be unreliable,
even if they were initially sent in a capsule.

If an intermediary receives an HTTP Datagram in a QUIC DATAGRAM frame
and is forwarding it on a connection that had originally registered this context MUST supports QUIC DATAGRAM
frames, the intermediary SHOULD NOT
try convert that HTTP Datagram to register another context with a
DATAGRAM capsule. If the same datagram format type
on this stream.

DENIED: This indicates that HTTP Datagram is too large to fit in a
DATAGRAM frame (for example because the sender has rejected path MTU of that QUIC
connection is too low or if the context
registration based maximum UDP payload size advertised
on its local policy. The endpoint that had
originally registered this context MUST NOT try connection is too low), the intermediary SHOULD drop the HTTP
Datagram instead of converting it to register
another context with a DATAGRAM capsule. This
preserves the same datagram format type and datagram
format data end-to-end unreliability characteristic that methods
such as Datagram Packetization Layer Path MTU Discovery (DPLPMTUD)
depend on this stream.

RESOURCE_LIMIT: This indicates [RFC8899]. An intermediary that the context was closed converts QUIC DATAGRAM
frames to save
resources. datagram capsules allows HTTP Datagrams to be arbitrarily
large without suffering any loss; this can misrepresent the true path
properties, defeating methods such a DPLPMTUD.

5. The recipient SHOULD limit its future registration H3_DATAGRAM HTTP/3 SETTINGS Parameter

Implementations of
resource-intensive contexts.

Receipt HTTP/3 that support HTTP Datagrams can indicate
that to their peer by sending the H3_DATAGRAM SETTINGS parameter with
a value of an unknown close code 1. The value of the H3_DATAGRAM SETTINGS parameter MUST
be treated as if the NO_ERROR
code was present. Close codes either 0 or 1. A value of 0 indicates that HTTP Datagrams are registered not
supported. An endpoint that receives the H3_DATAGRAM SETTINGS
parameter with IANA, see
Section 8.4.

4.4.4. The DATAGRAM Capsule

The a value that is neither 0 or 1 MUST terminate the
connection with error H3_SETTINGS_ERROR.

Endpoints MUST NOT send QUIC DATAGRAM capsule (see Section 8.2 for 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 capsule
type) server's
H3_DATAGRAM SETTINGS parameter. Doing so allows an endpoint the client to send a datagram frame over an HTTP
stream. This is particularly useful when using a version of HTTP
that does not support
QUIC DATAGRAM frames.

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

Figure 7: DATAGRAM Capsule Format

Context ID: A variable-length integer indicating 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 context ID of value they sent to the datagram (see Section 2.1). Whether or not this field is
present depends on which registration capsules were exchanged on client in the associated stream: if a REGISTER_DATAGRAM_CONTEXT capsule (see
Section 4.4.1) has been connection
where they sent or received on this stream, then them the
field is present; if NewSessionTicket message. If a REGISTER_DATAGRAM_NO_CONTEXT capsule (see
Section 4.4.2) has been sent or received, then this field is
absent; if neither has been sent or received, then it is not yet
possible to parse this datagram and client
stores the receiver value of the H3_DATAGRAM SETTINGS parameter with their
0-RTT state, they MUST either drop validate that datagram silently or buffer it temporarily while awaiting the
registration capsule.

HTTP Datagram Payload: The payload new value of the datagram, whose semantics
are defined by individual applications. Note that this field can
be empty.

Datagrams H3_DATAGRAM
SETTINGS parameter sent using the DATAGRAM Capsule have by the exact same
semantics as datagrams sent server in QUIC DATAGRAM frames. In particular, the restrictions on when it handshake is allowed to send an HTTP Datagram and
how to process them from Section 3 also apply greater
than or equal to HTTP 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. 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 an intermediary new draft revisions to reencode HTTP Datagrams
as it forwards them: in other words, an intermediary
make incompatible changes. Multiple draft versions MAY send a
DATAGRAM Capsule to forward an HTTP Datagram which was received be supported
by either endpoint in a
QUIC DATAGRAM frame, and vice versa.

