【网络组件】接受连接Acceptor

   本节介绍接受连接Acceptor，并给出实现；

接受连接

（1）Acceptor用于接受连接，是TcpServer的成员，生命周期由TcpServer控制；

（2）当Acceptor使用accept接受连接时，回调TcpServer的函数，来通知TcpServer创建TcpConnection；

（3）Acceptor的socket fd是一个listening，也就是是一个服务器的socket，当Epoller会回调Acceptor的_handleRead，在_handleRead中会使用accept接收新连接；

总体类图如下：

接受连接时序示意图如下：

Acceptor

Acceptor的声明

class Event;class EventLoop;class Acceptor final{public:  Acceptor(const Acceptor&) = delete;  Acceptor& operator=(const Acceptor&) = delete;  Acceptor(const InetAddress& listenAddr, EventLoop* loop);  ~Acceptor();  void setNewConnectionCallback(const NewConnectionCallback& cb)  {    _newConnectionCallback = cb;  }private:  void _handleRead();  void _bind();  void _listen();  static const int backlog = 10;  int _acceptfd;  InetAddress _listenAddr;  EventLoop* _loop;  std::unique_ptr<Event>  _acceptEvent;  NewConnectionCallback _newConnectionCallback;};

说明几点：

（1）_handleRead()为accept时的回调函数用来执行接受新连接；_acceptfd为监听的描述符；

（2）_newConnectionCallback为TcpServer注册给Acceptor的回调函数，当Acceptor的_handleRead函数执行时，将回调_newConnectionCallback来创建TcpConnection;

Acceptor的实现

Acceptor::Acceptor(const InetAddress& listenAddr, EventLoop* loop) :    _acceptfd(sockets::createNonBlockingSocket()),    _listenAddr(listenAddr),    _loop(loop),    _acceptEvent(new Event(_acceptfd, _loop)){  LOG_TRACE << "accept fd: " << _acceptfd;  sockets::setReuseAddr(_acceptfd);  _bind();  _listen();  _acceptEvent->setReadCallback(std::bind(&Acceptor::_handleRead, this));  _acceptEvent->enableReading();}Acceptor::~Acceptor(){  _acceptEvent->disableAll();  _acceptEvent->remove();  ::close(_acceptfd);}void Acceptor::_handleRead(){  InetAddress clientAddr;  int connfd = sockets::accept(_acceptfd, &clientAddr.address());    if (connfd < 0)    return;  if (_newConnectionCallback)    {      _newConnectionCallback(connfd, clientAddr);    }  else    {      ::close(connfd);    }}void Acceptor::_bind(){  sockets::bind(_acceptfd, _listenAddr.address());}void Acceptor::_listen(){  sockets::listen(_acceptfd, backlog);}

说明几点：

（1）在构造函数中，创建非阻塞的socket的_acceptfd描述符，绑定_acceptfd到服务器地址，以及监听_acceptfd；对于sockets::createNonBlockingSocket()、sockets::bind、sockets::listen下文介绍；

（2）_handleRead()用来处理接受连接， sockets::accept接受一个新连接，然后执行TcpServer的回调_newConnectionCallback；

Acceptor建立连接函数

void TcpServer::_newConnection(int connfd, const InetAddress& peerAddr){  EventLoop* loop;  if ( _loopPool)    {      loop =  _loopPool->getNextLoop();    }  else    {      loop = _loop;    }  LOG_INFO << "TcpServer::_newConnection [" << connfd << "] from " << peerAddr.hostNameString();  TcpConnectionPtr conn(new TcpConnection(connfd, loop, peerAddr, _serverAddr));  assert(_connectionMaps.find(connfd) == _connectionMaps.end());  _connectionMaps[connfd] = conn;  conn->setMessageCallback(_messageCallback);  conn->setConnectionCallback(_connectionCallback);  conn->setCloseConnectionCallback(std::bind(&TcpServer::_removeConnection, this, std::placeholders::_1));  conn->connectEstablished();}

