简介

函数evconnlistener_new_bind

struct evconnlistener *
evconnlistener_new_bind(struct event_base *base, evconnlistener_cb cb,
    void *ptr, unsigned flags, int backlog, const struct sockaddr *sa,
    int socklen)

参数解析：

base：事件集合

evconnlistener_cb：cb是call back的缩写，就是回调函数定义如下：

typedef void (*evconnlistener_cb)(struct evconnlistener *, evutil_socket_t, struct sockaddr *, int socklen, void *);

ptr：传递给cb的参数

flags：属性标志位，可取值9个(掰手指头数的)，下面是9个取值的宏定义，在evconnlistener_new_bind函数源码中也可以看出来。

/** Flag: Indicates that we should not make incoming sockets nonblocking
 * before passing them to the callback. */
#define LEV_OPT_LEAVE_SOCKETS_BLOCKING	(1u<<0)
/** Flag: Indicates that freeing the listener should close the underlying
 * socket. */
#define LEV_OPT_CLOSE_ON_FREE		(1u<<1)
/** Flag: Indicates that we should set the close-on-exec flag, if possible */
#define LEV_OPT_CLOSE_ON_EXEC		(1u<<2)
/** Flag: Indicates that we should disable the timeout (if any) between when
 * this socket is closed and when we can listen again on the same port. */
#define LEV_OPT_REUSEABLE		(1u<<3)
/** Flag: Indicates that the listener should be locked so it's safe to use
 * from multiple threadcs at once. */
#define LEV_OPT_THREADSAFE		(1u<<4)
/** Flag: Indicates that the listener should be created in disabled
 * state. Use evconnlistener_enable() to enable it later. */
#define LEV_OPT_DISABLED		(1u<<5)
/** Flag: Indicates that the listener should defer accept() until data is
 * available, if possible.  Ignored on platforms that do not support this.
 *
 * This option can help performance for protocols where the client transmits
 * immediately after connecting.  Do not use this option if your protocol
 * _doesn't_ start out with the client transmitting data, since in that case
 * this option will sometimes cause the kernel to never tell you about the
 * connection.
 *
 * This option is only supported by evconnlistener_new_bind(): it can't
 * work with evconnlistener_new_fd(), since the listener needs to be told
 * to use the option before it is actually bound.
 */
#define LEV_OPT_DEFERRED_ACCEPT		(1u<<6)
/** Flag: Indicates that we ask to allow multiple servers (processes or
 * threads) to bind to the same port if they each set the option. 
 * 
 * SO_REUSEPORT is what most people would expect SO_REUSEADDR to be, however
 * SO_REUSEPORT does not imply SO_REUSEADDR.
 *
 * This is only available on Linux and kernel 3.9+
 */
#define LEV_OPT_REUSEABLE_PORT		(1u<<7)
/** Flag: Indicates that the listener wants to work only in IPv6 socket.
 *
 * According to RFC3493 and most Linux distributions, default value is to
 * work in IPv4-mapped mode. If there is a requirement to bind same port
 * on same ip addresses but different handlers for both IPv4 and IPv6,
 * it is required to set IPV6_V6ONLY socket option to be sure that the
 * code works as expected without affected by bindv6only sysctl setting in
 * system.
 *
 * This socket option also supported by Windows.
 */
#define LEV_OPT_BIND_IPV6ONLY		(1u<<8)

backlog：设置监听队列的大小，同listen函数的第二个参数。

int listen(int s, int backlog);

sa：IP和端口，同bind函数的第二个参数

socklen：结构体长度，同bind函数的第三个参数

int bind(int sockfd, struct sockaddr *sa, socklen_t socklen)

返回值：struct evconnlistener *

从源码简单分析可知 evconnlistener_new_bind内部实现了创建socket，绑定IP地址和端口，最后监听socket。

/**
   Allocate a new evconnlistener object to listen for incoming TCP connections
   on a given address.

