Add duplex property to Request

[jakearchibald]

• At least two implementers are interested (and none opposed):
  • Chrome
  • Safari
• Tests are written and can be reviewed and commented upon at:
  • Request duplex property web-platform-tests/wpt#36051
• Implementation bugs are filed:
  • Chrome: https://bugs.chromium.org/p/chromium/issues/detail?id=1368092
  • Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1792434
  • Safari: https://bugs.webkit.org/show_bug.cgi?id=245671
  • Deno (not for CORS changes): Add duplex property to Request denoland/deno#16032

(See WHATWG Working Mode: Changes for more details.)

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Preview | Diff

[jakearchibald]

Tests added. I'll create the implementation bugs when this is reviewed.

[annevk]

Thanks, this looks good. I was initially thinking we might want to de-duplicate some of the domintro with the duplex dictionary member, but for now this actually seems fine as they are somewhat different features even if they share a name. And we can revise when we add "full".

[annevk]

I think we can land this once there are impl bugs. This is really a bug fix for #1457 as #1486 shows it's rather broken without it.

[annevk]

cc @lucacasonato

[lucacasonato]

I agree with the motivation for this change.

I do have a concern with this implementation though, namely that this effectively sets the default value for duplex to "half" (even if the user did not specify a value). This is incompatible with Deno, because our default value has always been "full" there (even though this is not explicitly exposed on a .duplex member on the Request object.

I think we'll just have to swallow the "implementation will vary from spec" pill here though, as we implemented full duplex streaming before standardization.

The user observable change here will be:

// Chrome
const req = new Request("Hello World");
req.duplex; // "half"

// Deno
const req = new Request("Hello World");
req.duplex; // "full"

This is not much worse than the status quo though, as the actual behaviour would be different between Deno and other browsers regardless of this PR. This PR just explicitly exposes this difference between the default duplex streaming behaviours in a string value that the user can see.

Also of note: this does not close the door to updating the default for duplex being "full" when a user specifies a ReadableStream body.

LGTM

[jakearchibald]

@annevk

I was initially thinking we might want to de-duplicate some of the domintro with the duplex dictionary member

Yeah, I felt the same, but figured developers may go straight to either bit of documentation, so the duplication seem ok.

[jakearchibald]

@annevk Implementation bugs added.

Could you take a look at web-platform-tests/wpt#36048 so (hopefully) browsers don't break the feature detect?