回声TCP服务器端/客户端

一、TCP服务端

1、TCP服务端的默认函数调用顺序

• socket()创建套接字
• bind()分配套接字地址
• listen()等待请求连接状态
• accept()允许连接
• read()/write()数据交换
• close()断开连接

2、进入等待连接请求状态

　　只有调用了listen函数，客户端才能进入可发出连接请求的状态。即这时客户端才能调用connect()函数（若提前调用将发生错误）。

　　int listen(int sock, int backlog);

　　成功返回0，失败返回-1。sock指服务器端套接字，backlog指连接请求队列的长度，若为5，则队列长度为5，表示最多使5个连接请求进入队列。

3、受理客户端连接请求

　　int accept();

　　accept函数受理连接请求队列中待处理的客户端连接请求。函数调用成功时，accept函数内部将产生用于数据IO的套接字，并返回其文件描述符。需要强调的是，套接字是自动创建的，并自动与发起连接请求的客户端建立连接。

二、TCP客户端

1、TCP客户端的默认函数调用顺序

• socket()创建套接字
• connect()请求连接
• read/write数据交换
• close()断开连接

2、connect()

　　客户端调用connect函数后，发生以下情况之一才会返回（完成函数调用）：

• 服务器端接收连接请求。
• 发生断网等异常情况而中断连接请求。

　　所谓的“接收连接”并不一位置服务器端调用accept函数，其实是服务器端把连接请求信息记录到等待队列。因此，connect函数返回后并不立即进行数据交换。

　　客户端的IP地址和端口是在调用connect函数时自动分配的。

三、回声服务端/客户端

1、linux

服务端：

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

 #define BUF_SIZE 1024
 void error_handling(char * messages);

 int main(int argc, char *argv[])
 {
     if(argc != )
     {
         printf("Usage : %s <port>\n", argv[]);
         exit();
     }
     int serverSock, clientSock;
     struct sockaddr_in serverAddr, clientAddr;
     socklen_t clientAddrSize;

     char message[BUF_SIZE];
     int strLen;

     serverSock =socket(PF_INET, SOCK_STREAM, );
     if(serverSock == -)
         error_handling("socket() error");

     memset(&serverAddr, , sizeof(serverAddr));
     serverAddr.sin_family = AF_INET;
     serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
     serverAddr.sin_port = htons(atoi(argv[]));

     if(bind(serverSock, (struct sockaddr*) &serverAddr, sizeof(serverAddr)) == -)
         error_handling("bind() error");
     if(listen(serverSock, ) == -)
         error_handling("listen() error");

     puts("Server start...");
     clientAddrSize = sizeof(clientAddr);
     for(int i = ; i < ; i++){
         clientSock = accept(serverSock, (struct sockaddr*) &clientAddr, &clientAddrSize);
         if(clientSock == -)
             error_handling("accept() error");
         else
             printf("Connected client %d\n", i+);
         while((strLen=read(clientSock, message, BUF_SIZE)) != ){
             puts("echo");
             write(clientSock, message, strLen);
         }
         printf("Close client %d\n", i+);
         close(clientSock);
     }

     close(serverSock);
     puts("Server close...");
     return ;
 }

 void error_handling(char * messages)
 {
     puts(messages);
     exit();
 }

客户端：

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

#define BUF_SIZE 1024
void error_handling(char * messages);

int main(int argc, char *argv[])
{
    if(argc != )
    {
        printf("Usage : %s <IP> <port>\n", argv[]);
        exit();
    }
    int sock;
    struct sockaddr_in serv_addr;
    char message[BUF_SIZE];
    int strLen;

    sock = socket(PF_INET, SOCK_STREAM, );
    if(sock == -)
        error_handling("socket() error");

    memset(&serv_addr, , sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr(argv[]);
    serv_addr.sin_port = htons(atoi(argv[]));

    if(connect(sock, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) == -)
        error_handling("connect() error");
    else
        puts("Connected...");
    while(){
        puts("Input message(Q to quit):");
        fgets(message, BUF_SIZE, stdin);
        if(!strcmp(message, "q\n") || !strcmp(message, "Q\n"))
            break;

