Uploading HTTP progress tracking

Question

I\'ve got WPF application I\'m writing that posts files to one of social networks. Upload itself working just fine, but I\'d like to provide some indication of how far along

Answer 1

This one has been bugging me for at least one day. I have started with using WebClient.UploadFileAsync, next tried the ProgressMessageHandler for HttpClient then rolled my own HttpContent for the HttpClient API. None of those approaches worked (for me).

It appears HttpWebRequest, which sits at the bottom of most (all?) .NET Http abstraction like WebClient and HttpClient, buffers the request and response stream by default, which I confirmed by looking at it in ILSpy.

As others have noted, you can make your request use chunked encoding one way or another which will effectively disable buffering the request stream, but still this is not going to fix the progress reporting.

I found that it was necessary to flush the request stream after each block that I send in order to accurately reflect sending progress, or else your data will simply be buffered one step further down the pipeline (probably somewhere in NetworkStream or OS, didn't check). The sample code below works for me and also does a minimalistic job at translating back from a HttpWebResponse to HttpResponseMessage (which you may not need, YMMV).

public async Task UploadFileAsync( string uploadUrl, string absoluteFilePath, Action progressPercentCallback )
    {
        var length = new FileInfo( absoluteFilePath ).Length;

        var request = new HttpWebRequest( new Uri(uploadUrl) ) {
            Method = "PUT",
            AllowWriteStreamBuffering = false,
            AllowReadStreamBuffering = false,
            ContentLength = length
        };

        const int chunkSize = 4096;
        var buffer = new byte[chunkSize];

        using (var req = await request.GetRequestStreamAsync())
        using (var readStream = File.OpenRead(absoluteFilePath))
        {
            progressPercentCallback(0);
            int read = 0;
            for (int i = 0; i < length; i += read)
            {
                read = await readStream.ReadAsync( buffer, 0, chunkSize );
                await req.WriteAsync( buffer, 0, read );
                await req.FlushAsync(); // flushing is required or else we jump to 100% very fast
                progressPercentCallback((int)(100.0 * i / length));
            }
            progressPercentCallback(100);
        }

        var response = (HttpWebResponse)await request.GetResponseAsync();
        var result = new HttpResponseMessage( response.StatusCode );
        result.Content = new StreamContent( response.GetResponseStream() );

        return result; 
    }