libevent源码bufferevent_socket_connect，bufferevent_socket_new

/**
   Launch a connect() attempt with a socket-based bufferevent.
　　使用一个socket-based bufferevent来启动connect()

   When the connect succeeds, the eventcb will be invoked with
   BEV_EVENT_CONNECTED set.当连接成功，事件回调会被置为BEV_EVENT_CONNECTED并进行调用

   If the bufferevent does not already have a socket set, we allocate a new
   socket here and make it nonblocking before we begin.
　　在开始前，如果bufferevent没有配置套接字，将会在这里分配一个新的套接字，并设置为非阻塞的

   If no address is provided, we assume that the socket is already connecting,
   and configure the bufferevent so that a BEV_EVENT_CONNECTED event will be
   yielded when it is done connecting.
　　如果未提供地址，则假设套接字已处于连接中（进行时），并配置了bufferevent，这样当连接完成时，会产生一个BEV_EVENT_CONNECTED事件

   @param bufev an existing bufferevent allocated with
       bufferevent_socket_new(). 通过bufferevetn_socket_new()分配的bufferevent
   @param addr the address we should connect to 将要连接的地址（服务端地址）
   @param socklen The length of the address 地址的长度
   @return 0 on success, -1 on failure. 0成功，-1失败
 */

int bufferevent_socket_connect(struct bufferevent *, const struct sockaddr *, int);

/**
  Create a new socket bufferevent over an existing socket.
　　基于一个已存在的套接字，创建一个新的socket bufferevent

  @param base the event base to associate with the new bufferevent. 和新bufferevent关联到一起的base
  @param fd the file descriptor from which data is read and written to. 数据将被读取和写入的描叙符
	    This file descriptor is not allowed to be a pipe(2). 这个文件描叙符不能是一个pipe（2）
	    It is safe to set the fd to -1, so long as you later
	    set it with bufferevent_setfd or bufferevent_socket_connect().文件描叙符可以设置为-1，只要稍后用bufferevent_setfd或者bufferevent_socket_connect()来设置它
  @param options Zero or more BEV_OPT_* flags 0或者其它的标识
  @return a pointer to a newly allocated bufferevent struct, or NULL if an
	  error occurred 一个指向新分配的bufferevent的指针，或者NULL（当有错误发生）
  @see bufferevent_free()
  */

struct bufferevent *bufferevent_socket_new(struct event_base *base, evutil_socket_t fd, int options);