System.UriFormatException : Invalid URI: The hostname could not be parsed.

[Tratcher]

From @nulltoken on July 2, 2018 12:39

Hello,

It's possible I may have found a bug (or at the very least a surprising behavior 😉 ).

Running an integration test, using the TestServer, against an Mvc backed API (monitored by ApplicationInsights), throws a UriFormatException.

It looks like (cf. the screenshots below) that the host being parsed end up being "localhost,localhost".

I've managed to trim down the code as much as possible into a repro case available at https://github.com/nulltoken/UriFormatException

Beware, that looks pretty random. The repro case breaks most of time with one failing test, and from time to time two tests fail.

FWIW, removing this line from the repro case makes the problem disappear.

Versions:

• .Net Core 2.1.1
• ApplicationInsightsAspNetCore 2.4-beta1

Copied from original issue: aspnet/Mvc#7997

[Tratcher]

From @nulltoken on July 2, 2018 19:9

FWIW this was working against .NET Core 2.0.5

[Tratcher]

From @pranavkm on July 2, 2018 20:25

cc @Tratcher

[Tratcher]

Confirmed, this is a bug in TestHost.

Minimized repro:

        [Fact]
        public async Task ManuallySetHost_Overwritten()
        {
            RequestDelegate appDelegate = ctx =>
                ctx.Response.WriteAsync(ctx.Request.Headers[HeaderNames.Host]);
            var builder = new WebHostBuilder().Configure(app => app.Run(appDelegate));
            var server = new TestServer(builder);
            var client = server.CreateClient();
            
            var request = new HttpRequestMessage(HttpMethod.Get, "http://localhost:12345");
            request.Headers.Host = "otherhost:5678";
            var response = await client.SendAsync(request);
            var responseBody = await response.Content.ReadAsStringAsync();
                
            Assert.Equal("localhost:12345", responseBody);
        }

Expected: localhost:12345
Actual: localhost:12345,otherhost:5678

The Host is set from the Url here:

Hosting/src/Microsoft.AspNetCore.TestHost/ClientHandler.cs

Line 75 in 97c9510

req.Host = HostString.FromUriComponent(request.RequestUri);

But then the request headers are copied over here:

Hosting/src/Microsoft.AspNetCore.TestHost/ClientHandler.cs

Lines 90 to 93 in 97c9510

	foreach (var header in request.Headers)
	{
	req.Headers.Append(header.Key, header.Value.ToArray());
	}

This adds an invalid second Host rather than overwriting.

Recommendation:
Host looks like the only request header we set, all the others are request line fields (e.g. path, query, etc..), it should get special cased so only one ends up in the request. The one from HttpRequestMessage.Headers should win over the one in HttpRequestMessage.RequestUri.Host.

[nulltoken]

@Tratcher Would you mind if I tried and gave a try at fixing it?

[Tratcher]

Go for it.

[nulltoken]

Go for it.

@Tratcher Done. That was indeed a pretty easy fix. You wonderfully paved the way with your detailed explanation. Thanks a lot!

The only things that keeps on bugging me is that in my initial repro, not all the tests were failing. Only some of them.

Condering that ClientHandler.SendAsync() performs this normalization for each and every call, all the tests should fail, shouldn't they?

[Tratcher]

I don't have a good answer for that. The error wouldn't happen until the Uri was constructed, and only AI does that. Either that wasn't happening on some requests, or the error was being handled differently on some code paths.