最近看了看socket网络编程,对于我这种一点经验都没有的选手来说只能理解一点点吧。所以在此记录一下最近的收获。
socket编程无非就那几个函数,对于服务端来说,主要的为socket(),bind(),listen(),accept(),close()。对于客户端来说主要为connect(),close()等。当然,我所说的只是针对tcp协议而言的。对于udp而言,就可以简单很多,服务端和客户端都建立socket并进行绑定,从而用sendto()和recvfrom()通信即可。
以下直接上一个关于tcp协议的客户端和服务端的程序。
//此为服务端的程序
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <netdb.h>
//当SIGCHLD信号出现时则执行此函数
//当子进程停止时,SIGCHLD信号会送给父进程,默认是忽略该信号
void sig_handler(int signo) {
pid_t pid;
int stat;
//用WNOHANG参数如果没有任何已终止的进程,它仍会立即返回,而不是像wait那样永远等下去
//waitpid如果成功的话返回子进程的pid,如果没有子进程退出则返回0
pid = waitpid(-1, &stat, WNOHANG);
while(pid > 0) {
printf("child process terminated (PID: %ld)\n", (long)getpid());
pid = waitpid(-1, &stat, WNOHANG);
}
return 0;
}
int main(int argc, char *argv[]) {
int listen_fd;
int com_fd;
int ret;
int i;
static char recv_buffer[1024];
int len;
int port;
pid_t pid;
/*
struct sockaddr {
unsigned short sa_family; //address family, AF_xxx
char sa_data[14]; //14 bytes of protocal address
};
struct sockaddr_in {
short int sin_family; //address family, AF_INET
unsigned short int sin_port; //port number
struct in_addr sin_addr; //internet address
unsigned char sin_zero[8]; //same sizeas struct sockaddr
};
struct in_addr {
uint32_t s_addr; //4 bytes
};
sockaddr是通用套接字地址,sockaddr_in是internet环境下套接字的地址形式,两者
结构一样,都为16个字节。
*/
struct sockaddr_in clt_addr;
struct sockaddr_in srv_addr;
//服务器运行时要给出端口信息,该端口为监听端口
if(argc != 2) {
printf("Usage: %s port\n", argv[0]);
return 1;
}
//atoi为ascii to integer,字符串转换为整型
port = atoi(argv[1]);
//设置处理信号函数
if(signal(SIGCHLD, sig_handler) < 0) {
perror("cannot set the signal");
return 1;
}
//创建套接字用于服务器的监听
if((listen_fd = socket(PF_INET, SOCK_STREAM, 0)) < 0) {
perror("cannot creat listening socket");
return 1;
}
//将srv_addr全部置零,INADDR_ANY就是inet_addr("0.0.0.0"),表示不确定
//地址,也就是表示本机的所有IP
memset(&srv_addr, 0, sizeof(srv_addr));
srv_addr.sin_family = AF_INET;
srv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
srv_addr.sin_port = htons(port);
if((ret = bind(listen_fd, (struct sockaddr*)&srv_addr, sizeof(srv_addr))) == -1) {
perror("cannot bind server socket");
close(listen_fd);
return 1;
}
//指定监听端口,连接5个客户端
if((ret = listen(listen_fd, 5)) == -1) {
perror("cannot listen the client connect request");
close(listen_fd);
return 1;
}
//对每个连接来的客户端创建一个进程,单独与其进行通信
//首先调用read函数读取客户端发送来的信息
//将其转换成为大写后发送回客户端
//当输入@时,程序退出
//用fork()函数的原因是保持服务器能容许多个客户端的连接
while(1) {
len = sizeof(clt_addr);
if((com_fd = accept(listen_fd, (struct sockaddr*)&clt_addr, &len)) < 0) {
//EINTR表示系统调用被信号中断
if(errno == EINTR) {
continue;
}
else {
perror("cannot accept client connect request");
close(listen_fd);
return 1;
}
}
pid = fork();
if(pid < 0) {
perror("cannot create the child process");
close(listen_fd);
return 1;
}
//当有客户端连接的时候,在子进程中进行客户端与服务端的通信
else if(pid == 0) {
while((len = read(com_fd, recv_buffer, 1024)) > 0) {
printf("Message from client(%d): %s\n", len, recv_buffer);
if(recv_buffer[0] == '@') {
break;
}
for(i = 0; i < len; i++) {
recv_buffer[i] = toupper(recv_buffer[i]);
}
write(com_fd, recv_buffer,len);
memset(recv_buffer, 0, 1024);
}
close(com_fd);
return 0;
}
//父进程直接结束此次循环等待下一个客户端进行连接
else {
close(com_fd);
}
}
return 0;
}
------------------------------------------------
//此为服务端的程序
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <netdb.h>
#include <unistd.h>
int main(int argc, char *argv[]) {
int connect_fd;
int ret;
char snd_buffer[1024];
int i;
int port;
int len;
static struct sockaddr_in srv_addr;
if(argc != 3) {
printf("Usage: %s server_ip_address port\n", argv[1]);
return 1;
}
port = atoi(argv[2]);
if((connect_fd = socket(PF_INET, SOCK_STREAM, 0)) < 0) {
perror("cannot creat communication socket");
return 1;
}
memset(&srv_addr, 0, sizeof(srv_addr));
srv_addr.sin_family = AF_INET;
srv_addr.sin_addr.s_addr = inet_addr(argv[1]);
srv_addr.sin_port = htons(port);
if((ret = connect(connect_fd, (struct sockaddr*)&srv_addr, sizeof(srv_addr))) == -1) {
perror("cannot connect to the server");
close(connect_fd);
return 1;
}
//memset(snd_buffer, 0, 1024);
while(1) {
memset(snd_buffer, 0, 1024);