说明几点：

（1）TcpServer的详细介绍，请见下一个博客；

（2）在_newConnection中，主要是创建 TcpConnection，并在最后 conn->connectEstablished();让管理TcpConnection的IO线程来处理TcpConnection上的事件处理函数；

InetAddress相关的SocketOps.cc函数

void sockets::setNonBlockingFd(int fd){  int flags;  if ((flags = fcntl(fd, F_GETFL, 0)) < 0)    {      LOG_SYSERR << "fcntl system error: " << strError();    }  flags |= O_NONBLOCK;  if ((flags = fcntl(fd, F_SETFL, flags)) < 0)    {      LOG_SYSERR << "fcntl system error: " << strError();    }}int sockets::createNonBlockingSocket(void){  int sockfd = ::socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, IPPROTO_TCP);  if (sockfd < 0)    {      LOG_SYSERR << "socket system error: " << strError();      abort();    }  return sockfd;}void sockets::bind(int sockfd, const struct sockaddr_in& addr){  socklen_t len = sizeof(addr);  if (::bind(sockfd, reinterpret_cast<const sockaddr*>(&addr), len) < 0)  //can not use C++ static_cast    {      LOG_SYSERR << "bind system error: " << strError();      //  abort();    }}void sockets::listen(int listenfd, int backlog){  if (::listen(listenfd, backlog) < 0)    {      LOG_SYSERR << "bind system error: " << strError();      abort();    }}int sockets::accept(int listenfd, struct sockaddr_in* clientAddr){  int connfd;  socklen_t len;#if _GNU_SOURCE  connfd = accept4(listenfd, reinterpret_cast<sockaddr*>(clientAddr), &len, SOCK_NONBLOCK | SOCK_CLOEXEC);#else  confd = accept(listenfd, reinterpret_cast<sockaddr*>(clientAddr), &len);  setNonBlockingFd(connfd);#endif  if (connfd < 0)    {      int savederrno = errno;      switch (savederrno)        {        case EAGAIN:  //EWOULDBLOCK:        case EINTR:        case EBADF:        case ECONNABORTED:          errno = savederrno;          LOG_SYSERR << "accept system expected error: " << strError();          break;        case ENOTSOCK:        case EOPNOTSUPP:        case ENOBUFS:        case EINVAL:        case EFAULT:          LOG_SYSERR << "accept system unexpected error: " << strError();          abort();          break;        default:          LOG_SYSERR << "accept system unknown error: " << strError();          abort();          break;        }    }  return connfd;}

说明几点：

（1）accept函数中可以使用accept4一次性得到非阻塞性的连接描述符；

InetAddress

使用InetAddress封装socket的IP地址和端口；方便取出IP的字符串名称等；

InetAddress声明

class InetAddress final{public:  InetAddress() = default;  InetAddress(const char* ip, uint16_t port);  uint16_t port() const;  std::string ipString() const;  std::string hostNameString() const;  struct sockaddr_in& address()  {    return _address;  }private:  struct sockaddr_in _address;};

InetAddress实现

InetAddress::InetAddress(const char* ip, uint16_t p){  ::memset(&_address, 0, sizeof(struct sockaddr_in));  sockets::stringToAddr(ip, &_address.sin_addr);  _address.sin_port = endian::hostToNet16(p);  _address.sin_family = AF_INET;             //impotant}uint16_t InetAddress::port() const{  return _address.sin_port;}std::string InetAddress::ipString() const{  return sockets::addrToString(_address.sin_addr);}std::string InetAddress::hostNameString() const{  char buf[32];  snprintf(buf, sizeof buf, ":%d", _address.sin_port);  return sockets::addrToString(_address.sin_addr) + buf;}

InetAddress相关的SocketOps.cc函数

void sockets::stringToAddr(const char* ip, struct in_addr* addr){  if (inet_aton(ip, addr) == 0)    {      LOG_ERROR << "invalid Ip address: " << strError();    }}std::string sockets::addrToString(const struct in_addr& addr){  return ::inet_ntoa(addr);}