学习Muduo中ChatRoom实现的各种细节和思考

Muduo中ChatRoom

1.长连接中的分包解决

• 固定消息长度， 比如说固定消息长度是16字节
• 使用特殊的字符作为分割符号，比如说 HTTP协议中的\r\n作为头部的分割符
• 每个消息头部加上长度字段，这在很多场景都用到过，比如之前的LEVELDB
• 消息本身的格式进行分包

这个聊天室的代码使用了加上长度字段作为消息的分割

2.消息格式

消息本身就是字符串，前4字节的头部存放字符串的长度。

消息之间没有分割符，也没有\0

3.使用间接层帮助收发消息

消息从onMessage函数中读取出来，但是我们并不希望用户还要处理这么麻烦的一些格式等

因此抽象了一层收发数据（封装成为string类型）

构造函数传入回调函数，调用server, or. client中的对于消息的处理的函数

#ifndef MUDUO_EXAMPLES_ASIO_CHAT_CODEC_H
#define MUDUO_EXAMPLES_ASIO_CHAT_CODEC_H

#include "muduo/base/Logging.h"
#include "muduo/net/Buffer.h"
#include "muduo/net/Endian.h"
#include "muduo/net/TcpConnection.h"

class LengthHeaderCodec : muduo::noncopyable
{
    
 public:
  //回调函数，处理完之后
  typedef std::function<void (const muduo::net::TcpConnectionPtr&,
                                const muduo::string& message,
                                muduo::Timestamp)> StringMessageCallback;

  explicit LengthHeaderCodec(const StringMessageCallback& cb)
    : messageCallback_(cb)
  {
    
  }

  //server或者client收发数据中最先调用的函数，进行原始buffer的处理
  //封装成为string后调用回调函数
  void onMessage(const muduo::net::TcpConnectionPtr& conn,
                 muduo::net::Buffer* buf,
                 muduo::Timestamp receiveTime)
  {
    
    while (buf->readableBytes() >= kHeaderLen) // kHeaderLen == 4
    {
    
      // FIXME: use Buffer::peekInt32()
      const void* data = buf->peek();
      int32_t be32 = *static_cast<const int32_t*>(data); // SIGBUS
      const int32_t len = muduo::net::sockets::networkToHost32(be32);
      if (len > 65536 || len < 0)
      {
    
        LOG_ERROR << "Invalid length " << len;
        conn->shutdown();  // FIXME: disable reading
        break;
      }
      else if (buf->readableBytes() >= len + kHeaderLen)
      {
    
        buf->retrieve(kHeaderLen);	//readIdx跳过消息头部的4个字节
        muduo::string message(buf->peek(), len);	//封装提取到的消息
        messageCallback_(conn, message, receiveTime);	//回调函数，将封装好的string发送过去
        buf->retrieve(len);	//跳过buffer中的消息，表示这个已经读取完了
      }
      else
      {
    
        break;
      }
    }
  }

  // FIXME: TcpConnectionPtr
  void send(muduo::net::TcpConnection* conn,
            const muduo::StringPiece& message)
  {
    
    muduo::net::Buffer buf;
    buf.append(message.data(), message.size());
    int32_t len = static_cast<int32_t>(message.size());
    int32_t be32 = muduo::net::sockets::hostToNetwork32(len);
    buf.prepend(&be32, sizeof be32);			//将长度放到buffer 的前8个字节
    conn->send(&buf);	
  }

 private:
  StringMessageCallback messageCallback_;
  const static size_t kHeaderLen = sizeof(int32_t);
};

#endif // MUDUO_EXAMPLES_ASIO_CHAT_CODEC_H

4.server端的实现

使用set将对于不同的客户端的连接进行封装起来，发送消息的时候直接遍历容器发送

typedef std::set<TcpConnectionPtr> ConnectionList

• 其中回调函数onStringMessage就是服务端onMessage接受到可读后进行处理，封装消息成为string之后回调的函数，用于处理服务端的逻辑，只需要关注消息发送即可

#include "examples/asio/chat/codec.h"

#include "muduo/base/Logging.h"
#include "muduo/base/Mutex.h"
#include "muduo/net/EventLoop.h"
#include "muduo/net/TcpServer.h"