write(STDOUT_FILENO, "input message: ", 15);
len = read(STDIN_FILENO, snd_buffer, 1024);
if(len > 0)
write(connect_fd, snd_buffer, len);
len = read(connect_fd, snd_buffer, len);
if(len > 0)
printf("Message from serverL %s\n", snd_buffer);
if(snd_buffer[0] == '@')
break;
}
close(connect_fd);
return 0;
}
当然,这属于老版本的socket程序,最新的socket编程推荐使用getaddrinfo()函数,这个函数是通过一个hints参数来当做地址的返回标准的。具体的getaddrinfo()函数如下:
struct addrinfo {
int ai_flags; //input flags
int ai_family; //address family
int ai_socktype; //SOCK_STREAM, SOCK_DGRAM
int ai_protocol; //socket protocol
size_t ai_addrlen; //size of structure pointed to by ai_addr
char *ai_cannonname; //canonical name of host
struct sockaddr *ai_addr; //pointer to socket address structure
struct addrinfo *ai_next; //next structure in linked list
};
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
int getaddrinfo(const char *node, //host name to connect to or an IP address
const char *service, //port number, /etc/services
const struct addrinfo *hints, //fill with relevant information, only ai_flags, ai_family, ai_socktype, ai_protocol
struct addrinfo **res
);
上面的服务端程序是通过fork()函数来实现容许多个客户端进行连接的,下面我要用select()函数来实现多个客户端的连接。当然,也同时用了getaddrinfo()这种新特性。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#define PORT "1234"
void *get_in_addr(struct sockaddr *sa) {
if(sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
}
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(void) {
fd_set master;
fd_set read_fds;
int fdmax;
int listener;
int newfd;
struct sockaddr_storage remoteaddr;
socklen_t addrlen;
char buf[256];
int len;
char remoteIP[INET6_ADDRSTRLEN];
int yes = 1;
int i, j, rv;
// int client[100], n;
struct addrinfo hints, *ai, *p;
FD_ZERO(&master);
FD_ZERO(&read_fds);
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
if((rv = getaddrinfo(NULL, PORT, &hints, &ai)) != 0) {
perror("getaddrinfo");
return 1;
}
for(p = ai; p != NULL; p = p->ai_next) {
listener = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
if(listener < 0) {
continue;
}
setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int));
if(bind(listener, p->ai_addr, p->ai_addrlen) < 0) {
close(listener);
continue;
}
break;
}
if(p == NULL) {
perror("socket and bind");
return 2;
}
freeaddrinfo(ai);
if(listen(listener, 10) == -1) {
perror("listen");
return 3;
}
FD_SET(listener, &master);
fdmax = listener;
while(1) {
printf("HERE!!! BEFORE SELECT\n");
read_fds = master;
if(select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1) {
perror("select");
return 4;
}
printf("HERE!!! AFTER SELECT\n");
for(i = 0; i <= fdmax; i++) {
printf("round i is %d\n", i );
if(FD_ISSET(i, &read_fds)) {
printf("isset i is %d\n", i );
if(i == listener) {
addrlen = sizeof(remoteaddr);
newfd = accept(listener, (struct sockaddr *)&remoteaddr, &addrlen);
printf("listener is %d, newfd is %d,listener i is %d\n", listener, newfd, i);
if(newfd == -1) {
perror("accept");
}
else {
FD_SET(newfd, &master);
if(newfd > fdmax) {
fdmax = newfd;
}
printf("selectserver: new connection form %s on socket %d\n",
inet_ntop(remoteaddr.ss_family, get_in_addr((struct sockaddr*)&remoteaddr), remoteIP, INET6_ADDRSTRLEN), newfd);
}
}
else {
// if(i != newfd) {
// printf("you are in other's zone\n");
// goto fail;
// }
newfd = i; //注意这步!!!很重要!!!
while(1) {
printf("in the newfd round\n");
if((len = read(newfd, buf, 256)) <= 0) {
perror("read");
break;
}
printf("newfd i is %d\n", i);
// while((len = read(newfd, buf, 256)) > 0) {
printf("Message form client(%d): %s", len, buf);
if(buf[0] == '@')
break;
for(j = 0; j < len; j++) {
buf[j] = toupper(buf[j]);
}
write(newfd, buf, len);
memset(buf, 0, 256);
// printf("remove client on fd %d\n", newfd);
// close(newfd);
// FD_CLR(newfd, &master);
}
// FD_CLR(newfd, &read_fds);
printf("remove client on fd %d\n", newfd);
close(newfd);
FD_CLR(newfd, &master);
}
}
}
}
// fail: return 8;
}
上面的代码里有我调试的打印信息,这样就可以更清晰得看到select()函数是如何得阻塞,如何得得知文件描述符的变化。当然,这个函数我也感觉没太弄清楚,等弄清楚之后在准备详细得写一篇关于I/O多路复用的小文章。同时,上面的代码还存在一个问题,那就是服务端只能一个一个得为客户端服务,也就是所谓的同步。
以上。