网络编程

1. 服务器端

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <ctype.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <string.h>
#include <strings.h>

#define SERVER_PORT 6666
#define SERVER_IP "127.0.0.1"

int main()
{
    int lfd=socket(AF_INET,SOCK_STREAM,0);
    struct sockaddr_in server_addr;
    bzero(&server_addr, sizeof(server_addr));
    server_addr.sin_family= AF_INET;
    server_addr.sin_port=htons(6666);
    server_addr.sin_addr.s_addr= htonl(INADDR_ANY);

    bind(lfd,(struct sockaddr*) &server_addr, sizeof(server_addr));

    listen(lfd,32);
    int cfd;
    struct sockaddr_in client_addr;
    socklen_t client_addr_len=sizeof(client_addr);
    cfd=accept(lfd,(struct sockaddr*) &client_addr, &client_addr_len);
    char client_ip_buf[BUFSIZ];
    inet_ntop(AF_INET,&client_addr.sin_addr.s_addr,client_ip_buf, sizeof(client_ip_buf));
    printf("client ip: %s   client port: %d
", client_ip_buf, ntohs(client_addr.sin_port));
    
    char buf[BUFSIZ];
    while(1){
        int n=read(cfd,buf,sizeof(buf));
        int i;
        for(i=0;i<n;i++){
            buf[i]=toupper(buf[i]);
        }
        write(cfd,buf,n);
    }
    close(lfd);
    close(cfd);

    return 0;
}

2. 客户端

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>    // struct sockaddr_in
#include <string.h>

#define SERVER_IP "127.0.0.1"

int main()
{
    int cfd;
    cfd=socket(AF_INET,SOCK_STREAM,0);
    
    struct sockaddr_in server_addr;

    memset(&server_addr,0,sizeof(server_addr));
    server_addr.sin_family=AF_INET;
    server_addr.sin_port=htons(6666);
    inet_pton(AF_INET,SERVER_IP, &server_addr.sin_addr.s_addr);
    connect(cfd,(struct sockaddr*) &server_addr, sizeof(server_addr));

    char buf[BUFSIZ];
    while(1){
        fgets(buf,sizeof(buf),stdin);
        write(cfd,buf,strlen(buf));

        int n;
        n=read(cfd,buf,sizeof(buf));
        write(STDOUT_FILENO,buf,n);
    }
    close(cfd);
    return 0;
}

如果先关server，再关client，则下次启动server时bind会报错，Address already in use.

关闭server后，端口并没有被释放。


代码改进，增加错误处理函数：
wrap.c

#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
void perr_exit(const char *s)
{
	perror(s);
	exit(1);
}
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr)
{
	int n;
	again:
	if ( (n = accept(fd, sa, salenptr)) < 0) {
		if ((errno == ECONNABORTED) || (errno == EINTR))       // accept为慢速系统调用。 EINTR  The system call was interrupted by a signal that was caught before a valid connection arrived.   CONNABORTED  A connection has been aborted.
			goto again;
		else
			perr_exit("accept error");
	}
	return n;
}
int Bind(int fd, const struct sockaddr *sa, socklen_t salen)
{
	int n;
	if ((n = bind(fd, sa, salen)) < 0)
		perr_exit("bind error");
	return n;
}
int Connect(int fd, const struct sockaddr *sa, socklen_t salen)
{
	int n;
	if ((n = connect(fd, sa, salen)) < 0)
		perr_exit("connect error");
	return n;
}
int Listen(int fd, int backlog)
{
	int n;
	if ((n = listen(fd, backlog)) < 0)
		perr_exit("listen error");
	return n;
}
int Socket(int family, int type, int protocol)
{
	int n;
	if ( (n = socket(family, type, protocol)) < 0)
		perr_exit("socket error");
	return n;
}
ssize_t Read(int fd, void *ptr, size_t nbytes) 
{
	ssize_t n;
again:
	if ( (n = read(fd, ptr, nbytes)) == -1) {  //慢速系统调用，有可能造成进程永久阻塞。
// read 返回值： 1. >0 表示实际读到的字节数； 2. =0  数据读完，即读到文件，管道，socket末尾。 3. =-1 异常，通过errno细分， errno=EINTR 说明被信号中断，选择重启or退出；errno=EAGAIN (EWOULDBLOCK) 以非阻塞方式读并且没有数据。errno=其他值， 错误。 
		if (errno == EINTR)
			goto again;
		else
			return -1;
	}
	return n;
}
ssize_t Write(int fd, const void *ptr, size_t nbytes)
{
	ssize_t n;
again:
	if ( (n = write(fd, ptr, nbytes)) == -1) {
		if (errno == EINTR)
			goto again;
		else
			return -1;
	}
	return n;
}
int Close(int fd)
{
	int n;
	if ((n = close(fd)) == -1)
		perr_exit("close error");
	return n;
}
ssize_t Readn(int fd, void *vptr, size_t n)  //需要读取n个字节，可能要分多次读
{
	size_t nleft;
	ssize_t nread;
	char *ptr;

	ptr = vptr;
	nleft = n;

	while (nleft > 0) {
		if ( (nread = read(fd, ptr, nleft)) < 0) {
			if (errno == EINTR)
				nread = 0;
			else
				return -1;
		} else if (nread == 0)
			break;
		nleft -= nread;
		ptr += nread;
	}
	return n - nleft;
}

ssize_t Writen(int fd, const void *vptr, size_t n)
{
	size_t nleft;
	ssize_t nwritten;
	const char *ptr;

	ptr = vptr;
	nleft = n;

	while (nleft > 0) {
		if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
			if (nwritten < 0 && errno == EINTR)
				nwritten = 0;
			else
				return -1;
		}
		nleft -= nwritten;
		ptr += nwritten;
	}
	return n;
}

