Linux网络编程——TCP和UDP通信

亦凉 2021-12-04 06:43 305阅读 0赞

*  TCP协议流程图、TCP建立即时聊天
 *  TCP即时聊天升级：服务器在客户端断开后不断开，客户端可以多次重连服务器进行即时聊天
 *  UDP协议流程图、UDP建立即时连接
 *  如果在已经处于 ESTABLISHED状态下的socket(一般由端口号和标志符区分）需调用closesocket（一般不会立即关闭而经历TIME\_WAIT的过程）后想继续重用该socket，但也可以直接用setsockopt和reuse。
 *  SO\_RCVLOWAT设置接收缓冲区下限

1、TCP协议的流程图

服务端：socket---bind---listen---while(1)\{---accept---recv---send---close---\}---close  
客户端：socket----------------------------------connect---send---recv-----------------close

![1556806258606][]

TCP建立即时聊天

tcp\_client.c

tcp\_server.c

#include <func.h>
    
    int main(int argc,char* argv[])
    {
        ARGS_CHECK(argc,3);
        int socketFd;
        socketFd = socket(AF_INET,SOCK_STREAM,0);
        ERROR_CHECK(socketFd, -1, "socket");
        struct sockaddr_in ser;
        bzero(&ser, sizeof(ser));
        ser.sin_family = AF_INET;
        ser.sin_port = htons(atoi(argv[2]));
        ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
        int ret;
        ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
        ERROR_CHECK(ret, -1, "bind");
        listen(socketFd, 10);//缓冲区的大小，一瞬间能够放入的客户端连接信息
        int new_fd;
        struct sockaddr_in client;
        bzero(&client, sizeof(client));
        int addrlen = sizeof(client);
        new_fd = accept(socketFd, (struct sockaddr*)&client, &addrlen);
        ERROR_CHECK(new_fd, -1, "accept");
        printf("client ip=%s, port=%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
        fd_set rdset;
        char buf[128] = {0};
        while(1){
            FD_ZERO(&rdset);
            FD_SET(STDIN_FILENO, &rdset);
            FD_SET(new_fd, &rdset);
            ret = select(new_fd + 1, &rdset, NULL, NULL, NULL);
            if(FD_ISSET(new_fd, &rdset)){
                bzero(buf, sizeof(buf));
                ret = recv(new_fd, buf, sizeof(buf), 0);
                ERROR_CHECK(ret, -1, "recv");
                if(ret == 0){
                    printf("byebye!\n");
                    break;
                }
                printf("%s\n", buf);
            }
            if(FD_ISSET(STDIN_FILENO, &rdset)){
                memset(buf, 0, sizeof(buf));
                ret = read(STDIN_FILENO, buf, sizeof(buf));
                if(ret == 0){
                    printf("byebye!\n");
                    break;
                }
                ret = send(new_fd, buf, strlen(buf) - 1, 0);
                ERROR_CHECK(ret, -1, "send");
            }
        }
        close(new_fd);
        close(socketFd);
        return 0;
    }

