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 != 2)
    {
        printf("Usage : %s <port>
", argv[0]);
        exit(1);
    }
    int serverSock, clientSock;
    struct sockaddr_in serverAddr, clientAddr;
    socklen_t clientAddrSize;

    char message[BUF_SIZE];
    int strLen;

    serverSock =socket(PF_INET, SOCK_STREAM, 0);
    if(serverSock == -1)
        error_handling("socket() error");

    memset(&serverAddr, 0, sizeof(serverAddr));
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
    serverAddr.sin_port = htons(atoi(argv[1]));

    if(bind(serverSock, (struct sockaddr*) &serverAddr, sizeof(serverAddr)) == -1)
        error_handling("bind() error");
    if(listen(serverSock, 5) == -1)
        error_handling("listen() error");

    puts("Server start...");
    clientAddrSize = sizeof(clientAddr);
    for(int i = 0; i < 5; i++){
        clientSock = accept(serverSock, (struct sockaddr*) &clientAddr, &clientAddrSize);
        if(clientSock == -1)
            error_handling("accept() error");
        else
            printf("Connected client %d
", i+1);
        while((strLen=read(clientSock, message, BUF_SIZE)) != 0){
            puts("echo");
            write(clientSock, message, strLen);
        }
        printf("Close client %d
", i+1);
        close(clientSock);
    }

    close(serverSock);
    puts("Server close...");
    return 0;
}

void error_handling(char * messages)
{
    puts(messages);
    exit(1);
}

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 != 3)
    {
        printf("Usage : %s <IP> <port>
", argv[0]);
        exit(1);
    }
    int sock;
    struct sockaddr_in serv_addr;
    char message[BUF_SIZE];
    int strLen;

    sock = socket(PF_INET, SOCK_STREAM, 0);
    if(sock == -1)
        error_handling("socket() error");

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
    serv_addr.sin_port = htons(atoi(argv[2]));

    if(connect(sock, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) == -1)
        error_handling("connect() error");
    else
        puts("Connected...");
    while(1){
        puts("Input message(Q to quit):");
        fgets(message, BUF_SIZE, stdin);
        if(!strcmp(message, "q
") || !strcmp(message, "Q
"))
            break;

        strLen=strlen(message);
        write(sock, message, strlen(message));
        int recvLen = 0;
        while(recvLen < strLen){
            int recvCnt = read(sock, &message[recvLen], BUF_SIZE-1);
            if(recvCnt == -1)
                error_handling("read() error");
            recvLen+=recvCnt;
        }
        message[recvLen]=0;
        printf("Message from server: %s
", message);
    }
    close(sock);
    return 0;
}

void error_handling(char * messages)
{
    puts(messages);
    exit(1);
}

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 != 2) {
        printf("Usage : %s <port>
", argv[0]);
        exit(1);
    }

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

    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0)
        ErrorHandling("WSAStartup() error");

    serverSock = socket(PF_INET, SOCK_STREAM, 0);
    if (serverSock == INVALID_SOCKET)
        ErrorHandling("socket() error");
    memset(&serverAddr, 0, sizeof(serverAddr));
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
    serverAddr.sin_port = htons(atoi(argv[1]));

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

    if (listen(serverSock, 5) == SOCKET_ERROR)
        ErrorHandling("listen() error");
    for (int i = 0; i < 5; ++i) {
        szClientAddr = sizeof(clientAddr);
        clientSock = accept(serverSock, (SOCKADDR*)&clientAddr, &szClientAddr);
        if (clientSock == INVALID_SOCKET)
            ErrorHandling("accept() error");
        else
            printf("Connected client %d
", i);
        while ((slen =recv(clientSock, message, BUF_SIZE, 0)) != 0)
        {
            send(clientSock, message, slen, 0);
        }
        closesocket(clientSock);
        printf("Closed client %d
", i);
    }
    closesocket(serverSock);
    WSACleanup();
    return 0;
}

void ErrorHandling(char *message) {
    fputs(message, stderr);
    fputc('
', 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 != 3) {
        printf("Usage : %s <IP> <port>
", argv[0]);
        exit(1);
    }

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

    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0)
        ErrorHandling("WSAStartup() error");

    sock = socket(PF_INET, SOCK_STREAM, 0);
    if (sock == INVALID_SOCKET)
        ErrorHandling("socket() error");

    memset(&serverAddr, 0, sizeof(serverAddr));
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_addr.s_addr = inet_addr(argv[1]);
    serverAddr.sin_port = htons(atoi(argv[2]));

    if (connect(sock, (SOCKADDR*)&serverAddr, sizeof(serverAddr)) == SOCKET_ERROR)
        ErrorHandling("connect() error");
    else
        printf("Connected.......
");
    while (1)
    {
        fputs("Input message(Q to quit):", stdout);
        fgets(message, BUF_SIZE, stdin);
        if(!strcmp(message, "q
") || !strcmp(message, "Q
"))
            break;
        sLen = send(sock, message, strlen(message), 0);
        recvLen = 0;
        while (recvLen < sLen) {
            int cnt = recv(sock, message, BUF_SIZE - 1, 0);
            if (cnt == -1)
                ErrorHandling("ercv() error");
            recvLen += cnt;
        }
        message[recvLen] = 0;
        printf("Message from server: %s
", message);
    }
    closesocket(sock);
    WSACleanup();
    return 0;
}

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