internal static Task CopyToAsync(this Stream stream,
                                         Stream destination,
                                         int bufferSize,
                                         CancellationToken cancellationToken)
        {
            byte[] buffer    = new byte[bufferSize];
            int    bytesRead = 0;

            return(InternalExtensions.WhileAsync(() => {
                return stream.ReadAsync(buffer, 0, bufferSize, cancellationToken).OnSuccess(readTask => {
                    bytesRead = readTask.Result;
                    return bytesRead > 0;
                });
            }, () => {
                cancellationToken.ThrowIfCancellationRequested();
                return destination.WriteAsync(buffer, 0, bytesRead, cancellationToken)
                .OnSuccess(_ => cancellationToken.ThrowIfCancellationRequested());
            }));
        }
        public Task <Tuple <HttpStatusCode, string> > ExecuteAsync(HttpRequest httpRequest,
                                                                   IProgress <AVUploadProgressEventArgs> uploadProgress,
                                                                   IProgress <AVDownloadProgressEventArgs> downloadProgress,
                                                                   CancellationToken cancellationToken)
        {
            try
            {
                uploadProgress   = uploadProgress ?? new Progress <AVUploadProgressEventArgs>();
                downloadProgress = downloadProgress ?? new Progress <AVDownloadProgressEventArgs>();

                HttpMethod         httpMethod = new HttpMethod(httpRequest.Method);
                HttpRequestMessage message    = new HttpRequestMessage(httpMethod, httpRequest.Uri);

                // Fill in zero-length data if method is post.
                Stream data = httpRequest.Data;
                if (httpRequest.Data == null && httpRequest.Method.ToLower().Equals("post"))
                {
                    data = new MemoryStream(new byte[0]);
                }

                if (data != null)
                {
                    message.Content = new StreamContent(data);
                }

                if (httpRequest.Headers != null)
                {
                    foreach (var header in httpRequest.Headers)
                    {
                        if (HttpContentHeaders.Contains(header.Key))
                        {
                            message.Content.Headers.Add(header.Key, header.Value);
                        }
                        else
                        {
                            message.Headers.Add(header.Key, header.Value);
                        }
                    }
                }

                // Avoid aggressive caching on Windows Phone 8.1.
                message.Headers.Add("Cache-Control", "no-cache");
                message.Headers.IfModifiedSince = DateTimeOffset.UtcNow;

                // TODO: (richardross) investigate progress here, maybe there's something we're missing in order to support this.
                uploadProgress.Report(new AVUploadProgressEventArgs {
                    Progress = 0
                });

                return(client.SendAsync(message, HttpCompletionOption.ResponseHeadersRead, cancellationToken)
                       .ContinueWith(httpMessageTask =>
                {
                    var response = httpMessageTask.Result;

                    uploadProgress.Report(new AVUploadProgressEventArgs {
                        Progress = 1
                    });

                    return response.Content.ReadAsStreamAsync().ContinueWith(streamTask =>
                    {
                        var resultStream = new MemoryStream();
                        var responseStream = streamTask.Result;

                        int bufferSize = 4096;
                        byte[] buffer = new byte[bufferSize];
                        int bytesRead = 0;
                        long totalLength = -1;
                        long readSoFar = 0;

                        try
                        {
                            totalLength = responseStream.Length;
                        }
                        catch (NotSupportedException)
                        {
                        }

                        return InternalExtensions.WhileAsync(() =>
                        {
                            return responseStream.ReadAsync(buffer, 0, bufferSize, cancellationToken).OnSuccess(readTask =>
                            {
                                bytesRead = readTask.Result;
                                return bytesRead > 0;
                            });
                        }, () =>
                        {
                            cancellationToken.ThrowIfCancellationRequested();

                            return resultStream.WriteAsync(buffer, 0, bytesRead, cancellationToken).OnSuccess(_ =>
                            {
                                cancellationToken.ThrowIfCancellationRequested();
                                readSoFar += bytesRead;

                                if (totalLength > -1)
                                {
                                    downloadProgress.Report(new AVDownloadProgressEventArgs {
                                        Progress = 1.0 * readSoFar / totalLength
                                    });
                                }
                            });
                        }).ContinueWith(_ =>
                        {
                            responseStream.Dispose();
                            return _;
                        }).Unwrap().OnSuccess(_ =>
                        {
                            // If getting stream size is not supported, then report download only once.
                            if (totalLength == -1)
                            {
                                downloadProgress.Report(new AVDownloadProgressEventArgs {
                                    Progress = 1.0
                                });
                            }

                            // Assume UTF-8 encoding.
                            var resultAsArray = resultStream.ToArray();
                            var resultString = Encoding.UTF8.GetString(resultAsArray, 0, resultAsArray.Length);
                            resultStream.Dispose();
                            return new Tuple <HttpStatusCode, string>(response.StatusCode, resultString);
                        });
                    });
                }).Unwrap().Unwrap());
            }
            catch (Exception)
            {
                var localError = new Dictionary <string, object>();
                localError["error"] = "local error when build http request";
                var localErrorStr = Json.Encode(localError);
                return(Task.FromResult(new Tuple <HttpStatusCode, string>(HttpStatusCode.ExpectationFailed, localErrorStr)));
            }
        }
        public Task <Tuple <HttpStatusCode, string> > ExecuteAsync(HttpRequest httpRequest,
                                                                   IProgress <AVUploadProgressEventArgs> uploadProgress,
                                                                   IProgress <AVDownloadProgressEventArgs> downloadProgress,
                                                                   CancellationToken cancellationToken)
        {
            var request = HttpWebRequest.Create(httpRequest.Uri);

            request.Method = httpRequest.Method;
            cancellationToken.Register(() => request.Abort());
            uploadProgress   = uploadProgress ?? new Progress <AVUploadProgressEventArgs>();
            downloadProgress = downloadProgress ?? new Progress <AVDownloadProgressEventArgs>();

