Using a proxy with .NET 4.5 HttpClient

Question

I'm troubleshooting a bug with a service I call through .NET's HttpClient, trying to route the request through a local proxy (Fiddler), but my proxy settings seem to not be taking effect.

Here's how I create the client:

private HttpClient CreateHttpClient(CommandContext ctx, string sid) {
    var cookies = new CookieContainer();

    var handler = new HttpClientHandler {
        CookieContainer = cookies,
        UseCookies = true,
        UseDefaultCredentials = false,
        Proxy = new WebProxy("http://localhost:8888", false, new string[]{}),
        UseProxy = true,
    };

    // snip out some irrelevant setting of authentication cookies

    var client = new HttpClient(handler) {
        BaseAddress = _prefServerBaseUrl,
    };

    client.DefaultRequestHeaders.Accept.Add(
        new MediaTypeWithQualityHeaderValue("application/json"));

    return client;
}

then I send the request by:

var response = CreateHttpClient(ctx, sid).PostAsJsonAsync("api/prefs/", smp).Result;

Request goes straight to the server without attempting to hit the proxy. What did I miss?

Answer 1

This code worked for me:

using System.Net;
using System.Net.Http;

var httpClientHandler = new HttpClientHandler
{
    Proxy    = new WebProxy(Address: "http://localhost:8888", BypassOnLocal: false),
    UseProxy = true
}

Note that I am not using the WebProxy constructor overload that accepts string\[\] bypassList, but your code does - perhaps that's the problem?

Answer 2

Ah, The BaseAddress I was pointing to was http://localhost:8081. Turns out that despite setting BypassOnLocal to false, evidently localhost is still special enough that it bypasses the proxy.

I added a domain binding in IIS, host file entry to point that domain to 127.0.0.1, used newly created domain, now it works.

Answer 3

Is Fiddler configured to capture traffic from all processes? Look at the status bar where you see "Capturing". It should show "All Processes" next to it. If it shows "Web browsers", click it and change it to all processes. This could be different depending on the version of Fiddler you use.