   @param base The event base to associate the listener with.
   @param cb A callback to be invoked when a new connection arrives. If the
      callback is NULL, the listener will be treated as disabled until the
      callback is set.
   @param ptr A user-supplied pointer to give to the callback.
   @param flags Any number of LEV_OPT_* flags
   @param backlog Passed to the listen() call to determine the length of the
      acceptable connection backlog.  Set to -1 for a reasonable default.
   @param addr The address to listen for connections on.
   @param socklen The length of the address.
 */
struct evconnlistener *
evconnlistener_new_bind(struct event_base *base, evconnlistener_cb cb,
    void *ptr, unsigned flags, int backlog, const struct sockaddr *sa,
    int socklen)
{
	struct evconnlistener *listener;
	evutil_socket_t fd;
	int on = 1;
	int family = sa ? sa->sa_family : AF_UNSPEC;
	int socktype = SOCK_STREAM | EVUTIL_SOCK_NONBLOCK;

	if (backlog == 0)
		return NULL;

	if (flags & LEV_OPT_CLOSE_ON_EXEC)
		socktype |= EVUTIL_SOCK_CLOEXEC;

	fd = evutil_socket_(family, socktype, 0);
	if (fd == -1)
		return NULL;

	if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, (void*)&on, sizeof(on))<0)
		goto err;

	if (flags & LEV_OPT_REUSEABLE) {
		if (evutil_make_listen_socket_reuseable(fd) < 0)
			goto err;
	}

	if (flags & LEV_OPT_REUSEABLE_PORT) {
		if (evutil_make_listen_socket_reuseable_port(fd) < 0)
			goto err;
	}

	if (flags & LEV_OPT_DEFERRED_ACCEPT) {
		if (evutil_make_tcp_listen_socket_deferred(fd) < 0)
			goto err;
	}

	if (flags & LEV_OPT_BIND_IPV6ONLY) {
		if (evutil_make_listen_socket_ipv6only(fd) < 0)
			goto err;
	}

	if (sa) {
		if (bind(fd, sa, socklen)<0)
			goto err;
	}

	listener = evconnlistener_new(base, cb, ptr, flags, backlog, fd);
	if (!listener)
		goto err;

	return listener;
err:
	evutil_closesocket(fd);
	return NULL;
}

实例：监听服务器

#include <sys/types.h>
#include <event2/event-config.h>
#include <event2/listener.h>
#include <stdio.h>
#include <event.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <string.h>
#include <signal.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define _DEBUG_INFO
#ifdef _DEBUG_INFO
#define DEBUG_INFO(format, ...) printf("%s:%d $$ " format "\n" \
,__func__,__LINE__ \
, ##__VA_ARGS__)
#else
#define DEBUG_INFO(format, ...)
#endif

/*

*/

void server_evconnlistener_cb(struct evconnlistener *listener, evutil_socket_t new_client, struct sockaddr *addr, int socklen, void *arg)
{
    struct sockaddr_in *paddr = (struct sockaddr_in *)addr;
    DEBUG_INFO("a new client fd = %d",new_client);
    //char *inet_ntoa(struct in_addr in);
    DEBUG_INFO("ip = %s,port = %d",inet_ntoa(paddr->sin_addr),ntohs(paddr->sin_port));
}

int main(int argc, char **argv){
    struct event_base *base;
    struct evconnlistener *listener;
    struct sockaddr_in addr;

    base = event_base_new();
    if(base == NULL){
        DEBUG_INFO("Couldn't create event_base");
        exit(-1);
    }

    addr.sin_family = AF_INET;
    // addr.sin_addr.s_addr = INADDR_ANY;
    // addr.sin_addr.s_addr = inet_addr("0.0.0.0");
    // addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    addr.sin_addr.s_addr = inet_addr("192.168.0.11");
    addr.sin_port = htons(6666);

    listener = evconnlistener_new_bind(
        base,
        server_evconnlistener_cb,
        NULL,//传给cb的参数，本例中就是server_evconnlistener_cb
        LEV_OPT_CLOSE_ON_EXEC|LEV_OPT_CLOSE_ON_FREE|LEV_OPT_REUSEABLE,
        5,//listen的第二个参数
        (struct sockaddr*)&addr,//bind的第二个参数
        sizeof(addr) //bind的第三个参数
    );
    if(listener == NULL){
        DEBUG_INFO("evconnlistener_new_bind error");
        exit(-1);
    }
    //开始监听集合中的事件
    event_base_dispatch(base);
    evconnlistener_free(listener);
    event_base_free(base);
    DEBUG_INFO("bye bye");
    return 0;
}

测试：

运行程序，使用网络调试助手连接服务器的6666端口