网络通信

网络通信概述

IP和端口

数据传输三要素：源、目的、长度 （网络传输中使用“IP和端口”表示源或目的）

网络传输两个对象（server、client）

两种传输方式：TCP/UDP

TCP和UDP原理上的区别

TCP/UDP网络通信交互图（1为tcp，2为udp）

网络编程主要函数

socket函数

int socket(int domain, int type, int protocol);

        

          
        
        
        

          

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bind函数

int bind(int sockfd, const struct sockaddr *addr,socklen_t addrlen);

        

          
        
        
        

          

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listen函数

int listen(int sockfd, int backlog);

        

          
        
        
        

          

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accept函数

int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);

        

          
        
        
        

          

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connect函数

int connect(int sockfd, const struct sockaddr *addr,socklen_t addrlen);

        

          
        
        
        

          

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send函数

ssize_t send(int sockfd, const void *buf, size_t len, int flags);

        

          
        
        
        

          

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recv函数

 ssize_t recv(int sockfd, void *buf, size_t len, int flags);

        

          
        
        
        

          

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recvfrom函数

ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags,struct sockaddr *src_addr, socklen_t *addrlen);

        

          
        
        
        

          

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sendto函数

ssize_t sendto(int sockfd, const void *buf, size_t len, int flags,const struct sockaddr *dest_addr, socklen_t addrlen);

        

          
        
        
        

          

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TCP编程

server

#include <sys/types.h>    /* See NOTES */
#include <sys/socket.h> //网络编程所需文件
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>

/* socket
 * bind
 * listen
 * accept
 * send/recv
 */

#define SERVER_PORT 8888 // 服务器端口号
#define BACKLOG 10         // listen函数中最大同时监听连接数

int main(int argc, char **argv)
{
   
   
    int iSocketServer;
    int iSocketClient;
    struct sockaddr_in tSocketServerAddr; // 服务器地址结构体
    struct sockaddr_in tSocketClientAddr; // 客户端地址结构体
    int iRet;
    int iAddrLen;

    int iRecvLen;
    unsigned char ucRecvBuf[1000];

    int iClientNum = -1;

    signal(SIGCHLD, SIG_IGN); // 忽略子进程退出信号，避免僵尸进程
    // 1.创建套接字 远程通信，TCP协议，0默认
    // 执行成功返回文件描述符，失败返回-1
    iSocketServer = socket(AF_INET, SOCK_STREAM, 0);
    if (-1 == iSocketServer)
    {
   
   
        printf("socket error!\n");
        return -1;
    }

    tSocketServerAddr.sin_family = AF_INET; // 网络通信
    // htons:主机字节序转网络字节序
    tSocketServerAddr.sin_port = htons(SERVER_PORT); /* host to net, short */
    tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;     // 表示可以和任何主机通信
    memset(tSocketServerAddr.sin_zero, 0, 8);         // 填充0

    // 2.绑定本地地址和端口
    iRet = bind(iSocketServer, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));
    if (-1 == iRet)
    {
   
   
        printf("bind error!\n");
        return -1;
    }

    // 3.监听 10个连接
    iRet = listen(iSocketServer, BACKLOG);
    if (-1 == iRet)
    {
   
   
        printf("listen error!\n");
        return -1;
    }

    while (1)
    {
   
   
        iAddrLen = sizeof(struct sockaddr);
        /* 调用accept函数来等待客户端来连接，客户连接成功返回一个值，连接失败返回-1; */
        iSocketClient = accept(iSocketServer, (struct sockaddr *)&tSocketClientAddr, &iAddrLen);
        if (-1 != iSocketClient)
        {
   
   
            iClientNum++;
            /* 支持多个客户端连接，每有一个就调用fork(),并创建一个子进程 */
            // inet_ntoa:将网络字节序IP地址转换为点分十进制IP地址
            printf("Get connect from client %d : %s\n", iClientNum, inet_ntoa(tSocketClientAddr.sin_addr));
            if (!fork()) /* 执行到fork()后马上复制一个代码完全一样的子进程*/
            {
   
                /* 父进程走fork()=0;子进程走fork()!=0; */
                         // fork函数：创建一个子进程，父进程返回子进程ID，子进程返回0 子进程的PID=父进程PID+1
                /*子进程的源码*/
                while (1)
                {
   
   
                    /* 接受客户端发来的数据并显示出来 */
                    iRecvLen = recv(iSocketClient, ucRecvBuf, 999, 0);
                    if (iRecvLen <= 0)
                    {
   
   
                        close(iSocketClient); /* 一直接受客户端传来的消息 */ // 关闭客户端套接字
                        return -1;
                    }
                    else
                    {
   
   
                        ucRecvBuf[iRecvLen] = '\0'; /* 接受到的数据以'\0'结尾 */
                        printf("Get Msg From Client %d: %s\n", iClientNum, ucRecvBuf);
                    }
                }
            }
        }
    }
    close(iSocketServer); // 关闭服务器套接字
    return 0;
}

        

          
        
        
        

          

