使用 PushStreamContent 从 HTTPClient 上传

Question

我想将大量数据从客户端机器上传到网络服务器。我直接跳到 PushStreamContent，这样我就可以直接写入流，因为结果的大小各不相同，而且可能相当大。

流程如下：

User runs query > Reader Ready Event Fires > Begin Upload

一旦 ready 事件被触发，监听器就会拾取它并迭代结果集，将数据作为多部分表单上传：

Console.WriteLine("Query ready, uploading");
        byte[] buffer = new byte[1024], form = new byte[200];
        int offset = 0, byteCount = 0;
        StringBuilder rowBuilder = new StringBuilder();
        string builderS;
        var content = new PushStreamContent(async (stream, httpContent, transportContext) =>
        //using (System.IO.Stream stream = new System.IO.FileStream("test.txt", System.IO.FileMode.OpenOrCreate))
        {
            int bytes = 0;
            string boundary = createFormBoundary();
            httpContent.Headers.Remove("Content-Type");
            httpContent.Headers.TryAddWithoutValidation("Content-Type", "multipart/form-data; boundary=" + boundary);
            await stream.WriteAsync(form, 0, form.Length);
            form = System.Text.Encoding.UTF8.GetBytes(createFormElement(boundary, "file"));
            await stream.WriteAsync(form, 0, form.Length);
            await Task.Run(async () =>
            {
                foreach (var row in rows)
                {
                    for (int i = 0; i < row.Length; i++)
                    {
                        rowBuilder.Append(row[i].Value);
                        if (i + 1 < row.Length)
                            rowBuilder.Append(',');
                        else
                        {
                            rowBuilder.Append("\r\n");
                        }
                    }
                    builderS = rowBuilder.ToString();
                    rowBuilder.Clear();
                    byteCount = System.Text.Encoding.UTF8.GetByteCount(builderS);
                    bytes += byteCount;
                    if (offset + byteCount > buffer.Length)
                    {
                        await stream.WriteAsync(buffer, 0, offset);
                        offset = 0;
                        if (byteCount > buffer.Length)
                        {
                            System.Diagnostics.Debug.WriteLine("Expanding buffer to {0} bytes", byteCount);
                            buffer = new byte[byteCount];
                        }
                    }
                    offset += System.Text.Encoding.UTF8.GetBytes(builderS, 0, builderS.Length, buffer, offset);
                }
            });
            await stream.WriteAsync(buffer, 0, offset);
            form = System.Text.Encoding.UTF8.GetBytes(boundary);
            await stream.WriteAsync(form, 0, form.Length);
            await stream.FlushAsync(); //pretty sure this does nothing
            System.Diagnostics.Debug.WriteLine("Wrote {0}.{1} megabytes of data", bytes / 1000000, bytes % 1000000);

如果我是服务器，我认为上面的代码会很好用，只需添加 stream.Close(); 即可完成它，但是由于我是这里的客户端，因此关闭它会导致错误 (TaskCancelled)。等待读取也不做任何事情，我认为是因为 PushStreamContent 不会结束请求，除非我明确关闭流。话虽如此，写入文件会产生我期望上传的内容，因此一切都可以完美写入。

关于我可以在这里做什么的任何想法？我可能完全滥用了PushStreamContent，但似乎这应该是一个合适的用例。

Answer 1

所以这个解决方案一开始有点令人困惑，但它似乎是有道理的，也许更重要的是，它有效：

using(var content = new MultipartFormDataContent()) 
{
  var pushContent = new PushStreamContent(async (stream, httpContent, transportContext) =>
  { 
    //do the stream writing stuff
    stream.Close();
  });
  content.add(pushContent);
  //post, put, etc. content here
}

之所以有效，是因为传递给PushStreamContent 方法的流不是实际的请求流，而是由HttpClient 处理的流，就像向请求流中添加文件一样。因此，关闭它表示 HttpContent 的这部分输入的结束，并允许最终确定请求。