1. Introduction
This section is non-normative.
This specification uses [WEB-TRANSPORT-HTTP3] and [WEB-TRANSPORT-HTTP2] to send data to and receive data from servers. It can be used like WebSockets but with support for multiple streams, unidirectional streams, out-of-order delivery, and reliable as well as unreliable transport.
Note: The API presented in this specification represents a preliminary proposal based on work-in-progress within the IETF WEBTRANS WG. Since the [WEB-TRANSPORT-HTTP3] and [WEB-TRANSPORT-HTTP2] specifications are a work-in-progress, both the protocol and API are likely to change significantly going forward.
2. Conformance
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC2119] and [RFC8174] when, and only when, they appear in all capitals, as shown here.
This specification defines conformance criteria that apply to a single product: the user agent that implements the interfaces that it contains.
Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)
Implementations that use ECMAScript to implement the APIs defined in this specification MUST implement them in a manner consistent with the ECMAScript Bindings defined in the Web IDL specification [WEBIDL], as this specification uses that specification and terminology.
3. Protocol concepts
There are two main protocol concepts for WebTransport: sessions and streams. Each WebTransport session can contain multiple WebTransport streams.
3.1. WebTransport session
A WebTransport session is a session of WebTransport over an HTTP/3 or HTTP/2 underlying connection. There may be multiple WebTransport sessions on one connection, when pooling is enabled.
A WebTransport session has the following capabilities defined in [WEB-TRANSPORT-OVERVIEW]:
capability | definition |
---|---|
send a datagram | [WEB-TRANSPORT-OVERVIEW] Section 4.2 |
receive a datagram | [WEB-TRANSPORT-OVERVIEW] Section 4.2 |
create an outgoing unidirectional stream | [WEB-TRANSPORT-OVERVIEW] Section 4.3 |
create a bidirectional stream | [WEB-TRANSPORT-OVERVIEW] Section 4.3 |
receive an incoming unidirectional stream | [WEB-TRANSPORT-OVERVIEW] Section 4.3 |
receive a bidirectional stream | [WEB-TRANSPORT-OVERVIEW] Section 4.3 |
To establish a WebTransport session with an origin origin,
follow [WEB-TRANSPORT-OVERVIEW] Section 4.1,
with using origin, serialized and isomorphic encoded,
as the `Origin
` header of the request.
When establishing a session, the client MUST NOT provide any credentials.
The resulting underlying transport stream is referred to as the session’s CONNECT stream.
A WebTransport session session is draining when the CONNECT stream receives an DRAIN_WEBTRANSPORT_SESSION capsule, or when a GOAWAY frame is received, as described in [WEB-TRANSPORT-HTTP3] Section 4.6.
To terminate a WebTransport session session with an optional integer code and an optional byte sequence reason, follow [WEB-TRANSPORT-OVERVIEW] Section 4.1.
A WebTransport session session is terminated, with optionally an integer code and a byte sequence reason, when the CONNECT stream is closed by the server, as described at [WEB-TRANSPORT-OVERVIEW] Section 4.1.
A WebTransport session has the following signals:
event | definition |
---|---|
DRAIN_WEBTRANSPORT_SESSION | [WEB-TRANSPORT-HTTP3] Section 4.6 |
GOAWAY | [WEB-TRANSPORT-HTTP3] Section 4.6 |
3.2. WebTransport stream
A WebTransport stream is a concept for a reliable in-order stream of bytes on a WebTransport session, as described in [WEB-TRANSPORT-OVERVIEW] Section 4.3.
A WebTransport stream is one of incoming unidirectional, outgoing unidirectional or bidirectional.
A WebTransport stream has the following capabilities:
capability | definition | incoming unidirectional | outgoing unidirectional | bidirectional |
---|---|---|---|---|
send bytes (potentially with FIN) | [WEB-TRANSPORT-OVERVIEW] Section 4.3 | No | Yes | Yes |
receive bytes (potentially with FIN) | [WEB-TRANSPORT-OVERVIEW] Section 4.3 | Yes | No | Yes |
send STOP_SENDING | [WEB-TRANSPORT-OVERVIEW] Section 4.3 | Yes | No | Yes |
reset a WebTransport stream | [WEB-TRANSPORT-OVERVIEW] Section 4.3 | No | Yes | Yes |
A WebTransport stream has the following signals:
event | definition | incoming unidirectional | outgoing unidirectional | bidirectional |
---|---|---|---|---|
STOP_SENDING | [WEB-TRANSPORT-OVERVIEW] Section 4.3 | No | Yes | Yes |
RESET_STREAM | [WEB-TRANSPORT-OVERVIEW] Section 4.3 | Yes | No | Yes |
flow control | [WEB-TRANSPORT-OVERVIEW] Section 4.3 | No | Yes | Yes |
4. WebTransportDatagramDuplexStream
Interface
A WebTransportDatagramDuplexStream
is a generic duplex stream.
[Exposed =(Window ,Worker ),SecureContext ]interface WebTransportDatagramDuplexStream {readonly attribute ReadableStream readable ;readonly attribute WritableStream writable ;readonly attribute unsigned long maxDatagramSize ;attribute unrestricted double ?incomingMaxAge ;attribute unrestricted double ?outgoingMaxAge ;attribute unrestricted double incomingHighWaterMark ;attribute unrestricted double outgoingHighWaterMark ; };
4.1. Internal slots
A WebTransportDatagramDuplexStream
object has the following internal slots.
Internal Slot | Description (non-normative) |
---|---|
[[Readable]]
| A ReadableStream for incoming datagrams.
|
[[Writable]]
| A WritableStream for outgoing datagrams.
|
[[IncomingDatagramsQueue]]
| A queue of pairs of an incoming datagram and a timestamp. |
[[IncomingDatagramsPullPromise]]
| A promise set by pullDatagrams, to wait for an incoming datagram. |
[[IncomingDatagramsHighWaterMark]]
| An unrestricted double representing the high water mark of the incoming datagrams.
|
[[IncomingDatagramsExpirationDuration]]
| An unrestricted double representing the
expiration duration for incoming datagrams (in milliseconds), or null.
|
[[OutgoingDatagramsQueue]]
| A queue of tuples of an outgoing datagram, a timestamp and a promise which is resolved when the datagram is sent or discarded. |
[[OutgoingDatagramsHighWaterMark]]
| An unrestricted double representing the high water mark of the outgoing datagrams.
|
[[OutgoingDatagramsExpirationDuration]]
| An unrestricted double value representing the
expiration duration for outgoing datagrams (in milliseconds), or null.
|
[[OutgoingMaxDatagramSize]]
| An integer representing the maximum size for an outgoing datagram. |
The user agent MAY update [[OutgoingMaxDatagramSize]]
for any WebTransport
object whose [[State]]
is either "connecting"
or "connected"
.
To create a WebTransportDatagramDuplexStream
given a readable, and
a writable,
perform the following steps.
-
Let stream be a new
WebTransportDatagramDuplexStream
, with:[[Readable]]
-
readable
[[Writable]]
-
writable
[[IncomingDatagramsQueue]]
-
an empty queue
[[IncomingDatagramsPullPromise]]
-
null
[[IncomingDatagramsHighWaterMark]]
-
an implementation-defined value
[[IncomingDatagramsExpirationDuration]]
-
null
[[OutgoingDatagramsQueue]]
-
an empty queue
[[OutgoingDatagramsHighWaterMark]]
-
an implementation-defined value
This implementation-defined value should be tuned to ensure decent throughput, without jeopardizing the timeliness of transmitted data.
[[OutgoingDatagramsExpirationDuration]]
-
null
[[OutgoingMaxDatagramSize]]
-
an implementation-defined integer.
-
Return stream.
4.2. Attributes
readable
, of type ReadableStream, readonly-
The getter steps are:
-
Return this.
[[Readable]]
.
-
writable
, of type WritableStream, readonly-
The getter steps are:
-
Return this.
[[Writable]]
.
-
incomingMaxAge
, of type unrestricted double, nullable-
The getter steps are:
The setter steps, given value, are:
-
If value is negative or NaN, throw a
RangeError
. -
If value is
0
, set value to null. -
Set this.
[[IncomingDatagramsExpirationDuration]]
to value.
maxDatagramSize
, of type unsigned long, readonly-
The maximum size data that may be passed to
writable
. The getter steps are to return this.[[OutgoingMaxDatagramSize]]
. outgoingMaxAge
, of type unrestricted double, nullable-
The getter steps are:
-
Return this's
[[OutgoingDatagramsExpirationDuration]]
.
The setter steps, given value, are:
-
If value is negative or NaN, throw a
RangeError
. -
If value is
0
, set value to null. -
Set this.
[[OutgoingDatagramsExpirationDuration]]
to value.
-
incomingHighWaterMark
, of type unrestricted double-
The getter steps are:
The setter steps, given value, are:
-
If value is negative or NaN, throw a
RangeError
. -
If value is <
1
, set value to1
. -
Set this.
[[IncomingDatagramsHighWaterMark]]
to value.
outgoingHighWaterMark
, of type unrestricted double-
The getter steps are:
The setter steps, given value, are:
-
If value is negative or NaN, throw a
RangeError
. -
If value is <
1
, set value to1
. -
Set this.
[[OutgoingDatagramsHighWaterMark]]
to value.
4.3. Procedures
To pullDatagrams, given a WebTransport
object transport, run these steps:
-
Let datagrams be transport.
[[Datagrams]]
. -
Assert: datagrams.
[[IncomingDatagramsPullPromise]]
is null. -
Let queue be datagrams.
[[IncomingDatagramsQueue]]
. -
If queue is empty, then:
-
Set datagrams.
[[IncomingDatagramsPullPromise]]
to a new promise. -
Return datagrams.
[[IncomingDatagramsPullPromise]]
.
-
-
Let datagram and timestamp be the result of dequeuing queue.
-
If datagrams.
[[Readable]]
's current BYOB request view is not null, then:-
Let view be datagrams.
[[Readable]]
's current BYOB request view. -
If view’s byte length is less than the size of datagram, return a promise rejected with a
RangeError
. -
Let elementSize be the element size specified in the typed array constructors table for view.[[TypedArrayName]]. If view does not have a [[TypedArrayName]] internal slot (i.e. it is a
DataView
), let elementSize be 0. -
If elementSize is not 1, return a promise rejected with a
TypeError
.
-
-
Pull from bytes datagram into datagrams.
[[Readable]]
. -
Return a promise resolved with undefined.
To receiveDatagrams, given a WebTransport
object transport, run these steps:
-
Let timestamp be a timestamp representing now.
-
Let queue be datagrams.
[[IncomingDatagramsQueue]]
. -
Let duration be datagrams.
[[IncomingDatagramsExpirationDuration]]
. -
If duration is null, then set duration to an implementation-defined value.
-
Let session be transport.
[[Session]]
. -
While there are available incoming datagrams on session:
-
Let datagram be the result of receiving a datagram with session.
-
Let timestamp be a timestamp representing now.
-
Let chunk be a pair of datagram and timestamp.
-
Enqueue chunk to queue.
-
-
Let toBeRemoved be the length of queue minus datagrams.
[[IncomingDatagramsHighWaterMark]]
. -
If toBeRemoved is positive, repeat dequeuing queue toBeRemoved (rounded down) times.
-
While queue is not empty:
-
If queue is not empty and datagrams.
[[IncomingDatagramsPullPromise]]
is non-null, then:-
Let bytes and timestamp be the result of dequeuing queue.
-
Let promise be datagrams.
[[IncomingDatagramsPullPromise]]
. -
Set datagrams.
[[IncomingDatagramsPullPromise]]
to null. -
Queue a network task with transport to run the following steps:
-
Let chunk be a new
Uint8Array
object representing bytes. -
Enqueue chunk to datagrams.
[[Readable]]
. -
Resolve promise with undefined.
-
-
The user agent SHOULD run receiveDatagrams for any WebTransport
object whose [[State]]
is "connected"
as soon as reasonably possible whenever the algorithm can make
progress.
