3个学习Socket编程的简单例子：TCP Server/Client, Select

      以前都是采用ACE的编写网络应用，最近由于工作需要，需要直接只用socket接口编写CS的代码，重新学习这方面的知识，给出自己所用到的3个简单例子，都是拷贝别人的程序。如果你能完全理解这3个例子，估计socket编程就已经基本入门了。

      建议：1) 多多查查所用到的网络接口; 2) 最好有一本书，如UNIX环境高级编程，UNIX网络编程，可查询；3) 可以直接使用书上的例子更好。

      TCP Client代码：

#include <sys/stat.h> #include <sys/types.h> #include <sys/socket.h> #include <stdio.h> #include <malloc.h> #include <netdb.h> #include <fcntl.h> #include <unistd.h> #include <netinet/in.h> #include <arpa/inet.h> #define RES_LENGTH 10240 //接受字符的最大长度 int connect_socket(char * server,int serverPort); int send_msg(int sockfd,char * sendBuff); char * recv_msg(int sockfd); int close_socket(int sockfd); int main(int argc, char ** argv) { int sockfd=0; char sendMsg[30]="abc.org\r\n\r"; char* res; int port = 4242; char ip[128] = {0}; strncpy(ip, "127.0.0.1", 128); if(argc > 2) { strncpy(ip, argv[1], 128); port = atoi(argv[2]); printf("Input IP: %s, port : %d\n", ip, port); } else if(argc > 1) { port = atoi(argv[1]); printf("Input port : %d\n", port); } sockfd=connect_socket(ip, port); send_msg(sockfd,sendMsg); /* res=recv_msg(sockfd); */ printf("return from recv function\n"); printf(res); free(res); close_socket(sockfd); return 0; } /************************************************************ * 连接SOCKET服务器，如果出错返回-1，否则返回socket处理代码 * server：服务器地址(域名或者IP),serverport：端口 * ********************************************************/ int connect_socket(char * server,int serverPort){ int sockfd=0; struct sockaddr_in addr; struct hostent * phost; //向系统注册，通知系统建立一个通信端口 //AF_INET表示使用IPv4协议 //SOCK_STREAM表示使用TCP协议 if((sockfd=socket(AF_INET,SOCK_STREAM,0))<0){ herror("Init socket error!"); return -1; } bzero(&addr,sizeof(addr)); addr.sin_family = AF_INET; addr.sin_port = htons(serverPort); addr.sin_addr.s_addr = inet_addr(server);//按IP初始化 if(addr.sin_addr.s_addr == INADDR_NONE){//如果输入的是域名 phost = (struct hostent*)gethostbyname(server); if(phost==NULL){ herror("Init socket s_addr error!"); return -1; } addr.sin_addr.s_addr =((struct in_addr*)phost->h_addr)->s_addr; } if(connect(sockfd,(struct sockaddr*)&addr, sizeof(addr))<0) { perror("Connect server fail!"); return -1; //0表示成功，-1表示失败 } else return sockfd; } /************************************************************** * 发送消息，如果出错返回-1，否则返回发送的字符长度 * sockfd：socket标识，sendBuff：发送的字符串 * *********************************************************/ int send_msg(int sockfd,char * sendBuff) { int sendSize=0; if((sendSize=send(sockfd,sendBuff,strlen(sendBuff),0))<=0){ herror("Send msg error!"); return -1; }else return sendSize; } /**************************************************************** *接受消息，如果出错返回NULL，否则返回接受字符串的指针(动态分配，注意释放) *sockfd：socket标识 * *********************************************************/ char* recv_msg(int sockfd){ char * response; int flag=0,recLenth=0; response=(char *)malloc(RES_LENGTH); memset(response,0,RES_LENGTH); for(flag=0;;) { printf("======recv data:\n"); if(( recLenth=recv(sockfd,response+flag,RES_LENGTH-flag,0))==-1 ) { free(response); printf("Return value : %d\n", recLenth); perror("Recv msg error : "); return NULL; } else if(recLenth==0) break; else { printf("%d char recieved data : %s.\n", recLenth, response+flag); flag+=recLenth; recLenth=0; } } printf("Return value : %d\n", recLenth); response[flag]='\0'; return response; } /************************************************** *关闭连接 * **********************************************/ int close_socket(int sockfd) { close(sockfd); return 0; }

      TCP Server:

