自测之Lesson15：TCP&UDP网络编程

时间：2022-11-18 03:52:21

题目：编写一个TCP通信的程序。

实现代码：

#include <stdio.h>

#include <sys/socket.h>

#include <unistd.h>

#include <sys/types.h>

#include <string.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#define PORT 0xaaaa

// 服务端

void startServe()

{

        int iRet;

        // socket()

        int fd;                                         // 文件描述符

        fd = socket(PF_INET, SOCK_STREAM, 0);           // 创建文件描述符，并确定是用TCP还是UDP等

        if (fd < 0) {

                perror("fail socket");

                return;

        }

        // bind()

        struct sockaddr_in addr;

        addr.sin_family = AF_INET;

        addr.sin_port = htons(PORT);

        addr.sin_addr.s_addr = htonl(INADDR_ANY);       // 即使目标地址不是我，只要发到该计算机上，我就能接收

        iRet = bind(fd, (struct sockaddr*)&addr, sizeof(addr)); // 将文件描述符与本机地址绑定

        if (iRet < 0) {

                perror("fail bind");

                close(fd);                              // 释放资源

                return;

        }    

        // listen()

        iRet = listen(fd, 5);                   // 最多监听5个连接请求

        if (iRet < 0) {

                perror("fail listen");

                close(fd);

                return;

        }

        printf("Server start OK, wait connect...\n");

        // accept()

        char szBuf[1024];

        char szMsg[] = "Welcome...";

        struct sockaddr_in clientAddr;                  // 客户端地址

        socklen_t addrlen = sizeof(clientAddr);

        while(1) {

                int newFd;                              // 此newFd用于与客户端通信

                newFd = accept(fd, (struct sockaddr*)&clientAddr, &addrlen);

                if (newFd < 0) {

                        perror("fail accept");

                        break;

                }

                char *pClientAddr = inet_ntoa(clientAddr.sin_addr);     // 整数IP转字符串IP

                int clientPort = ntohs(clientAddr.sin_port);            // 网络字节序转主机字节序

                printf("Connect from %s:%d\n", pClientAddr, clientPort);

                memset(szBuf, 0, 1024);

                iRet = read(newFd, szBuf, 1024);

                if (iRet < 0) {

                        perror("fail read");

                        break;

                }

                printf("Recv:%s\n", szBuf);

                write(newFd, szMsg, strlen(szMsg));

                close(newFd);           // 关闭当前accept创建的文件描述符

        }

        close(fd);

        return;

}

// 客户端

void startClient()

{

        int iRet;

        // socket()

        int fd;

        fd = socket(PF_INET, SOCK_STREAM, 0);

        if(fd < 0) {

                perror("fail socket");

                return;

        }

        // connect()

        struct sockaddr_in srvAddr;

        srvAddr.sin_family = AF_INET;

        srvAddr.sin_addr.s_addr = inet_addr("192.168.85.128");          // 服务端的ip地址

        srvAddr.sin_port = htons(PORT);                                 // 服务端的端口号

        iRet = connect(fd, (struct sockaddr*)&srvAddr, sizeof(srvAddr));

        if (iRet != 0) {

                perror("fail connect");

                return;

        }

        printf("Connect success\n");

        fprintf(stderr, "Send:");

        // read() & write()

        char szBuf[1024];

        memset(szBuf, 0, 1024);

        read(STDIN_FILENO, szBuf, 1024);                // 从标准输入 输入消息

        write(fd, szBuf, strlen(szBuf));

        char szRcv[1024];

        memset(szRcv, 0, 1024);

        read(fd, szRcv, 1024);

        printf("[CLIENT]Rcv:%s\n", szRcv);

        close(fd);

        return;

}

int main(int argc, char **argv)

{

        if (argc != 2 ||

            (strcmp(argv[1], "s") && strcmp(argv[1], "c"))) {

                printf("Usage: %s [ s | c ]\n", argv[0]);

                printf("\ts: start server\n");

                printf("\tc: start client\n");

                return 0;

        }

        if (argv[1][0] == 's') {

                startServe();

