Transferring raw bytes over http using the ASP.Net WebAPI 2

Question

I have a very simple ASP.Net WebAPI 2 method that I hoped would send a small array of bytes over HTTP:

[Route("api/assemblybytes")]
public byte[] GetAssemblyBytes()
{
    //byte[] bytes = null;
    //if (File.Exists("BasePCBScreenAssembly.dll"))
    //{
    //    using (var fs = File.Open("BasePCBScreenAssembly.dll", FileMode.Open, FileAccess.Read))
    //    {
    //        fs.Read(bytes, 0, (int)fs.Length);
    //    }
    //}
    //return bytes;
    return new byte[] { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20 };
}

To test the function I have replaced the intended code (commented out in the above) with a simple array containing the byte 0x20 seven times. To test my code I have a simple web page:

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>Assembly Distribution WebAPI Test Page</title>
    <script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-2.0.3.min.js"></script>
    <script>
        var uri = 'api/assemblybytes';
        $(document).ready(function () {
            $.getJSON(uri)
                .done(function (data) {
                    var bytes = [];
                    for (var i = 0; i < data.length; ++i) {
                        bytes.push(data.charCodeAt(i));
                    }
                    $('#AssemblyBytes').text(bytes)
                });
        });
    </script>
</head>
<body>
    <div>
        <h2>GetAssemblyBytes</h2>
        <pre id='AssemblyBytes'/>
    </div>
</body>
</html>

I was hoping to use the web page to see what bytes or text were added to the beginning or the end of the byte array. But instead I see this and the bytes returned to the web page:

73,67,65,103,73,67,65,103,73,65,61,61

So my 0x20 (32 in decimal) does not even show up once.

(N.B. This may seem a contrived example. The actual client will not be a web page but a .Net Micro Framework embedded device that will (I hope) download small dynamic assemblies as byte arrays from the WebAPI.)

What have I got wrong or omitted? What is the best way to transfer an array of bytes over HTTP using the ASP.Net WebAPI?

Anyone who lands wanting to return the bytes via a stream via web api and IHTTPActionResult then see here: nodogmablog.bryanhogan.net/2017/02/… — IbrarMumtaz
– IbrarMumtaz, Commented Nov 7, 2017 at 13:01

Cory Nelson · Accepted Answer · 2014-01-25 07:48:36Z

6

If you do not return a HttpResponseMessage, WebAPI will serialize the value into some format (JSON, XML, etc.) depending on Accept headers and installed media type formatters.

To send raw data:

HttpResponseMessage res = CreateResponse(HttpStatusCode.OK);
res.Content = new ByteArrayContent(bytes);
return res;

Or, since you have a Stream:

HttpResponseMessage res = CreateResponse(HttpStatusCode.OK);
res.Content = new StreamContent(File.Open(...));
return res;

answered Jan 25, 2014 at 7:48

Cory Nelson

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2 Comments

dumbledad Over a year ago

This works, thanks. I had to change CreateResponse to Request.CreateResponse. One odd thing is that although the bytes make it through I can only pick them up in getJSON's .fail function as it throws a parse error

dumbledad Over a year ago

Ah, of course. The parse failure is because the $.getJSON jquery function expects to receive ... JSON! Doh.

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