.NET Core reverse proxy middleware and signalR

Question

I need to do a reverse proxy middleware in ASP.NET Core. I have something like this. But it doesn't work with SignalR.

Reverse proxy has address 192.168.187.72:5000; SignalR 192.168.187.62:5000. Client connects to proxy, proxy changes the url to SignalR hub url, but in client I always get this error:

The server disconnected before the handshake could be started

Code:

public ReverseProxyMiddleware(RequestDelegate nextMiddleware,ILogger<ReverseProxyMiddleware> logger)
{
    _nextMiddleware = nextMiddleware;
    _logger = logger;
}

public async Task Invoke(HttpContext context)
{
     var targetUri = BuildTargetUri(context.Request);
       
     if (targetUri != null)
     {
         var targetRequestMessage = CreateTargetMessage(context, targetUri);
           
         using (var responseMessage = await _httpClient.SendAsync(targetRequestMessage, HttpCompletionOption.ResponseHeadersRead, context.RequestAborted))
         {
             context.Response.StatusCode = (int)responseMessage.StatusCode;
                
             CopyFromTargetResponseHeaders(context, responseMessage);
             await responseMessage.Content.CopyToAsync(context.Response.Body);
         }

         return;
    }

    await _nextMiddleware(context);
}

private HttpRequestMessage CreateTargetMessage(HttpContext context, Uri targetUri)
{
    var requestMessage = new HttpRequestMessage();

    CopyFromOriginalRequestContentAndHeaders(context, requestMessage);

    requestMessage.RequestUri = targetUri;
    requestMessage.Headers.Host = targetUri.Host;
    requestMessage.Method = GetMethod(context.Request.Method);

    return requestMessage;
}

private void CopyFromOriginalRequestContentAndHeaders(HttpContext context, HttpRequestMessage requestMessage)
{
    var requestMethod = context.Request.Method;
       
    var streamContent = new StreamContent(context.Request.Body);
    requestMessage.Content = streamContent;

    foreach (var header in context.Request.Headers)
    {
        requestMessage.Content?.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray());
    }
}

private void CopyFromTargetResponseHeaders(HttpContext context, HttpResponseMessage responseMessage)
{
    foreach (var header in responseMessage.Headers)
    {
        context.Response.Headers[header.Key] = header.Value.ToArray();
    }

    foreach (var header in responseMessage.Content.Headers)
    {
        context.Response.Headers[header.Key] = header.Value.ToArray();
    }

    context.Response.Headers.Remove("transfer-encoding");
}

private static HttpMethod GetMethod(string method)
{
    if (HttpMethods.IsDelete(method)) return HttpMethod.Delete;
    if (HttpMethods.IsGet(method)) return HttpMethod.Get;
    if (HttpMethods.IsHead(method)) return HttpMethod.Head;
    if (HttpMethods.IsOptions(method)) return HttpMethod.Options;
    if (HttpMethods.IsPost(method)) return HttpMethod.Post;
    if (HttpMethods.IsPut(method)) return HttpMethod.Put;
    if (HttpMethods.IsTrace(method)) return HttpMethod.Trace;

    return new HttpMethod(method);
}

private Uri BuildTargetUri(HttpRequest request)
{
    Uri targetUri = null;
    StringValues clientId = string.Empty;

    targetUri = new Uri($"http://192.168.187.62:5000{request.Path}{request.QueryString}");

    _logger.LogInformation($"Request URL {request.Host + request.Path + request.QueryString} Target URL {targetUri.ToString()}");

    return targetUri;
}

Answer 1

Are you sure you want to create such functionality manually?

There are many great libraries for reverse proxying, Microsoft has a new project called YARP (https://microsoft.github.io/reverse-proxy/) which is an open source reverse proxy told to be high performance and highly customizable.

If you like I can show you a sample how you can use yarp in an ASP.NET Core app.