The writeDatagrams algorithm is given a transport as parameter and data as input. It is defined by running the following steps:
-
Let timestamp be a timestamp representing now.
-
If data is not a
BufferSource
object, then return a promise rejected with aTypeError
. -
Let datagrams be transport.
[[Datagrams]]
. -
If datagrams.
[[OutgoingMaxDatagramSize]]
is less than data’s [[ByteLength]], return a promise resolved with undefined. -
Let promise be a new promise.
-
Let bytes be a copy of bytes which data represents.
-
Let chunk be a tuple of bytes, timestamp and promise.
-
Enqueue chunk to datagrams.
[[OutgoingDatagramsQueue]]
. -
If the length of datagrams.
[[OutgoingDatagramsQueue]]
is less than datagrams.[[OutgoingDatagramsHighWaterMark]]
, then resolve promise with undefined. -
Return promise.
Note: The associated WritableStream
calls writeDatagrams only when all the promises that
have been returned by writeDatagrams have been resolved. Hence the timestamp and the expiration
duration work well only when the web developer pays attention to WritableStreamDefaultWriter.ready
.
To sendDatagrams, given a WebTransport
object transport, run these steps:
-
Let queue be datagrams.
[[OutgoingDatagramsQueue]]
. -
Let duration be datagrams.
[[OutgoingDatagramsExpirationDuration]]
. -
If duration is null, then set duration to an implementation-defined value.
-
While queue is not empty:
-
Let bytes, timestamp and promise be queue’s first element.
-
If more than duration milliseconds have passed since timestamp, then:
-
Remove the first element from queue.
-
Queue a network task with transport to resolve promise with undefined.
-
-
Otherwise, break this loop.
-
-
If transport.
[[State]]
is not"connected"
, then return. -
Let maxSize be datagrams.
[[OutgoingMaxDatagramSize]]
. -
While queue is not empty:
-
Let bytes, timestamp and promise be queue’s first element.
-
If bytes’s length ≤ maxSize:
-
If it is not possible to send bytes to the network immediately, then break this loop.
-
Send a datagram, with transport.
[[Session]]
and bytes.
-
-
Remove the first element from queue.
-
Queue a network task with transport to resolve promise with undefined.
-
The user agent SHOULD run sendDatagrams for any WebTransport
object whose [[State]]
is "connecting"
or "connected"
as soon as reasonably possible whenever the
algorithm can make progress.
Note: Writing datagrams while the transport’s [[State]]
is "connecting"
is allowed. The
datagrams are stored in [[OutgoingDatagramsQueue]]
, and they can be discarded
in the same manner as when in the "connected"
state. Once the transport’s [[State]]
becomes "connected"
, it will start sending the queued datagrams.
5. WebTransport
Interface
WebTransport
provides an API to the underlying transport functionality
defined in [WEB-TRANSPORT-OVERVIEW].
[Exposed =(Window ,Worker ),SecureContext ]interface {
WebTransport (
constructor USVString ,
url optional WebTransportOptions = {});
options Promise <WebTransportConnectionStats >getStats ();readonly attribute Promise <undefined >ready ;readonly attribute WebTransportReliabilityMode reliability ;readonly attribute WebTransportCongestionControl congestionControl ; [EnforceRange ]attribute unsigned short ?anticipatedConcurrentIncomingUnidirectionalStreams ; [EnforceRange ]attribute unsigned short ?anticipatedConcurrentIncomingBidirectionalStreams ;readonly attribute Promise <WebTransportCloseInfo >closed ;readonly attribute Promise <undefined >draining ;undefined close (optional WebTransportCloseInfo = {});
closeInfo readonly attribute WebTransportDatagramDuplexStream datagrams ;Promise <WebTransportBidirectionalStream >createBidirectionalStream (optional WebTransportSendStreamOptions = {}); /* a ReadableStream of WebTransportBidirectionalStream objects */
options readonly attribute ReadableStream incomingBidirectionalStreams ;Promise <WebTransportSendStream >createUnidirectionalStream (optional WebTransportSendStreamOptions = {}); /* a ReadableStream of WebTransportReceiveStream objects */
options readonly attribute ReadableStream incomingUnidirectionalStreams ;WebTransportSendGroup createSendGroup ();static readonly attribute boolean supportsReliableOnly ; };enum {
WebTransportReliabilityMode ,
"pending" ,
"reliable-only" , };
"supports-unreliable"
5.1. Internal slots
A WebTransport
object has the following internal slots.
Internal Slot | Description (non-normative) |
---|---|
[[SendStreams]]
| An ordered set of WebTransportSendStream s owned by this WebTransport .
|
[[ReceiveStreams]]
| An ordered set of WebTransportReceiveStream s owned by this WebTransport .
|
[[IncomingBidirectionalStreams]]
| A ReadableStream consisting of WebTransportBidirectionalStream objects.
|
[[IncomingUnidirectionalStreams]]
| A ReadableStream consisting of WebTransportReceiveStream s.
|
[[State]]
| An enum indicating the state of the transport. One of "connecting" , "connected" , "draining" , "closed" , and "failed" .
|
[[Ready]]
| A promise fulfilled when the associated WebTransport session gets established, or rejected if the establishment process failed. |
[[Reliability]]
| A WebTransportReliabilityMode indicating whether
the first hop supports unreliable (UDP) transport or whether only reliable
(TCP fallback) transport is available. Returns "pending" until a connection
has been established.
|
[[CongestionControl]]
| A WebTransportCongestionControl indicating
whether a preference for a congestion control algorithm optimized for
throughput or low latency was requested by the application and satisfied
by the user agent, or "default" .
|
[[AnticipatedConcurrentIncomingUnidirectionalStreams]]
| The number of concurrently open incoming unidirectional streams the application anticipates the server creating, or null. |
[[AnticipatedConcurrentIncomingBidirectionalStreams]]
| The number of concurrently open bidirectional streams the application anticipates the server creating, or null. |
[[Closed]]
| A promise fulfilled when the associated WebTransport object is
closed gracefully, or rejected when it is closed abruptly or failed on initialization.
|
[[Draining]]
| A promise fulfilled when the associated WebTransport session receives a DRAIN_WEBTRANSPORT_SESSION capsule or a GOAWAY frame. |
[[Datagrams]]
| A WebTransportDatagramDuplexStream .
|
[[Session]]
| A WebTransport session for this WebTransport object, or null.
|
5.2. Constructor
WebTransport()
constructor is invoked, the user
agent MUST run the following steps:
-
Let baseURL be this's relevant settings object's API base URL.
-
Let parsedURL be the URL record resulting from parsing
url
with baseURL. -
If parsedURL is a failure, throw a
SyntaxError
exception. -
If parsedURL scheme is not
https
, throw aSyntaxError
exception. -
If parsedURL fragment is not null, throw a
SyntaxError
exception. -
Let allowPooling be
options
'sallowPooling
. -
Let dedicated be the negation of allowPooling.
-
Let serverCertificateHashes be
options
'sserverCertificateHashes
if it exists, and null otherwise. -
If dedicated is false and serverCertificateHashes is non-null, then throw a
NotSupportedError
exception. -
Let requireUnreliable be
options
'srequireUnreliable
. -
Let congestionControl be
options
'scongestionControl
. -
If congestionControl is not
"default"
, and the user agent does not support any congestion control algorithms that optimize for congestionControl, as allowed by [RFC9002] Section 7, then set congestionControl to"default"
. -
Let anticipatedConcurrentIncomingUnidirectionalStreams be
options
'santicipatedConcurrentIncomingUnidirectionalStreams
. -
Let anticipatedConcurrentIncomingBidirectionalStreams be
options
'santicipatedConcurrentIncomingBidirectionalStreams
. -
Let incomingDatagrams be a new
ReadableStream
. -
Let outgoingDatagrams be a new
WritableStream
. -
Let datagrams be the result of creating a
WebTransportDatagramDuplexStream
, its readable set to incomingDatagrams and its writable set to outgoingDatagrams. -
Let transport be a newly constructed
WebTransport
object, with:[[SendStreams]]
-
an empty ordered set
[[ReceiveStreams]]
-
an empty ordered set
[[IncomingBidirectionalStreams]]
-
a new
ReadableStream
[[IncomingUnidirectionalStreams]]
-
a new
ReadableStream
[[State]]
-
"connecting"
[[Ready]]
-
a new promise
[[Reliability]]
-
"pending"
[[CongestionControl]]
-
congestionControl
[[AnticipatedConcurrentIncomingUnidirectionalStreams]]
-
anticipatedConcurrentIncomingUnidirectionalStreams
[[AnticipatedConcurrentIncomingBidirectionalStreams]]
-
anticipatedConcurrentIncomingBidirectionalStreams
[[Closed]]
-
a new promise
[[Draining]]
-
a new promise
[[Datagrams]]
-
datagrams
[[Session]]
-
null
-
Let pullDatagramsAlgorithm be an action that runs pullDatagrams with transport.
-
Let writeDatagramsAlgorithm be an action that runs writeDatagrams with transport.
Note: Using 64kB buffers with datagrams is recommended because the effective maximum WebTransport datagram frame size has an upper bound of the QUIC maximum datagram frame size which is recommended to be 64kB (See [QUIC-DATAGRAM] Section 3). This will ensure the stream is not errored due to a datagram being larger than the buffer.
-
Set up with byte reading support incomingDatagrams with pullAlgorithm set to pullDatagramsAlgorithm, and highWaterMark set to 0.
-
Set up outgoingDatagrams with writeAlgorithm set to writeDatagramsAlgorithm.
-
Let pullBidirectionalStreamAlgorithm be an action that runs pullBidirectionalStream with transport.
-
Set up transport.
[[IncomingBidirectionalStreams]]
with pullAlgorithm set to pullBidirectionalStreamAlgorithm, and highWaterMark set to 0. -
Let pullUnidirectionalStreamAlgorithm be an action that runs pullUnidirectionalStream with transport.
-
Set up transport.
[[IncomingUnidirectionalStreams]]
with pullAlgorithm set to pullUnidirectionalStreamAlgorithm, and highWaterMark set to 0. -
Initialize WebTransport over HTTP with transport, parsedURL, dedicated, requireUnreliable, congestionControl, and serverCertificateHashes.
-
Return transport.
WebTransport
object transport, a URL record url, a boolean dedicated, a boolean http3Only, a WebTransportCongestionControl
congestionControl, and a
sequence<WebTransportHash
> serverCertificateHashes, run these steps.
-
Let client be transport’s relevant settings object.
-
Let origin be client’s origin.
-
Let request be a new request whose URL is url, client is client, policy container is client’s policy container, destination is an empty string, and origin is origin.
-
If should request be blocked by Content Security Policy? with request returns "Blocked", or if request should be blocked due to a bad port returns blocked, then abort the remaining steps and queue a network task with transport to run these steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, then abort these steps. -
Let error be a newly created
WebTransportError
whosesource
is"session"
. -
Cleanup transport with error.
-
-
Let networkPartitionKey be the result of determining the network partition key with transport’s relevant settings object.
-
Run the following steps in parallel, but abort when transport.
[[State]]
becomes"closed"
or"failed"
:-
Let newConnection be "
no
" if dedicated is false; otherwise "yes-and-dedicated
". -
Let connection be the result of obtaining a connection with networkPartitionKey, url, false, newConnection, and http3Only. If the user agent supports more than one congestion control algorithm, choose one appropriate for congestionControl for sending of data on this connection. When obtaining a connection, if serverCertificateHashes is specified, instead of using the default certificate verification algorithm, consider the certificate valid if it meets the custom certificate requirements and if verifying the certificate hash against serverCertificateHashes returns true. If either condition is not met, let connection be failure.
-
If connection is failure, then abort the remaining steps and queue a network task with transport to run these steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, then abort these steps. -
Let error be a newly created
WebTransportError
whosesource
is"session"
. -
Cleanup transport with error.
