wdiff draft-ietf-masque-h3-datagram-00.txt draft-ietf-masque-h3-datagram-01.txt

Network Working Group
MASQUE D. Schinazi
Internet-Draft Google LLC
Intended status: Standards Track L. Pardue
Expires: 2 August 14 November 2021 Cloudflare
29 January
13 May 2021

Using QUIC Datagrams with HTTP/3
draft-ietf-masque-h3-datagram-00
draft-ietf-masque-h3-datagram-01

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 defines describes how to use QUIC
DATAGRAM frames when the application protocol running over QUIC is HTTP/3 by
adding an identifier at the start of the frame payload. This allows
HTTP messages to convey related information using unreliable DATAGRAM
frames, ensuring those frames are properly associated
HTTP/3. It associates datagrams with client-initiated bidirectional
streams and defines an HTTP
message. optional additional demultiplexing layer.

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

Status of This Memo

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

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This Internet-Draft will expire on 2 August 14 November 2021.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3
2. Flow Identifiers Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Flow Identifier Allocation
2.1. Datagram Contexts . . . . . . . . . . . . . . . . . . . . 3
4.
2.2. Context ID Allocation . . . . . . . . . . . . . . . . . . 4
3. HTTP/3 DATAGRAM Frame Format . . . . . . . . . . . . . . . . 4
4. CAPSULE HTTP/3 Frame Definition . . . . . . . . . . . . . . . 5
4.1. The REGISTER_DATAGRAM_CONTEXT Capsule . . . . . . . . . . 6
4.2. The CLOSE_DATAGRAM_CONTEXT Capsule . . . . . . . . . . . 7
4.3. The DATAGRAM Capsule . . . . . . . . . . . . . . . . . . 8
5. The H3_DATAGRAM HTTP/3 SETTINGS Parameter . . . . . . . . . . 4 9
6. Datagram-Flow-Id Header Field Definition HTTP/1.x and HTTP/2 Support . . . . . . . . . . 5
7. HTTP Intermediaries . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . 7 . . . . . 10
8. Security IANA Considerations . . . . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . 10
8.1. HTTP/3 CAPSULE Frame . . . . . . . . . . . . . . . . . . 7
9.1. 10
8.2. HTTP SETTINGS Parameter . . . . . . . . . . . . . . . . . 7
9.2. HTTP Header Field 10
8.3. Capsule Types . . . . . . . . . . . . . . . . . . . . 8
9.3. Flow Identifier Parameters . . 10
8.4. Context Extension Keys . . . . . . . . . . . . . 8
10. . . . . 11
9. Normative References . . . . . . . . . . . . . . . . . . . . 8 11
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 12
A.1. CONNECT-UDP . . . . . . . . . . . . . . . . . . . . . . . 12
A.2. CONNECT-UDP with Timestamp Extension . . . . . . . . . . 13
A.3. CONNECT-IP with IP compression . . . . . . . . . . . . . 14
A.4. WebTransport . . . . . . . . . . . . . . . . . . . . . . 15
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 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 defines describes how to use
QUIC DATAGRAM frames when the application protocol running over QUIC
is HTTP/3 [H3] by adding an identifier at the start of the frame
payload. This allows HTTP messages to convey related information
using unreliable DATAGRAM frames, ensuring those frames are properly
associated [H3]. It associates datagrams with client-initiated
bidirectional streams and defines an HTTP message.

This design mimics the use of Stream Types in HTTP/3, which provide a optional additional
demultiplexing identifier at the start of each unidirectional stream. layer.

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. Flow Identifiers

Flow identifiers represent bidirectional flows Multiplexing

In order to allow multiple exchanges of datagrams within to coexist on a
single
given QUIC connection. These are conceptually similar to streams in connection, HTTP datagrams contain two layers of
multiplexing. First, the QUIC DATAGRAM frame payload starts with an
encoded stream identifier that associates the sense datagram with a given
QUIC stream. Second, datagrams carry a context identifier (see
Section 2.1) that they allow allows multiplexing multiple datagram contexts
related to a given HTTP request. Conceptually, the first layer of application data. Flows
lack any of
multiplexing is per-hop, while the ordering or reliability guarantees second is end-to-end.

2.1. Datagram Contexts

Within the scope of streams.

Beyond this, a sender SHOULD ensure that DATAGRAM frames within a
single flow are transmitted in order relative given HTTP request, contexts provide an
additional demultiplexing layer. Contexts determine the encoding of
datagrams, and can be used to one another. If
multiple DATAGRAM frames implicitly convey metadata. For
example, contexts can be packed into a single QUIC packet, used for compression to elide some parts of
the
sender SHOULD group them by flow datagram: the context identifier then maps to promote fate-sharing
within a specific flow and improve compression
context that the ability receiver can use to process batches reconstruct the elided data.