            // Fill in zero-length data if method is post.
            Stream data = httpRequest.Data;

            if (data == null && httpRequest.Method.ToLower().Equals("post"))
            {
                data = new MemoryStream(new byte[0]);
            }

            // Fill in the headers
            if (httpRequest.Headers != null)
            {
                foreach (var header in httpRequest.Headers)
                {
                    if (header.Key == "Content-Type")
                    {
                        // Move over Content-Type header into Content.
                        request.ContentType = header.Value;
                    }
                    else
                    {
                        request.Headers[header.Key] = header.Value;
                    }
                }
            }
            // Avoid aggresive caching on Windows Phone 8.1.
            request.Headers[HttpRequestHeader.CacheControl]    = "no-cache";
            request.Headers[HttpRequestHeader.IfModifiedSince] = DateTime.UtcNow.ToString();

            Task uploadTask = null;

            if (data != null)
            {
                Task copyTask    = null;
                long totalLength = -1;

                try {
                    totalLength           = data.Length;
                    request.ContentLength = totalLength;
                } catch (NotSupportedException) {
                }

                // If the length can't be determined, read it into memory first.
                if (totalLength == -1)
                {
                    var memStream = new MemoryStream();
                    copyTask = data.CopyToAsync(memStream).OnSuccess(_ => {
                        memStream.Seek(0, SeekOrigin.Begin);
                        totalLength           = memStream.Length;
                        request.ContentLength = totalLength;

                        data = memStream;
                    });
                }

                uploadProgress.Report(new AVUploadProgressEventArgs {
                    Progress = 0
                });

                uploadTask = copyTask.Safe().ContinueWith(_ => {
                    return(new TaskFactory <Stream>(cancellationToken).FromAsync(
                               request.BeginGetRequestStream,
                               request.EndGetRequestStream,
                               TaskCreationOptions.None));
                }).Unwrap()
                             .OnSuccess(t => {
                    var requestStream = t.Result;

                    int bufferSize = 4096;
                    byte[] buffer  = new byte[bufferSize];
                    int bytesRead  = 0;
                    long readSoFar = 0;

                    return(InternalExtensions.WhileAsync(() => {
                        return data.ReadAsync(buffer, 0, bufferSize, cancellationToken).OnSuccess(readTask => {
                            bytesRead = readTask.Result;
                            return bytesRead > 0;
                        });
                    }, () => {
                        cancellationToken.ThrowIfCancellationRequested();
                        return requestStream.WriteAsync(buffer, 0, bytesRead, cancellationToken).OnSuccess(_ => {
                            cancellationToken.ThrowIfCancellationRequested();
                            readSoFar += bytesRead;
                            uploadProgress.Report(new AVUploadProgressEventArgs {
                                Progress = 1.0 * readSoFar / totalLength
                            });
                        });
                    }).ContinueWith(_ => {
                        requestStream.Close();
                    }));
                }).Unwrap();
            }

            return(uploadTask.Safe().ContinueWith(_ => {
                return new TaskFactory <WebResponse>(cancellationToken).FromAsync(
                    request.BeginGetResponse,
                    request.EndGetResponse,
                    TaskCreationOptions.None);
            }).Unwrap()
                   .ContinueWith(t => {
                // Handle canceled
                cancellationToken.ThrowIfCancellationRequested();

                var resultStream = new MemoryStream();
                HttpWebResponse response = null;
                if (t.IsFaulted)
                {
                    if (t.Exception.InnerException is WebException)
                    {
                        var webException = t.Exception.InnerException as WebException;
                        response = (HttpWebResponse)webException.Response;
                    }
                    else
                    {
                        TaskCompletionSource <Tuple <HttpStatusCode, string> > tcs = new TaskCompletionSource <Tuple <HttpStatusCode, string> >();
                        tcs.TrySetException(t.Exception);

                        return tcs.Task;
                    }
                }
                else
                {
                    response = (HttpWebResponse)t.Result;
                }

                var responseStream = response.GetResponseStream();
                int bufferSize = 4096;
                byte[] buffer = new byte[bufferSize];
                int bytesRead = 0;
                long totalLength = -1;
                long readSoFar = 0;

                try {
                    totalLength = responseStream.Length;
                } catch (NotSupportedException) {
                }

                return InternalExtensions.WhileAsync(() => {
                    return responseStream.ReadAsync(buffer, 0, bufferSize, cancellationToken).OnSuccess(readTask => {
                        bytesRead = readTask.Result;
                        return bytesRead > 0;
                    });
                }, () => {
                    cancellationToken.ThrowIfCancellationRequested();

                    return resultStream.WriteAsync(buffer, 0, bytesRead, cancellationToken).OnSuccess(_ => {
                        cancellationToken.ThrowIfCancellationRequested();
                        readSoFar += bytesRead;

                        if (totalLength > -1)
                        {
                            downloadProgress.Report(new AVDownloadProgressEventArgs {
                                Progress = 1.0 * readSoFar / totalLength
                            });
                        }
                    });
                }).ContinueWith(_ => {
                    responseStream.Close();

                    // If getting stream size is not supported, then report download only once.
                    if (totalLength == -1)
                    {
                        downloadProgress.Report(new AVDownloadProgressEventArgs {
                            Progress = 1.0
                        });
                    }

                    // Assume UTF-8 encoding.
                    var resultAsArray = resultStream.ToArray();
                    var resultString = Encoding.UTF8.GetString(resultAsArray, 0, resultAsArray.Length);
                    resultStream.Close();
                    return new Tuple <HttpStatusCode, string>(response.StatusCode, resultString);
                });
            }).Unwrap());
        }