-
-
Wait for connection to receive the first SETTINGS frame, and let settings be a dictionary that represents the SETTINGS frame.
-
If settings doesn’t contain SETTINGS_ENABLE_WEBTRANPORT with a value of 1, or it doesn’t contain H3_DATAGRAM with a value of 1, then abort the remaining steps and queue a network task with transport to run these steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, then abort these steps. -
Let error be a newly created
WebTransportError
whosesource
is"session"
. -
Cleanup transport with error.
-
-
Establish a WebTransport session with origin on connection.
Note: This step also contains the transport parameter exchange specified in [QUIC-DATAGRAM].
-
If the previous step fails, abort the remaining steps and queue a network task with transport to run these steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, then abort these steps. -
Let error be a newly created
WebTransportError
whosesource
is"session"
. -
Cleanup transport with error.
-
-
Let session be the established WebTransport session.
-
Assert: maxDatagramSize is an integer.
-
Queue a network task with transport to run these steps:
-
If transport.
[[State]]
is not"connecting"
:-
In parallel, terminate session.
-
Abort these steps.
-
-
Set transport.
[[State]]
to"connected"
. -
Set transport.
[[Session]]
to session. -
If the connection is an HTTP/3 connection, set transport’s
[[Reliability]]
to"supports-unreliable"
. -
If the connection is an HTTP/2 connection [WEB-TRANSPORT-HTTP2], set transport’s
[[Reliability]]
to"reliable-only"
.
-
-
WebTransport
object transport, run
these steps.
-
If transport.
[[State]]
is"connecting"
, then return the result of performing the following steps upon fulfillment of transport.[[Ready]]
:-
Return the result of pullBidirectionalStream with transport.
-
-
If transport.
[[State]]
is not"connected"
, then return a new rejected promise with anInvalidStateError
. -
Let session be transport.
[[Session]]
. -
Let p be a new promise.
-
Run the following steps in parallel:
-
Wait until there is an available incoming bidirectional stream.
-
Let internalStream be the result of receiving a bidirectional stream.
-
Queue a network task with transport to run these steps:
-
Let stream be the result of creating a
WebTransportBidirectionalStream
with internalStream and transport. -
Enqueue stream to transport.
[[IncomingBidirectionalStreams]]
. -
Resolve p with undefined.
-
-
-
Return p.
WebTransport
object transport, run
these steps.
-
If transport.
[[State]]
is"connecting"
, then return the result of performing the following steps upon fulfillment of transport.[[Ready]]
:-
Return the result of pullUnidirectionalStream with transport.
-
-
If transport.
[[State]]
is not"connected"
, then return a new rejected promise with anInvalidStateError
. -
Let session be transport.
[[Session]]
. -
Let p be a new promise.
-
Run the following steps in parallel:
-
Wait until there is an available incoming unidirectional stream.
-
Let internalStream be the result of receiving an incoming unidirectional stream.
-
Queue a network task with transport to run these steps:
-
Let stream be the result of creating a
WebTransportReceiveStream
with internalStream and transport. -
Enqueue stream to transport.
[[IncomingUnidirectionalStreams]]
. -
Resolve p with undefined.
-
-
-
Return p.
5.3. Attributes
ready
, of type Promise<undefined>, readonlyclosed
, of type Promise<WebTransportCloseInfo>, readonly-
On getting, it MUST return this's
[[Closed]]
. draining
, of type Promise<undefined>, readonly-
On getting, it MUST return this's
[[Draining]]
. datagrams
, of type WebTransportDatagramDuplexStream, readonly-
A single duplex stream for sending and receiving datagrams over this session. The getter steps for the
datagrams
attribute SHALL be:-
Return this's
[[Datagrams]]
.
-
incomingBidirectionalStreams
, of type ReadableStream, readonly-
Returns a
ReadableStream
ofWebTransportBidirectionalStream
s that have been received from the server. The getter steps for theincomingBidirectionalStreams
attribute SHALL be:-
Return this's
[[IncomingBidirectionalStreams]]
.
-
incomingUnidirectionalStreams
, of type ReadableStream, readonly-
A
ReadableStream
of unidirectional streams, each represented by aWebTransportReceiveStream
, that have been received from the server. The getter steps forincomingUnidirectionalStreams
are: reliability
, of type WebTransportReliabilityMode, readonly-
Whether connection supports unreliable (over UDP) transport or only reliable (over TCP fallback) transport. Returns
"pending"
until a connection has been established. The getter steps are to return this's[[Reliability]]
. congestionControl
, of type WebTransportCongestionControl, readonly-
The application’s preference, if requested in the constructor, and satisfied by the user agent, for a congestion control algorithm optimized for either throughput or low latency for sending on this connection. If a preference was requested but not satisfied, then the value is
"default"
The getter steps are to return this's[[CongestionControl]]
. supportsReliableOnly
, of type boolean, readonly-
Returns true if the user agent supports WebTransport sessions over exclusively reliable connections, otherwise false.
anticipatedConcurrentIncomingUnidirectionalStreams
, of type unsigned short, nullable-
Optionally lets an application specify the number of concurrently open incoming unidirectional streams it anticipates the server creating. If not null, the user agent SHOULD attempt to reduce future round-trips by taking
[[AnticipatedConcurrentIncomingUnidirectionalStreams]]
into consideration in its negotiations with the server.The getter steps are to return this's
[[AnticipatedConcurrentIncomingUnidirectionalStreams]]
.The setter steps, given value, are to set this's
[[AnticipatedConcurrentIncomingUnidirectionalStreams]]
to value. anticipatedConcurrentIncomingBidirectionalStreams
, of type unsigned short, nullable-
Optionally lets an application specify the number of concurrently open bidirectional streams it anticipates the server creating. If not null, the user agent SHOULD attempt to reduce future round-trips by taking
[[AnticipatedConcurrentIncomingBidirectionalStreams]]
into consideration in its negotiations with the server.The getter steps are to return this's
[[AnticipatedConcurrentIncomingBidirectionalStreams]]
.The setter steps, given value, are to set this's
[[AnticipatedConcurrentIncomingBidirectionalStreams]]
to value.
Note: Setting anticipatedConcurrentIncomingUnidirectionalStreams
or anticipatedConcurrentIncomingBidirectionalStreams
does not guarantee
the application will receive the number of streams it anticipates.
5.4. Methods
close(closeInfo)
-
Terminates the WebTransport session associated with the WebTransport object.
When close is called, the user agent MUST run the following steps:
-
Let transport be this.
-
If transport.
[[State]]
is"closed"
or"failed"
, then abort these steps. -
If transport.
[[State]]
is"connecting"
:-
Let error be a newly created
WebTransportError
whosesource
is"session"
. -
Cleanup transport with error.
-
Abort these steps.
-
-
Let session be transport.
[[Session]]
. -
Let code be closeInfo.
closeCode
. -
Let reasonString be the maximal code unit prefix of closeInfo.
reason
where the length of the UTF-8 encoded prefix doesn’t exceed 1024. -
Let reason be reasonString, UTF-8 encoded.
-
In parallel, terminate session with code and reason.
Note: This also resets or sends STOP_SENDING WebTransport streams contained in transport.
[[SendStreams]]
and[[ReceiveStreams]]
. -
Cleanup transport with
AbortError
and closeInfo.
-
getStats()
-
Gathers stats for this
WebTransport
's underlying connection and reports the result asynchronously.When getStats is called, the user agent MUST run the following steps:
-
Let transport be this.
-
Let p be a new promise.
-
If transport.
[[State]]
is"failed"
, reject p with anInvalidStateError
and abort these steps. -
Run the following steps in parallel:
-
If transport.
[[State]]
is"connecting"
, wait until it changes. -
If transport.
[[State]]
is"failed"
, reject p with anInvalidStateError
and abort these steps.
-
-
If transport.
[[State]]
is"closed"
, resolve p with the most recent stats available for the connection and abort these steps. The exact point at which those stats are collected is implementation-defined. -
Gather the stats from the underlying connection, including stats on datagrams.
-
Queue a network task with transport to run the following steps:
-
Let stats be a new
WebTransportConnectionStats
object representing the gathered stats. -
Resolve p with stats.
-
-
Return p.
-
-
createBidirectionalStream()
-
Creates a
WebTransportBidirectionalStream
object for an outgoing bidirectional stream. Note that the mere creation of a stream is not immediately visible to the peer until it is used to send data.When
createBidirectionalStream
is called, the user agent MUST run the following steps:-
Let transport be this.
-
If transport.
[[State]]
is"closed"
or"failed"
, return a new rejected promise with anInvalidStateError
. -
Let waitUntilAvailable be
options
'swaitUntilAvailable
. -
Let p be a new promise.
-
Run the following steps in parallel, but abort when transport’s
[[State]]
becomes"closed"
or"failed"
, and instead queue a network task with transport to reject p with anInvalidStateError
:-
Let streamId be a new stream ID that is valid and unique for transport.
[[Session]]
, as defined in [QUIC] Section 19.11. If one is not immediately available due to exhaustion, wait for it to become available if waitUntilAvailable is true, reject p with aQuotaExceededError
and abort these steps otherwise. -
Let internalStream be the result of creating a bidirectional stream with transport.
[[Session]]
and streamId. -
Queue a network task with transport to run the following steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, reject p with anInvalidStateError
and abort these steps. -
Let stream be the result of creating a
WebTransportBidirectionalStream
with internalStream, transport, sendGroup, and sendOrder. -
Resolve p with stream.
-
-
-
Return p.
-
createUnidirectionalStream()
-
Creates a
WebTransportSendStream
for an outgoing unidirectional stream. Note that the mere creation of a stream is not immediately visible to the server until it is used to send data.When
createUnidirectionalStream()
method is called, the user agent MUST run the following steps:-
Let transport be this.
-
If transport.
[[State]]
is"closed"
or"failed"
, return a new rejected promise with anInvalidStateError
. -
Let waitUntilAvailable be
options
'swaitUntilAvailable
. -
Let p be a new promise.
-
Run the following steps in parallel, but abort when transport’s
[[State]]
becomes"closed"
or"failed"
, and instead queue a network task with transport to reject p with anInvalidStateError
:-
Let streamId be a new stream ID that is valid and unique for transport.
[[Session]]
, as defined in [QUIC] Section 19.11. If one is not immediately available due to exhaustion, wait for it to become available if waitUntilAvailable is true, reject p with aQuotaExceededError
and abort these steps otherwise. -
Let internalStream be the result of creating an outgoing unidirectional stream with transport.
[[Session]]
and streamId. -
Queue a network task with transport to run the following steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, reject p with anInvalidStateError
and abort these steps. -
Let stream be the result of creating a
WebTransportSendStream
with internalStream, transport, sendGroup, and sendOrder. -
Resolve p with stream.
-
-
-
return p.
-
createSendGroup()
-
Creates a
WebTransportSendGroup
.When
createSendGroup()
method is called, the user agent MUST run the following steps:-
Let transport be this.
-
If transport.
[[State]]
is"closed"
or"failed"
, throw anInvalidStateError
. -
Return the result of creating a
WebTransportSendGroup
with transport.
-
5.5. Procedures
WebTransport
transport with error and
optionally closeInfo, run these steps:
-
Let sendStreams be a copy of transport.
[[SendStreams]]
. -
Let receiveStreams be a copy of transport.
[[ReceiveStreams]]
. -
Let outgoingDatagrams be transport.
[[Datagrams]]
.[[Writable]]
. -
Let incomingDatagrams be transport.
[[Datagrams]]
.[[Readable]]
. -
Let ready be transport.
[[Ready]]
. -
Let closed be transport.
[[Closed]]
. -
Let incomingBidirectionalStreams be transport.
[[IncomingBidirectionalStreams]]
. -
Let incomingUnidirectionalStreams be transport.
[[IncomingUnidirectionalStreams]]
. -
Set transport.
[[SendStreams]]
to an empty set. -
Set transport.
