使用HttpClient将文件上传到ASP.NET WebApi 2

Question

I have this HttpClient for posting files:

var content = new MultipartFormDataContent(Guid.NewGuid().ToString())
{
    new StringContent(JsonConvert.SerializeObject(parameters), Encoding.UTF8, "application/json")
};

foreach (var file in files)
{
    var byteContent = new ByteArrayContent(file.Data);

    content.Add(byteContent, file.FieldName, file.FileName);
}

return await _client.PostAsync(_apiUrl + apiRelativeUrl, content);

But my ASP.NET WebApi Controller gives error 500 with this exception:

System.IO.IOException: Unexpected end of MIME multipart stream. MIME multipart message is not complete.

The WebApi controller code is

if (Request.Content.IsMimeMultipartContent())
{
    var multipart = await Request.Content.ReadAsMultipartAsync(); //this line throws the exception
    var fileContent = multipart.Contents.FirstOrDefault();

    if (fileContent != null)
    {
        var photo = await fileContent.ReadAsByteArrayAsync();
    }
}

What am I doing wrong?

Answer 1

Basically I used a custom stream to append the newline that asp.net web api is expecting.

Stream reqStream = Request.Content.ReadAsStreamAsync().Result;
MemoryStream tempStream = new MemoryStream();
reqStream.CopyTo(tempStream);



tempStream.Seek(0, SeekOrigin.End);
StreamWriter writer = new StreamWriter(tempStream);
writer.WriteLine();
writer.Flush();
tempStream.Position = 0;


 StreamContent streamContent = new StreamContent(tempStream);
 foreach(var header in Request.Content.Headers)
 {
     streamContent.Headers.Add(header.Key, header.Value);
 }

// Read the form data and return an async task.
 await streamContent.ReadAsMultipartAsync(provider);

and add following code in web.config

<system.web>
    <httpRuntime maxRequestLength="30000000" />
</system.web>

<system.webServer>
    <security>
      <requestFiltering>
        <requestLimits maxAllowedContentLength="30000000" />
      </requestFiltering>
    </security>
</system.webServer>

Hope this helps.

Answer 2

Try add header of the files type you upload like this:

 byteContent.Headers.ContentType =
            MediaTypeHeaderValue.Parse("image/jpeg");

This works fine for me.

Answer 3

I created two new empty projects, one for webapi and one for httpclient.

I tried copying the existing client code and the existing server code to the new projects.

I discovered that the problem was the parameter to the webapi action, it seems to broke the stream.

So if someone need to upload multipart form data to ASP.NET WebApi don't use parameters in the action, it won't resolve any model and it broke the multipart stream.