Rockford Lhotka

VP, Open Source Creator, Author, Speaker

Posting binary data using HttpClient on Android

18 Apr 2024

There is an issue folks have encountered when using the .NET HttpClient service to do a POST to an ASP.NET Core controller, where the payload of the post is binary data.

For example:

      var client = new HttpClient();
      var content = new ByteArrayContent(serialized);
      var httpResponse = await client.PostAsync(
        "<server url>",

The result is an exception: Unable to read beyond end of stream

It turns out that the problem is that the default HttpClient configuration on Android sends the data over the network with the wrong HTTP Content-Type header.

The Content-Type should be either application/octet-stream or left off completely since that is the default.

Instead, what is sent is application/x-www-form-urlencoded. Totally invalid in this context.

As a result, the ASP.NET Core server doesn’t properly handle the binary payload, because it is following the instructions based on the incorrect Content-Type header.

How do you solve this?

Configure the HttpClient service differently on the client:

  var client = new HttpClient(new SocketsHttpHandler()));

The SocketsHttpHandler properly handles the ByteArrayContent content object and sends the correct header to the server.

Because I think this is a bug in the default HttpClient implementation on Android, I’ve filed a bug:

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