1. 只能被一个client 链接 socket例子
此例子用于socket 例子，
该例子只能用于一个客户端连接server。
不能用于多个client 连接 server
socket_server_support_one_clientconnect.c
/*
此例子用于socket 例子，
该例子只能用于一个客户端连接server。
不能用于多个client 连接 server*/
#include "wrap.h"
#define SERVER_PORT 8888int main(int argc, const char* argv[]) {int lfd;// 第一步：创建 lfdlfd = Socket(AF_INET, SOCK_STREAM, 0);// 第二步： 给lfd 绑定 IP 和 PORT，这里需要将 port 和IP 从小端转成大端struct sockaddr_in sockaddrin_server;sockaddrin_server.sin_family = AF_INET;sockaddrin_server.sin_port = htons(SERVER_PORT);sockaddrin_server.sin_addr.s_addr = htonl(INADDR_ANY);Bind(lfd,(struct sockaddr *)&sockaddrin_server,sizeof(sockaddrin_server));//第三步：设定监听上限,这个监听上限的意思是：同时只能有8个客户端和此 server连接，我们这个server只能要一个客户端和我们连接，因此这个值在这里没有具体意义Listen(lfd, 8);// 第四步 ：阻塞，并等待客户端连接. accept的第二个参数是传入传出参数，代表的是：成功于服务器连接的客户端的 地址结构struct sockaddr_in sockaddrin_client;socklen_t sockaddrin_clientsocklen_t = sizeof(sockaddrin_client);int cfd = Accept(lfd, (struct sockaddr *)&sockaddrin_client, &sockaddrin_clientsocklen_t);char clientip[33] = { 0 };const char* clientipresult = inet_ntop(AF_INET, &sockaddrin_client.sin_addr.s_addr, clientip, 32);if (clientipresult == NULL) {printf("inet_ntop error\n");}else {printf("client addr port = %d,addr ip = %s \n", ntohs(sockaddrin_client.sin_port), clientipresult);}printf("client addr port = %d,addr ip = %s \n",ntohs(sockaddrin_client.sin_port), clientip);//只要客户端连接上了， 没有错误，就会走到这一步。//第五步：连接上后，server端就可以循环的 使用read函数 读取客户端发送过来的数据了。//注意的是，read函数默认是阻塞读取的char readbuffer[256] = { 0 };int readbufferlen = 0;while (1) {readbufferlen = Read(cfd, readbuffer, 256);printf("read buffer from client %s \n", readbuffer);for (int i = 0; i < readbufferlen; ++i) {readbuffer[i] = toupper(readbuffer[i]);}Write(cfd, readbuffer, readbufferlen);Write(STDOUT_FILENO, readbuffer, readbufferlen);}
}wrap.h
#ifndef __WRAP_H_
#define __WRAP_H_#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <ctype.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
wrap.c
#include <stdlib.h>
#include <stdio.h>
#include <unistd.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;elseperr_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;elsereturn -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;elsereturn -1;}return n;
}int Close(int fd)
{int n;if ((n = close(fd)) == -1)perr_exit("close error");return n;
}/*参三: 应该读取的字节数*/
ssize_t Readn(int fd, void* vptr, size_t n)
{size_t nleft; //usigned int 剩余未读取的字节数ssize_t nread; //int 实际读到的字节数char* ptr;ptr = vptr;nleft = n;while (nleft > 0) {if ((nread = read(fd, ptr, nleft)) < 0) {if (errno == EINTR)nread = 0;elsereturn -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;elsereturn -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 == '\n')break;}else if (rc == 0) {*ptr = 0;return n - 1;}elsereturn -1;}*ptr = 0;return n;
}编译命令
gcc socket_server_support_one_clientconnect.c wrap.c -o socket_server_support_one_clientconnect.out
这里使用的是 gcc build, 如果使用g++,则会有build error，因为g++的语法检查，要比 gcc 严格一些。
error 信息如下g++ socket_server_support_one_clientconnect.c wrap.c -o socket_server_support_one_clientconnect.out
wrap.c: In function ‘ssize_t Readn(int, void*, size_t)’:
wrap.c:111:8: error: invalid conversion from ‘void*’ to ‘char*’ [-fpermissive]ptr = vptr;^~~~
wrap.c: In function ‘ssize_t Writen(int, const void*, size_t)’:
wrap.c:136:8: error: invalid conversion from ‘const void*’ to ‘const char*’ [-fpermissive]ptr = vptr;^~~~
wrap.c: In function ‘ssize_t Readline(int, void*, size_t)’:
wrap.c:180:8: error: invalid conversion from ‘void*’ to ‘char*’ [-fpermissive]ptr = vptr;
