.net - 为什么我的客户端套接字没有收到我的服务器套接字发送的内容？

Question

使用阻塞流式传输 .NET socket我正在连接到服务器。每当我读取少量数据时，一切顺利，数据被接收到我的缓冲区中:

using (var socket = new Socket(SocketType.Stream, ProtocolType.IP))
{
    socket.Connect(IPAddress.Parse("127.0.0.1"), 5000);

    byte[] buffer = new byte[BufferSize];

    socket.Receive(buffer);

    // Here buffer doesn't always contain all data the server sent me?
    Console.WriteLine(Encoding.Default.GetString(buffer));
}

但在某些情况下，我没有收到服务器发送给我的所有内容。数据似乎被切断了。这可能是什么原因？

Answer 1

这是documented in the Receive() method ，强调我的:

The Receive method reads data into the buffer parameter and returns the number of bytes successfully read. You can call Receive from both connection-oriented and connectionless sockets.

忽略返回值时，您将不知道缓冲区的哪一部分实际包含相关数据。根据所使用的协议(protocol)，您可能会或可能不会提前知道内容长度。一些协议(protocol)提供此长度，其他协议(protocol)在完成后关闭连接，还有一些协议(protocol)可以使用消息边界。

您必须将接收到的数据保存在另一个缓冲区中，并在没有更多数据可用或预期时返回或输出整个消息缓冲区。这可以这样做:

int BufferSize = 1024;

using (var socket = new Socket(SocketType.Stream, ProtocolType.IP))
{
    socket.Connect(IPAddress.Parse("127.0.0.1"), 5000);

    byte[] buffer = new byte[BufferSize];
    string message = "";

    int bytesReceived;
    do
    {
        bytesReceived = socket.Receive(buffer);
        message += Encoding.ASCII.GetString(buffer, 0, bytesReceived);

    } while (bytesReceived > 0);

    Console.WriteLine(message);
}

接收到的字节是 ASCII 字符(在组成的协议(protocol)中定义)，因此接收到的每个字节都表示一个字符(您不能转换部分接收到的多字节 unicode 字符)。字节被转换为字符串并附加到 message多变的。代码循环直到服务器关闭连接。

同样，当事先知道消息大小时，根据所使用的协议(protocol)，您可以创建一个消息缓冲区并将数据复制到每个 Receive() 上。 :

// Received using another Receive() call
int messageSize = 1234;
int totalBytesReceived = 0;
byte[] messageBuffer = new byte[messageSize];

byte[] buffer = new byte[BufferSize];

int bytesReceived;
do
{
    bytesReceived = socket.Receive(buffer);

    // Copy the receive buffer into the message buffer, appending after 
    // previously received data (totalBytesReceived).
    Buffer.BlockCopy(buffer, 0, messageBuffer, totalBytesReceived, bytesReceived);
    totalBytesReceived += bytesReceived;

} while (bytesReceived > 0);

// This assumes the connection wasn't closed prematurely.
Console.WriteLine(Encoding.ASCII.GetString(messageBuffer));

这又可以放在一个可重复使用的方法中:

public byte[] ReceiveMessage(Socket socket, int messageSize)
{
    byte[] messageBuffer = new byte[messageSize];

    int bytesReceived = 0;
    int totalBytesReceived = 0;
    do
    {
        byte[] buffer = new byte[BufferSize];

        // Receive at most the requested number of bytes, or the amount the 
        // buffer can hold, whichever is smaller.
        int toReceive = Math.Min(messageSize - totalBytesReceived, BufferSize);
        bytesReceived = socket.Receive(buffer, toReceive, SocketFlags.None);

        // Copy the receive buffer into the message buffer, appending after 
        // previously received data (totalBytesReceived).
        Buffer.BlockCopy(buffer, 0, messageBuffer, totalBytesReceived, bytesReceived);

        totalBytesReceived += bytesReceived;

    } while (bytesReceived > 0);

    if (totalBytesReceived < messageSize)
    {
        throw new Exception("Server closed connection prematurely");
    }

    return messageBuffer;
}

有 NetworkStream 它包裹了一个套接字，但它 has the same reading issues作为套接字本身。您必须监控返回值并继续调用 Read()直到您收到所有字节。 TcpClient that has a GetStream() method 也是如此，您还将在其返回值上 have to continue reading until you've read all data .