make the HTTP settings available to the client

[marten-seemann]

This is needed to correctly implement WebTransport. The client has to check that the server sent the WebTransport setting in SETTINGS, for example.

[tanghaowillow]

How about adding a new option in http3.RoundTripOpt, for example WaitForSettings, which indicates the client to not send the request until peer's settings frame is received. The http.RoundTripper struct can have a SettingsHandler callback, which will be passed into roundTripperOpts like StreamHijacker, to decide wether to accept the peer's settings.

type RoundTripOpt struct {
    ...
    // If set, the client will not send the request until the settings frame is received on the control stream.
    WaitForSettings bool
}

type RoundTripper struct {
    ...
    // If non-nil, it will be called once the settings frame is received.
    // If a non-nil error is returned, the request will not be sent and the client will close the QUIC
    // connection with an ErrCodeSettingsError.
    SettingsHandler(*settingsFrame) error
    ...
}

[tanghaowillow]

@marten-seemann could you share your view on this? really want to get this done and make the work on http/3 datagram and WebTransport move forward.

[marten-seemann]

Currently on vacation, so it will be some time until I can comment here.

I don’t think this issue is needed for datagram support in WebTransport though, since datagrams are a requirement for the protocol anyway.