Contexts 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 messages efficiently travels through one or more
intermediaries on its way from client to server, the receiver.

3. Flow Identifier stream ID will
most likely change from hop to hop, but the context ID will remain
the same. Context IDs are opaque to intermediaries.

2.2. Context ID Allocation

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

Even-numbered flow identifiers context IDs are client-initiated, while odd-
numbered flow identifiers odd-numbered
context IDs are server-initiated. This means that an HTTP/3 client
implementation of the flow identifier context ID allocation service MUST only provide
even-numbered identifiers, IDs, while a server implementation MUST only provide
odd-numbered identifiers. IDs. Note that, once allocated, any flow identifier context ID can be
used by both client and server - only allocation carries separate
namespaces to avoid requiring synchronization.

The flow allocation service SHOULD also provide a mechanism for
applications to indicate they have completed their usage of a flow
identifier and will no longer be using Additionally, note
that flow identifier, this
process the context ID namespace is called "retiring" a flow identifier. Applications MUST
NOT retire tied to a flow identifier until after they have received
confirmation that given HTTP request: it is
possible for the peer has also stopped using that flow
identifier. The flow identifier allocation service MAY reuse
previously retired flow identifiers once they have ascertained that
there are no packets with DATAGRAM frames using that flow identifier
still same numeral context ID to be used simultaneously in flight. Reusing flow identifiers can improve performance by
transmitting the flow identifier using a shorter variable-length
integer encoding.

4.
distinct requests.

3. HTTP/3 DATAGRAM Frame 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 Frame Datagram {
Flow Identifier
Quarter Stream ID (i),
Context ID (i),
HTTP/3 Datagram Payload (..),
}

Figure 1: HTTP/3 DATAGRAM Frame Format

Flow Identifier:

Quarter Stream ID: A variable-length integer that contains the value
of the client-initiated bidirectional stream that this datagram is
associated with, divided by four. (The division by four stems
from the fact that HTTP requests are sent on client-initiated
bidirectional streams, and those have stream IDs that are
divisible by four.)

Context ID: A variable-length integer indicating the Flow
Identifier context ID of
the datagram (see Section 2). 2.1).

HTTP/3 Datagram Payload: The payload of the datagram, whose
semantics are defined by individual applications. Note that this
field can be empty.

Endpoints

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 receipt it
as an HTTP/3 connection error of type H3_GENERAL_PROTOCOL_ERROR.
Intermediaries 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 parse allow parsing the flow identifier 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.

If a DATAGRAM frame is received and its Quarter Stream ID maps to a
stream that has already been closed, the receiver MUST silently drop
that frame. If a DATAGRAM frame is received and its Quarter Stream
ID maps to a stream that has not yet been created, the receiver SHALL
either drop that frame silently or buffer it temporarily while
awaiting the creation of the corresponding stream.

4. CAPSULE HTTP/3 Frame Definition

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

CAPSULE is an HTTP/3 Frame (as opposed to a QUIC frame) which SHALL
only be sent in client-initiated bidirectional streams.
Intermediaries MUST forward all received CAPSULE frames in their
unmodified entirety on the same stream where it would forward DATA
frames. Intermediaries MUST NOT send any CAPSULE frames other than
the ones it is forwarding.

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

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

Figure 2: CAPSULE HTTP/3 Frame Format

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

Capsule Type: The type of this capsule.

Capsule Data: Data whose semantics depends on the Capsule Type.

Endpoints which receive a Capsule with an unknown Capsule Type MUST
silently drop that Capsule. Intermediaries MUST forward Capsules,
even if they do not know the Capsule Type or cannot parse the Capsule
Data.

4.1. The REGISTER_DATAGRAM_CONTEXT Capsule

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

REGISTER_DATAGRAM_CONTEXT Capsule {
Context ID (i),
Extension String (..),
}

Figure 3: REGISTER_DATAGRAM_CONTEXT Capsule Format

Context ID: The context ID to register.

Extension String: A string of comma-separated key-value pairs to
enable extensibility. Keys are registered with IANA, see
Section 8.4.