        }

        else if (argv[1][0] == 'c') {

                startClient();

        }

        return 0;

}

/* ReadMe */

/*

 * 先启动服务端 --> ./a.out s

 * 再启动客户端 --> ./a.out c

 */

题目：编写一个UDP通信的程序。

　　

实现代码：

#include <stdio.h>

#include <unistd.h>

#include <string.h>

#include <arpa/inet.h>

#include <sys/socket.h>

#include <netinet/in.h>

#define SRV_PORT 0xaaaa                 // 服务端 端口号

#define CLI_PORT 0xbbbb                 // 客户端 端口号

#define IP_ADDRESS "10.162.73.120"

void startServer()

{

        int iRet;

        // socket()

        int fd;

        fd = socket(PF_INET, SOCK_DGRAM, 0);

        if (fd < 0) {

                perror("fail socket");

                return;

        }

        // bind()

        struct sockaddr_in addr;

        addr.sin_family = AF_INET;

        addr.sin_addr.s_addr = htonl(INADDR_ANY);

        addr.sin_port = htons(SRV_PORT);

        iRet = bind(fd, (struct sockaddr*)&addr, sizeof(addr));

        if (iRet != 0) {

                perror("fail bind");

                return;

        }

        // recvfrom() & sendto()

        struct sockaddr_in cliAddr;

        socklen_t addrLen = sizeof(cliAddr);

        char szRcv[1024];

        char szSnd[1024];

        while(1) {

                // recvfrom()

                memset(szRcv, 0, 1024);

                iRet = recvfrom(fd, szRcv, 1024, 0, (struct sockaddr*)&cliAddr, &addrLen);

                if (iRet < 0) {

                        perror("fail recvfrom");

                        close(fd);

                        break;

                }

                char *pcliAddr = inet_ntoa(cliAddr.sin_addr);

                int cliPort = ntohs(cliAddr.sin_port);

                printf("Recv from client[%s:%d]\n", pcliAddr, cliPort);

                printf("Recv:%s\n", szRcv);

                // sendto()

                fprintf(stderr, "Send:");

                memset(szSnd, 0, 1024);

                read(STDIN_FILENO, szSnd, 1024);

                iRet = sendto(fd, szSnd, strlen(szSnd), 0, (struct sockaddr*)&cliAddr, addrLen);

        }

        close(fd);

}

void startClient()

{

        int iRet;

        // socket()

        int fd;

        fd = socket(PF_INET, SOCK_DGRAM, 0);

        if (fd < 0) {

                perror("fail socket");

                return;

        }

        // bind()

        struct sockaddr_in addr;

        addr.sin_family = AF_INET;

        addr.sin_addr.s_addr = htonl(INADDR_ANY);

        addr.sin_port = htons(CLI_PORT);

        iRet = bind(fd, (struct sockaddr*)&addr, sizeof(addr));

        if (iRet != 0) {

                perror("fail bind");

                return;

        }

        // recvfrom() & sendto()

        struct sockaddr_in srvAddr;

        socklen_t addrLen = sizeof(srvAddr);

        // 对端的地址信息，用于sendto()函数

        srvAddr.sin_family = AF_INET;

        srvAddr.sin_addr.s_addr = inet_addr(IP_ADDRESS);

        srvAddr.sin_port = htons(SRV_PORT);

        char szRcv[1024];

        char szSnd[1024];

        while(1) {

                // sendto()

                fprintf(stderr, "Send:");

                memset(szSnd, 0, 1024);

                read(STDIN_FILENO, szSnd, 1024);

                sendto(fd, szSnd, strlen(szSnd), 0, (struct sockaddr*)&srvAddr, addrLen);

                // read()

                memset(szRcv, 0, 1024);

                read(fd, szRcv, 1024);          // 上面的sendto()已经获得对端地址，此处可简写

                printf("Recv:%s\n", szRcv);

        }

        close(fd);

}

int main(int argc, char **argv)

{

        if (argc != 2 ||

                (strcmp(argv[1], "c") && strcmp(argv[1], "s")))

