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Add headers constructor option and readonly response wt.headers attribute #713

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Add headers constructor option and readonly response wt.headers attri…
jan-ivar Dec 15, 2025
7f03142
Describe headers option and fix algorithm
jan-ivar Dec 15, 2025
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35 changes: 32 additions & 3 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -727,6 +727,7 @@ interface WebTransport {
readonly attribute WebTransportCongestionControl congestionControl;
[EnforceRange] attribute unsigned short? anticipatedConcurrentIncomingUnidirectionalStreams;
[EnforceRange] attribute unsigned short? anticipatedConcurrentIncomingBidirectionalStreams;
[SameObject] readonly attribute Headers? headers;
readonly attribute DOMString protocol;

readonly attribute Promise<WebTransportCloseInfo> closed;
Expand Down Expand Up @@ -821,6 +822,10 @@ A {{WebTransport}} object has the following internal slots.
<td class="non-normative">The number of concurrently open
[=bidirectional=] streams the application anticipates the server creating, or null.
</tr>
<tr>
<td><dfn>`[[Headers]]`</dfn>
<td class="non-normative">A {{Headers}} object or null. Initially null.
</tr>
<tr>
<td><dfn>`[[Protocol]]`</dfn>
<td class="non-normative">A string indicating the application-level protocol selected by the server,
Expand Down Expand Up @@ -924,6 +929,8 @@ agent MUST run the following steps:
:: |anticipatedConcurrentIncomingUnidirectionalStreams|
: {{[[AnticipatedConcurrentIncomingBidirectionalStreams]]}}
:: |anticipatedConcurrentIncomingBidirectionalStreams|
: {{[[Headers]]}}
:: null
: {{[[Protocol]]}}
:: an empty string
: {{[[Closed]]}}
Expand Down Expand Up @@ -980,6 +987,13 @@ agent MUST run the following steps:

1. Set |request|'s [=request/method=] to "`CONNECT`", and set the method's associated
`:protocol` <dfn>pseudo-header</dfn> to `"webtransport"`.
1. Let |headers| be {{WebTransport/constructor(url, options)/options}}["{{WebTransportOptions/headers}}"].
1. If |headers| is a not a {{Headers}} object, then set |headers| to a new {{Headers}}
object [=Headers/filled=] with
{{WebTransport/constructor(url, options)/options}}["{{WebTransportOptions/headers}}"].
1. Set |request|'s [=request/header list=] to a copy of |headers|'s [=Headers/header list=].
1. If |request|'s [=request/header list=] [=header list/contains=] `WT-Available-Protocols`, then
throw a {{TypeError}}.
Comment on lines +990 to +996
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@annevk annevk Dec 18, 2025

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It seems you are not validating the Headers object and just copy all its headers straight onto request. Are you sure that's what you want? @wilaw's comment below suggests you are expecting some kind of validation at least.

This is why the Request constructor for instance creates its own instance always and then attempts to forward the headers (which might end up throwing).

Perhaps we could/should create some kind of abstraction for this which can be shared by Fetch and WebTransport.

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@jan-ivar jan-ivar Dec 18, 2025

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Good catch! We definitely want filtering by the forbidden request header list

1. If |protocols| is not empty, [=header list/set a structured field value=] with
(`WT-Available-Protocols`, a
<a href="https://html.spec.whatwg.org/#http-structured-header-list">
Expand All @@ -989,7 +1003,7 @@ agent MUST run the following steps:
[=header list=].
1. [=Fetch=] |request|, with [=useParallelQueue=] set to true, and [=processResponse=]
set to the following steps given a |response|:
1. [=Process a WebTransport fetch response=] with |response|, |origin|, |protocols|, and |congestionControl|.
1. [=Process a WebTransport fetch response=] with |response| and |transport|.
1. Return |transport|.

</div>
Expand Down Expand Up @@ -1035,7 +1049,7 @@ To <dfn export>obtain a WebTransport connection</dfn>, given a [=network partiti
</div>

<div algorithm="process a WebTransport fetch response">
To <dfn>process a WebTransport fetch response</dfn>, given a |response|, and |congestionControl|, run these steps:
To <dfn>process a WebTransport fetch response</dfn>, given a |response| and |transport|, run these steps:
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@annevk annevk Dec 18, 2025

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Nit: consider specifying the types of the arguments here.

