Better support for HTTP/2 in SignalR .NET client

[BrennanConroy]

We don't need to specify HTTP/1.1 for negotiate and sends anymore due to #17081 being fixed on all supported server versions!

This change also flows the HttpClient to the WebSocketTransport so that WebSockets over HTTP/2.0 can reuse the potentially already HTTP/2 connection.

I'm leaning towards not specifying webSocket.Options.HttpVersion = HttpVersion.Version20 by default and letting customers specify it via HttpConnectionOptions.WebSocketConfiguration. While the connection should fallback to HTTP/1.1 if HTTP/2 isn't supported, it would add additional connection startup latency in those cases.

Blocked on a few issues in Runtime around the new ClientWebSocket.ConnectAsync method.

Unfortunately, when using HTTP/2 websockets, settings like cookie and certs on the websocket options are ignored and the HttpClient settings are used instead. This is why the PR avoids passing the HttpClient to WebSocket.ConnectAsync for HTTP/1.1 currently. And we should probably document this behavior when setting HTTP/2.

[BrennanConroy]

Hmm, issue with this change is that now all the DelegatingHandler wrappers run for WebSocket requests, which is a problem in the AccessTokenHttpMessageHandler case when running in WASM due to headers not being settable. Not sure if the header would just be ignored, but regardless, the access token factory would be called again which would be unnecessary, unless we changed the handler to detect a WebSocket request and removed the access token factory call from WebSocketsTransport.

[halter73]

How hard is it now to force HTTP/1.1 for all requests to get the old behavior if you really want to?

[BrennanConroy]

In order to force HTTP/1.1 on all requests now (if for some reason ALPN negotiation isn't gracefully falling back to HTTP/1.1 or some other reason), you can write the following code:

private class Http11Handler : DelegatingHandler
{
    public Http11Handler(HttpMessageHandler handler)
        : base(handler)
    { }

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        request.Version = HttpVersion.Version11;
        return base.SendAsync(request, cancellationToken);
    }
}

HubConnection CreateConnection()
{
    return new HubConnectionBuilder().WithUrl(url, options =>
    {
        options.HttpMessageHandlerFactory = handler =>
        {
            return new Http11Handler((HttpClientHandler)handler);
        };
    }).Build();
}

[halter73]

I figured it might take something difficult like a DelegatingHandler to revert to the old behavior, but at least there's a way. Hopefully nobody will need to.

[ghost]

@BrennanConroy, this change will be considered for inclusion in the blog post for the release it'll ship in. Nice work!

Please ensure that the original comment in this thread contains a clear explanation of what the change does, why it's important (what problem does it solve?), and, if relevant, include things like code samples and/or performance numbers.

This content may not be exactly what goes into the blog post, but it will help the team putting together the announcement.

Thanks!

[BrennanConroy]

@adityamandaleeka Additional testing added. Approve and merge at will 😃

[adityamandaleeka]

Thanks @BrennanConroy!