        {

                printf("Usage:%s [ s | c ]\n", argv[0]);

                printf("\ts: start to server\n");

                printf("\tc: start to client\n");

                return 0;

        }

        if (argv[1][0] == 's') {

                startServer();

        }

        else if (argv[1][0] == 'c') {

                startClient();

        }

        return 0;

}

　　

题目：编写一个抓包程序，要求抓取封装TCP报文段的包，并打印出包的头部信息。

实现代码：

#include <stdio.h>

#include <sys/socket.h>

#include <unistd.h>

#include <sys/types.h>

#include <string.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#define PORT 0Xaaaa                     // 此端口仅用于bind()，而该程序可抓发送到任意端口的包

typedef struct _ipHeader {

//      unsigned char ucVer:4;

//      unsigned char ucHeadLen:4;

        unsigned char ucVerHeadLen;             // 不应该在此处用位域，可在后面提取位数

        unsigned char ucTos;

        unsigned short usLen;

        unsigned short usIdent;

//      unsigned short usFlag:3;

//      unsigned short usOffset:13;

        unsigned short usFlagOffset;

        unsigned char ucTTL;

        unsigned char ucProtocol;

        unsigned short usChkSum;

//      unsigned int uiSrcIp;

//      unsigned int uiDestIp;

        struct in_addr SrcIp;

        struct in_addr DestIp;

        char data[0];

} IP_HEADER;

typedef struct _tcpHeader {

        unsigned short SrcPort;

        unsigned short DestPort;

        unsigned int Seq;

        unsigned int Ack;

//      unsigned short HeadLen:4;

//      unsigned short Save:6;

//      unsigned short URG:1;

//      unsigned short ACK:1;

//      unsigned short PSH:1;

//      unsigned short RST:1;

//      unsigned short SYN:1;

//      unsigned short FIN:1;

        unsigned short HeadLenFlag;             // 包括首部长度、保留、URG标志等字段

        unsigned short Window;

        unsigned short ChkSum;

        unsigned short UrgPoint;

        char data[0];

} TCP_HEADER;

void printIpHeader(char szBuf[])

{

        IP_HEADER *pHeader = (IP_HEADER*)szBuf;

        printf("\n================IP HEADER================\n");

        printf("\tVersion:%d\n", (pHeader->ucVerHeadLen) >> 4);

        printf("\tHeadLen:%d\n", (pHeader->ucVerHeadLen) & 0x0f);

        printf("\tSOUR IP:%s\n", inet_ntoa(pHeader->SrcIp));

        printf("\tDEST IP:%s\n", inet_ntoa(pHeader->DestIp));

        printf("=========================================\n");

}

void printTcpHeader(char szBuf[])

{

        TCP_HEADER *pHeader = (TCP_HEADER*)szBuf;

        printf("\n===============TCP HEADER================\n");

        printf("\tSOUR PORT:%d\n", ntohs(pHeader->SrcPort));

        printf("\tDEST PORT:%d\n", ntohs(pHeader->DestPort));

        printf("=========================================\n");

}

void startCapturePacket()

{

        int iRet;

        int fd;

        fd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP/* = NUM'6' */);      // 抓取封装TCP报文段的IP数据报

        if (fd < 0) {

                perror("fail socket");

                return;

        }

        struct sockaddr_in addr;

        addr.sin_family = AF_INET;

        addr.sin_port = htons(PORT);

        addr.sin_addr.s_addr = htonl(INADDR_ANY);

        iRet = bind(fd, (struct sockaddr*)&addr, sizeof(addr));

        if (iRet < 0) {

                perror("fail bind");

                close(fd);

                return;

        }

        char szBuf[1024];

        while(1) {

                memset(szBuf, 0, 1024);

                read(fd, szBuf, 1024);                  // 将抓到的包整个存到szBuf中，此处szBuf的大小不是很合适

                printIpHeader(szBuf);                   // 打印IP头部部分信息

                printTcpHeader(szBuf);                  // 打印TCP报文端头部部分信息

        }

        close(fd);

        return;

}

int main()

{

        startCapturePacket();

        return 0;

}

　　

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