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RFC 169: WebRTC Echo server #169

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RFC 169: WebRTC Echo server #169

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RFC xx: WebRTC Echo server
fippo Oct 18, 2023
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Update rfcs/webrtc_test_server.md
jgraham Nov 7, 2023
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40 changes: 40 additions & 0 deletions rfcs/webrtc_test_server.md
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# RFC 169: WebRTC Test Server


## Summary

Add a [WebRTC](https://datatracker.ietf.org/doc/html/rfc8834) server to wpt. The server is used to test the [WebRTC Web APIs](https://w3c.github.io/webrtc/). The server requires Python 3.

The server uses a WebSocket connection to negotiate the WebRTC connection.
It terminates STUN, DTLS and SRTP and forwards unencrypted RTP or RTCP packets to the browser.
This allows the tests to receive and inspect any packets received.

Future versions may use WebTransport instead of WebSockets for signaling and transport of packets to the client and allow the client to send packets over the WebSocket to be forwarded
via WebRTC.

## Details

### Implementation

The WebRTC test server is built on top of `aiortc`, similar to how the WebTransport/H3 test server is based on `aioquic`.

The server will be implemented under `tools/webrtc` directory.

### `wptserve` integration

When the WebRTC test server runs as a part of `wptserve`, `$ROOT` will be the same as `$WPT_ROOT`.

`wptserve` runs the WebRTC test server in a way similar to [pywebsocket](https://github.com/web-platform-tests/wpt/blob/246a32576020cb9c4241b7cfbc296f92d944ff6b/tools/serve/serve.py#L713):
`wptserve` launches the server as a daemon and passes relevant configurations (port number, root directory etc) to the server. The daemon is monitored by `wptserve` like other daemons.

### Dependencies

As of writing this RFC, the only dependency is `aiortc`.
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Nice!


## Risks

Risks are similar to [RFC #42](https://github.com/web-platform-tests/rfcs/blob/master/rfcs/quic.md#risks).
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Does this involve new binary dependencies? I assume it does, but it would help to be specific here since those require special handling, especially in vedor repos where we can't depend on pypi. They also add some maintenance risk (as we've seen with aioquic not updating its releases for newer Python versions)

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Python bindings for libsrtp and google-crc32c should be the only new dependencies I think. @jlaine might know more.

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@gsnedders gsnedders Dec 1, 2023 •
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https://github.com/aiortc/aiortc/blob/0ecc5379762883fbf6454d4633b948c2ad50dec8/pyproject.toml#L28-L38 shows quite a lot of (direct) Python dependencies:

dependencies = [
    "aioice>=0.9.0,<1.0.0",
    "av>=9.0.0,<12.0.0",
    "cffi>=1.0.0",
    "cryptography>=2.2",
    'dataclasses; python_version < "3.7"',
    "google-crc32c>=1.1",
    "pyee>=9.0.0",
    "pylibsrtp>=0.5.6",
    "pyopenssl>=23.1.0",
]

I think av is the dependency that worries me most here—especially insofar as it has a pretty major dependency (ffmpeg—which is a dependency likely to make legal departments nervous given the patent status of many codecs it supports—and is also just a pretty sizeable project which is more likely to cause issue on new platforms).

(There's a few other notable new dependencies: aiortc itself depends on opus and libvpx, and pylibstrp depends on libsrtp, but these are probably less problematic)

Are we actually planning on doing any testing that actually requires media codecs?

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Are we actually planning on doing any testing that actually requires media codecs?

Yes.

The initial proposals (passing the RTP packets back to the test for analysis) would not need media codecs on the server, but once we have experience with those, running media codecs on the server is a definite option.
In order to do the tests, we have to negotiate use of media codecs; I have no idea whether it's possible to build aiortc in such a way that it can claim to have media codecs but actually not have them.

The argument for doing these tests in wpt is that we would get wpt's infrastructure for tracking and sharing tests with a relatively small investment in engineering on the webrtc support side (by using aiortc). If we start asking to reengineer aiortc in order to integrate it, the value of this approach starts dropping.

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@fippo fippo Dec 11, 2023 •
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Now forking to remove "av" as a dependency is possible: https://github.com/aiortc/aiortc/compare/main...fippo:aiortc:no-av?expand=1
but that gets to a point where the maintenance cost will add up.

Just running this in Chromium's CI would be ok as the tests will be testing low-level libWebRTC behavior which is going to be largely identical in consuming browsers like Safari.


The WebRTC test server itself is standalone and the maintenance cost of the code will be low from the `wptserve`'s perspective.
The WebRTC team at Google and Microsoft will be responsible for maintaining the integration point and the server.
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@alvestrand can you confirm Google's WebRTC can commit to maintain this together with Microsoft?

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Yes. We plan to submit and maintain WPT tests that use this facility.

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Thanks for confirming!