        strLen=strlen(message);
        write(sock, message, strlen(message));
        int recvLen = ;
        while(recvLen < strLen){
            int recvCnt = read(sock, &message[recvLen], BUF_SIZE-);
            if(recvCnt == -)
                error_handling("read() error");
            recvLen+=recvCnt;
        }
        message[recvLen]=;
        printf("Message from server: %s\n", message);
    }
    close(sock);
    return ;
}

void error_handling(char * messages)
{
    puts(messages);
    exit();
}

2、windows

服务端：

 #include <stdio.h>
 #include <stdlib.h>
 #include <WinSock2.h>

 #define BUF_SIZE 1024
 void ErrorHandling(char *message);

 int main(int argc, char *argv[])
 {
     if (argc != ) {
         printf("Usage : %s <port>\n", argv[]);
         exit();
     }

     WSADATA wsaData;
     SOCKET serverSock, clientSock;
     SOCKADDR_IN serverAddr, clientAddr;
     int szClientAddr;
     char message[BUF_SIZE];
     int slen;

     if (WSAStartup(MAKEWORD(, ), &wsaData) != )
         ErrorHandling("WSAStartup() error");

     serverSock = socket(PF_INET, SOCK_STREAM, );
     if (serverSock == INVALID_SOCKET)
         ErrorHandling("socket() error");
     memset(&serverAddr, , sizeof(serverAddr));
     serverAddr.sin_family = AF_INET;
     serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
     serverAddr.sin_port = htons(atoi(argv[]));

     if (bind(serverSock, (SOCKADDR*)&serverAddr, sizeof(serverAddr)) == SOCKET_ERROR)
         ErrorHandling("bind() error");

     if (listen(serverSock, ) == SOCKET_ERROR)
         ErrorHandling("listen() error");
     for (int i = ; i < ; ++i) {
         szClientAddr = sizeof(clientAddr);
         clientSock = accept(serverSock, (SOCKADDR*)&clientAddr, &szClientAddr);
         if (clientSock == INVALID_SOCKET)
             ErrorHandling("accept() error");
         else
             printf("Connected client %d\n", i);
         while ((slen =recv(clientSock, message, BUF_SIZE, )) != )
         {
             send(clientSock, message, slen, );
         }
         closesocket(clientSock);
         printf("Closed client %d\n", i);
     }
     closesocket(serverSock);
     WSACleanup();
     return ;
 }

 void ErrorHandling(char *message) {
     fputs(message, stderr);
     fputc('\n', stderr);
 }

客户端：

 #pragma warning(disable:4996)
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <winsock2.h>

 #define BUF_SIZE 1024
 void ErrorHandling(char *message);

 int main(int argc, char* argv[]) {
     if (argc != ) {
         printf("Usage : %s <IP> <port>\n", argv[]);
         exit();
     }

     WSADATA wsaData;
     SOCKET sock;
     SOCKADDR_IN serverAddr;
     char message[BUF_SIZE];
     int sLen, recvLen;

     if (WSAStartup(MAKEWORD(, ), &wsaData) != )
         ErrorHandling("WSAStartup() error");

     sock = socket(PF_INET, SOCK_STREAM, );
     if (sock == INVALID_SOCKET)
         ErrorHandling("socket() error");

     memset(&serverAddr, , sizeof(serverAddr));
     serverAddr.sin_family = AF_INET;
     serverAddr.sin_addr.s_addr = inet_addr(argv[]);
     serverAddr.sin_port = htons(atoi(argv[]));

     if (connect(sock, (SOCKADDR*)&serverAddr, sizeof(serverAddr)) == SOCKET_ERROR)
         ErrorHandling("connect() error");
     else
         printf("Connected.......\n");
     while ()
     {
         fputs("Input message(Q to quit):", stdout);
         fgets(message, BUF_SIZE, stdin);
         if(!strcmp(message, "q\n") || !strcmp(message, "Q\n"))
             break;
         sLen = send(sock, message, strlen(message), );
         recvLen = ;
         while (recvLen < sLen) {
             int cnt = recv(sock, message, BUF_SIZE - , );
             if (cnt == -)
                 ErrorHandling("ercv() error");
             recvLen += cnt;
         }
         message[recvLen] = ;
         printf("Message from server: %s\n", message);
     }
     closesocket(sock);
     WSACleanup();
     return ;
 }

 void ErrorHandling(char *message) {
     fputs(message, stderr);
     fputc('\n', stderr);
 }