#include <set>
#include <stdio.h>
#include <unistd.h>

using namespace muduo;
using namespace muduo::net;

class ChatServer : noncopyable
{
    
 public:
  ChatServer(EventLoop* loop,
             const InetAddress& listenAddr)
  : server_(loop, listenAddr, "ChatServer"),
    codec_(std::bind(&ChatServer::onStringMessage, this, _1, _2, _3))
  {
    
    server_.setConnectionCallback(
        std::bind(&ChatServer::onConnection, this, _1));
    server_.setMessageCallback(
        std::bind(&LengthHeaderCodec::onMessage, &codec_, _1, _2, _3));
  }

  void start()
  {
    
    server_.start();
  }

 private:
  void onConnection(const TcpConnectionPtr& conn)
  {
    
    LOG_INFO << conn->peerAddress().toIpPort() << " -> "
             << conn->localAddress().toIpPort() << " is "
             << (conn->connected() ? "UP" : "DOWN");

    if (conn->connected())
    {
    
      connections_.insert(conn);
    }
    else
    {
    
      connections_.erase(conn);
    }
  }

  void onStringMessage(const TcpConnectionPtr&,
                       const string& message,
                       Timestamp)
  {
    
    for (ConnectionList::iterator it = connections_.begin();
        it != connections_.end();
        ++it)
    {
    
      codec_.send(get_pointer(*it), message);
    }
  }

  typedef std::set<TcpConnectionPtr> ConnectionList;
  TcpServer server_;
  LengthHeaderCodec codec_;
  ConnectionList connections_;
};

int main(int argc, char* argv[])
{
    
  LOG_INFO << "pid = " << getpid();
  if (argc > 1)
  {
    
    EventLoop loop;
    uint16_t port = static_cast<uint16_t>(atoi(argv[1]));
    InetAddress serverAddr(port);
    ChatServer server(&loop, serverAddr);
    server.start();
    loop.loop();
  }
  else
  {
    
    printf("Usage: %s port\n", argv[0]);
  }
}

5.client端的实现

其中client端同server端的流程也是大概相似的，还是调用回调函数进行处理

不需要关注于格式问题，能够进行发送肯定是已经封装好了（由codec.h帮助实现）

#include "examples/asio/chat/codec.h"

#include "muduo/base/Logging.h"
#include "muduo/base/Mutex.h"
#include "muduo/net/EventLoopThread.h"
#include "muduo/net/TcpClient.h"

#include <iostream>
#include <stdio.h>
#include <unistd.h>

using namespace muduo;
using namespace muduo::net;

class ChatClient : noncopyable
{
    
 public:
  ChatClient(EventLoop* loop, const InetAddress& serverAddr)
    : client_(loop, serverAddr, "ChatClient"),
      codec_(std::bind(&ChatClient::onStringMessage, this, _1, _2, _3))
  {
    
    client_.setConnectionCallback(
        std::bind(&ChatClient::onConnection, this, _1));
    client_.setMessageCallback(
        std::bind(&LengthHeaderCodec::onMessage, &codec_, _1, _2, _3));
    client_.enableRetry();
  }

  void connect()
  {
    
    client_.connect();
  }

  void disconnect()
  {
    
    client_.disconnect();
  }

  void write(const StringPiece& message)
  {
    
    MutexLockGuard lock(mutex_);
    if (connection_)
    {
    
      codec_.send(get_pointer(connection_), message);
    }
  }

 private:
  void onConnection(const TcpConnectionPtr& conn)
  {
    
    LOG_INFO << conn->localAddress().toIpPort() << " -> "
             << conn->peerAddress().toIpPort() << " is "
             << (conn->connected() ? "UP" : "DOWN");

    MutexLockGuard lock(mutex_);
    if (conn->connected())
    {
    
      connection_ = conn;
    }
    else
    {
    
      connection_.reset();
    }
  }

  void onStringMessage(const TcpConnectionPtr&,
                       const string& message,
                       Timestamp)
  {
    
    printf("<<< %s\n", message.c_str());
  }

  TcpClient client_;
  LengthHeaderCodec codec_;
  MutexLock mutex_;
  TcpConnectionPtr connection_ GUARDED_BY(mutex_);
};

int main(int argc, char* argv[])
{
    
  LOG_INFO << "pid = " << getpid();
  if (argc > 2)
  {
    
    EventLoopThread loopThread;
    uint16_t port = static_cast<uint16_t>(atoi(argv[2]));
    InetAddress serverAddr(argv[1], port);

    ChatClient client(loopThread.startLoop(), serverAddr);
    client.connect();
    std::string line;
    while (std::getline(std::cin, line))
    {
    
      client.write(line);
    }
    client.disconnect();
    CurrentThread::sleepUsec(1000*1000);  // wait for disconnect, see ace/logging/client.cc
  }
  else
  {
    
    printf("Usage: %s host_ip port\n", argv[0]);
  }
}