Try something like this:
I faced same issue. I fixed it by implementing custom `HttpContent`. I use this object to track percentage of upload progress, you can add an event to and listen it. You should customize `SerializeToStreamAsync` method.
internal class ProgressableStreamContent : HttpContent { private const int defaultBufferSize = 4096;
private Stream content; private int bufferSize; private bool contentConsumed; private Download downloader;
public ProgressableStreamContent(Stream content, Download downloader) : this(content, defaultBufferSize, downloader) {}
public ProgressableStreamContent(Stream content, int bufferSize, Download downloader) { if(content == null) { throw new ArgumentNullException("content"); } if(bufferSize <= 0) { throw new ArgumentOutOfRangeException("bufferSize"); }
this.content = content; this.bufferSize = bufferSize; this.downloader = downloader; } protected override Task SerializeToStreamAsync(Stream stream, TransportContext context) { Contract.Assert(stream != null);
PrepareContent();
return Task.Run(() => { var buffer = new Byte[this.bufferSize]; var size = content.Length; var uploaded = 0;
downloader.ChangeState(DownloadState.PendingUpload);
using(content) while(true) { var length = content.Read(buffer, 0, buffer.Length); if(length <= 0) break;
downloader.Uploaded = uploaded += length;
stream.Write(buffer, 0, length);
downloader.ChangeState(DownloadState.Uploading); }
downloader.ChangeState(DownloadState.PendingResponse); }); }
protected override bool TryComputeLength(out long length) { length = content.Length; return true; }
protected override void Dispose(bool disposing) { if(disposing) { content.Dispose(); } base.Dispose(disposing); }

private void PrepareContent() { if(contentConsumed) { // If the content needs to be written to a target stream a 2nd time, then the stream must support // seeking (e.g. a FileStream), otherwise the stream can't be copied a second time to a target // stream (e.g. a NetworkStream). if(content.CanSeek) { content.Position = 0; } else { throw new InvalidOperationException("SR.net_http_content_stream_already_read"); } }
contentConsumed = true; } }
****
Refer :
- https://github.com/paulcbetts/ModernHttpClient/issues/80 - https://stackoverflow.com/questions/21130362/progress-bar-for-httpclient-uploading - https://forums.xamarin.com/discussion/18649/best-practice-to-upload-image-selected-to-a-web-api

I faced same issue. I fixed it by implementing custom `HttpContent`. I use this object to track percentage of upload progress, you can add an event to and listen it. You should customize `SerializeToStreamAsync` method.
internal class ProgressableStreamContent : HttpContent { private const int defaultBufferSize = 4096;
private Stream content; private int bufferSize; private bool contentConsumed; private Download downloader;
public ProgressableStreamContent(Stream content, Download downloader) : this(content, defaultBufferSize, downloader) {}
public ProgressableStreamContent(Stream content, int bufferSize, Download downloader) { if(content == null) { throw new ArgumentNullException("content"); } if(bufferSize <= 0) { throw new ArgumentOutOfRangeException("bufferSize"); }
this.content = content; this.bufferSize = bufferSize; this.downloader = downloader; } protected override Task SerializeToStreamAsync(Stream stream, TransportContext context) { Contract.Assert(stream != null);
PrepareContent();
return Task.Run(() => { var buffer = new Byte[this.bufferSize]; var size = content.Length; var uploaded = 0;
downloader.ChangeState(DownloadState.PendingUpload);
using(content) while(true) { var length = content.Read(buffer, 0, buffer.Length); if(length <= 0) break;
downloader.Uploaded = uploaded += length;
stream.Write(buffer, 0, length);
downloader.ChangeState(DownloadState.Uploading); }
downloader.ChangeState(DownloadState.PendingResponse); }); }
protected override bool TryComputeLength(out long length) { length = content.Length; return true; }
protected override void Dispose(bool disposing) { if(disposing) { content.Dispose(); } base.Dispose(disposing); }

private void PrepareContent() { if(contentConsumed) { // If the content needs to be written to a target stream a 2nd time, then the stream must support // seeking (e.g. a FileStream), otherwise the stream can't be copied a second time to a target // stream (e.g. a NetworkStream). if(content.CanSeek) { content.Position = 0; } else { throw new InvalidOperationException("SR.net_http_content_stream_already_read"); } }
contentConsumed = true; } }

----------
Just for reference:
public interface IDownload { event EventHandler<DownloadStateEventArgs> StateChanged; event EventHandler<DownloadStateEventArgs> Completed; DownloadState State { get; } Guid Id { get; } string Uri { get; } long Filesize { get; } long Downloaded { get; } Task DownloadAsync(); }