#include <unistd.h> /* fork, close */ #include <stdlib.h> /* exit */ #include <string.h> /* strlen */ #include <stdio.h> /* perror, fdopen, fgets */ #include <sys/socket.h> #include <sys/wait.h> /* waitpid */ #include <netdb.h> /* getaddrinfo */ #define die(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0) #define PORT "4242" #define NUM_CHILDREN 3 #define MAXLEN 1024 int readline(int fd, char *buf, int maxlen); // forward declaration int recvdata(int fd, char *buf, int maxlen); // forward declaration int main(int argc, char** argv) { int i, n, sockfd, clientfd; int yes = 1; // used in setsockopt(2) struct addrinfo *ai; struct sockaddr_in *client; socklen_t client_t; pid_t cpid; // child pid char line[MAXLEN]; char cpid_s[32]; char welcome[32]; /* Create a socket and get its file descriptor -- socket(2) */ sockfd = socket(AF_INET, SOCK_STREAM, 0); if (sockfd == -1) { die("Couldn't create a socket"); } /* Prevents those dreaded "Address already in use" errors */ if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (const void *)&yes, sizeof(int)) == -1) { die("Couldn't setsockopt"); } /* Fill the address info struct (host + port) -- getaddrinfo(3) */ if (getaddrinfo(NULL, PORT, NULL, &ai) != 0) { // get localhost die("Couldn't get address"); } /* Assign address to this socket's fd */ if (bind(sockfd, ai->ai_addr, ai->ai_addrlen) != 0) { // only bind on localhost ip die("Couldn't bind socket to address"); } /* Free the memory used by our address info struct */ freeaddrinfo(ai); /* Mark this socket as able to accept incoming connections */ /* printf("Process %d Listening\n", getpid()); */ if (listen(sockfd, 10) == -1) { die("Couldn't make socket listen"); } printf("One new connection is coming!\n"); /* Fork you some child processes. */ for (i = 0; i < NUM_CHILDREN; i++) { cpid = fork(); if (cpid == -1) { die("Couldn't fork"); } if (cpid == 0) { // We're in the child ... for (;;) { // Run forever ... /* Necessary initialization for accept(2) */ client_t = sizeof client; /* Blocks! */ printf("Waiting new connection!\n"); clientfd = accept(sockfd, (struct sockaddr *)&client, &client_t); if (clientfd == -1) { die("Couldn't accept a connection"); } /* Send a welcome message/prompt */ bzero(cpid_s, 32); bzero(welcome, 32); sprintf(cpid_s, "%d", getpid()); sprintf(welcome, "Child %s echo> ", cpid_s); send(clientfd, welcome, strlen(welcome), 0); /* Read a line from the client socket ... */ /* n = readline(clientfd, line, MAXLEN); if (n == -1) { die("Couldn't read line from connection"); } */ n = recvdata(clientfd, line, MAXLEN); printf("recieve data: %s", line); /* ... and echo it back */ send(clientfd, line, n, 0); /* Clean up the client socket */ close(clientfd); printf("Close client socket.\n"); } } } /* Sit back and wait for all child processes to exit */ while (waitpid(-1, NULL, 0) > 0); /* Close up our socket */ close(sockfd); printf("Close server socket.\n"); return 0; } /** * Simple utility function that reads a line from a file descriptor fd, * up to maxlen bytes -- ripped from Unix Network Programming, Stevens. */ int readline(int fd, char *buf, int maxlen) { int n, rc; char c; for (n = 1; n < maxlen; n++) { if ((rc = read(fd, &c, 1)) == 1) { *buf++ = c; if (c == '\n') break; } else if (rc == 0) { if (n == 1) return 0; // EOF, no data read else break; // EOF, read some data } else return -1; // error } *buf = '\0'; // null-terminate return n; } int recvdata(int fd, char *buf, int maxlen) { return recv(fd, buf, maxlen, 0); }

      采用Select的TCP Server:

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <string.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #define MYPORT 1234 // the port users will be connecting to #define BACKLOG 5 // how many pending connections queue will hold #define BUF_SIZE 1024 int fd_A[BACKLOG]; // accepted connection fd int conn_amount; // current connection amount void showclient() { int i; printf("client amount: %d\n", conn_amount); for (i = 0; i < BACKLOG; i++) { printf("[%d]:%d ", i, fd_A[i]); } printf("\n\n"); } int main(void) { int sock_fd, new_fd; // listen on sock_fd, new connection on new_fd struct sockaddr_in server_addr; // server address information struct sockaddr_in client_addr; // connector's address information socklen_t sin_size; int yes = 1; char buf[BUF_SIZE]; int ret; int i; if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) { perror("socket"); exit(1); } if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) { perror("setsockopt"); exit(1); } server_addr.sin_family = AF_INET; // host byte order server_addr.sin_port = htons(MYPORT); // short, network byte order server_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP memset(server_addr.sin_zero, '\0', sizeof(server_addr.sin_zero)); if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) { perror("bind"); exit(1); } if (listen(sock_fd, BACKLOG) == -1) { perror("listen"); exit(1); } printf("listen port %d\n", MYPORT); fd_set fdsr; int maxsock; struct timeval tv; conn_amount = 0; sin_size = sizeof(client_addr); maxsock = sock_fd; while (1) { // initialize file descriptor set FD_ZERO(&fdsr); FD_SET(sock_fd, &fdsr); // add fd // timeout setting tv.tv_sec = 30; tv.tv_usec = 0; // add active connection to fd set for (i = 0; i < BACKLOG; i++) { if (fd_A[i] != 0) { FD_SET(fd_A[i], &fdsr); } } ret = select(maxsock + 1, &fdsr, NULL, NULL, &tv); if (ret < 0) { // error perror("select"); break; } else if (ret == 0) { // time out printf("timeout\n"); continue; } // check every fd in the set for (i = 0; i < conn_amount; i++) { if (FD_ISSET(fd_A[i], &fdsr)) // check which fd is ready { ret = recv(fd_A[i], buf, sizeof(buf), 0); if (ret <= 0) { // client close printf("ret : %d and client[%d] close\n", ret, i); close(fd_A[i]); FD_CLR(fd_A[i], &fdsr); // delete fd fd_A[i] = 0; conn_amount--; } else { // receive data if (ret < BUF_SIZE) memset(&buf[ret], '\0', 1); // add NULL('\0') printf("client[%d] send:%s\n", i, buf); } } } // check whether a new connection comes if (FD_ISSET(sock_fd, &fdsr)) // accept new connection { new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &sin_size); if (new_fd <= 0) { perror("accept"); continue; } // add to fd queue if (conn_amount < BACKLOG) { fd_A[conn_amount++] = new_fd; printf("new connection client[%d] %s:%d\n", conn_amount, inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port)); if (new_fd > maxsock) // update the maxsock fd for select function maxsock = new_fd; } else { printf("max connections arrive, exit\n"); send(new_fd, "bye", 4, 0); close(new_fd); break; } } showclient(); } // close other connections for (i = 0; i < BACKLOG; i++) { if (fd_A[i] != 0) { close(fd_A[i]); } } exit(0); }