The ABNF for the Extension String field is as follows (using syntax
from Section 3.2.6 of [RFC7230]):

extension-string = [ ext-member *( "," ext-member ) ]
ext-member = ext-member-key "=" ext-member-value
ext-member-key = token
ext-member-value = token

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

Endpoints MUST NOT send DATAGRAM frames using a Context ID until they
have either sent or received a REGISTER_DATAGRAM_CONTEXT Capsule with
the same Context ID. However, due to reordering, an endpoint that
receives a DATAGRAM frame with an unknown Context ID MUST NOT treat
it as an error, it SHALL instead drop the DATAGRAM frame silently, or
buffer it temporarily while awaiting the corresponding
REGISTER_DATAGRAM_CONTEXT Capsule.

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

4.2. The CLOSE_DATAGRAM_CONTEXT Capsule

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

CLOSE_DATAGRAM_CONTEXT Capsule {
Context ID (i),
Extension String (..),
}

Figure 4: CLOSE_DATAGRAM_CONTEXT Capsule Format

Context ID: The context ID to close.

Extension String: A string of comma-separated key-value pairs to
enable extensibility, see the definition of the same field in
Section 4.1 for details.

Note that this close is unilateral and bidirectional: the sender of
the frame unilaterally informs its peer of the closure. Endpoints
can use CLOSE_DATAGRAM_CONTEXT capsules to close a context that was
initially registered by either themselves, or by their peer.
Endpoints MAY use the CLOSE_DATAGRAM_CONTEXT capsule to immediately
reject a context that was just registered using a
REGISTER_DATAGRAM_CONTEXT capsule if they find its Extension String
to be unacceptable.

After an endpoint has either sent or received a
CLOSE_DATAGRAM_CONTEXT frame, it MUST NOT send any DATAGRAM frames
with that Context ID. However, due to reordering, an endpoint that
receives a DATAGRAM frame with a closed Context ID MUST NOT treat it
as an error, it SHALL instead drop the DATAGRAM frame silently.

Endpoints MUST NOT close a Context ID that was not previously
registered. Endpoints MUST NOT close a Context ID that has already
been closed. If an endpoint receives a CLOSE_DATAGRAM_CONTEXT
capsule that violates one or more of these requirements, the endpoint
MUST abruptly terminate the corresponding stream with a stream error
of type H3_GENERAL_PROTOCOL_ERROR.

4.3. The DATAGRAM Capsule

The DATAGRAM capsule (type=0x02) allows an endpoint to send a
datagram frame over an HTTP stream. This is particularly useful when
using a version of HTTP that does not support QUIC DATAGRAM frames.
Its Capsule Data field consists of:

DATAGRAM Capsule {
Context ID (i),
HTTP/3 Datagram Payload (..),
}

Figure 5: DATAGRAM Capsule Format

Context ID: A variable-length integer indicating the context ID of
the datagram (see Section 2.1).

HTTP/3 Datagram Payload: The payload of the datagram, whose
semantics are defined by individual applications. Note that this
field can be empty.

Datagrams sent using the DATAGRAM Capsule have the exact same
semantics as datagrams sent in QUIC DATAGRAM frames.

5. The H3_DATAGRAM HTTP/3 SETTINGS Parameter

Implementations of HTTP/3 that support this mechanism can indicate
that to their peer by sending the H3_DATAGRAM SETTINGS parameter with
a value of 1. The value of the H3_DATAGRAM SETTINGS parameter MUST
be either 0 or 1. A value of 0 indicates that this mechanism is not
supported. An endpoint that receives the H3_DATAGRAM SETTINGS
parameter with a value that is neither 0 or 1 MUST terminate the
connection with error H3_SETTINGS_ERROR.

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

When clients use 0-RTT, they MAY store the value of the server's
H3_DATAGRAM SETTINGS parameter. Doing so allows the client to use
HTTP/3 datagrams in 0-RTT packets. When servers decide to accept
0-RTT data, they MUST send a H3_DATAGRAM SETTINGS parameter greater
than or equal to the value they sent to the client in the connection
where they sent them the NewSessionTicket message. If a client
stores the value of the H3_DATAGRAM SETTINGS parameter with their
0-RTT state, they MUST validate that the new value of the H3_DATAGRAM
SETTINGS parameter sent by the server in the handshake is greater
than or equal to the stored value; if not, the client MUST terminate
the connection with error H3_SETTINGS_ERROR. In all cases, the
maximum permitted value of the H3_DATAGRAM SETTINGS parameter is 1.

