Libevent库笔记（一）下载和编译，测试demo

1.下载及编译

1.1.下载

官网：http://libevent.org/
1.4和2.x系列版本，1.4 比较老，但源码简单，适合学习；
2.x 比较新，使用时建议用2.x版本，与1.4版本接口不兼容。
当前2个系列版本状态（2020.02.09）
libevent-release-1.4.15-stable.tar.gz
libevent-2.1.11-stable.tar.gz

1.2.编译

1.2.1.说明

./configure 检查安装环境，生成makefile
make 生成目标文件和可执行文件
sudo make install 将相关头文件、库文件复制到系统目录

1.2.2.Ubuntu平台编译和安装

这里以2.11版本为例
解压
tar -zxvf libevent-2.1.11-stable.tar.gz

进入解压后的目录
cd libevent-2.1.11-stable/
./configure #检查安装环境，生成makefile
make #生成目标文件和可执行文件
sudo make install #将相关头文件、库文件复制到系统目录

提示库已经安装到/usr/local/lib
可进入目录查看相关库

另外头文件位于/usr/local/include

其中event2是一个目录，

1.2.3.编译和测试demo

进入sample目录：
cd sample

$ gcc -o hello hello-world.c -levent
运行demo：
./hello
运行一个客户端连接
$nc 127.0.0.1 9995

客户端连接服务端后，服务端反馈hello，world后，立马进行FIN挥手，客户端进行ACK应答。
使用wireshark抓包查看

1.2.4.Demo代码

大致可以看出监听端口号为9995
事件中交互一个MESSAGE（为字符串"Hello, World!\n";）

/*
  This example program provides a trivial server program that listens for TCP
  connections on port 9995.  When they arrive, it writes a short message to
  each client connection, and closes each connection once it is flushed.

  Where possible, it exits cleanly in response to a SIGINT (ctrl-c).
*/


#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <signal.h>
#ifndef _WIN32
#include <netinet/in.h>
# ifdef _XOPEN_SOURCE_EXTENDED
#  include <arpa/inet.h>
# endif
#include <sys/socket.h>
#endif

#include <event2/bufferevent.h>
#include <event2/buffer.h>
#include <event2/listener.h>
#include <event2/util.h>
#include <event2/event.h>

static const char MESSAGE[] = "Hello, World!\n";

static const int PORT = 9995;

static void listener_cb(struct evconnlistener *, evutil_socket_t,
    struct sockaddr *, int socklen, void *);
static void conn_writecb(struct bufferevent *, void *);
static void conn_eventcb(struct bufferevent *, short, void *);
static void signal_cb(evutil_socket_t, short, void *);

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

	struct sockaddr_in sin;
#ifdef _WIN32
	WSADATA wsa_data;
	WSAStartup(0x0201, &wsa_data);
#endif

	base = event_base_new();
	if (!base) {
    
    
		fprintf(stderr, "Could not initialize libevent!\n");
		return 1;
	}

	memset(&sin, 0, sizeof(sin));
	sin.sin_family = AF_INET;
	sin.sin_port = htons(PORT);

	listener = evconnlistener_new_bind(base, listener_cb, (void *)base,
	    LEV_OPT_REUSEABLE|LEV_OPT_CLOSE_ON_FREE, -1,
	    (struct sockaddr*)&sin,
	    sizeof(sin));

	if (!listener) {
    
    
		fprintf(stderr, "Could not create a listener!\n");
		return 1;
	}

	signal_event = evsignal_new(base, SIGINT, signal_cb, (void *)base);

	if (!signal_event || event_add(signal_event, NULL)<0) {
    
    
		fprintf(stderr, "Could not create/add a signal event!\n");
		return 1;
	}

	event_base_dispatch(base);

	evconnlistener_free(listener);
	event_free(signal_event);
	event_base_free(base);

	printf("done\n");
	return 0;
}

static void
listener_cb(struct evconnlistener *listener, evutil_socket_t fd,
    struct sockaddr *sa, int socklen, void *user_data)
{
    
    
	struct event_base *base = user_data;
	struct bufferevent *bev;

	bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
	if (!bev) {
    
    
		fprintf(stderr, "Error constructing bufferevent!");
		event_base_loopbreak(base);
		return;
	}
	bufferevent_setcb(bev, NULL, conn_writecb, conn_eventcb, NULL);
	bufferevent_enable(bev, EV_WRITE);
	bufferevent_disable(bev, EV_READ);

	bufferevent_write(bev, MESSAGE, strlen(MESSAGE));
}

static void
conn_writecb(struct bufferevent *bev, void *user_data)
{
    
    
	struct evbuffer *output = bufferevent_get_output(bev);
	if (evbuffer_get_length(output) == 0) {
    
    
		printf("flushed answer\n");
		bufferevent_free(bev);
	}
}

static void
conn_eventcb(struct bufferevent *bev, short events, void *user_data)
{
    
    
	if (events & BEV_EVENT_EOF) {
    
    
		printf("Connection closed.\n");
	} else if (events & BEV_EVENT_ERROR) {
    
    
		printf("Got an error on the connection: %s\n",
		    strerror(errno));/*XXX win32*/
	}
	/* None of the other events can happen here, since we haven't enabled
	 * timeouts */
	bufferevent_free(bev);
}

static void
signal_cb(evutil_socket_t sig, short events, void *user_data)
{
    
    
	struct event_base *base = user_data;
	struct timeval delay = {
    
     2, 0 };

	printf("Caught an interrupt signal; exiting cleanly in two seconds.\n");

	event_base_loopexit(base, &delay);
}

2.附录 nc命令

功能：netcat的简写，是一个简单而有用的工具。可以作为各种TCP和UDP监听和连接测试用途。
可用参数
$ nc -help
OpenBSD netcat (Debian patchlevel 1.187-1ubuntu0.1)
usage: nc [-46CDdFhklNnrStUuvZz] [-I length] [-i interval] [-M ttl]
[-m minttl] [-O length] [-P proxy_username] [-p source_port]
[-q seconds] [-s source] [-T keyword] [-V rtable] [-W recvlimit] [-w timeout]
[-X proxy_protocol] [-x proxy_address[:port]] [destination] [port]
Command Summary:
-4 Use IPv4
-6 Use IPv6
-b Allow broadcast
-C Send CRLF as line-ending
-D Enable the debug socket option
-d Detach from stdin
-F Pass socket fd
-h This help text
-I length TCP receive buffer length
-i interval Delay interval for lines sent, ports scanned
-k Keep inbound sockets open for multiple connects
-l Listen mode, for inbound connects
-M ttl Outgoing TTL / Hop Limit
-m minttl Minimum incoming TTL / Hop Limit
-N Shutdown the network socket after EOF on stdin
-n Suppress name/port resolutions
-O length TCP send buffer length
-P proxyuser Username for proxy authentication
-p port Specify local port for remote connects
-q secs quit after EOF on stdin and delay of secs
-r Randomize remote ports
-S Enable the TCP MD5 signature option
-s source Local source address
-T keyword TOS value
-t Answer TELNET negotiation
-U Use UNIX domain socket
-u UDP mode
-V rtable Specify alternate routing table
-v Verbose
-W recvlimit Terminate after receiving a number of packets
-w timeout Timeout for connects and final net reads
-X proto Proxy protocol: “4”, “5” (SOCKS) or “connect”
-x addr[:port] Specify proxy address and port
-Z DCCP mode
-z Zero-I/O mode [used for scanning]
Port numbers can be individual or ranges: lo-hi [inclusive]