[[ReceiveStreams]]
to an empty set. -
Set transport.
[[Datagrams]]
.[[OutgoingDatagramsQueue]]
to an empty queue. -
Set transport.
[[Datagrams]]
.[[IncomingDatagramsQueue]]
to an empty queue. -
If closeInfo is given, then set transport.
[[State]]
to"closed"
. Otherwise, set transport.[[State]]
to"failed"
. -
For each stream in sendStreams, run the following steps:
-
If stream.
[[PendingOperation]]
is not null, reject stream.[[PendingOperation]]
with error. -
Error stream with error.
-
-
For each stream in receiveStreams, error stream with error.
Note: Script authors can inject code which runs in Promise resolution synchronously. Hence from here, do not touch transport as it may be mutated by scripts in an unpredictable way. This applies to logic calling this procedure, too.
-
If closeInfo is given, then:
-
Otherwise:
To queue a network task with a WebTransport
transport and a
series of steps steps, run these steps:
-
Queue a global task on the network task source with transport’s relevant global object to run steps.
5.6. Session termination not initiated by the client
WebTransport
transport is terminated with optionally code and reasonBytes, run these steps:
-
Queue a network task with transport to run these steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, abort these steps. -
Let error be a newly created
WebTransportError
whosesource
is"session"
. -
Let closeInfo be a new
WebTransportCloseInfo
. -
If code is given, set closeInfo’s
closeCode
to code. -
If reasonBytes is given, set closeInfo’s
reason
to reasonBytes, UTF-8 decoded.Note: No language or direction metadata is available with reasonBytes. First-strong heuristics can be used for direction when displaying the value.
-
Cleanup transport with error and closeInfo.
-
WebTransport
transport’s underlying connection gets a connection error,
run these steps:
-
Queue a network task with transport to run these steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, abort these steps. -
Let error be a newly created
WebTransportError
whosesource
is"session"
. -
Cleanup transport with error.
-
5.7. Context cleanup steps
This specification defines context cleanup steps as the following steps, given WebTransport
transport:
-
If transport.
[[State]]
is"connected"
, then:-
Set transport.
[[State]]
to"failed"
. -
In parallel, terminate transport.
[[Session]]
. -
Queue a network task with transport to run the following steps:
-
Let error be a newly created
WebTransportError
whosesource
is"session"
. -
Cleanup transport with error.
-
-
-
If transport.
[[State]]
is"connecting"
, set transport.[[State]]
to"failed"
.This needs to be done in workers too. See #127 and whatwg/html#6731.
5.8. Garbage Collection
A WebTransport
object whose [[State]]
is "connecting"
must not be garbage collected if [[IncomingBidirectionalStreams]]
, [[IncomingUnidirectionalStreams]]
, any WebTransportReceiveStream
, or [[Datagrams]]
.[[Readable]]
are locked, or if the ready
, draining
, or closed
promise is being observed.
A WebTransport
object whose [[State]]
is "connected"
must not be garbage collected if [[IncomingBidirectionalStreams]]
, [[IncomingUnidirectionalStreams]]
, any WebTransportReceiveStream
, or [[Datagrams]]
.[[Readable]]
are locked, or if the draining
or closed
promise is being observed.
A WebTransport
object whose [[State]]
is "draining"
must not be garbage collected if [[IncomingBidirectionalStreams]]
, [[IncomingUnidirectionalStreams]]
, any WebTransportReceiveStream
, or [[Datagrams]]
.[[Readable]]
are locked, or if the closed
promise is being observed.
A WebTransport
object with an established WebTransport session that has data queued to be transmitted to the network, including datagrams in [[Datagrams]]
.[[OutgoingDatagramsQueue]]
, must not be garbage collected.
If a WebTransport
object is garbage collected while the underlying connection is still open, the user agent must terminate the WebTransport session with an Application Error Code of 0
and Application Error Message of ""
.
5.9. Configuration
dictionary {
WebTransportHash DOMString ;
algorithm BufferSource ; };
value dictionary WebTransportOptions {boolean allowPooling =false ;boolean requireUnreliable =false ;sequence <WebTransportHash >serverCertificateHashes ;WebTransportCongestionControl congestionControl = "default"; [EnforceRange ]unsigned short ?anticipatedConcurrentIncomingUnidirectionalStreams =null ; [EnforceRange ]unsigned short ?anticipatedConcurrentIncomingBidirectionalStreams =null ; };enum {
WebTransportCongestionControl ,
"default" ,
"throughput" , };
"low-latency"
WebTransportOptions
is a dictionary of parameters
that determine how the WebTransport session is established and used.
allowPooling
, of type boolean, defaulting tofalse
-
When set to true, the WebTransport session can be pooled, that is, its underlying connection can be shared with other WebTransport sessions.
requireUnreliable
, of type boolean, defaulting tofalse
-
When set to true, the WebTransport session cannot be established over an HTTP/2 connection if an HTTP/3 connection is not possible.
serverCertificateHashes
, of type sequence<WebTransportHash>-
This option is only supported for transports using dedicated connections. For transport protocols that do not support this feature, having this field non-empty SHALL result in a
NotSupportedError
exception being thrown.If supported and non-empty, the user agent SHALL deem a server certificate trusted if and only if it can successfully verify a certificate hash against
serverCertificateHashes
and satisfies custom certificate requirements. The user agent SHALL ignore any hash that uses an unknownalgorithm
. If empty, the user agent SHALL use certificate verification procedures it would use for normal fetch operations.This cannot be used with
allowPooling
. congestionControl
, of type WebTransportCongestionControl, defaulting to"default"
-
Optionally specifies an application’s preference for a congestion control algorithm tuned for either throughput or low-latency to be used when sending data over this connection. This is a hint to the user agent.
anticipatedConcurrentIncomingUnidirectionalStreams
, of type unsigned short, nullable, defaulting tonull
-
Optionally lets an application specify the number of concurrently open incoming unidirectional streams it anticipates the server creating. The user agent MUST initially allow at least 100 incoming unidirectional streams from the server. If not null, the user agent SHOULD attempt to reduce round-trips by taking
[[AnticipatedConcurrentIncomingUnidirectionalStreams]]
into consideration in its negotiations with the server. anticipatedConcurrentIncomingBidirectionalStreams
, of type unsigned short, nullable, defaulting tonull
-
Optionally lets an application specify the number of concurrently open bidirectional streams it anticipates a server creating. The user agent MUST initially allow the server to create at least 100 bidirectional streams. If not null, the user agent SHOULD attempt to reduce round-trips by taking
[[AnticipatedConcurrentIncomingBidirectionalStreams]]
into consideration in its negotiations with the server.
-
Let cert be certificate, represented as a DER encoding of Certificate message defined in [RFC5280].
-
Compute the SHA-256 hash of cert and return the computed value.
-
Let referenceHash be the result of computing a certificate hash with certificate.
-
For every hash hash in hashes:
-
If hash.
value
is not null and hash.algorithm
is an ASCII case-insensitive match with "sha-256":-
Let hashValue be the byte sequence which hash.
value
represents. -
If hashValue is equal to referenceHash, return true.
-
-
-
Return false.
The custom certificate requirements are as follows: the certificate MUST be an X.509v3 certificate as defined in [RFC5280], the key used in the Subject Public Key field MUST be one of the allowed public key algorithms, the current time MUST be within the validity period of the certificate as defined in Section 4.1.2.5 of [RFC5280] and the total length of the validity period MUST NOT exceed two weeks. The user agent MAY impose additional implementation-defined requirements on the certificate.
The exact list of allowed public key algorithms used in the Subject Public Key Info field (and, as a consequence, in the TLS CertificateVerify message) is implementation-defined; however, it MUST include ECDSA with the secp256r1 (NIST P-256) named group ([RFC3279], Section 2.3.5; [RFC8422]) to provide an interoperable default. It MUST NOT contain RSA keys ([RFC3279], Section 2.3.1).
5.10. WebTransportCloseInfo
Dictionary
The WebTransportCloseInfo
dictionary includes information
relating to the error code for closing a WebTransport
. This
information is used to set the error code and reason for a CONNECTION_CLOSE
frame.
dictionary WebTransportCloseInfo {unsigned long closeCode = 0;USVString reason = ""; };
The dictionary SHALL have the following attributes:
closeCode
, of type unsigned long, defaulting to0
-
The error code communicated to the peer.
reason
, of type USVString, defaulting to""
-
The reason for closing the
WebTransport
.
5.11. WebTransportSendStreamOptions
Dictionary
The WebTransportSendStreamOptions
is a
dictionary of parameters that affect how WebTransportSendStream
s created by createUnidirectionalStream
and createBidirectionalStream
behave.
dictionary WebTransportSendStreamOptions {WebTransportSendGroup ?sendGroup =null ;long long sendOrder = 0;boolean waitUntilAvailable =false ; };
The dictionary SHALL have the following attributes:
sendGroup
, of type WebTransportSendGroup, nullable, defaulting tonull
-
An optional
WebTransportSendGroup
to group thisWebTransportSendStream
under, or null. sendOrder
, of type long long, defaulting to0
-
A send order number that, if provided, opts the created
WebTransportSendStream
in to participating in strict ordering. Bytes currently queued on strictly orderedWebTransportSendStream
s will be sent ahead of bytes currently queued on other strictly orderedWebTransportSendStream
s created with lower send order numbers.If no send order number is provided, then the order in which the user agent sends bytes from it relative to other
WebTransportSendStream
s is implementation-defined. User agents are strongly encouraged however to divide bandwidth fairly between all streams that aren’t starved by lower send order numbers.Note: This is sender-side data prioritization which does not guarantee reception order.
waitUntilAvailable
, of type boolean, defaulting tofalse
-
If true, the promise returned by the
createUnidirectionalStream
orcreateBidirectionalStream
call will not be settled until either the underlying connection has sufficient flow control credit to create the stream, or the connection reaches a state in which no further outgoing streams are possible. If false, the promise will be rejected if no flow control window is available at the time of the call.
5.12. WebTransportConnectionStats
Dictionary
The WebTransportConnectionStats
dictionary includes information
on WebTransport-specific stats about the WebTransport session's underlying connection.
Note: When pooling is used, multiple WebTransport sessions pooled on the same connection all receive the same information, i.e. the information is disclosed across pooled sessions holding the same network partition key.
Note: Any unavailable stats will be absent from the WebTransportConnectionStats
dictionary.
dictionary WebTransportConnectionStats {unsigned long long bytesSent ;unsigned long long packetsSent ;unsigned long long bytesLost ;unsigned long long packetsLost ;unsigned long long bytesReceived ;unsigned long long packetsReceived ;DOMHighResTimeStamp smoothedRtt ;DOMHighResTimeStamp rttVariation ;DOMHighResTimeStamp minRtt ;WebTransportDatagramStats ;
datagrams unsigned long long ?estimatedSendRate ; };
The dictionary SHALL have the following attributes:
bytesSent
, of type unsigned long long-
The number of bytes sent on the underlying connection, including retransmissions. Does not include UDP or any other outer framing.
packetsSent
, of type unsigned long long-
The number of packets sent on the underlying connection, including those that are determined to have been lost.
bytesLost
, of type unsigned long long-
The number of bytes lost on the underlying connection (does not monotonically increase, because packets that are declared lost can subsequently be received). Does not include UDP or any other outer framing.
packetsLost
, of type unsigned long long-
The number of packets lost on the underlying connection (does not monotonically increase, because packets that are declared lost can subsequently be received).
bytesReceived
, of type unsigned long long-
The number of total bytes received on the underlying connection, including duplicate data for streams. Does not include UDP or any other outer framing.
packetsReceived
, of type unsigned long long-
The number of total packets received on the underlying connection, including packets that were not processable.
smoothedRtt
, of type DOMHighResTimeStamp-
The smoothed round-trip time (RTT) currently observed on the connection, as defined in [RFC9002] Section 5.3.
rttVariation
, of type DOMHighResTimeStamp-
The mean variation in round-trip time samples currently observed on the connection, as defined in [RFC9002] Section 5.3.
minRtt
, of type DOMHighResTimeStamp-
The minimum round-trip time observed on the entire connection.
estimatedSendRate
, of type unsigned long long, nullable-
The estimated rate at which queued data will be sent by the user agent, in bits per second. This rate applies to all streams and datagrams that share a WebTransport session and is calculated by the congestion control algorithm (potentially chosen by
congestionControl
). If the user agent does not currently have an estimate, the member MUST be thenull
value. The member can benull
even if it was notnull
in previous results.