1. If |response| is [=network error=], then abort the remaining steps and [=queue a network task=] with
|transport| to run these steps:
1. If |transport|.{{[[State]]}} is `"closed"` or `"failed"`, then abort these steps.
Expand All @@ -1059,14 +1073,18 @@ To <dfn>process a WebTransport fetch response</dfn>, given a |response|, and |co
{{WebTransportErrorOptions/source}} is `"session"`.
1. [=Cleanup=] |transport| with |error|.
1. If the user agent supports more than one congestion control algorithm, choose one
appropriate for |congestionControl| for sending of data on this |connection|.
appropriate for |transport|'s {{[[CongestionControl]]}} for sending of data on this |connection|.
1. [=Queue a network task=] with |transport| to run these steps:
1. Assert: [=this=]'s {{[[Datagrams]]}}'s {{[[OutgoingMaxDatagramSize]]}} is an integer.
1. If |transport|.{{[[State]]}} is not `"connecting"`:
1. [=In parallel=], [=session/terminate=] |session|.
1. Abort these steps.
1. Set |transport|.{{[[State]]}} to `"connected"`.
1. Set |transport|.{{[[Session]]}} to |session|.
1. Let |headers| be a copy of |response|’s [=response/header list=].
1. Remove from |headers| each header whose name is a [=byte-case-insensitive=] match for `WT-Protocol`.
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@annevk annevk Dec 18, 2025

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Use https://fetch.spec.whatwg.org/#concept-header-list-delete?

1. Set |transport|.{{[[Headers]]}} to a new {{Headers}} object with |transport|'s [=relevant realm=],
whose [=Headers/header list=] is |headers| and guard is "`immutable`".
1. Set |transport|.{{[[Protocol]]}} to either the string value of the negotiated application
protocol if present, following [[!WEB-TRANSPORT-OVERVIEW]]
[Section 3.1](https://datatracker.ietf.org/doc/html/draft-ietf-webtrans-overview-09/#section-3.1),
Expand Down Expand Up @@ -1199,6 +1217,11 @@ Note: Setting {{WebTransport/anticipatedConcurrentIncomingUnidirectionalStreams}
{{WebTransport/anticipatedConcurrentIncomingBidirectionalStreams}} does not guarantee
the application will receive the number of streams it anticipates.

: <dfn for="WebTransport" attribute>headers</dfn>
:: Once a [=WebTransport session=] has been established, holds the application-level
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@annevk annevk Dec 18, 2025

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Suggested change
:: Once a [=WebTransport session=] has been established, holds the application-level
:: Once a [=WebTransport session=] has been established, it holds the application-level

?

headers set by the server, if any. Initially null.
The getter steps are to return [=this=]'s {{[[Headers]]}}.
Comment on lines +1221 to +1223
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@wilaw wilaw Dec 17, 2025

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Would it be clearer if we added some text indicating that these headers are subject to the forbidden request-header list as defined by https://fetch.spec.whatwg.org/#methods section 2.2.2?

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@annevk annevk Dec 18, 2025

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This is a little hand-wavy. Shouldn't you define somewhere a slot that holds null or a Headers object?

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@jan-ivar jan-ivar Dec 18, 2025

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@annevk isn't that https://pr-preview.s3.amazonaws.com/jan-ivar/webtransport/pull/713.html#dom-webtransport-headers-slot? Or did you mean something else?

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@annevk annevk Dec 18, 2025

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Oh sorry, I missed [[ and ]] and thought this was referring to the object.


: <dfn for="WebTransport" attribute>protocol</dfn>
:: Once a [=WebTransport session=] has been established and the {{protocols}}
constructor option was used to provide a non-empty array, returns the application-level protocol
Expand Down Expand Up @@ -1530,6 +1553,7 @@ dictionary WebTransportHash {
dictionary WebTransportOptions {
boolean allowPooling = false;
boolean requireUnreliable = false;
HeadersInit headers = {};
sequence&lt;WebTransportHash&gt; serverCertificateHashes = [];
WebTransportCongestionControl congestionControl = "default";
[EnforceRange] unsigned short? anticipatedConcurrentIncomingUnidirectionalStreams = null;
Expand Down Expand Up @@ -1558,6 +1582,11 @@ that determine how the [=WebTransport session=] is established and used.
:: When set to true, the [=WebTransport session=] cannot be established over an
HTTP/2 [=connection=] if an HTTP/3 [=connection=] is not possible.

: <dfn for="WebTransportOptions" dict-member>headers</dfn>
:: Optionally, a {{Headers}} object, an object literal, or an array of two-item arrays
to set the [=request=] [=request/header list=] to use when [=session/establishing=]
a [=WebTransport session=].

: <dfn for="WebTransportOptions" dict-member>serverCertificateHashes</dfn>
:: This option is only supported for transports using dedicated connections.
For transport protocols that do not support this feature, having this
Expand Down