static ssize_t my_read(int fd, char *ptr)
{
	static int read_cnt;
	static char *read_ptr;
	static char read_buf[100];

	if (read_cnt <= 0) {
again:
		if ((read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {
			if (errno == EINTR)
				goto again;
			return -1;	
		} else if (read_cnt == 0)
			return 0;
		read_ptr = read_buf;
	}
	read_cnt--;
	*ptr = *read_ptr++;
	return 1;
}

ssize_t Readline(int fd, void *vptr, size_t maxlen)
{
	ssize_t n, rc;
	char c, *ptr;
	ptr = vptr;

	for (n = 1; n < maxlen; n++) {
		if ( (rc = my_read(fd, &c)) == 1) {
			*ptr++ = c;
			if (c == '
')
				break;
		} else if (rc == 0) {
			*ptr = 0;
			return n - 1;
		} else
			return -1;
	}
	*ptr = 0;
	return n;
}

多进程并发服务器：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include "wrap.h"
#include <string.h>
#include <ctype.h>
#include <sys/wait.h>

#define SERVER_PORT 8888

void wait_child(int signo){
    while(waitpid(0,NULL,WNOHANG)>0);
    return;
}

int main()
{
    int lfd,cfd;
    lfd=Socket(AF_INET,SOCK_STREAM,0);

    struct sockaddr_in serv_addr, client_addr;

    bzero(&serv_addr,sizeof(serv_addr));
    serv_addr.sin_family=AF_INET;
    serv_addr.sin_port=htons(SERVER_PORT);
    serv_addr.sin_addr.s_addr=htonl(INADDR_ANY);
    //inet_pton(AF_INET,"127.0.0.1", &serv_addr.sin_addr.s_addr);

    Bind(lfd,(struct sockaddr*)&serv_addr, sizeof(serv_addr));

    Listen(lfd,128);
    pid_t pid;
    int n,i;
    char buf[BUFSIZ];
    char ip_buf[BUFSIZ];

    while(1){
        socklen_t client_addr_len=sizeof(client_addr);
        cfd= Accept(lfd,(struct sockaddr*)&client_addr, &client_addr_len);
        
        printf("client ip: %s-----client port: %d
",
               inet_ntop(AF_INET, &client_addr.sin_addr.s_addr, ip_buf, sizeof(ip_buf)),
                 ntohs(client_addr.sin_port));
        
        pid=fork();
        if(pid<0){
            perror("fork error");
            exit(1);
        }
        if(pid==0){
            close(lfd);
            break;
        }
        close(cfd);
        signal(SIGCHLD,wait_child);
    }
    if(pid==0){
        while(1){
            n=Read(cfd,buf,sizeof(buf));        
            if(n==0){
                close(cfd);
                return 0;
            }
            if(n==-1){
                perror("read err");
                exit(1);
            }
            for(i=0;i<n;i++){
                buf[i]=toupper(buf[i]);
            }
            Write(cfd,buf,n);
        }

    }
    return 0;
}

多线程版：

#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <ctype.h>
#include <unistd.h>
#include <fcntl.h>

#include "wrap.h"

#define MAXLINE 8192
#define SERV_PORT 8000

struct s_info {                     //定义一个结构体, 将地址结构跟cfd捆绑
    struct sockaddr_in cliaddr;
    int connfd;
};

void *do_work(void *arg)
{
    int n,i;
    struct s_info *ts = (struct s_info*)arg;
    char buf[MAXLINE];
    char str[INET_ADDRSTRLEN];      //#define INET_ADDRSTRLEN 16  可用"[+d"查看

    while (1) {
        n = Read(ts->connfd, buf, MAXLINE);                     //读客户端
        if (n == 0) {
            printf("the client %d closed...
", ts->connfd);
            break;                                              //跳出循环,关闭cfd
        }
        printf("received from %s at PORT %d
",
                inet_ntop(AF_INET, &(*ts).cliaddr.sin_addr.s_addr, str, sizeof(str)),
                ntohs((*ts).cliaddr.sin_port));                 //打印客户端信息(IP/PORT)

        for (i = 0; i < n; i++) 
            buf[i] = toupper(buf[i]);                           //小写-->大写

        Write(STDOUT_FILENO, buf, n);                           //写出至屏幕
        Write(ts->connfd, buf, n);                              //回写给客户端
    }
    Close(ts->connfd);

    return (void *)0;
}

int main(void)
{
    struct sockaddr_in servaddr, cliaddr;
    socklen_t cliaddr_len;
    int listenfd, connfd;
    pthread_t tid;
    struct s_info ts[256];      //根据最大线程数创建结构体数组.
    int i = 0;

    listenfd = Socket(AF_INET, SOCK_STREAM, 0);                     //创建一个socket, 得到lfd

    bzero(&servaddr, sizeof(servaddr));                             //地址结构清零
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);                   //指定本地任意IP
    servaddr.sin_port = htons(SERV_PORT);                           //指定端口号 8000

    Bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)); //绑定

    Listen(listenfd, 128);      //设置同一时刻链接服务器上限数

    printf("Accepting client connect ...
");

    while (1) {
        cliaddr_len = sizeof(cliaddr);
        connfd = Accept(listenfd, (struct sockaddr *)&cliaddr, &cliaddr_len);   //阻塞监听客户端链接请求
        ts[i].cliaddr = cliaddr;
        ts[i].connfd = connfd;

        /* 达到线程最大数时，pthread_create出错处理, 增加服务器稳定性 */
        pthread_create(&tid, NULL, do_work, (void*)&ts[i]);
        pthread_detach(tid);                                                    //子线程分离,防止僵线程产生.
        i++;
    }

    return 0;
}