6. Datagram-Flow-Id Header Field Definition

"Datagram-Flow-Id" is a List Structured Field [STRUCT-FIELD], whose
members MUST all be Items of type Integer. Its ABNF is:

Datagram-Flow-Id = sf-list

The "Datagram-Flow-Id" header field is used to associate one or more
datagram flow identifiers with an HTTP message. As a simple example
using a single identifier, the definition of an HTTP method could
instruct the client to use its flow identifier allocation service to
allocate a new flow identifier, HTTP/1.x and then the client will add the
"Datagram-Flow-Id" header field to its request to communicate that
value to the server. In this example, the resulting header field
could look like:

Datagram-Flow-Id = 2

List members are flow identifier elements, which HTTP/2 Support

We can be named or
unnamed. One element in the list is allowed to be unnamed, but all
but one elements MUST carry a name. The name of an element is
encoded provide DATAGRAM support in HTTP/2 by defining the key of the first parameter of that element (parameters
are defined CAPSULE
frame in Section 3.1.2 of [STRUCT-FIELD]). Each name MUST NOT
appear more than once HTTP/2.

We can provide DATAGRAM support in the list. The value of the first parameter
of each named element (whose corresponding key conveys the element
name) MUST be of type Boolean and equal to true. The value of the
first parameter of the unnamed element MUST NOT be of type Boolean.
The ordering of the list does not carry any semantics. For example,
an HTTP method that wishes to use four datagram flow identifiers for
the lifetime of HTTP/1.x by defining its request data
stream could look like this:

Datagram-Flow-Id = 42, 44; ecn-ect0, 46; ecn-ect1, 48; ecn-ce

In this example, 42 is the unnamed flow identifier, 44 represents the
name "ecn-ect0", 46 represents "ecn-ect1", and 48 represents "ecn-
ce". Note that, since the list ordering does not carry semantics,
this example can be equivalently encoded as:

Datagram-Flow-Id = 44; ecn-ect0, 42, 48; ecn-ce, 46; ecn-ect1

Even if a sender attempts format to communicate the meaning of a flow
identifier before it uses it in an HTTP/3 datagram, it is possible
that its peer will receive an HTTP/3 datagram with a flow identifier
that it does not know as it has not yet received the corresponding
"Datagram-Flow-Id" header field. (For example, sequence of length-value capsules.

TODO: Refactor this could happen if
the QUIC STREAM frame that contains the "Datagram-Flow-Id" header
field is reordered document into "HTTP Datagrams" with definitions
for HTTP/1.x, HTTP/2, and arrives afer the DATAGRAM frame.) Endpoints
MUST NOT treat that scenario as HTTP/3.

7. Security Considerations

Since this feature requires sending an error; they MUST either silently
discard the datagram or buffer HTTP/3 Settings parameter, it until they receive the "Datagram-
Flow-Id" header field.

Distinct HTTP requests MAY refer to the same flow identifier in their
respective "Datagram-Flow-Id" header fields.

Note that integer structured fields
"sticks out". In other words, probing clients can only encode values up to
10^15-1, therefore the maximum possible value of an element of the
"Datagram-Flow-Id" header field is lower then the theoretical maximum
value of a flow identifier which is 2^62-1 due to the QUIC variable
length integer encoding. If the flow identifier allocation service
of an endpoint runs out of values lower than 10^15-1, the endpoint
MUST fail the flow identifier allocation. An HTTP message that
carries a "Datagram-Flow-Id" header field with a flow identifier
value above 10^15-1 is malformed (see Section 8.1.2.6 of [H2]).

7. HTTP Intermediaries

HTTP/3 DATAGRAM flow identifiers are specific to learn whether a given HTTP/3
connection. However, in some cases, an HTTP request may travel
across multiple HTTP connections if there are HTTP intermediaries
involved; see Section 2.3 of [RFC7230].

If an intermediary has sent the H3_DATAGRAM SETTINGS parameter with a
value of 1 on its client-facing connection, it MUST inspect all HTTP
requests from that connection and check for the presence of the
"Datagram-Flow-Id" header field. If the HTTP method of the request
is not supported by the intermediary, it MUST remove the "Datagram-
Flow-Id" header field before forwarding the request. If the
intermediary
server supports the method, it MUST either remove the header
field or adhere to the requirements leveraged by this feature. Implementations that method on
intermediaries.

If an intermediary has sent the H3_DATAGRAM SETTINGS support this
feature SHOULD always send this Settings parameter with a
value of 1 on its server-facing connection, it MUST inspect all HTTP
responses from that connection and check for the presence of the
"Datagram-Flow-Id" header field. If the HTTP method of the request
is not supported by the intermediary, it MUST remove the "Datagram-
Flow-Id" header field before forwarding the response. If the
intermediary supports the method, it MUST either remove the header
field or adhere to the requirements leveraged by that method on
intermediaries.