Note that while DATAGRAM capsules are connection. Such endpoints MUST send
multiple values for H3_DATAGRAM. Once an endpoint has sent on a stream,
intermediaries can reencode HTTP Datagrams into QUIC DATAGRAM frames
over the next hop, and those could be dropped. Because
received SETTINGS, it MUST compute the intersection of this,
applications have to always consider HTTP Datagrams to be unreliable,
even if they were initially the values it
has sent in a capsule.

If an intermediary receives an HTTP Datagram in a QUIC DATAGRAM frame and is forwarding received, and then it on a connection that supports QUIC DATAGRAM
frames, MUST select and use the intermediary SHOULD NOT convert most
recent draft version from the intersection set. This ensures that HTTP Datagram to a
DATAGRAM capsule. If
both endpoints negotiate the same draft version.

6. The Sec-Use-Datagram-Contexts HTTP Datagram is too large to fit in a
DATAGRAM frame (for example because the path MTU of that QUIC
connection is too low or if the maximum UDP payload size advertised
on that connection is too low), the intermediary SHOULD drop the HTTP
Datagram instead of converting it to a DATAGRAM capsule. This
preserves the end-to-end unreliability characteristic that methods
such as Datagram Packetization Layer Path MTU Discovery (DPLPMTUD)
depend on [RFC8899]. An intermediary that converts QUIC DATAGRAM
frames to DATAGRAM capsules allows HTTP Datagrams to be arbitrarily
large without suffering any loss; this can misrepresent the true path
properties, defeating methods such a DPLPMTUD.

5. The H3_DATAGRAM HTTP/3 SETTINGS Parameter

Implementations of HTTP/3 that support HTTP Datagrams can Header

Endpoints indicate
that to their peer support for datagram contexts by sending the H3_DATAGRAM SETTINGS parameter
Sec-Use-Datagram-Contexts header with a value of 1. The value of ?1. If the H3_DATAGRAM SETTINGS parameter MUST
be either 0 header
is missing or 1. A has a value of 0 different from ?1, that indicates that HTTP Datagrams are its
sender does not
supported. An endpoint wish to use datagram contexts. Endpoints that receives wish
to use datagram contexts SHALL send the H3_DATAGRAM SETTINGS
parameter Sec-Use-Datagram-Contexts
header with a value of ?1 on requests and responses that use the
capsule protocol.

"Sec-Use-Datagram-Contexts" is neither 0 or 1 an Item Structured Header [RFC8941].
Its value MUST terminate the
connection with error H3_SETTINGS_ERROR. 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 QUIC DATAGRAM frames until they have both
sent
context-related capsules, and MUST silently ignore any received the H3_DATAGRAM SETTINGS parameter with a value of
1.

When clients use 0-RTT,
context-related capsules.

Both endpoints unilaterally decide whether 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 wish to accept
0-RTT data, they MUST send use datagram
contexts on a H3_DATAGRAM SETTINGS parameter greater
than or equal to the value given stream. Contexts are used on a given stream if
and only if both endpoints indicate they sent wish to use them on this
stream. Once an endpoint has received the client 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 connection
where they sent them client chooses the NewSessionTicket message. datagram format for all datagrams when
datagram contexts are not in use.

If datagram contexts are not in use on a client
stores the value of the H3_DATAGRAM SETTINGS parameter with their
0-RTT state, they stream, endpoints MUST validate that the new value of NOT
send context-related capsules to the H3_DATAGRAM
SETTINGS parameter sent by peer on that stream. Clients
MAY optimistically send context-related capsules before learning
whether the server in the handshake is greater
than wishes to support datagram contexts or equal not.

This allows a client to optimistically use extensions that rely on
datagram contexts without knowing a priori whether the stored value; if not, server
supports them, and without incurring a latency cost to negotiate
extension support. In this scenario, the client MUST terminate
the connection would send its
request with error H3_SETTINGS_ERROR. In all cases, the
maximum permitted value of Sec-Use-Datagram-Contexts header set to ?1, and
register two datagram contexts: 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 main context would use context ID
0 and the extension context would use context ID 2. The client then
sends a different value (the
Identifier field of a Setting in REGISTER_DATAGRAM capsule to register the HTTP/3 SETTINGS frame) for main context, and a
REGISTER_DATAGRAM_CONTEXT to register the
H3_DATAGRAM Settings Parameter. This allows new draft revisions extension context. The
client can then immediately send DATAGRAM capsules 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 main
datagrams and
received SETTINGS, DATAGRAM_WITH_CONTEXT capsules to send extension
datagrams.

