SignalR wth gzip compression

Question

Having some problem developing a SignalR client for a Hub hosted in asp.net website with gzip compression enabled. Since we are using IIS compression, the response from SignalR also gets compressed, but, the client does not understand the response and we get a Json parsing error on the client side.

SignalR internally uses HttpWebRequest to make make http requests and HttpWebRequest can be configured to automatically decompress the response using AutomaticDecompression property. So, if somehow I can get hold of the HttpWebRequest object used by SignalR to make the request, I should be able to set the enable automatic decompression.

I thought I should be able to get access to the HttpWebRequest by providing HubConnection.Start with my custom implementation of IHttpClient, IHttpClient.GetAsync takes a prepareRequest action which I thought should give me access to the HttpWebRequest, but, HttpHelper.GetAsync wraps the HttpWebRequest with HttpWebRequestWrapper before passing to prepareRequest and HttpWebRequestWrapper does not provide access to HttpWebRequest.

HttpHelper class is internal so can't use it as well, so, I am not exactly sure how to enable automatic decompression with SignalR.

I can expose the HttpWebRequest in HttpWebRequestWrapper, but, would prefer a simpler solution if one exists. Any thougths?

I am using SignalR version 0.5.1.10822

My auto decompression HttpClient:

public class HttpClientWithAutoDecompression : IHttpClient
{
    readonly DefaultHttpClient _httpClient = new DefaultHttpClient();

    private readonly DecompressionMethods _decompressionMethods;
    public HttpClientWithAutoDecompression(DecompressionMethods decompressionMethods)
    {
        _decompressionMethods = decompressionMethods;
    }

    public Task<IResponse> GetAsync(string url, Action<IRequest> prepareRequest)
    {
        Task<IResponse> task = _httpClient.GetAsync(url, 
            request =>
                {
                    [ERROR: request is actually HttpRequestWrapper and
                     does not expose HttpWebRequest]**              ] 
                    var httpWebRequest = (HttpWebRequest) request; 
                    httpWebRequest.AutomaticDecompression = _decompressionMethods;
                    prepareRequest(request);
                });

        return task.ContinueWith(response =>
        {
            Log.Debug(this, "Response: {0}", response.Result.ReadAsString());
            return response.Result;
        });

    }
....
}

I've now checked on a server that also has gzip compression enabled and found out that SignalR.Client doesn't send Accept-Encoding: gzip by default, so my server responds with an uncompressed message and everything works as expected. It appears that either your client incorrectly sends the Accept-Encoding header or your sever forces every response to gzip (which the built-in IIS compression does not). Can you check with Fiddler what's going on? — Alexander Köplinger

Drew Marsh Drew Marsh · Accepted Answer · 2012-10-04T06:45:44

To the best of my knowledge GZip encoding and streaming do not mix. In the case of the forever frame transport the client wouldn't be able to decode any on the streaming content until the entire response, or at least a significant block of data, is received (due to the way the data is decoded). In the case of web sockets there is not support for encoding of any kind at this time, although there is apparently an extension to the specification for per message encoding being worked on.

That said, if you wanted to attempt to provide support for the LongPolling transport, the only way I can see this being possible is to provide your own SignalR IHttpClient implementation. You can see right now that the DefaultHttpClient class uses HttpHelper::GetAsync which creates the HttpWebRequest internally and you can never get your hands on that because you only have access to the IRequest which is HttpWebRequestWrapper at that point.

By creating your own IHttpClient you can take over the initial instantiation of the HttpWebRequest, set the AutomaticDecompression and then wrap that up yourself with the HttpWebRequestWrapper.

SignalR wth gzip compression

1 Answers