5.13. WebTransportDatagramStats
Dictionary
The WebTransportDatagramStats
dictionary includes statistics
on datagram transmission over the underlying connection.
dictionary WebTransportDatagramStats {unsigned long long droppedIncoming ;unsigned long long expiredIncoming ;unsigned long long expiredOutgoing ;unsigned long long lostOutgoing ; };
The dictionary SHALL have the following attributes:
droppedIncoming
, of type unsigned long long-
The number of incoming datagrams that were dropped due to the application not reading from
datagrams
'readable
before new datagrams overflow the receive queue. expiredIncoming
, of type unsigned long long-
The number of incoming datagrams that were dropped due to being older than
incomingMaxAge
before they were read fromdatagrams
'readable
. expiredOutgoing
, of type unsigned long long-
The number of datagrams queued for sending that were dropped due to being older than
outgoingMaxAge
before they were able to be sent. lostOutgoing
, of type unsigned long long-
The number of sent datagrams that were declared lost, as defined in [RFC9002] Section 6.1.
6. Interface WebTransportSendStream
A WebTransportSendStream
is a WritableStream
providing outgoing streaming
features with an outgoing unidirectional or bidirectional WebTransport stream.
It is a WritableStream
of Uint8Array
that can be written to, to send
data to the server.
[Exposed =(Window ,Worker ),SecureContext ,Transferable ]interface :
WebTransportSendStream WritableStream {attribute WebTransportSendGroup ?sendGroup ;attribute long long sendOrder ;Promise <WebTransportSendStreamStats >getStats ();WebTransportWriter getWriter (); };
A WebTransportSendStream
is always created by the create procedure.
The WebTransportSendStream
's transfer steps and transfer-receiving steps are those of WritableStream
.
6.1. Attributes
sendGroup
, of type WebTransportSendGroup, nullable-
The getter steps are:
-
Return this's
[[SendGroup]]
.
The setter steps, given value, are:
-
If value is non-null, and value.
[[Transport]]
is not this.[[Transport]]
, throw anInvalidStateError
. -
Set this.
[[SendGroup]]
to value.
-
sendOrder
, of type long long-
The getter steps are:
-
Return this's
[[SendOrder]]
.
The setter steps, given value, are:
-
Set this.
[[SendOrder]]
to value.
-
6.2. Methods
getStats()
-
Gathers stats specific to this
WebTransportSendStream
's performance, and reports the result asynchronously.When getStats is called, the user agent MUST run the following steps:
-
Let p be a new promise.
-
Run the following steps in parallel:
-
Gather the stats specific to this
WebTransportSendStream
. -
Wait for the stats to be ready.
-
Queue a network task with transport to run the following steps:
-
Let stats be a new
WebTransportSendStreamStats
object representing the gathered stats. -
Resolve p with stats.
-
-
-
Return p.
-
getWriter()
-
This method must be implemented in the same manner as
getWriter
inherited fromWritableStream
, except in place of creating aWritableStreamDefaultWriter
, it must instead create aWebTransportWriter
with this.
6.3. Internal Slots
A WebTransportSendStream
has the following internal slots.
Internal Slot | Description (non-normative) |
---|---|
[[InternalStream]]
| An outgoing unidirectional or bidirectional WebTransport stream. |
[[PendingOperation]]
| A promise representing a pending write or close operation, or null. |
[[Transport]]
| A WebTransport which owns this WebTransportSendStream .
|
[[SendGroup]]
| An optional WebTransportSendGroup , or null.
|
[[SendOrder]]
| An optional send order number, defaulting to 0. |
[[AtomicWriteRequests]]
| An ordered set of promises, keeping track of the subset of write requests that are atomic among those queued to be processed by the underlying sink. |
6.4. Procedures
To create a WebTransportSendStream
, with an outgoing unidirectional or bidirectional WebTransport stream internalStream, a WebTransport
transport, sendGroup, and a sendOrder, run these steps:
-
Let stream be a new
WebTransportSendStream
, with:[[InternalStream]]
-
internalStream
[[PendingOperation]]
-
null
[[Transport]]
-
transport
[[SendGroup]]
-
sendGroup
[[SendOrder]]
-
sendOrder
[[AtomicWriteRequests]]
-
An empty ordered set of promises.
-
Let writeAlgorithm be an action that writes chunk to stream, given chunk.
-
Let closeAlgorithm be an action that closes stream.
-
Let abortAlgorithm be an action that aborts stream with reason, given reason.
-
Set up stream with writeAlgorithm set to writeAlgorithm, closeAlgorithm set to closeAlgorithm, abortAlgorithm set to abortAlgorithm.
-
Let abortSignal be stream’s [[controller]].[[abortController]].[[signal]].
-
Add the following steps to abortSignal.
-
Let pendingOperation be stream.
[[PendingOperation]]
. -
If pendingOperation is null, then abort these steps.
-
Set stream.
[[PendingOperation]]
to null. -
Let reason be abortSignal’s abort reason.
-
Let promise be the result of aborting stream with reason.
-
Upon fulfillment of promise, reject pendingOperation with reason.
-
-
Append stream to transport.
[[SendStreams]]
. -
Return stream.
WebTransportSendStream
stream, run these steps:
-
Let transport be stream.
[[Transport]]
. -
If chunk is not a
BufferSource
, return a promise rejected with aTypeError
. -
Let promise be a new promise.
-
Let bytes be a copy of the byte sequence which chunk represents.
-
Set stream.
[[PendingOperation]]
to promise. -
Let inFlightWriteRequest be stream.inFlightWriteRequest.
-
Let atomic be true if stream.
[[AtomicWriteRequests]]
contains inFlightWriteRequest, otherwise false. -
Run the following steps in parallel:
-
If atomic is true and the current flow control window is too small for bytes to be sent in its entirety, then abort the remaining steps and queue a network task with transport to run these sub-steps:
-
Set stream.
[[PendingOperation]]
to null. -
Abort all atomic write requests on stream.
-
-
Otherwise, send bytes on stream.
[[InternalStream]]
and wait for the operation to complete. This sending MAY be interleaved with sending of previously queued streams and datagrams, as well as streams and datagrams yet to be queued to be sent over this transport.The user-agent MAY have a buffer to improve the transfer performance. Such a buffer SHOULD have a fixed upper limit, to carry the backpressure information to the user of the
WebTransportSendStream
.This sending MUST starve until all bytes queued for sending on
WebTransportSendStream
s with the same[[SendGroup]]
and a higher[[SendOrder]]
, that are neither errored nor blocked by flow control, have been sent.We access stream.
[[SendOrder]]
in parallel here. User agents SHOULD respond to live updates of these values during sending, though the details are implementation-defined.Note: Ordering of retransmissions is implementation-defined, but user agents are strongly encouraged to prioritize retransmissions of data with higher
[[SendOrder]]
values.This sending MUST NOT starve otherwise, except for flow control reasons or error.
The user agent SHOULD divide bandwidth fairly between all streams that aren’t starved.
Note: The definition of fairness here is implementation-defined.
-
If the previous step failed due to a network error, abort the remaining steps.
Note: We don’t reject promise here because we handle network errors elsewhere, and those steps reject stream.
[[PendingOperation]]
. -
Otherwise, queue a network task with transport to run these steps:
-
Set stream.
[[PendingOperation]]
to null. -
If stream.
[[AtomicWriteRequests]]
contains inFlightWriteRequest, remove inFlightWriteRequest. -
Resolve promise with undefined.
-
-
-
Return promise.
Note: The fulfillment of the promise returned from this algorithm (or, write(chunk)
) does NOT necessarily mean that the chunk is acked by
the server [QUIC]. It may just mean that the chunk is appended to the buffer. To make sure that
the chunk arrives at the server, the server needs to send an application-level acknowledgment message.
WebTransportSendStream
stream, run these steps:
-
Let transport be stream.
[[Transport]]
. -
Let promise be a new promise.
-
Remove stream from transport.
[[SendStreams]]
. -
Set stream.
[[PendingOperation]]
to promise. -
Run the following steps in parallel:
-
Send FIN on stream.
[[InternalStream]]
and wait for the operation to complete. -
Wait for stream.
[[InternalStream]]
to enter the "Data Recvd" state. [QUIC] -
Queue a network task with transport to run these steps:
-
Set stream.
[[PendingOperation]]
to null. -
Resolve promise with undefined.
-
-
-
Return promise.
WebTransportSendStream
stream with reason, run these steps:
-
Let transport be stream.
[[Transport]]
. -
Let promise be a new promise.
-
Let code be 0.
-
Remove stream from transport.
[[SendStreams]]
. -
If reason is a
WebTransportError
and reason.[[StreamErrorCode]]
is not null, then set code to reason.[[StreamErrorCode]]
. -
If code < 0, then set code to 0.
-
If code > 4294967295, then set code to 4294967295.
Note: Valid values of code are from 0 to 4294967295 inclusive. If the underlying connection is using HTTP/3, the code will be encoded to a number in [0x52e4a40fa8db, 0x52e5ac983162] as decribed in [WEB-TRANSPORT-HTTP3].
-
Run the following steps in parallel:
-
Reset stream.
[[InternalStream]]
with code. -
Queue a network task with transport to resolve promise with undefined.
-
-
Return promise.
WebTransportSendStream
stream, run these steps:
-
Let writeRequests be stream.writeRequests.
-
Let requestsToAbort be stream.
[[AtomicWriteRequests]]
. -
If writeRequests contains a promise not in requestsToAbort, then error stream with
AbortError
, and abort these steps. -
For each promise in requestsToAbort, reject promise with
AbortError
. -
In parallel, for each promise in requestsToAbort, abort the sending of bytes associated with promise.
6.5. STOP_SENDING signal coming from the server
WebTransportSendStream
stream gets a STOP_SENDING signal from the server, run these steps:
-
Let transport be stream.
[[Transport]]
. -
Let code be the application protocol error code attached to the STOP_SENDING frame. [QUIC]
Note: Valid values of code are from 0 to 4294967295 inclusive. If the underlying connection is using HTTP/3, the code will be encoded to a number in [0x52e4a40fa8db, 0x52e5ac983162] as decribed in [WEB-TRANSPORT-HTTP3].
-
Queue a network task with transport to run these steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, abort these steps. -
Remove stream from transport.
[[SendStreams]]
. -
Let error be a newly created
WebTransportError
whosesource
is"stream"
andstreamErrorCode
is code. -
If stream.
[[PendingOperation]]
is not null, reject stream.[[PendingOperation]]
with error. -
Error stream with error.
-
6.6. WebTransportSendStreamStats
Dictionary
The WebTransportSendStreamStats
dictionary includes information
on stats specific to one WebTransportSendStream
.
dictionary WebTransportSendStreamStats {unsigned long long bytesWritten ;unsigned long long bytesSent ;unsigned long long bytesAcknowledged ; };
The dictionary SHALL have the following attributes:
bytesWritten
, of type unsigned long long-
The total number of bytes the application has successfully written to this
WebTransportSendStream
. This number can only increase. bytesSent
, of type unsigned long long-
An indicator of progress on how many of the application bytes written to this
WebTransportSendStream
has been sent at least once. This number can only increase, and is always less than or equal tobytesWritten
.Note: this is progress of app data sent on a single stream only, and does not include any network overhead.
bytesAcknowledged
, of type unsigned long long-
An indicator of progress on how many of the application bytes written to this
WebTransportSendStream
have been sent and acknowledged as received by the server using QUIC’s ACK mechanism. Only sequential bytes up to, but not including, the first non-acknowledged byte, are counted. This number can only increase and is always less than or equal tobytesSent
.Note: This value will match
bytesSent
when the connection is over HTTP/2.