* If the server wishes to use datagram contexts, it MUST compute will set Sec-
Use-Datagram-Contexts to ?1 on its response and correctly parse
all the intersection of received capsules.

* If the values server does not wish to use datagram contexts (for example
if the server implementation does not support them), it
has sent and received, and will not
set Sec-Use-Datagram-Contexts to ?1 on its response. It will then it MUST select
parse the REGISTER_DATAGRAM and DATAGRAM capsules without datagram
contexts being in use on this stream, and parse the most
recent draft version from main datagrams
correctly while silently dropping the intersection set. This ensures that
both endpoints negotiate extension datagrams. Once
the same draft version.

6. client receives the server's response, it will know datagram
contexts are not in use, and then will be able to send HTTP
Datagrams via the QUIC DATAGRAM frame.

Extensions MAY define a different mechanism to communicate whether
contexts are in use, and they MAY do so in a way which is opaque to
intermediaries.

7. Prioritization

Data streams (see Section 4.1) can be prioritized using any means
suited to stream or request prioritization. For example, see
Section 11 of [PRIORITY].

Prioritization of HTTP/3 datagrams is not defined in this document.
Future extensions MAY define how to prioritize datagrams, and MAY
define signaling to allow endpoints to communicate their
prioritization preferences.

8. Security Considerations

Since this feature requires sending an HTTP/3 Settings parameter, it
"sticks out". In other words, probing clients can learn whether a
server supports this feature. Implementations that support this
feature SHOULD always send this Settings parameter to avoid leaking
the fact that there are applications using HTTP/3 datagrams enabled
on this endpoint.

9. IANA Considerations

8.1.

9.1. HTTP/3 SETTINGS Parameter

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

Table 1: New HTTP/3 Settings

8.2. Capsule Types

9.2. HTTP Header Field Name

This document establishes a registry for HTTP capsule type codes.
The will request IANA to register the following entry in
the "HTTP Field Name" registry:

Field Name: Sec-Use-Datagram-Contexts

Template: None

Status: provisional (permanent if this document is approved)

Reference: This document

Comments: None

9.3. Capsule Types

This document establishes a registry for HTTP capsule type codes.
The "HTTP Capsule Types" registry governs a 62-bit space.
Registrations in this registry MUST include the following fields:

Type: A name or label for the capsule type.

Value: The value of the Capsule Type field (see Section 4.1) is a
62-bit integer.

Reference: An optional reference to a specification for the type.
This field MAY be empty.

Registrations follow the "First Come First Served" policy (see
Section 4.4 of [IANA-POLICY]) where two registrations MUST NOT have
the same Type.

This registry initially contains the following entries:

+==============================+==========+===============+

+===========================+==========+===============+
| Capsule Type | Value | Specification |
+==============================+==========+===============+
+===========================+==========+===============+
| DATAGRAM REGISTER_DATAGRAM_CONTEXT | 0xff37a0 0xff37a1 | This Document |
+------------------------------+----------+---------------+
+---------------------------+----------+---------------+
| REGISTER_DATAGRAM_CONTEXT REGISTER_DATAGRAM | 0xff37a1 0xff37a2 | This Document |
+------------------------------+----------+---------------+
+---------------------------+----------+---------------+
| REGISTER_DATAGRAM_NO_CONTEXT CLOSE_DATAGRAM_CONTEXT | 0xff37a2 0xff37a3 | This Document |
+------------------------------+----------+---------------+
+---------------------------+----------+---------------+
| CLOSE_DATAGRAM_CONTEXT DATAGRAM_WITH_CONTEXT | 0xff37a3 0xff37a4 | This Document |
+---------------------------+----------+---------------+
| DATAGRAM | 0xff37a5 | This Document |
+------------------------------+----------+---------------+
+---------------------------+----------+---------------+

Table 2: Initial Capsule Types Registry Entries

Capsule types with a value of the form 41 * N + 23 for integer values
of N are reserved to exercise the requirement that unknown capsule
types be ignored. These capsules have no semantics and can carry
arbitrary values. These values MUST NOT be assigned by IANA and MUST
NOT appear in the listing of assigned values.