If an intermediary processes distinct HTTP requests that refer to avoid leaking
the
same flow identifier in their respective "Datagram-Flow-Id" header
fields, it MUST ensure fact that those requests there are routed to the same
backend. applications using HTTP/3 datagrams enabled
on this endpoint.

8. Security IANA Considerations

8.1. HTTP/3 CAPSULE Frame

This document does not have additional security considerations beyond
those defined in [QUIC] and [DGRAM].

9. will request IANA Considerations

9.1. to register the following entry in
the "HTTP/3 Frames" registry:

8.2. HTTP SETTINGS Parameter

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

+--------------+-------+---------------+---------+

9.2. HTTP Header Field
+--------------+----------+---------------+---------+

8.3. Capsule Types

This document will request IANA establishes a registry for HTTP/3 frame type codes.
The "HTTP Capsule Types" registry governs a 62-bit space.
Registrations in this registry MUST include the following fields:

Type:

A name or label for the capsule type.

Value: The value of the Capsule Type field (see Section 4) is a
62bit integer.

Reference: An optional reference to register a specification for the "Datagram-Flow-Id"
header type.
This field in MAY be empty.

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

This registry
maintained at <https://www.iana.org/assignments/message-headers>.

+-------------------+----------+--------+---------------+ initially contains the following entries:

9.3. Flow Identifier Parameters This Document |
+---------------------------+-------+---------------+

8.4. Context Extension Keys

REGISTER_DATAGRAM_CONTEXT capsules carry key-value pairs, see
Section 4.1. This document will request IANA to create an "HTTP
Datagram Flow
Identifier Parameters" Context Extension Keys" registry. Registrations in this
registry MUST include the following fields:

Key: The key of a parameter that is associated with a datagram flow
identifier list member (see Section 6). 4.1). Keys MUST be valid
structured field parameter keys (see tokens as
defined in Section 3.1.2 3.2.6 of
[STRUCT-FIELD]). [RFC7230].

Description: A brief description of the parameter key semantics, which MAY be
a summary if a specification reference is provided.

Is Name: This field MUST be either Yes or No. Yes indicates that
this parameter is the name of a named element (see Section 6). No
indicates that it is a parameter that is not a name.

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 Key. This registry is initially empty.

10.

9. 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-01, 24 August 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-
datagram-01.txt>.

[H2] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>. draft-ietf-quic-datagram-02, 16 February 2021,
<https://tools.ietf.org/html/draft-ietf-quic-datagram-02>.

[H3] Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-33, 15 December 2020, <http://www.ietf.org/
internet-drafts/draft-ietf-quic-http-33.txt>.
quic-http-34, 2 February 2021,
<https://tools.ietf.org/html/draft-ietf-quic-http-34>.

[IANA-POLICY]
Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
<https://www.rfc-editor.org/rfc/rfc8126>.

[QUIC] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", Work in Progress, Internet-Draft,
draft-ietf-quic-transport-34, 14 January 2021,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-
transport-34.txt>.
<https://tools.ietf.org/html/draft-ietf-quic-transport-
34>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
<https://www.rfc-editor.org/rfc/rfc2119>.

[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
<https://www.rfc-editor.org/rfc/rfc7230>.

[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/info/rfc8174>.

[STRUCT-FIELD]
Nottingham, M. and P. Kamp, "Structured Field Values <https://www.rfc-editor.org/rfc/rfc8174>.

Appendix A. Examples

A.1. CONNECT-UDP
Client Server

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

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

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

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

/* Wait for
HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-header-structure-19, 3 June 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-httpbis-
header-structure-19.txt>. target server to respond to UDP packet. */

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

A.2. CONNECT-UDP with Timestamp Extension
Client Server

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

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

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

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

/* Wait for target server to respond to UDP packet. */

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

STREAM(44): CAPSULE -------->
Capsule Type = REGISTER_DATAGRAM_CONTEXT
Context ID = 2
Extension String = "timestamp"

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

A.3. CONNECT-IP with IP compression
Client Server

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

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

/* Exchange CONNECT-IP configuration information. */

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

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

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

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

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

STREAM(44): CAPSULE -------->
Capsule Type = REGISTER_DATAGRAM_CONTEXT
Context ID = 2
Extension String = "ip=192.0.2.42,port=443"

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

A.4. WebTransport
Client Server

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

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

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

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

Acknowledgments

The DATAGRAM flow context identifier was previously part of the DATAGRAM
frame definition itself, the author authors would like to acknowledge the
authors of that document and the members of the IETF MASQUE working
group for their suggestions. Additionally, the author 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