2、TCP即时聊天升级：服务器在客户端断开后不断开，客户端可以多次重连服务器进行即时聊天

tcp\_server.c

#include <func.h>
    
    int main(int argc,char* argv[])
    {
        ARGS_CHECK(argc,3);
        int socketFd;
        socketFd = socket(AF_INET,SOCK_STREAM,0);
        ERROR_CHECK(socketFd, -1, "socket");
        struct sockaddr_in ser;
        bzero(&ser, sizeof(ser));
        ser.sin_family = AF_INET;
        ser.sin_port = htons(atoi(argv[2]));
        ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
        int ret;
        ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
        ERROR_CHECK(ret, -1, "bind");
        listen(socketFd, 10);//缓冲区的大小，一瞬间能够放入的客户端连接信息
        int new_fd;
        struct sockaddr_in client;
        bzero(&client, sizeof(client));
        int addrlen = sizeof(client);
        char buf[128] = {0};
        fd_set rdset; 
        fd_set needMonitorSet; //需要监听的描述符集合
        FD_ZERO(&needMonitorSet);  
        FD_SET(STDIN_FILENO, &needMonitorSet);
        FD_SET(socketFd, &needMonitorSet);
        while(1){
            memcpy(&rdset, &needMonitorSet, sizeof(fd_set));
            ret = select(11, &rdset, NULL, NULL, NULL); //设最大监控描述符为10
            if(FD_ISSET(socketFd, &rdset)){ //如果监听到客户端则accept接受远程计算机的连接请求
                new_fd = accept(socketFd, (struct sockaddr*)&client, &addrlen); //accept函数接受一个连接时，会返回一个新的socket标识符，以后数据的数据传输和读取就要通过这个新的socket编号来处理，原来的socket继续监听其他客户机的连接请求。
                ERROR_CHECK(new_fd, -1, "accept");
                printf("client ip=%s, port=%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
                FD_SET(new_fd, &needMonitorSet);    
            }
            if(FD_ISSET(new_fd, &rdset)){
                bzero(buf, sizeof(buf));
                ret = recv(new_fd, buf, sizeof(buf), 0);
                ERROR_CHECK(ret, -1, "recv");
                if(ret == 0){
                    printf("byebye!\n");
                    FD_CLR(new_fd, &needMonitorSet);  //从needMonitorSet中删除new_fd
                    close(new_fd);
                    continue;
                }
                printf("%s\n", buf);
            }
            if(FD_ISSET(STDIN_FILENO, &rdset)){
                memset(buf, 0, sizeof(buf));
                ret = read(STDIN_FILENO, buf, sizeof(buf));
                if(ret == 0){
                    printf("byebye!\n");
                    break;
                }
                ret = send(new_fd, buf, strlen(buf) - 1, 0);
                ERROR_CHECK(ret, -1, "send");
            }
        }
        close(socketFd);
        return 0;
    }

tcp\_client.c和1同

3、使用UDP协议的流程图

服务端：socket---bind---recvfrom---sendto---close  
客户端：socket----------sendto---recvfrom---close

![1556806183309][]

*  sendto()函数原型：  
    **int sendto(int sockfd, const void *msg,int len,unsigned int flags,const struct sockaddr* to, int tolen);**
    
    该函数比send()函数多了两个参数，to表示目地机的IP地址和端口号信息，而tolen常常被赋值为sizeof (struct sockaddr)。sendto 函数也返回实际发送的数据字节长度或在出现发送错误时返回-1。
 *  recvfrom()函数原型：
    
    \*\*int recvfrom(int sockfd,void *buf,int len,unsigned int flags,struct sockaddr* from,int \*fromlen);\*\*  
    from是一个struct sockaddr类型的变量，该变量保存连接机的IP地址及端口号。fromlen常置为sizeof (struct sockaddr)。当recvfrom()返回时，fromlen包含实际存入from中的数据字节数。Recvfrom()函数返回接收到的字节数或当出现错误时返回-1，并置相应的errno。
    
    UDP传输一个数据报示例：
    
    udp\_server.c

#include <func.h>
    
    int main(int argc, char **argv){
        ARGS_CHECK(argc, 3);
        int socketFd;
        socketFd = socket(AF_INET, SOCK_DGRAM, 0);
        ERROR_CHECK(socketFd, -1, "socket");
        struct sockaddr_in ser;
        bzero(&ser,sizeof(ser));
        ser.sin_family = AF_INET;
        ser.sin_port = htons(atoi(argv[2]));
        ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
        int ret;
        ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
        ERROR_CHECK(ret, -1, "bind");
        char buf[128] = {0};
        struct sockaddr_in client;
        int addrlen = sizeof(client);
        ret = recvfrom(socketFd, buf, 5, 0, (struct sockaddr*)&client, &addrlen);
        ERROR_CHECK(ret, -1, "recvfrom");
        printf("client ip = %s, port = %d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
        printf("udp server gets %s\n", buf);
        //bzero(buf, sizeof(buf));
        //ret = recvfrom(socketFd, buf, 5, 0, (struct sockaddr*)&client, &addrlen);
        //ERROR_CHECK(ret, -1, "recvfrom");
        //printf("udp server gets %s\n", buf);
        ret = sendto(socketFd, "world", 5, 0, (struct sockaddr*)&client, sizeof(client));
        ERROR_CHECK(ret, -1, "sendto");
        close(socketFd);
        return 0;
    }

