使用 HttpWebRequest 流式传输大文件时出现内存不足异常

Question

使用大文件的 Http.Put 时出现内存不足异常。我正在使用代码中显示的异步模型。我正在尝试将 8K 数据块发送到 Windows 2008 R2 服务器。当我尝试写入超过 536,868,864 字节的数据块时，始终会发生异常。异常发生在下面代码 sn-p 中的 requestStream.Write 方法上。

寻找原因？

注意：较小的文件可以放置。如果我写入本地 FileStream，逻辑也可以工作。在 Win 7 Ultimate 客户端计算机上运行 VS 2010、.Net 4.0。

   HttpWebRequest request = (HttpWebRequest)WebRequest.Create("Http://website/FileServer/filename");
   request.Method = WebRequestMethods.Http.Put;
   request.SendChunked = true;
   request.AllowWriteStreamBuffering = true;
   ...

   request.BeginGetRequestStream( new AsyncCallback(EndGetStreamCallback), state);
   ...

   int chunk = 8192; // other values give same result
   ....

   private static void EndGetStreamCallback(IAsyncResult ar) {
        long limit = 0;
        long fileLength;
        HttpState state = (HttpState)ar.AsyncState;

        Stream requestStream = null;
        // End the asynchronous call to get the request stream.

        try {
            requestStream = state.Request.EndGetRequestStream(ar);
            // Copy the file contents to the request stream.

            FileStream stream = new FileStream(state.FileName, FileMode.Open, FileAccess.Read, FileShare.None, chunk, FileOptions.SequentialScan);

            BinaryReader binReader = new BinaryReader(stream);
            fileLength = stream.Length;

            // Set Position to the beginning of the stream.
            binReader.BaseStream.Position = 0;

            byte[] fileContents = new byte[chunk];

            // Read File from Buffer 
            while (limit < fileLength)
            {
                fileContents = binReader.ReadBytes(chunk);

                // the next 2 lines attempt to write to network and server
                requestStream.Write(fileContents, 0, chunk);   // causes Out of memory after 536,868,864 bytes
                requestStream.Flush();  // I get same result with or without Flush

                limit += chunk;
            }

            // IMPORTANT: Close the request stream before sending the request.
            stream.Close();

            requestStream.Close();
        }
    }

Answer 1

你显然有this documented problem。当AllowWriteStreamBuffering 为true 时，它会缓冲写入请求的所有数据！所以，“解决方案”是将该属性设置为false：

要解决此问题，请将 HttpWebRequest.AllowWriteStreamBuffering 属性设置为 false。