libevent源碼bufferevent_socket_connect，bufferevent_socket_new

/**
   Launch a connect() attempt with a socket-based bufferevent.
　　使用一個socket-based bufferevent來啟動connect()

   When the connect succeeds, the eventcb will be invoked with
   BEV_EVENT_CONNECTED set.當連接成功，事件回調會被置為BEV_EVENT_CONNECTED並進行調用

   If the bufferevent does not already have a socket set, we allocate a new
   socket here and make it nonblocking before we begin.
　　在開始前，如果bufferevent沒有配置套接字，將會在這里分配一個新的套接字，並設置為非阻塞的

   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，則假設套接字已處於連接中（進行時），並配置了bufferevent，這樣當連接完成時，會產生一個BEV_EVENT_CONNECTED事件

   @param bufev an existing bufferevent allocated with
       bufferevent_socket_new(). 通過bufferevetn_socket_new()分配的bufferevent
   @param addr the address we should connect to 將要連接的地址（服務端地址）
   @param socklen The length of the address 地址的長度
   @return 0 on success, -1 on failure. 0成功，-1失敗
 */

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

/**
  Create a new socket bufferevent over an existing socket.
　　基於一個已存在的套接字，創建一個新的socket bufferevent

  @param base the event base to associate with the new bufferevent. 和新bufferevent關聯到一起的base
  @param fd the file descriptor from which data is read and written to. 數據將被讀取和寫入的描敘符
	    This file descriptor is not allowed to be a pipe(2). 這個文件描敘符不能是一個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().文件描敘符可以設置為-1，只要稍后用bufferevent_setfd或者bufferevent_socket_connect()來設置它
  @param options Zero or more BEV_OPT_* flags 0或者其它的標識
  @return a pointer to a newly allocated bufferevent struct, or NULL if an
	  error occurred 一個指向新分配的bufferevent的指針，或者NULL（當有錯誤發生）
  @see bufferevent_free()
  */

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