7. Interface WebTransportSendGroup
A WebTransportSendGroup
is an optional organizational object that tracks
transmission of data spread across many individual
(typically strictly ordered) WebTransportSendStream
s.
WebTransportSendStream
s can, at their creation or through assignment of
their sendGroup
attribute, be grouped under at most one WebTransportSendGroup
at any time. By default, they are ungrouped.
The user agent considers WebTransportSendGroup
s as equals when allocating
bandwidth for sending WebTransportSendStream
s. Each WebTransportSendGroup
also establishes a separate numberspace for evaluating sendOrder
numbers.
[Exposed =(Window ,Worker ),SecureContext ]interface {
WebTransportSendGroup Promise <WebTransportSendStreamStats >getStats (); };
A WebTransportSendGroup
is always created by the create procedure.
7.1. Methods
getStats()
-
Aggregates stats from all
WebTransportSendStream
s grouped under this sendGroup, and reports the result asynchronously.When getStats is called, the user agent MUST run the following steps:
-
Let p be a new promise.
-
Let streams be all
WebTransportSendStream
s whose[[SendGroup]]
is this. -
Run the following steps in parallel:
-
Gather stream statistics from all streams in streams.
-
Queue a network task with transport to run the following steps:
-
Let stats be a new
WebTransportSendStreamStats
object representing the aggregate numbers of the gathered stats. -
Resolve p with stats.
-
-
-
Return p.
-
7.2. Internal Slots
A WebTransportSendGroup
has the following internal slots.
Internal Slot | Description (non-normative) |
---|---|
[[Transport]]
| The WebTransport object owning this WebTransportSendGroup .
|
7.3. Procedures
To create a WebTransportSendGroup
, with a WebTransport
transport, run these steps:
-
Let sendGroup be a new
WebTransportSendGroup
, with:[[Transport]]
-
transport
-
Return sendGroup.
8. Interface WebTransportReceiveStream
A WebTransportReceiveStream
is a ReadableStream
providing incoming streaming
features with an incoming unidirectional or bidirectional WebTransport stream.
It is a ReadableStream
of Uint8Array
that can be read from, to consume
data received from the server. WebTransportReceiveStream
is a readable byte stream,
and hence it allows
its consumers to use a BYOB reader as well as a default reader.
[Exposed =(Window ,Worker ),SecureContext ,Transferable ]interface :
WebTransportReceiveStream ReadableStream {Promise <WebTransportReceiveStreamStats >getStats (); };
A WebTransportReceiveStream
is always created by the create procedure.
The WebTransportReceiveStream
's transfer steps and transfer-receiving steps are those of ReadableStream
.
8.1. Methods
getStats()
-
Gathers stats specific to this
WebTransportReceiveStream
's performance, and reports the result asynchronously.When getStats is called, the user agent MUST run the following steps:
-
Let p be a new promise.
-
Run the following steps in parallel:
-
Gather the stats specific to this
WebTransportReceiveStream
. -
Queue a network task with transport to run the following steps:
-
Let stats be a new
WebTransportReceiveStreamStats
object representing the gathered stats. -
Resolve p with stats.
-
-
-
Return p.
-
8.2. Internal Slots
A WebTransportReceiveStream
has the following internal slots.
Internal Slot | Description (non-normative) |
---|---|
[[InternalStream]]
| An incoming unidirectional or bidirectional WebTransport stream. |
[[Transport]]
| The WebTransport object owning this WebTransportReceiveStream .
|
8.3. Procedures
To create a WebTransportReceiveStream
, with an incoming unidirectional or bidirectional WebTransport stream internalStream and a WebTransport
transport, run these steps:
-
Let stream be a new
WebTransportReceiveStream
, with:[[InternalStream]]
-
internalStream
[[Transport]]
-
transport
-
Let pullAlgorithm be an action that pulls bytes from stream.
-
Let cancelAlgorithm be an action that cancels stream with reason, given reason.
-
Set up with byte reading support stream with pullAlgorithm set to pullAlgorithm and cancelAlgorithm set to cancelAlgorithm.
-
Append stream to transport.
[[ReceiveStreams]]
. -
Return stream.
To pull bytes from a WebTransportReceiveStream
stream, run these steps.
-
Let transport be stream.
[[Transport]]
. -
Let internalStream be stream.
[[InternalStream]]
. -
Let promise be a new promise.
-
Let buffer, offset, and maxBytes be null.
-
If stream’s current BYOB request view for stream is not null:
-
Set offset to stream’s current BYOB request view.[[ByteOffset]].
-
Set maxBytes to stream’s current BYOB request view's byte length.
-
Set buffer to stream’s current BYOB request view's underlying buffer.
-
-
Otherwise:
-
Set offset to 0.
-
Set maxBytes to an implementation-defined size.
-
Set buffer be a new
ArrayBuffer
with maxBytes size. If allocating theArrayBuffer
fails, return a promise rejected with aRangeError
.
-
-
Run the following steps in parallel:
-
Write the bytes that area read from internalStream into buffer with offset offset, up to maxBytes bytes. Wait until either at least one byte is read or FIN is received. Let read be the number of read bytes, and let hasReceivedFIN be whether FIN was accompanied.
The user-agent MAY have a buffer to improve the transfer performance. Such a buffer SHOULD have a fixed upper limit, to carry the backpressure information to the server.
Note: This operation may return before filling up all of bytes.
-
If the previous step failed, abort the remaining steps.
Note: We don’t reject promise here because we handle network errors elsewhere, and those steps error stream, which rejects any read requests awaiting this pull.
-
Queue a network task with transport to run these steps:
Note: If the buffer described above is available in the event loop where this procedure is running, the following steps may run immediately.
-
If read > 0:
-
Set view to a new
Uint8Array
with buffer, offset and read. -
Enqueue view into stream.
-
-
If hasReceivedFIN is true:
-
Remove stream from transport.
[[ReceiveStreams]]
. -
Close stream.
-
-
Resolve promise with undefined.
-
-
-
Return promise.
To cancel a WebTransportReceiveStream
stream with reason, run these
steps.
-
Let transport be stream.
[[Transport]]
. -
Let internalStream be stream.
[[InternalStream]]
. -
Let promise be a new promise.
-
Let code be 0.
-
If reason is a
WebTransportError
and reason.[[StreamErrorCode]]
is not null, then set code to reason.[[StreamErrorCode]]
. -
If code < 0, then set code to 0.
-
If code > 4294967295, then set code to 4294967295.
Note: Valid values of code are from 0 to 4294967295 inclusive. If the underlying connection is using HTTP/3, the code will be encoded to a number in [0x52e4a40fa8db, 0x52e5ac983162] as decribed in [WEB-TRANSPORT-HTTP3].
-
Remove stream from transport.
[[SendStreams]]
. -
Run the following steps in parallel:
-
Send STOP_SENDING with internalStream and code.
-
Queue a network task with transport to run these steps:
Note: If the buffer described above is available in the event loop where this procedure is running, the following steps may run immediately.
-
Remove stream from transport.
[[ReceiveStreams]]
. -
Resolve promise with undefined.
-
-
-
Return promise.
8.4. Reset signal coming from the server
WebTransportReceiveStream
stream gets a RESET_STREAM signal from the server, run these steps:
-
Let transport be stream.
[[Transport]]
. -
Let code be the application protocol error code attached to the RESET_STREAM frame. [QUIC]
Note: Valid values of code are from 0 to 4294967295 inclusive. If the underlying connection is using HTTP/3, the code will be encoded to a number in [0x52e4a40fa8db, 0x52e5ac983162] as decribed in [WEB-TRANSPORT-HTTP3].
-
Queue a network task with transport to run these steps:
-
If transport.
[[State]]
is"closed"
or"failed"
, abort these steps. -
Remove stream from transport.
[[ReceiveStreams]]
. -
Let error be a newly created
WebTransportError
whosesource
is"stream"
andstreamErrorCode
is code. -
Error stream with error.
-
8.5. WebTransportReceiveStreamStats
Dictionary
The WebTransportReceiveStreamStats
dictionary includes
information on stats specific to one WebTransportReceiveStream
.
dictionary WebTransportReceiveStreamStats {unsigned long long bytesReceived ;unsigned long long bytesRead ; };
The dictionary SHALL have the following attributes:
bytesReceived
, of type unsigned long long-
An indicator of progress on how many of the server application’s bytes intended for this
WebTransportReceiveStream
have been received so far. Only sequential bytes up to, but not including, the first missing byte, are counted. This number can only increase.Note: this is progress of app data received on a single stream only, and does not include any network overhead.
bytesRead
, of type unsigned long long-
The total number of bytes the application has successfully read from this
WebTransportReceiveStream
. This number can only increase, and is always less than or equal tobytesReceived
.
9. Interface WebTransportBidirectionalStream
[Exposed =(Window ,Worker ),SecureContext ]interface {
WebTransportBidirectionalStream readonly attribute WebTransportReceiveStream readable ;readonly attribute WebTransportSendStream writable ; };
9.1. Internal slots
A WebTransportBidirectionalStream
has the following internal slots.
Internal Slot | Description (non-normative) |
---|---|
[[Readable]]
| A WebTransportReceiveStream .
|
[[Writable]]
| A WebTransportSendStream .
|
[[Transport]]
| The WebTransport object owning this WebTransportBidirectionalStream .
|
9.2. Attributes
readable
, of type WebTransportReceiveStream, readonly-
The getter steps are to return this's
[[Readable]]
. writable
, of type WebTransportSendStream, readonly-
The getter steps are to return this's
[[Writable]]
.
9.3. Procedures
WebTransportBidirectionalStream
with a bidirectional WebTransport stream internalStream, a WebTransport
object transport, and a sendOrder, run these steps.
-
Let readable be the result of creating a
WebTransportReceiveStream
with internalStream and transport. -
Let writable be the result of creating a
WebTransportSendStream
with internalStream, transport, and sendOrder. -
Let stream be a new
WebTransportBidirectionalStream
, with:[[Readable]]
-
readable
[[Writable]]
-
writable
[[Transport]]
-
transport
-
Return stream.
10. WebTransportWriter
Interface
WebTransportWriter
is a subclass of WritableStreamDefaultWriter
that
adds one method.
A WebTransportWriter
is always created by the create procedure.
[Exposed=*,SecureContext ]interface :
WebTransportWriter WritableStreamDefaultWriter {Promise <undefined >atomicWrite (optional any ); };
chunk
10.1. Methods
atomicWrite(chunk)
-
The
atomicWrite
method will reject if the chunk given to it could not be sent in its entirety within the flow control window that is current at the time of sending. This behavior is designed to satisfy niche transactional applications sensitive to flow control deadlocks ([RFC9308] Section 4.4).Note:
atomicWrite
can still reject after sending some data. Though it provides atomicity with respect to flow control, other errors may occur.atomicWrite
does not prevent data from being split between packets or being interleaved with other data. Only the sender learns ifatomicWrite
fails due to lack of available flow control credit.Note: Atomic writes can still block if queued behind non-atomic writes. If the atomic write is rejected, everything queued behind it at that moment will be rejected as well. Any non-atomic writes rejected in this way will error the stream. Applications are therefore encouraged to always await atomic writes.
When
atomicWrite
is called, the user agent MUST run the following steps:-
Let p be the result of
write(chunk)
onWritableStreamDefaultWriter
with chunk. -
Append p to stream.
[[AtomicWriteRequests]]
. -
Return the result of reacting to p with the following steps:
-
If stream.
[[AtomicWriteRequests]]
contains p, remove p. -
If p was rejected with reason r, then return a promise rejected with r.
-
Return undefined.