udp\_client.c

4、使用UDP协议建立即时连接

udp\_server.c

#include <func.h>
    
    int main(int argc, char **argv){
        ARGS_CHECK(argc, 3);
        int socketFd;
        socketFd = socket(AF_INET, SOCK_DGRAM, 0);
        ERROR_CHECK(socketFd, -1, "socket");
        struct sockaddr_in ser;
        bzero(&ser,sizeof(ser));
        ser.sin_family = AF_INET;
        ser.sin_port = htons(atoi(argv[2]));
        ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
        int ret;
        ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
        ERROR_CHECK(ret, -1, "bind");
        char buf[128] = {0};
        struct sockaddr_in client;
        int addrlen = sizeof(client);
        printf("client ip = %s, port = %d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
        fd_set rdset;
        while(1){
            FD_ZERO(&rdset);
            FD_SET(STDIN_FILENO, &rdset);
            FD_SET(socketFd, &rdset);
            ret = select(socketFd + 1, &rdset, NULL, NULL, NULL);
            if(FD_ISSET(socketFd, &rdset)){
                bzero(buf, sizeof(buf));
                ret = recvfrom(socketFd, buf, sizeof(buf), 0, (struct sockaddr*)&client, &addrlen);
                ERROR_CHECK(ret, -1, "recvfrom");
                printf("%s\n", buf);
            }
            if(FD_ISSET(STDIN_FILENO, &rdset)){
                bzero(buf, sizeof(buf));
                ret = read(STDIN_FILENO, buf, sizeof(buf));
                if(0 == ret){
                    printf("byeybye\n");
                    break;
                }
                ret = sendto(socketFd, buf, strlen(buf) - 1, 0, (struct sockaddr*)&client, sizeof(client));
                ERROR_CHECK(ret, -1, "sendto");
            }
        }
        close(socketFd);
        return 0;
    }

udp\_client.c

#include <func.h>
    
    int main(int argc, char *argv[]){
        ARGS_CHECK(argc, 3);
        int socketFd;
        socketFd = socket(AF_INET, SOCK_DGRAM, 0);
        ERROR_CHECK(socketFd, -1, "socket");
        struct sockaddr_in ser;
        bzero(&ser, sizeof(ser));
        ser.sin_family = AF_INET;
        ser.sin_port = htons(atoi(argv[2]));
        ser.sin_addr.s_addr = inet_addr(argv[1]);
        int ret;
        char buf[128] = {0};
        fd_set rdset;
        while(1){
            FD_ZERO(&rdset);
            FD_SET(STDIN_FILENO, &rdset);
            FD_SET(socketFd, &rdset);
            ret = select(socketFd + 1, &rdset, NULL, NULL, NULL);
            if(FD_ISSET(socketFd, &rdset)){
                bzero(buf, sizeof(buf));
                ret = recvfrom(socketFd, buf, sizeof(buf), 0, NULL, NULL);
                ERROR_CHECK(ret, -1, "recvfrom");
                printf("%s\n", buf);
            }
            if(FD_ISSET(STDIN_FILENO, &rdset)){
                bzero(buf, sizeof(buf));
                ret = read(STDIN_FILENO, buf, sizeof(buf));
                if(0 == ret){
                    printf("byeybye\n");
                    break;
                }
                ret = sendto(socketFd, buf, strlen(buf) - 1, 0, (struct sockaddr*)&ser, sizeof(ser));
                ERROR_CHECK(ret, -1, "sendto");
            }
        }
        close(socketFd);
        return 0;
    }

5、如果在已经处于 ESTABLISHED状态下的socket(一般由端口号和标志符区分）需调用closesocket（一般不会立即关闭而经历TIME\_WAIT的过程）后想继续重用该socket，但也可以直接用setsockopt和reuse。

int reuse=1;
    setsockopt(s,SOL_SOCKET ,SO_REUSEADDR,(const char*)&reuse,sizeof(int));