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client

#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>

/* socket
 * connect
 * send/recv
 */

#define SERVER_PORT 8888

int main(int argc, char **argv)
{
   
   
    int iSocketClient;
    struct sockaddr_in tSocketServerAddr;

    int iRet;
    unsigned char ucSendBuf[1000];
    int iSendLen;

    if (argc != 2)
    {
   
   
        printf("Usage:\n");
        printf("%s <server_ip>\n", argv[0]);
        return -1;
    }

    // 1.创建套接字
    iSocketClient = socket(AF_INET, SOCK_STREAM, 0); // 远程通信，TCP协议，0默认

    tSocketServerAddr.sin_family = AF_INET;
    tSocketServerAddr.sin_port = htons(SERVER_PORT); /* host to net, short */
    // tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;
    if (0 == inet_aton(argv[1], &tSocketServerAddr.sin_addr))
    {
   
   
        printf("invalid server_ip\n");
        return -1;
    }
    memset(tSocketServerAddr.sin_zero, 0, 8);

    // 2.发送连接请求连接服务器
    iRet = connect(iSocketClient, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));
    if (-1 == iRet)
    {
   
   
        printf("connect error!\n");
        return -1;
    }

    while (1)
    {
   
   
        if (fgets(ucSendBuf, 999, stdin))
        {
   
   
            // 3.发送数据
            iSendLen = send(iSocketClient, ucSendBuf, strlen(ucSendBuf), 0);
            if (iSendLen <= 0)
            {
   
   
                // 4.关闭套接字
                close(iSocketClient);
                return -1;
            }
        }
    }

    return 0;
}

        

          
        
        
        

          

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执行过程：在linux下先编译两个程序，然后执行server再打开新终端执行client，执行需要输入ip地址，此时在客户端发送字符串，服务器端可以接收到字符串

UDP编程

server

#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>

/* socket
 * bind
 * sendto/recvfrom
 */

#define SERVER_PORT 8888

int main(int argc, char **argv)
{
   
   
    int iSocketServer;
    int iSocketClient;
    struct sockaddr_in tSocketServerAddr;
    struct sockaddr_in tSocketClientAddr;
    int iRet;
    int iAddrLen;

    int iRecvLen;
    unsigned char ucRecvBuf[1000];

    int iClientNum = -1;

    // 1.创建socket套接字
    iSocketServer = socket(AF_INET, SOCK_DGRAM, 0);
    if (-1 == iSocketServer)
    {
   
   
        printf("socket error!\n");
        return -1;
    }

    tSocketServerAddr.sin_family = AF_INET;
    tSocketServerAddr.sin_port = htons(SERVER_PORT); /* host to net, short */
    tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;
    memset(tSocketServerAddr.sin_zero, 0, 8);

    // 2.绑定本地ip地址和端口号
    iRet = bind(iSocketServer, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));
    if (-1 == iRet)
    {
   
   
        printf("bind error!\n");
        return -1;
    }

    while (1)
    {
   
   
        iAddrLen = sizeof(struct sockaddr);
        // 3.接收数据 recvfrom常用于无连接的udp通信
        iRecvLen = recvfrom(iSocketServer, ucRecvBuf, 999, 0, (struct sockaddr *)&tSocketClientAddr, &iAddrLen);
        if (iRecvLen > 0)
        {
   
   
            ucRecvBuf[iRecvLen] = '\0';
            printf("Get Msg From %s : %s\n", inet_ntoa(tSocketClientAddr.sin_addr), ucRecvBuf);
        }
    }
    // 4.关闭socket套接字
    close(iSocketServer);
    return 0;
}

        

          
        
        
        

          

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client

#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>

/* socket
 * connect
 * send/recv
 */

#define SERVER_PORT 8888

int main(int argc, char **argv)
{
   
   
    int iSocketClient;
    struct sockaddr_in tSocketServerAddr;

    int iRet;
    unsigned char ucSendBuf[1000];
    int iSendLen;

    if (argc != 2)
    {
   
   
        printf("Usage:\n");
        printf("%s <server_ip>\n", argv[0]);
        return -1;
    }
    // 1.创建socket套接字
    iSocketClient = socket(AF_INET, SOCK_DGRAM, 0);

    tSocketServerAddr.sin_family = AF_INET;
    tSocketServerAddr.sin_port = htons(SERVER_PORT); /* host to net, short */
    // tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;
    if (0 == inet_aton(argv[1], &tSocketServerAddr.sin_addr))
    {
   
   
        printf("invalid server_ip\n");
        return -1;
    }
    memset(tSocketServerAddr.sin_zero, 0, 8);

    // 2.连接服务器
    iRet = connect(iSocketClient, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));
    if (-1 == iRet)
    {
   
   
        printf("connect error!\n");
        return -1;
    }

    while (1)
    {
   
   
        if (fgets(ucSendBuf, 999, stdin))
        {
   
   
            // 3.发送数据
            iSendLen = send(iSocketClient, ucSendBuf, strlen(ucSendBuf), 0);
            if (iSendLen <= 0)
            {
   
   
                // 4.关闭套接字
                close(iSocketClient);
                return -1;
            }
        }
    }

    return 0;
}

        

          
        
        
        

          

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总结：TCP和UPD编程的区别