-
-
10.2. Procedures
To create a WebTransportWriter
, with a WebTransportSendStream
stream, run these
steps:
-
Let writer be a new
WebTransportWriter
. -
Run the new WritableStreamDefaultWriter(stream) constructor steps passing writer as this, and stream as the constructor argument.
-
Return writer.
11. WebTransportError
Interface
WebTransportError
is a subclass of DOMException
that represents
-
An error coming from the server or the network, or
-
A reason for a client-initiated abort operation.
[Exposed =(Window ,Worker ),Serializable ,SecureContext ]interface WebTransportError :DOMException {constructor (optional DOMString = "",
message optional WebTransportErrorOptions = {});
options readonly attribute WebTransportErrorSource source ;readonly attribute unsigned long ?streamErrorCode ; };dictionary {
WebTransportErrorOptions WebTransportErrorSource = "stream"; [
source Clamp ]unsigned long ?=
streamErrorCode null ; };enum {
WebTransportErrorSource ,
"stream" , };
"session"
11.1. Internal slots
A WebTransportError
has the following internal slots.
Internal Slot | Description (non-normative) |
---|---|
[[Source]]
| A WebTransportErrorSource indicating the source of this error.
|
[[StreamErrorCode]]
| The application protocol error code for this error, or null. |
11.2. Constructor
The new WebTransportError(message, options)
constructor steps are:
-
Set this’s name to
"WebTransportError"
. -
Set this’s message to message.
-
Set this’s internal slots as follows:
[[Source]]
-
options.
source
[[StreamErrorCode]]
-
options.
streamErrorCode
Note: This name does not have a mapping to a legacy code, so this's
code
is 0.
11.3. Attributes
source
, of type WebTransportErrorSource, readonly-
The getter steps are to return this's
[[Source]]
. streamErrorCode
, of type unsigned long, readonly, nullable-
The getter steps are to return this's
[[StreamErrorCode]]
.
11.4. Serialization
WebTransportError
objects are serializable objects.
Their serialization steps, given value and serialized, are:
-
Run the
DOMException
serialization steps given value and serialized. -
Set serialized.
[[Source]]
to value.[[Source]]
. -
Set serialized.
[[StreamErrorCode]]
to value.[[StreamErrorCode]]
.
Their deserialization steps, given serialized and value, are:
-
Run the
DOMException
deserialization steps given serialized and value. -
Set value.
[[Source]]
to serialized.[[Source]]
. -
Set value.
[[StreamErrorCode]]
serialized.[[StreamErrorCode]]
.
12. Protocol Mappings
This section is non-normative.
This section describes the underlying protocol behavior of methods defined in this specification, utilizing [WEB-TRANSPORT-OVERVIEW]. Cause and effect may not be immediate due to buffering.
WebTransport Protocol Action | API Effect |
---|---|
received DRAIN_WEBTRANSPORT_SESSION | await wt.draining
|
If the underlying connection is using HTTP/3, the following protocol behaviors from [WEB-TRANSPORT-HTTP3] apply.
The application streamErrorCode
in the WebTransportError
error is
converted to an httpErrorCode, and vice versa, as specified in [WEB-TRANSPORT-HTTP3] Section 4.3.
API Method | QUIC Protocol Action |
---|---|
writable .abort (error)
| sends RESET_STREAM with httpErrorCode |
writable .close ()
| sends STREAM with FIN bit set |
writable .getWriter().write(chunk) ()
| sends STREAM |
writable .getWriter().close ()
| sends STREAM with FIN bit set |
writable .getWriter().abort (error)
| sends RESET_STREAM with httpErrorCode |
readable .cancel (error)
| sends STOP_SENDING with httpErrorCode |
readable .getReader().cancel (error)
| sends STOP_SENDING with httpErrorCode |
wt.close (closeInfo)
| terminates session with closeInfo |
QUIC Protocol Action | API Effect |
---|---|
received STOP_SENDING with httpErrorCode | errors writable with streamErrorCode
|
received STREAM | (await readable .getReader().read ()).value
|
received STREAM with FIN bit set | (await readable .getReader().read ()).done
|
received RESET_STREAM with httpErrorCode | errors readable with streamErrorCode
|
Session cleanly terminated with closeInfo | (await wt.closed ).closeInfo, and errors open streams
|
Network error | (await wt.closed ) rejects, and errors open streams
|
Note: As discussed in [QUIC] Section 3.2, receipt of a RESET_STREAM frame is not always indicated to the application. Receipt of the RESET_STREAM can be signaled immediately, interrupting delivery of stream data with any data not consumed being discarded. However, immediate signaling is not required. Also, if stream data is completely received but has not yet been read by the application, the RESET_STREAM signal can be suppressed.
HTTP/3 Protocol Action | API Effect |
---|---|
received GOAWAY | await wt.draining
|
If the underlying connection is using HTTP/2, the following protocol behaviors from [WEB-TRANSPORT-HTTP2] apply. Note that, unlike for HTTP/3, the stream error code does not need to be converted to an HTTP error code, and vice versa.
API Method | HTTP/2 Protocol Action |
---|---|
writable .abort (error)
| sends WT_RESET_STREAM with error |
writable .close ()
| sends WT_STREAM with FIN bit set |
writable .getWriter().write ()
| sends WT_STREAM |
writable .getWriter().close ()
| sends WT_STREAM with FIN bit set |
writable .getWriter().abort (error)
| sends WT_RESET_STREAM with error |
readable .cancel (error)
| sends WT_STOP_SENDING with error |
readable .getReader().cancel (error)
| sends WT_STOP_SENDING with error |
wt.close (closeInfo)
| terminates session with closeInfo |
HTTP/2 Protocol Action | API Effect |
---|---|
received WT_STOP_SENDING with error | errors writable with streamErrorCode
|
received WT_STREAM | (await readable .getReader().read ()).value
|
received WT_STREAM with FIN bit set | (await readable .getReader().read ()).done
|
received WT_RESET_STREAM with error | errors readable with streamErrorCode
|
Session cleanly terminated with closeInfo | (await wt.closed ).closeInfo, and errors open streams
|
Network error | (await wt.closed ) rejects, and errors open streams
|
received GOAWAY | await wt.draining
|
13. Privacy and Security Considerations
This section is non-normative; it specifies no new behaviour, but instead summarizes information already present in other parts of the specification.
13.1. Confidentiality of Communications
The fact that communication is taking place cannot be hidden from adversaries that can observe the network, so this has to be regarded as public information.
All of the transport protocols described in this document use either TLS [RFC8446] or a semantically equivalent protocol, thus providing all of the security properties of TLS, including confidentiality and integrity of the traffic. WebTransport over HTTP uses the same certificate verification mechanism as outbound HTTP requests, thus relying on the same public key infrastructure for authentication of the remote server. In WebTransport, certificate verification errors are fatal; no interstitial allowing bypassing certificate validation is available.
13.2. State Persistence
WebTransport does not by itself create any new unique identifiers or new ways to persistently store state, nor does it automatically expose any of the existing persistent state to the server. For instance, neither [WEB-TRANSPORT-HTTP3] nor [WEB-TRANSPORT-HTTP2] send cookies or support HTTP authentication or caching invalidation mechanisms. Since they do use TLS, they inherit TLS persistent state such as TLS session tickets, which while not visible to passive network observers, could be used by the server to correlate different connections from the same client.
13.3. Protocol Security
WebTransport imposes a set of requirements as described in [WEB-TRANSPORT-OVERVIEW], including:
-
Ensuring that the remote server is aware that the WebTransport protocol is in use and confirming that the remote server is willing to use the WebTransport protocol. [WEB-TRANSPORT-HTTP3] uses a combination of ALPN [RFC7301], an HTTP/3 setting, and a
:protocol
pseudo-header to identify the WebTransport protocol. [WEB-TRANSPORT-HTTP2] uses a combination of ALPN, an HTTP/2 setting, and a:protocol
pseudo-header to identify the WebTransport protocol. -
Allowing the server to filter connections based on the origin of the resource originating the transport session. The
Origin
header field on the session establishment request carries this information.
Protocol security related considerations are described in the Security Considerations sections of [WEB-TRANSPORT-HTTP3] and [WEB-TRANSPORT-HTTP2].
Networking APIs can be commonly used to scan the local network for available hosts, and thus be used for fingerprinting and other forms of attacks. WebTransport follows the WebSocket approach to this problem: the specific connection error is not returned until an endpoint is verified to be a WebTransport endpoint; thus, the Web application cannot distinguish between a non-existing endpoint and the endpoint that is not willing to accept connections from the Web.
13.4. Authentication using Certificate Hashes {#certificate-hashes}
Normally, a user agent authenticates a TLS connection between itself and a remote endpoint by verifying the validity of the TLS server certificate provided against the server name in the URL [RFC9525]. This is accomplished by chaining server certificates to one of the trust anchors maintained by the user agent; the trust anchors in question are responsible for authenticating the server names in the certificates. We will refer to this system as Web PKI.
This API provides web applications with a capability to connect to a remote network endpoint authenticated by a specific server certificate, rather than its server name. This mechanism enables connections to endpoints for which getting long-term certificates can be challenging, including hosts that are ephemeral in nature (e.g. short-lived virtual machines), or that are not publicly routable. Since this mechanism substitutes Web PKI-based authentication for an individual connection, we need to compare the security properties of both.
A remote server will be able to successfully perform a TLS handshake only if it posesses the private key corresponding to the public key of the certificate specified. The API identifies the certificates using their hashes. That is only secure as long as the cryptographic hash function used has second-preimage resistance. The only function defined in this document is SHA-256; the API provides a way to introduce new hash functions through allowing multiple algorithm-hash pairs to be specified.
It is important to note that Web PKI provides additional security mechanisms in addition to simply establishing a chain of trust for a server name. One of them is handling certificate revocation. In cases where the certificate used is ephemeral, such a mechanism is not necessary. In other cases, the Web application has to consider the mechanism by which the certificate hashes are provisioned; for instance, if the hash is provided as a cached HTTP resource, the cache needs to be invalidated if the corresponding certificate has been rotated due to compromise. Another security feature provided by the Web PKI are safeguards against certain issues with key generation, such as rejecting certificates with known weak keys; while this specification does not provide any specific guidance, browsers MAY reject those as a part of implementation-defined behavior.
Web PKI enforces an expiry period requirement on the certificates. This requirement limits the scope of potential key compromise; it also forces server operators to design systems that support and actively perform key rotation. For this reason, WebTransport imposes a similar expiry requirement; as the certificates are expected to be ephemeral or short-lived, the expiry period is limited to two weeks. The two weeks limit is a balance between setting the expiry limit as low as possible to minimize consequences of a key compromise, and maintaining it sufficiently high to accomodate for clock skew across devices, and to lower the costs of synchronizing certificates between the client and the server side.
The WebTransport API lets the application specify multiple certificate hashes at once, allowing the client to accept multiple certificates for a period in which a new certificate is being rolled out.
Unlike a similar mechanism in WebRTC, the server certificate hash API in WebTransport does not provide any means of authenticating the client; the fact that the client knows what the server certificate is or how to contact it is not sufficient. The application has to establish the identity of the client in-band if necessary.
13.5. Fingerprinting and Tracking
This API provides sites with the ability to generate network activity and closely observe the effect of this activity. The information obtained in this way might be identifying.
It is important to recognize that very similar networking capabilities are provided by other web platform APIs (such as fetch and [webrtc]). The net adverse effect on privacy due to adding WebTransport is therefore minimal. The considerations in this section applies equally to other networking capabilities.
Measuring network characteristics requires that the network be used and that the effect of that usage be measured, both of which are enabled by this API. WebTransport provides sites with an ability to generate network activity toward a server of their choice and observe the effects. Observations of both the stable properties of a network path and dynamic effect of network usage are possible.
Information about the network is available to the server either directly through its own networking stack, indirectly through the rate at which data is consumed or transmitted by the client, or as part of the statistics provided by the API (see § 5.12 WebTransportConnectionStats Dictionary). Consequently, restrictions on information in user agents is not the only mechanism that might be needed to manage these privacy risks.