tcp\_server.c

#include <func.h>
    
    int main(int argc,char* argv[])
    {
        ARGS_CHECK(argc,3);
        int socketFd;
        socketFd = socket(AF_INET,SOCK_STREAM,0);
        ERROR_CHECK(socketFd, -1, "socket");
        int ret;
        int reuse = 1;
        ret = setsockopt(socketFd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(int));
        ERROR_CHECK(ret, -1, "setsockopt");
        struct sockaddr_in ser;
        bzero(&ser, sizeof(ser));
        ser.sin_family = AF_INET;
        ser.sin_port = htons(atoi(argv[2]));
        ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
        ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
        ERROR_CHECK(ret, -1, "bind");
        listen(socketFd, 10);//缓冲区的大小，一瞬间能够放入的客户端连接信息
        int new_fd;
        struct sockaddr_in client;
        bzero(&client, sizeof(client));
        int addrlen = sizeof(client);
        new_fd = accept(socketFd, (struct sockaddr*)&client, &addrlen);
        ERROR_CHECK(new_fd, -1, "accept");
        printf("client ip=%s, port=%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
        fd_set rdset;
        char buf[128] = {0};
        while(1){
            FD_ZERO(&rdset);
            FD_SET(STDIN_FILENO, &rdset);
            FD_SET(new_fd, &rdset);
            ret = select(new_fd + 1, &rdset, NULL, NULL, NULL);
            if(FD_ISSET(new_fd, &rdset)){
                bzero(buf, sizeof(buf));
                ret = recv(new_fd, buf, sizeof(buf), 0);
                ERROR_CHECK(ret, -1, "recv");
                if(ret == 0){
                    printf("byebye!\n");
                    break;
                }
                printf("%s\n", buf);
            }
            if(FD_ISSET(STDIN_FILENO, &rdset)){
                memset(buf, 0, sizeof(buf));
                ret = read(STDIN_FILENO, buf, sizeof(buf));
                if(ret == 0){
                    printf("byebye!\n");
                    break;
                }
                ret = send(new_fd, buf, strlen(buf) - 1, 0);
                ERROR_CHECK(ret, -1, "send");
            }
        }
        close(new_fd);
        close(socketFd);
        return 0;
    }

tcp\_client.c和1同

6、SO\_RCVLOWAT：接收缓冲区下限

tcp\_server\_rcvlowat.c

#include <func.h>
    
    int main(int argc,char* argv[])
    {
        ARGS_CHECK(argc,3);
        int socketFd;
        socketFd = socket(AF_INET,SOCK_STREAM,0);
        ERROR_CHECK(socketFd, -1, "socket");
        int ret;
        int reuse = 1;
        ret = setsockopt(socketFd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(int));
        ERROR_CHECK(ret, -1, "setsockopt");
        struct sockaddr_in ser;
        bzero(&ser, sizeof(ser));
        ser.sin_family = AF_INET;
        ser.sin_port = htons(atoi(argv[2]));
        ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
        ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
        ERROR_CHECK(ret, -1, "bind");
        listen(socketFd, 10);//缓冲区的大小，一瞬间能够放入的客户端连接信息
        int new_fd;
        struct sockaddr_in client;
        bzero(&client, sizeof(client));
        int addrlen = sizeof(client);
        new_fd = accept(socketFd, (struct sockaddr*)&client, &addrlen);
        ERROR_CHECK(new_fd, -1, "accept");
        printf("client ip=%s, port=%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
        fd_set rdset;
        char buf[128] = {0};
        int rcvLowAt = 10;
        ret=setsockopt(new_fd,SOL_SOCKET,SO_RCVLOWAT,&rcvLowAt,sizeof(int));
    
        ERROR_CHECK(ret, -1, "setsockopt");
        while(1){
            FD_ZERO(&rdset);
            FD_SET(STDIN_FILENO, &rdset);
            FD_SET(new_fd, &rdset);
            ret = select(new_fd + 1, &rdset, NULL, NULL, NULL);
            if(FD_ISSET(new_fd, &rdset)){
                bzero(buf, sizeof(buf));
                ret = recv(new_fd, buf, sizeof(buf), 0);
                ERROR_CHECK(ret, -1, "recv");
                if(ret == 0){
                    printf("byebye!\n");
                    break;
                }
                printf("%s\n", buf);
            }
            if(FD_ISSET(STDIN_FILENO, &rdset)){
                memset(buf, 0, sizeof(buf));
                ret = read(STDIN_FILENO, buf, sizeof(buf));
                if(ret == 0){
                    printf("byebye!\n");
                    break;
                }
                ret = send(new_fd, buf, strlen(buf) - 1, 0);
                ERROR_CHECK(ret, -1, "send");
            }
        }
        close(new_fd);
        close(socketFd);
        return 0;
    }

tcp\_client.c和1同

转载于:https://www.cnblogs.com/Mered1th/p/10803634.html

[1556806258606]: /images/20211204/2cf01fc71f794061a4cb2bd04d69a518.png
[1556806183309]: /images/20211204/39ddb5de7f4f4bc39791a4d91dc8cee8.png