简单的TCP通信

//客户端：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <string.h>

#define MAXLINE 1024
int main(int argc, char** argv)
{
    int sockfd, ret;
    struct sockaddr_in servaddr;
    char recvline[MAXLINE];

    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        fprintf(stderr, "socket error.\n");
        return -1;
    }
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(20015);
    if((inet_pton(AF_INET, (char*)"192.168.0.130", &servaddr.sin_addr)) <= 0)
    {
        fprintf(stderr, "inet_pton error.\n");
        return -1;
    }
    
    if(connect(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
    {
        fprintf(stderr, "connect error.\n");
        return -1;
    }
    
    while((ret = read(sockfd, recvline, sizeof(recvline))) > 0)
    {
        recvline[ret] = 0;
        if(fputs(recvline, stdout) == EOF)
        {
            fprintf(stderr, "fputs error..\n");
            return -1;
        }
    }
    if(ret < 0)
        fprintf(stderr, "read error..\n");
    printf("\n");
    exit(0);
}

//服务器端
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <ctime>

int main(int argc, char** argv)
{
    int listenfd, connfd, ret;
    struct sockaddr_in servaddr, cliaddr;
    time_t now;
    char cliIp[1024] = {0};
    char buff[1024];

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(20015);
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    
    if((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        fprintf(stderr, "socket error.\n");
        return -1;
    }
    ret = bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr));
    if(ret < 0)
    {
        fprintf(stderr, "bind error..%d\n", ret);
        return -1;
    }

    listen(listenfd, 5);

    for(;;)
    {
        socklen_t clilen = sizeof(clilen);
        connfd = accept(listenfd, (struct sockaddr*)&cliaddr, &clilen);
        if(connect < 0)
        {
            fprintf(stderr, "accept error..\n");
            return -1;
        }
        now = time(NULL);
        snprintf(cliIp, sizeof(cliIp), "From %s:%d:\n   ", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port) ;
        snprintf(buff, sizeof(buff), "%s\n", ctime(&now));
        strcat(cliIp, buff);
        ret = write(connfd, cliIp, sizeof(cliIp));
        ret = close(connfd);
        if(ret < 0)
        {
            fprintf(stderr, "close error..\n");
            return -1;
        }
    }
    
}

结果：

$ ./a.out 
From 0.176.121.183:10124:
   Sun Jul  5 11:56:26 2015

MSS：（最大分节大小）

用于向对端TCP通告对端在每个分节中能够发送的最大TCP数据量。

MSS=MTU-IP和TCP首部固定长度。

以太网：IPV4的MSS = 1460  ipv6:1440