13.5.1. Static Observations
A site can observe available network capacity or round trip time (RTT) between a user agent and a chosen server. This information can be identifying when combined with other tracking vectors. RTT can also reveal something about the physical location of a user agent, especially if multiple measurements can be made from multiple vantage points.
Though networking is shared, network use is often sporadic, which means that sites are often able to observe the capacity and round trip times of an uncontested or lightly loaded network path. These properties are stable for many people as their network location does not change and the position of network bottlenecks--which determine available capacity--can be close to a user agent.
13.5.2. Shared Networking
Contested links present sites with opportunities to enable cross-site recognition, which might be used to perform unsanctioned tracking [UNSANCTIONED-TRACKING]. Network capacity is a finite shared resource, so a user agent that concurrently accesses different sites might reveal a connection between the identity presented to each site.
The use of networking capabilities on one site reduces the capacity available to other sites, which can be observed using networking APIs. Network usage and metrics can change dynamically, so any change can be observed in real time. This might allow sites to increase confidence that activity on different sites originates from the same user.
A user agent could limit or degrade access to feedback mechanisms such as statistics (§ 5.12 WebTransportConnectionStats Dictionary) for sites that are inactive or do not have focus (HTML § 6.6 Focus). As noted, this does not prevent a server from making observations about changes in the network.
13.5.3. Pooled Sessions
Similar to shared networking scenarios, when sessions are pooled on a single connection, information from one session is affected by the activity of another session. One session could infer information about the activity of another session, such as the rate at which another application is sending data.
The use of a shared connection already allows the server to correlate sessions. Use of a network partition key disables pooling where use of a shared session might enable unwanted cross-site recognition.
14. Examples
14.1. Sending a buffer of datagrams
This section is non-normative.
Sending a buffer of datagrams can be achieved by using the datagrams
' writable
attribute. In the
following example datagrams are only sent if the transport is ready to send.
async function sendDatagrams( url, datagrams) { const wt= new WebTransport( url); const writer= wt. datagrams. writable. getWriter(); for ( const bytesof datagrams) { await writer. ready; writer. write( bytes). catch (() => {}); } }
14.2. Sending datagrams at a fixed rate
This section is non-normative.
Sending datagrams at a fixed rate regardless if the transport is ready to send
can be achieved by simply using datagrams
' writable
and not using the ready
attribute. More complex
scenarios can utilize the ready
attribute.
// Sends datagrams every 100 ms. async function sendFixedRate( url, createDatagram, ms= 100 ) { const wt= new WebTransport( url); await wt. ready; const writer= wt. datagrams. writable. getWriter(); const bytes= createDatagram(); setInterval(() => writer. write( bytes). catch (() => {}), ms); }
14.3. Receiving datagrams
This section is non-normative.
Datagrams can be received by reading from the
transport.datagrams
.readable
attribute. Null values may indicate that packets are not being processed quickly
enough.
async function receiveDatagrams( url) { const wt= new WebTransport( url); for await ( const datagramof wt. datagrams. readable) { // Process the datagram } }
14.4. Receiving datagrams with a BYOB reader
This section is non-normative.
As datagrams
are readable byte streams, you can acquire a BYOB reader for them, which allows more precise control over buffer allocation
in order to avoid copies. This example reads the datagram into a 64kB memory buffer.
const wt= new WebTransport( url); for await ( const datagramof wt. datagrams. readable) { const reader= datagram. getReader({ mode: "byob" }); let array_buffer= new ArrayBuffer( 65536 ); const buffer= await readInto( array_buffer); } async function readInto( buffer) { let offset= 0 ; while ( offset< buffer. byteLength) { const { value: view, done} = await reader. read( new Uint8Array( buffer, offset, buffer. byteLength- offset)); buffer= view. buffer; if ( done) { break ; } offset+= view. byteLength; } return buffer; }
14.5. Sending a stream
This section is non-normative.
Sending data as a one-way stream can be achieved by using the createUnidirectionalStream
function and the resulting stream’s writer.
async function sendData( url, ... data) { const wt= new WebTransport( url); const writable= await wt. createUnidirectionalStream(); const writer= writable. getWriter(); for ( const bytesof data) { await writer. ready; writer. write( bytes). catch (() => {}); } await writer. close(); }
The streams spec discourages awaiting the promise from write().
Encoding can also be done through pipes from a ReadableStream
, for example using TextEncoderStream
.
async function sendText( url, readableStreamOfTextData) { const wt= new WebTransport( url); const writable= await wt. createUnidirectionalStream(); await readableStreamOfTextData. pipeThrough( new TextEncoderStream( "utf-8" )) . pipeTo( writable); }
14.6. Receiving incoming streams
This section is non-normative.
Reading incoming streams can be achieved by iterating over the incomingUnidirectionalStreams
attribute,
and then consuming each WebTransportReceiveStream
by iterating over its chunks.
async function receiveData( url, processTheData) { const wt= new WebTransport( url); for await ( const readableof wt. incomingUnidirectionalStreams) { // consume streams individually using IFFEs, reporting per-stream errors (( async () => { try { for await ( const bytesof readable) { processTheData( bytes); } } catch ( e) { console. error( e); } })()); } }
Decoding can also be done through pipes to new WritableStreams, for example using TextDecoderStream
. This example assumes text output should not be
interleaved, and therefore only reads one stream at a time.
async function receiveText( url, createWritableStreamForTextData) { const wt= new WebTransport( url); for await ( const readableof wt. incomingUnidirectionalStreams) { // consume sequentially to not interleave output, reporting per-stream errors try { await readable. pipeThrough( new TextDecoderStream( "utf-8" )) . pipeTo( createWritableStreamForTextData()); } catch ( e) { console. error( e); } } }
14.7. Receiving a stream with a BYOB reader
This section is non-normative.
As WebTransportReceiveStream
s are readable byte streams, you can acquire a BYOB reader for them, which allows more precise control over buffer allocation
in order to avoid copies. This example reads the first 1024 bytes from a WebTransportReceiveStream
into a single memory buffer.
const wt= new WebTransport( url); const reader= wt. incomingUnidirectionalStreams. getReader(); const { value: recv_stream, done} = await reader. read(); const byob_reader= recv_stream. getReader({ mode: "byob" }); let array_buffer= new ArrayBuffer( 1024 ); const buffer= await readInto( array_buffer); async function readInto( buffer) { let offset= 0 ; while ( offset< buffer. byteLength) { const { value: view, done} = await reader. read( new Uint8Array( buffer, offset, buffer. byteLength- offset)); buffer= view. buffer; if ( done) { break ; } offset+= view. byteLength; } return buffer; }
14.8. Sending a transactional chunk on a stream
This section is non-normative.
Sending a transactional piece of data on a unidirectional stream, only if it can be done
entirely without blocking on flow control, can be achieved by using the getWriter
function and the resulting writer.
async function sendTransactionalData( wt, bytes) { const writable= await wt. createUnidirectionalStream(); const writer= writable. getWriter(); await writer. ready; try { await writer. atomicWrite( bytes); } catch ( e) { if ( e. name!= "AbortError" ) throw e; // rejected to avoid blocking on flow control // The writable remains un-errored provided no non-atomic writes are pending } finally { writer. releaseLock(); } }
14.9. Using a server certificate hash
This section is non-normative.
A WebTransport session can override the default trust evaluation performed by
the client with a check against the hash of the certificate provided to the
server. In the example below, hashValue
is a BufferSource
containing the
SHA-256 hash of a server certificate that the underlying connection should
consider to be valid.
const wt= new WebTransport( url, { serverCertificateHashes: [ { algorithm: "sha-256" , value: hashValue, } ] }); await wt. ready;
14.10. Complete example
This section is non-normative.
This example illustrates use of the closed and ready promises, opening of uni-directional and bi-directional streams by either the client or the server, and sending and receiving datagrams.
// Adds an entry to the event log on the page, optionally applying a specified // CSS class. let wt, streamNumber, datagramWriter; connect. onclick= async () => { try { const url= document. getElementById( 'url' ). value; wt= new WebTransport( url); addToEventLog( 'Initiating connection...' ); await wt. ready; addToEventLog( ` ${ ( wt. reliability== "reliable-only" ) ? "TCP" : "UDP" } ` + `connection ready.` ); wt. closed. then(() => addToEventLog( 'Connection closed normally.' )) . catch (() => addToEventLog( 'Connection closed abruptly.' , 'error' )); streamNumber= 1 ; datagramWriter= wt. datagrams. writable. getWriter(); readDatagrams(); acceptUnidirectionalStreams(); document. forms. sending. elements. send. disabled= false ; document. getElementById( 'connect' ). disabled= true ; } catch ( e) { addToEventLog( `Connection failed. ${ e} ` , 'error' ); } } sendData. onclick= async () => { const form= document. forms. sending. elements; const data= sending. data. value; const bytes= new TextEncoder( 'utf-8' ). encode( data); try { switch ( form. sendtype. value) { case 'datagram' : { await datagramWriter. ready; datagramWriter. write( bytes). catch (() => {}); addToEventLog( `Sent datagram: ${ data} ` ); break ; } case 'unidi' : { const writable= await wt. createUnidirectionalStream(); const writer= writable. getWriter(); writer. write( bytes). catch (() => {}); await writer. close(); addToEventLog( `Sent a unidirectional stream with data: ${ data} ` ); break ; } case 'bidi' : { const duplexStream= await wt. createBidirectionalStream(); const n= streamNumber++ ; readFromIncomingStream( duplexStream. readable, n); const writer= duplexStream. writable. getWriter(); writer. write( bytes). catch (() => {}); await writer. close(); addToEventLog( `Sent bidirectional stream # ${ n} with data: ${ data} ` ); break ; } } } catch ( e) { addToEventLog( `Error while sending data: ${ e} ` , 'error' ); } } // Reads datagrams into the event log until EOF is reached. async function readDatagrams() { try { const decoder= new TextDecoderStream( 'utf-8' ); for await ( const dataof wt. datagrams. readable. pipeThrough( decoder)) { addToEventLog( `Datagram received: ${ data} ` ); } addToEventLog( 'Done reading datagrams!' ); } catch ( e) { addToEventLog( `Error while reading datagrams: ${ e} ` , 'error' ); } } async function acceptUnidirectionalStreams() { try { for await ( const readableof wt. incomingUnidirectionalStreams) { const number= streamNumber++ ; addToEventLog( `New incoming unidirectional stream # ${ number} ` ); readFromIncomingStream( readable, number); } addToEventLog( 'Done accepting unidirectional streams!' ); } catch ( e) { addToEventLog( `Error while accepting streams ${ e} ` , 'error' ); } } async function readFromIncomingStream( readable, number) { try { const decoder= new TextDecoderStream( 'utf-8' ); for await ( const dataof readable. pipeThrough( decoder)) { addToEventLog( `Received data on stream # ${ number} : ${ data} ` ); } addToEventLog( `Stream # ${ number} closed` ); } catch ( e) { addToEventLog( `Error while reading from stream # ${ number} : ${ e} ` , 'error' ); addToEventLog( ` ${ e. message} ` ); } } function addToEventLog( text, severity= 'info' ) { const log= document. getElementById( 'event-log' ); const previous= log. lastElementChild; const entry= document. createElement( 'li' ); entry. innerText= text; entry. className= `log- ${ severity} ` ; log. appendChild( entry); // If the previous entry in the log was visible, scroll to the new element. if ( previous&& previous. getBoundingClientRect(). top< log. getBoundingClientRect(). bottom) { entry. scrollIntoView(); } }
15. Acknowledgements
The editors wish to thank the Working Group chairs and Team Contact, Jan-Ivar Bruaroey, Will Law and Yves Lafon, for their support.The WebTransport
interface is based on the QuicTransport
interface
initially described in the W3C ORTC CG,
and has been adapted for use in this specification.