Linux 初識Libevent網絡庫

初識Libevent

libevent是用c寫的高併發網絡io庫，只要有文件描述符，就均可使用libevent。

libevent使用回調函數（callback） 。

有了libevent，網絡編程我有

1, FIFO的進程間通訊。

利用FIFO的進程間通訊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的進程間通訊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通訊。

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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