Question

我需要在ResourceIntensiveTask中发布一个5MB的文件，其中操作系统设置的最大内存使用量为5MB。因此，尝试直接从存储流式传输文件，但与HttpWebRequest关联的Stream的大小不断增长。这是代码：

        public void writeStream(Stream writer, string filesource, string filename)
        {
            var store = System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForApplication();
            var f = store.OpenFile(filesource, FileMode.Open, FileAccess.Read);
            store.Dispose();

            byte[] buffer = Encoding.UTF8.GetBytes(String.Format(@"Content-Disposition: form-data; name=""file""; filename=""{0}""\n", filename));
            writer.Write(buffer, 0, buffer.Length);

            buffer = Encoding.UTF8.GetBytes("Content-Type: application/octet-stream\n");
            writer.Write(buffer, 0, buffer.Length);

            long initialMemory = Microsoft.Phone.Info.DeviceStatus.ApplicationCurrentMemoryUsage;

            buffer = new byte[2048]; 
            int DataRead = 0;
            do
            {
                DataRead = f.Read(buffer, 0, 2048);
                if (DataRead > 0)
                {
                    writer.Write(buffer, 0, DataRead);
                    Array.Clear(buffer, 0, 2048);
                }
            } while (DataRead > 0);

            double increasedMemory = ((double)Microsoft.Phone.Info.DeviceStatus.ApplicationCurrentMemoryUsage - initialMemory) / 1000000;                

            buffer = Encoding.UTF8.GetBytes("\n--" + boundary + "\n--");
            writer.Write(buffer, 0, buffer.Length);
            writer.Flush();
        }

increaseMemory 调试变量用于在读取文件和传输到HttpWebRequest之前和之后获取差异内存，并且它几乎提供了文件的确切大小（5MB），这意味着该过程内存增加了5MB。

我也将 AllowReadStreamBuffering = false设置为HttpWebRequest。

如何保持记忆力低？内存使用限制为5MB时如何上传大文件？

Answer 1

问题是，如果无法关闭写缓冲，则在关闭请求流（使用WireShark验证）之后调用BeginGetResponse()之前甚至不会建立与服务器的连接。

我能想到解决这个问题的唯一方法就是直接使用套接字（尽管如果使用SSL连接会更复杂）。

此代码适用于我，并且在向服务器发送数据时不会增加内存使用量。我没有在后台任务中测试它，但没有看到它不起作用的任何原因。

Socket _socket;
const int BUFFERSIZE = 4096;
byte[] writebuffer = new byte[BUFFERSIZE];
string hostName = "www.testdomain.com";
string hostPath = "/test/testupload.aspx";
IsolatedStorageFileStream isoFile;


public void SocketPOST(string hostName, string filesource)
{
    using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication())
    {
        if (store.FileExists(filesource))
        {
            isoFile = store.OpenFile(filesource, FileMode.Open, FileAccess.Read);
        }
    }

    _socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    _socket.SetNetworkRequirement(NetworkSelectionCharacteristics.NonCellular);

    SocketAsyncEventArgs socketEventArg = new SocketAsyncEventArgs();
    socketEventArg.RemoteEndPoint = new DnsEndPoint(hostName, 80);
    socketEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(Socket_Completed);

    _socket.ConnectAsync(socketEventArg);
}


private void Socket_Completed(object sender, SocketAsyncEventArgs e)
{
    if (e.SocketError == SocketError.Success)
    {
        switch (e.LastOperation)
        {
            case SocketAsyncOperation.Connect:   // Connected so started sending data, headers first

                if (e.ConnectSocket.Connected)
                {
                    StringBuilder sbHeaders = new StringBuilder("POST " + hostPath + " HTTP/1.1\r\n");
                    sbHeaders.Append("HOST: " + hostName + "\r\n");
                    sbHeaders.Append("USER-AGENT: MyWP7App/1.0\r\n");
                    sbHeaders.Append("Content-Type: text/plain; charset=\"utf-8\"\r\n");
                    sbHeaders.Append("Content-Length: " + isoFile.Length.ToString() + "\r\n\r\n");

                    byte[] headerBuffer = Encoding.UTF8.GetBytes(sbHeaders.ToString());
                    e.SetBuffer(headerBuffer, 0, headerBuffer.Length);

                    if (!e.ConnectSocket.SendAsync(e)) Socket_Completed(e.ConnectSocket, e);
                }

                break;

            case SocketAsyncOperation.Send:
            case SocketAsyncOperation.SendTo:   // Previous buffer sent so send next one if stream not finished

                Array.Clear(writebuffer, 0, BUFFERSIZE);

                int DataRead = 0;

                DataRead = isoFile.Read(writebuffer, 0, BUFFERSIZE);
                if (DataRead > 0)
                {
                    e.SetBuffer(writebuffer, 0, DataRead);
                    if (!_socket.SendAsync(e)) Socket_Completed(e.ConnectSocket, e);
                }
                else
                {
                    isoFile.Dispose();
                    if (!_socket.ReceiveAsync(e)) Socket_Completed(e.ConnectSocket, e);
                }

                break;

            case SocketAsyncOperation.Receive:
            case SocketAsyncOperation.ReceiveFrom:

                if (e.BytesTransferred > 0)
                {
                    string response = Encoding.UTF8.GetString(e.Buffer, e.Offset, e.BytesTransferred).Trim('\0');

                    // Check response if necessary 

                    e.ConnectSocket.Shutdown(SocketShutdown.Both);
                    e.ConnectSocket.Dispose();
                }

                break;

            default:
                break;
        }

    }
}

注意：我已经离开了很多错误处理以保持示例简短。

SSL注意：由于SSL在TCP级别工作且WP7当前不支持SSL套接字（SslStream），因此您需要自己处理证书握手，密码交换等在套接字上设置SSL连接，然后使用约定的算法加密发送的所有内容（并解密收到的所有内容）。使用Bouncy Castle API取得了一些成功，因此可以实现（请参阅this博文）。

Answer 2

我注意到一件事：你忘了处理f！

我个人会使用这样的代码：

public void writeStream(Stream writer, string filesource, string filename)
{
    using (var store = System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForApplication())
    {
        long initialMemory = Microsoft.Phone.Info.DeviceStatus.ApplicationCurrentMemoryUsage;

        using (var f = store.OpenFile(filesource, FileMode.Open, FileAccess.Read))
        {
            byte[] buffer = Encoding.UTF8.GetBytes(string.Format(@"Content-Disposition: form-data; name=""file""; filename=""{0}""\n", filename));
            writer.Write(buffer, 0, buffer.Length);

            buffer = Encoding.UTF8.GetBytes("Content-Type: application/octet-stream\n");
            writer.Write(buffer, 0, buffer.Length);

            buffer = new byte[2048];
            int DataRead = 0;

            do
            {
                DataRead = f.Read(buffer, 0, 2048);
                if (DataRead > 0)
                {
                    writer.Write(buffer, 0, DataRead);
                }
            } while (DataRead > 0);

            buffer = Encoding.UTF8.GetBytes("\n--" + boundary + "\n--");
            writer.Write(buffer, 0, buffer.Length);
            writer.Flush();
        }

        double increasedMemory = ((double)Microsoft.Phone.Info.DeviceStatus.ApplicationCurrentMemoryUsage - initialMemory) / 1000000;
    }
}

似乎缺少boundary var，因此编码错误仍然存在！

后台代理/ HttpWebRequest流缓冲区上的发布文件不断增长？

2 个答案: