Bug 2970 - System.Net.WebClient.UploadFileAsync is broken
Summary: System.Net.WebClient.UploadFileAsync is broken
Status: RESOLVED FIXED
Alias: None
Product: Android
Classification: Xamarin
Component: BCL Class Libraries ()
Version: 4.0
Hardware: Other Other
: --- normal
Target Milestone: ---
Assignee: Bugzilla
URL:
Depends on:
Blocks:
 
Reported: 2012-01-19 11:06 UTC by info
Modified: 2012-01-19 12:25 UTC (History)
2 users (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
RESOLVED FIXED

Description info 2012-01-19 11:06:16 UTC
The Mono implementation of the WebClient.UploadFileAsync() method falsely wraps the uploaded data with a form data encoding header and trailer. For example:

--------------8cea4d9249390f8
Content-Disposition: form-data; name="file"; filename="Android.sub"
Content-Type: application/octet-stream

[...actual file data...]

--------------8cea4d9249390f8--

Instead it must send the raw file data without any header or trailer, just like the real Windows .NET Framework 2.0 implementation does. By adding the header and trailer existing Windows file uploading code actually corrupts files when uploading from Mono for Android.

BTW: I also tried this same with MonoTouch, which makes exactly the same mistake like Mono for Android.
Comment 1 Gonzalo Paniagua Javier 2012-01-19 11:38:42 UTC
This is not a bug.

The following program:
---------------

using System;
using System.Net;
using System.Threading;

class Test {
	static void Main ()
	{
		ManualResetEvent evt = new ManualResetEvent (false);
		WebClient wc = new WebClient ();
		wc.UploadFileCompleted +=  new UploadFileCompletedEventHandler (CB);
		wc.UploadFileAsync (new Uri ("http://127.0.0.1:9000/"), "POST", "uploadfile.cs", evt);
		evt.WaitOne ();
	}

	static void CB (object sender, UploadFileCompletedEventArgs e)
	{
		if (!e.Cancelled && e.Error == null) {
			Console.WriteLine ("File uploaded");
		} else {
			Console.WriteLine ("Something went wrong");
			Console.WriteLine (e.Error);
		}
		((ManualResetEvent) e.UserState).Set ();

	}
}
--------------

when run under MS.NET has this at the beginning of the body:
 -----------------------8cea4b4aff65c6b
 Content-Disposition: form-data; name="file"; filename="uploadfile.cs"
 Content-Type: application/octet-stream

The same program run using Mono yields:
--------------8cea4b552ea3188
Content-Disposition: form-data; name="file"; filename="uploadfile.cs"
Content-Type: application/octet-stream

Perhaps what you want is more like:
   file.ReadAllBytes ("yourfile");
   wc.UploadData (...).
Comment 2 Gonzalo Paniagua Javier 2012-01-19 12:25:57 UTC
Turns out that using "PUT" instead of "POST" sends the file as-is without headers.

The fix is in master/c621b27 and will soon be backported to mono-2-10, where Mono for Android and MonoTouch will pick it up.

Thanks!