Self-hosted HttpListener gets empty file collection and input stream for multipart PUT or POST requests

[BenLubar]

Steps to Reproduce

1. Build MonoMultipartRepro in Visual Studio.
2. Run MonoMultipartRepro.exe

Current Behavior

Program outputs:

files: 0

(on Mono)

Expected Behavior

Program outputs:

files: 1

(which it does on Microsoft's implementation of .NET)

On which platforms did you notice this

[ ] macOS
[x] Linux
[ ] Windows

(only tested on Linux Mono)

Version Used:

(Docker)

Mono JIT compiler version 5.4.1.6 (tarball Wed Nov  8 20:37:24 UTC 2017)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
        TLS:           __thread
        SIGSEGV:       altstack
        Notifications: epoll
        Architecture:  amd64
        Disabled:      none
        Misc:          softdebug 
        LLVM:          supported, not enabled.
        GC:            sgen (concurrent by default)

Stacktrace

(no stack trace as there is no exception thrown)

[akoeplinger]

@BenLubar can you reproduce this without System.Web as well, i.e. just a console app that uses an HttpListener?

[BenLubar]

using System;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

namespace MonoMultipartRepro2
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var listener = new HttpListener())
            {
                listener.Prefixes.Add("http://127.0.0.1:8123/");
                listener.Start();

                var task = Task.Run(async () =>
                {
                    using (var client = new HttpClient())
                    using (var content = new MultipartFormDataContent())
                    {
                        content.Add(new StringContent("Hello, World!", Encoding.UTF8, "text/plain"), "foo", "foo.txt");

                        using (var response = await client.PostAsync("http://127.0.0.1:8123/", content))
                        {
                            return await response.Content.ReadAsStringAsync();
                        }
                    }
                });

                var context = listener.GetContext();
                context.Request.InputStream.CopyTo(context.Response.OutputStream);
                context.Response.OutputStream.Close();
                context.Response.Close();

                Console.WriteLine(task.Result);
            }
        }
    }
}

Output on Windows (Microsoft .NET 4.5.2 implementation):

--0579ebb2-17f2-40f5-9b97-258c0a82bd40
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name=foo; filename=foo.txt; filename*=utf-8''foo.txt

Hello, World!
--0579ebb2-17f2-40f5-9b97-258c0a82bd40--

Output on Linux (Docker, mono version listed above):

--9106158a-072a-4012-b903-6d91a5919a6a
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name=foo; filename=foo.txt; filename*=utf-8''foo.txt

Hello, World!
--9106158a-072a-4012-b903-6d91a5919a6a--

So this is a System.Web problem.

[akoeplinger]

Ok good to know. Unfortunately we don't have a lot of resources to spend on System.Web so you might want to take a look at the sources yourself to figure out the problem.

[BenLubar]

The problem is here:

mono/mcs/class/System.Web/System.Web/HttpRequest.cs

Lines 2069 to 2101 in 4b8e0be

	static string GetContentDispositionAttribute (string l, string name)
	{
	int idx = l.IndexOf (name + "=\"");
	if (idx < 0)
	return null;
	int begin = idx + name.Length + "=\"".Length;
	int end = l.IndexOf ('"', begin);
	if (end < 0)
	return null;
	if (begin == end)
	return "";
	return l.Substring (begin, end - begin);
	}
	string GetContentDispositionAttributeWithEncoding (string l, string name)
	{
	int idx = l.IndexOf (name + "=\"");
	if (idx < 0)
	return null;
	int begin = idx + name.Length + "=\"".Length;
	int end = l.IndexOf ('"', begin);
	if (end < 0)
	return null;
	if (begin == end)
	return "";
	string temp = l.Substring (begin, end - begin);
	byte [] source = new byte [temp.Length];
	for (int i = temp.Length - 1; i >= 0; i--)
	source [i] = (byte) temp [i];
	return encoding.GetString (source);
	}

The code incorrectly assumes that Content-Disposition headers are double-quoted, so the header generated by System.Net.Http is considered invalid:

Content-Disposition: form-data; name=foo; filename=foo.txt; filename*=utf-8''foo.txt

The Microsoft reference source for the equivalent method is here: http://referencesource.microsoft.com/#System.Web/MultipartContentParser.cs,143

Removing the quote characters from the two "=\"" strings and replacing the int end = ... lines in the two functions above with this should work:

            int end;
            if (l.Length > begin && l[begin] == '"') {
                begin++;
                end = l.IndexOf ('"', begin);
            } else {
                end = l.IndexOf (';', begin);
                if (end == -1)
                    end = l.Length;
            }

[akoeplinger]

awesome, would you mind sending a pull request?