8.3.

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.

8.4.

9.5. Context Close Codes

This document establishes a registry for HTTP context close codes.
The "HTTP Context Close Codes" registry governs a 62-bit space.
Registrations in this registry MUST include the following fields:

Type: A name or label for the close code.

Value: The value of the Close Code field (see Section 4.4.3) 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. References

9.1.

10.1. Normative References

[DGRAM] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", Work in Progress, Internet-
Draft, draft-ietf-quic-datagram-06, 5 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
datagram-06>.

[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>.

[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>.

9.2.

[RFC8941] 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. Informative References

[PRIORITY] Oku, K. and L. Pardue, "Extensible Prioritization Scheme
for HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-priority-06, 30 September
httpbis-priority-07, 25 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
priority-06>.
priority-07>.

[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/rfc/rfc8899>.

Appendix A. Examples

A.1. CONNECT-UDP

In this example, the client does not support any CONNECT-UDP nor HTTP
Datagram extensions, and therefore has no use for datagram contexts
on this stream.

Client Server

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

STREAM(44): DATA -------->
Capsule Type = REGISTER_DATAGRAM
Datagram Format Type = UDP_PAYLOAD
Datagram Format Additional Data = ""

DATAGRAM -------->
Quarter Stream ID = 11
Payload = Encapsulated UDP Payload

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

/* 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-UDP CONNECT
:protocol = connect-udp
:scheme = https
:path = / /target.example.org/443/
:authority = target.example.org:443 proxy.example.org:443
Sec-Use-Datagram-Contexts = ?1

STREAM(44): DATA -------->
Capsule Type = REGISTER_DATAGRAM_CONTEXT
Context ID = 0 REGISTER_DATAGRAM
Datagram Format Type = UDP_PAYLOAD
Datagram Format Additional Data = ""

DATAGRAM

STREAM(44): DATA -------->
Quarter Stream ID = 11
Context ID
Capsule Type = 0 DATAGRAM
Payload = Encapsulated UDP Payload

<-------- STREAM(44): HEADERS
:status = 200
Sec-Use-Datagram-Contexts = ?1

/* Wait for target server to respond to UDP packet. Datagram contexts are in use on this stream */

<-------- DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated UDP Payload

A.2. CONNECT-UDP with

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 Extension

A.4. Optimistic but Unsupported

Client Server

STREAM(44): DATA -------->
Capsule Type = REGISTER_DATAGRAM_CONTEXT
Context ID = 0 REGISTER_DATAGRAM
Datagram Format Type = UDP_PAYLOAD
Datagram Format Additional Data = ""

DATAGRAM

STREAM(44): DATA -------->
Quarter Stream ID = 11
Context ID
Capsule Type = 0 DATAGRAM
Payload = Encapsulated UDP Payload

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

/* Wait for target server to respond to UDP packet. Datagram contexts are not in use on this stream */

<-------- DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated UDP Payload

STREAM(44): DATA -------->
Capsule Type = REGISTER_DATAGRAM_CONTEXT
Context ID = 2
Datagram Format Type = UDP_PAYLOAD_WITH_TIMESTAMP
Datagram Format Additional Data = ""

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

A.3.

A.5. CONNECT-IP with IP compression

Client Server

STREAM(44): HEADERS -------->
:method = CONNECT-IP 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.4.

A.6. WebTransport
Client Server

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

STREAM(44): DATA -------->
Capsule Type = REGISTER_DATAGRAM_NO_CONTEXT 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 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

Email: dschinazi.ietf@gmail.com

Lucas Pardue
Cloudflare

Email: lucaspardue.24.7@gmail.com