socket编程实例-TCP

第一版：实现简单功能

客户端从标准输入读入字符串传给服务端，服务端把字符串中的小写字母转化为大写字母传回客户端

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

#define SERV_IP "127.0.0.1"
#define SERV_PORT 6666

int main()
{
        int cfd;
        struct sockaddr_in serv_addr;
        socklen_t serv_addr_len;
        char buf[BUFSIZ];
        int n;

        cfd = socket(AF_INET, SOCK_STREAM, 0);

        memset(&serv_addr, 0, sizeof(serv_addr));
        serv_addr.sin_family = AF_INET;
        serv_addr.sin_port = htons(SERV_PORT);
        //serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
        inet_pton(AF_INET, SERV_IP, &serv_addr.sin_addr.s_addr);

        //客户端可以不用bind()绑定ip和端口号，操作系会默认分配

        connect(cfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

        while(1)
        {
                fgets(buf, sizeof(buf), stdin);
                write(cfd, buf, strlen(buf));
                n = read(cfd, buf, sizeof(buf));
                write(STDOUT_FILENO, buf, n);
        }

        close(cfd);

        return 0;
}

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

#define SERV_PORT 6666

int main()
{
        int sfd, cfd;
        struct sockaddr_in serv_addr, clie_addr;
        socklen_t clie_addr_len;
        char buf[BUFSIZ];
        int n, i;

        sfd = socket(AF_INET, SOCK_STREAM, 0);

        serv_addr.sin_family = AF_INET;
        serv_addr.sin_port = htons(SERV_PORT);
        serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);

        bind(sfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

        listen(sfd, 128);

        clie_addr_len = sizeof(clie_addr);
        cfd = accept(sfd, (struct sockaddr*)&clie_addr, &clie_addr_len);

        while(1)
        {
                n = read(cfd, buf, sizeof(buf));
                for(i=0; i<n; i++)
                {
                        buf[i] = toupper(buf[i]);
                }
                write(cfd, buf, n);
        }

        close(sfd);
        close(cfd);

        return 0;
}

第二版：加入错误封装

上面没有对错误进行处理，我们知道，系统调用不能保证每次都成功，必须进行出错处理，这样一方面可以保证程序逻辑正常，另一方面可以迅速得到故障信息。为使错误处理的代码不影响主程序的可读性，我们把与socket相关的一些系统函数加上错误处理代码包装成新的函数（新函数和原函数调用的区别仅仅在于新函数名首字母大写了），做成一个模块wrap.c，这样在调用socket函数时，调用我们封装了错误处理的函数就可以了。

#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))
            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) {
        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)
{
    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;
}

#ifndef __WRAP_H_
#define __WRAP_H_
void perr_exit(const char *s);
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr);
int Bind(int fd, const struct sockaddr *sa, socklen_t salen);
int Connect(int fd, const struct sockaddr *sa, socklen_t salen);
int Listen(int fd, int backlog);
int Socket(int family, int type, int protocol);
ssize_t Read(int fd, void *ptr, size_t nbytes);
ssize_t Write(int fd, const void *ptr, size_t nbytes);
int Close(int fd);
ssize_t Readn(int fd, void *vptr, size_t n);
ssize_t Writen(int fd, const void *vptr, size_t n);
ssize_t my_read(int fd, char *ptr);
ssize_t Readline(int fd, void *vptr, size_t maxlen);
#endif

第三版：使用多进程技术在服务端实现高并发

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

#include "wrap.h"

#define SERV_PORT 6666

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

int main()
{
        pid_t pid;
        int sfd, cfd;
        struct sockaddr_in serv_addr, clie_addr;
        socklen_t clie_addr_len;
        char buf[BUFSIZ], clie_IP[BUFSIZ];
        int n, i;

        sfd = Socket(AF_INET, SOCK_STREAM, 0);

        bzero(&serv_addr, sizeof(serv_addr));
        serv_addr.sin_family = AF_INET;
        serv_addr.sin_port = htons(SERV_PORT);
        serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);

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

        Listen(sfd, 128);

        while(1)
        {
                clie_addr_len = sizeof(clie_addr);
                cfd = Accept(sfd, (struct sockaddr*)&clie_addr, &clie_addr_len);
                printf("client IP: %s, port: %d
", inet_ntop(AF_INET, &clie_addr.sin_addr.s_addr, clie_IP, sizeof(clie_IP)), ntohs(clie_addr.sin_port));

                pid = fork();
                if(pid < 0)
                {
                        perror("fork error");
                        exit(1);
                }
                else if(pid == 0)
                {
                        close(sfd);
                        break;
                }
                else
                {
                        close(cfd);
                        signal(SIGCHLD, wait_child);
                }
        }

        if(pid == 0)
        {
                while(1)
                {
                        n = Read(cfd, buf, sizeof(buf));
                        if(n == 0)
                        {
                                close(cfd);
                                return 0;
                        }
                        else if(n == -1)
                        {
                                perror("read error");
                                exit(1);
                        }
                        else
                        {
                                for(i=0; i<n; i++)
                                {
                                        buf[i] = toupper(buf[i]);
                                }
                                write(cfd, buf, n);
                                write(STDOUT_FILENO, buf, n);
                        }
                }
        }

        return 0;
}

第四版：使用多线程技术在服务端实现高并发

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

#include "wrap.h"

#define SERV_PORT 6666
#define MAXLINE 8192

struct s_info{
        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];

        while(1){
                n = Read(ts->connfd, buf, MAXLINE);
                if(n == 0){
                        printf("the client %d closed...
", ts->connfd);
                        break;
                }
                printf("received from %s at PORT %d
", inet_ntop(AF_INET, &(*ts).cliaddr.sin_addr, str, sizeof(str)), ntohs((*ts).cliaddr.sin_port));
                for(i=0; i<n; i++){
                        buf[i] = toupper(buf[i]);
                }
                write(ts->connfd, buf, n);
                write(STDOUT_FILENO, buf, n);
        }
        Close(ts->connfd);

        return (void *)0;
}

int main()
{
        int sfd, cfd;
        struct sockaddr_in serv_addr, clie_addr;
        socklen_t clie_addr_len;
        struct s_info ts[256];
        pthread_t tid;
        int i = 0;

        sfd = Socket(AF_INET, SOCK_STREAM, 0);

        bzero(&serv_addr, sizeof(serv_addr));
        serv_addr.sin_family = AF_INET;
        serv_addr.sin_port = htons(SERV_PORT);
        serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);

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

        Listen(sfd, 128);

        while(1)
        {
                clie_addr_len = sizeof(clie_addr);
                cfd = Accept(sfd, (struct sockaddr*)&clie_addr, &clie_addr_len);
                ts[i].cliaddr = clie_addr;
                ts[i].connfd = cfd;

                pthread_create(&tid, NULL, do_work, (void*)&ts[i]);
                pthread_detach(tid);
                i++;
        }

        return 0;
}