Linux 初识Libevent网络库

初识libevent

libevent是用c写的高并发网络io库，只要有文件描述符，就都可使用libevent。

libevent使用回调函数（callback） 。

有了libevent，网络编程我有

1, fifo的进程间通信。

利用fifo的进程间通信read端：

#include <event2/event.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define myfifo "myfifo"

//call back
void readcb(evutil_socket_t fd, short what, void* arg){
  //read fifo
  char buf[24] = {0};
  int len = read(fd, buf, sizeof(buf));
  buf[len] = '\0';
  printf("data len = %d, buf = %s\n", len, buf);
  printf("read event:%s\n", what & ev_read ? "yes" : "no");
}

int main(){
  unlink(myfifo);
  mkfifo(myfifo, 0664);

  int fd = open(myfifo, o_rdonly | o_nonblock);
  //int fd = open(myfifo, o_rdonly);

  struct event_base* base;
  base = event_base_new();

  //create event
  struct event* ev = null;
  ev = event_new(base, fd, ev_read | ev_persist | ev_et, readcb, null);

  //add event
  event_add(ev, null);

  //start
  event_base_dispatch(base);

  //free event
  event_free(ev);
  event_base_free(base);
  close(fd);

  return 0;
}

利用fifo的进程间通信write端：

#include <event2/event.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

#define myfifo "myfifo"

//call back
void writecb(evutil_socket_t fd, short what, void* arg){
  //write fifo
  char buf[24] = {0};
  static int num = 0;
  sprintf(buf, "num = %d", num++);
  write(fd, buf, strlen(buf) + 1);
}

int main(){

  int fd = open(myfifo, o_wronly | o_nonblock);

  struct event_base* base;
  base = event_base_new();

  //create event
  struct event* ev = null;
  ev = event_new(base, fd, ev_write | ev_persist | ev_et, writecb, null);

  //add event
  event_add(ev, null);

  //start
  event_base_dispatch(base);

  //free event
  event_free(ev);
  event_base_free(base);
  close(fd);

  return 0;
}

2, socket通信。

server端：

#include <event2/event.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <event2/bufferevent.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <event2/listener.h>

//write callback
void write_cb(struct bufferevent* bev, void* ctx){
  printf("all is sent\n");
}

//read callback
void read_cb(struct bufferevent *bev, void *ctx){
  char buf[64];
  size_t ret = bufferevent_read(bev, buf, sizeof(buf));
  buf[ret] = '\0';
  printf("server recf:%s\n", buf);

  bufferevent_write(bev, "hahaha", 6);
}

//event callback
void event_cb(struct bufferevent *bev, short what, void *ctx){

  if(what & bev_event_eof){
    printf("eof\n");
  }
  if(what & bev_event_connected){
    printf("connected\n");
  }
}

//listener call back
void listencb(struct evconnlistener* listener, evutil_socket_t fd,
          struct sockaddr* cli, int len, void* ptr){

  struct event_base* base = evconnlistener_get_base(listener);
  struct bufferevent* bev =
    bufferevent_socket_new(base, fd, bev_opt_close_on_free);

  //set callback function
  bufferevent_setcb(bev, read_cb, write_cb, event_cb, null);
  bufferevent_enable(bev, ev_read | ev_write);

  
  //set water
  bufferevent_setwatermark(bev, ev_read, 10, 0);
  bufferevent_setwatermark(bev, ev_write, 1, 2);

}

int main(int argc, char** argv){

  int port = atoi(argv[1]);
  struct event_base* base;
  base = event_base_new();
  if(!base){
    perror("event_base_new");
    exit(1);
  }

  struct sockaddr_in s;
  s.sin_family = af_inet;
  s.sin_port = htons(port);
  s.sin_addr.s_addr = htonl(inaddr_any);
  struct evconnlistener* listener =
    evconnlistener_new_bind(base, listencb, null, lev_opt_close_on_free,
                -1, (struct sockaddr*)&s, sizeof(s));
  if(!listener){
    perror("bind");
    exit(1);
  }
  event_base_dispatch(base);
  event_base_free(base);
}

client端:

#include <event2/event.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <event2/bufferevent.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <event2/listener.h>
#include <event2/dns.h>
#include <stdlib.h>
#include <event2/util.h>

//read write callback
void readcb(struct bufferevent *bev, void *ctx){
  char buf[64];
  size_t ret = bufferevent_read(bev, buf, sizeof(buf));
  buf[ret] = '\0';
  printf("client recf:%s\n", buf);

}

//event callback
void eventcb(struct bufferevent *bev, short what, void *ctx){
  if(what & bev_event_connected){
    printf("connect okay\n");  
  }
  else if(what & bev_event_error){
    struct event_base* base = ctx;
    int err = bufferevent_socket_get_dns_error(bev);
    if(err){
      printf("dns error:%s\n", evutil_gai_strerror(err));
    }
    printf("closing\n");
    bufferevent_free(bev);
    event_base_loopexit(base, null);
  }
}

//terminal read callback
void termicb(evutil_socket_t fd, short what, void* ptr){
  char buf[64] = {0};
  int len = read(fd, buf, sizeof(buf));
  buf[len] = '\0';
  printf("in termicb\n");
  struct bufferevent* bev = ptr;
  bufferevent_write(bev, buf, len);
}
int main(int artc, char** argv){

  struct event_base* base;
  base = event_base_new();
 
  struct evdns_base* dns_base;
  dns_base = evdns_base_new(base, 1);

  struct bufferevent* bev;
  bev = bufferevent_socket_new(base, -1, bev_opt_close_on_free);

  int port = atoi(argv[2]);
  bufferevent_setcb(bev, readcb, null, eventcb, base);
  bufferevent_enable(bev, ev_read);
  bufferevent_socket_connect_hostname(bev, dns_base, af_inet, argv[1], port);

  struct event* ev = event_new(base, stdin_fileno, ev_read | ev_persist, termicb, bev);
  event_add(ev, null);
  event_base_dispatch(base);
  event_base_free(base);
}

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