我最近编写了一个简单而快速的概念验证代理服务器，使用C#语言实现，旨在让一个Java Web应用程序与驻留在另一台服务器上的遗留VB6应用程序进行通信。它非常简单：
代理服务器和客户端都使用相同的消息格式；在代码中，我使用 ProxyMessage 类来表示客户端的请求和服务器生成的响应：
public class ProxyMessage
{
int Length; // message length (not including the length bytes themselves)
string Body; // an XML string containing a request/response
// writes this message instance in the proper network format to stream
// (helper for response messages)
WriteToStream(Stream stream) { ... }
}
信息非常简单：正文长度+消息正文。
我有一个独立的ProxyClient类，它代表与客户端的连接。它处理代理和单个客户端之间的所有交互。
我在想的是，是否有设计模式或最佳实践可以简化与异步套接字编程相关的样板代码？例如，您需要小心地管理读取缓冲区，以便不会意外损失字节，并且需要跟踪当前消息处理的进度。在我的当前代码中，我在回调函数中完成了所有这些工作 TcpClient.BeginRead，并借助一些实例变量管理缓冲区和当前消息处理状态的状态。
我要传递给BeginRead的回调函数的代码如下，以及相关的实例变量以进行上下文。代码似乎“原样”正常工作，但我想知道它是否可以重构一下以使其更清晰（或者它已经是这样了吗？）。
private enum BufferStates
{
GetMessageLength,
GetMessageBody
}
// The read buffer. Initially 4 bytes because we are initially
// waiting to receive the message length (a 32-bit int) from the client
// on first connecting. By constraining the buffer length to exactly 4 bytes,
// we make the buffer management a bit simpler, because
// we don t have to worry about cases where the buffer might contain
// the message length plus a few bytes of the message body.
// Additional bytes will simply be buffered by the OS until we request them.
byte[] _buffer = new byte[4];
// A count of how many bytes read so far in a particular BufferState.
int _totalBytesRead = 0;
// The state of the our buffer processing. Initially, we want
// to read in the message length, as it s the first thing
// a client will send
BufferStates _bufferState = BufferStates.GetMessageLength;
// ...ADDITIONAL CODE OMITTED FOR BREVITY...
// This is called every time we receive data from
// the client.
private void ReadCallback(IAsyncResult ar)
{
try
{
int bytesRead = _tcpClient.GetStream().EndRead(ar);
if (bytesRead == 0)
{
// No more data/socket was closed.
this.Dispose();
return;
}
// The state passed to BeginRead is used to hold a ProxyMessage
// instance that we use to build to up the message
// as it arrives.
ProxyMessage message = (ProxyMessage)ar.AsyncState;
if(message == null)
message = new ProxyMessage();
switch (_bufferState)
{
case BufferStates.GetMessageLength:
_totalBytesRead += bytesRead;
// if we have the message length (a 32-bit int)
// read it in from the buffer, grow the buffer
// to fit the incoming message, and change
// state so that the next read will start appending
// bytes to the message body
if (_totalBytesRead == 4)
{
int length = BitConverter.ToInt32(_buffer, 0);
message.Length = length;
_totalBytesRead = 0;
_buffer = new byte[message.Length];
_bufferState = BufferStates.GetMessageBody;
}
break;
case BufferStates.GetMessageBody:
string bodySegment = Encoding.ASCII.GetString(_buffer, _totalBytesRead, bytesRead);
_totalBytesRead += bytesRead;
message.Body += bodySegment;
if (_totalBytesRead >= message.Length)
{
// Got a complete message.
// Notify anyone interested.
// Pass a response ProxyMessage object to
// with the event so that receivers of OnReceiveMessage
// can send a response back to the client after processing
// the request.
ProxyMessage response = new ProxyMessage();
OnReceiveMessage(this, new ProxyMessageEventArgs(message, response));
// Send the response to the client
response.WriteToStream(_tcpClient.GetStream());
// Re-initialize our state so that we re
// ready to receive additional requests...
message = new ProxyMessage();
_totalBytesRead = 0;
_buffer = new byte[4]; //message length is 32-bit int (4 bytes)
_bufferState = BufferStates.GetMessageLength;
}
break;
}
// Wait for more data...
_tcpClient.GetStream().BeginRead(_buffer, 0, _buffer.Length, this.ReadCallback, message);
}
catch
{
// do nothing
}
}
到目前为止，我唯一的真正想法是将缓冲相关的东西提取到一个单独的MessageBuffer类中，只需在读取回调中按照到达的顺序将新字节附加到其中。MessageBuffer然后会关注当前的BufferState之类的问题，并在接收到完整消息时触发事件，ProxyClient然后可以将其进一步传播到主代理服务器代码中，进行处理请求。