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UDP客户端服务器在端口更改后无法交换消息

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我目前正在开发UDP客户端-服务器程序，在该程序中，我正在逐步实现一些比当前UDP更高的TCP功能。需要注意的重要一点是，到目前为止，此代码仅适用于单个客户端（稍后可能会实现更多客户端）。

我设法正确设置了3种方式的握手，并且在客户端和服务器之间正确交换了消息。我正在使用SYN-ACK消息从服务器中提取新的端口号，客户端将使用该端口来交换数据（在这种情况下只是消息）。但是，完成同步并更改端口客户端之后，我无法继续进行消息交换，并且服务器再也没有收到客户端发送的信息。

这是服务器代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <sys/time.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define DOMAIN AF_INET
#define TYPE SOCK_DGRAM
#define PROTOCOL 0
#define BUFFER_SIZE 1025
#define TIMEOUT_SECONDS 1
#define TIMEOUT_micrO 0

int main(int argc,char* argv[])
{
    // INITIALIZATION
    int port_sync,port_data;
    if (argc < 3)
    {
        printf("Too few arguments given.\n");
        printf("Format: ./server <port_sync> <port_data>\n");
        exit(1);
    }
    else if (argc > 3)
    {
        printf("Too many arguments given.\n");
        printf("Format: ./server <port_sync> <port_data>\n");
        exit(1);
    }
    else
    {
        port_sync = atoi(argv[1]);
        port_data = atoi(argv[2]);
    }

    // SELECT RETURN
    int select_return;

    // SOCKET OPTION
    int opt = 1;

    // FILE DESCRIPTOR
    fd_set read_fd_set;

    // SYNCHRONIZATION SOCKET
    struct sockaddr_in server_addr;
    memset((char*)&server_addr,sizeof(server_addr));

    int socket_fd;
    if ((socket_fd = socket(DOMAIN,TYPE,PROTOCOL)) < 0)
    {
        perror("[-] Connection error");
        exit(1);
    }
    printf("[+] Synchronization socket created.\n");

    if(setsockopt(socket_fd,SOL_SOCKET,SO_REUSEADDR,(char *)&opt,sizeof(opt)) < 0)
    {
        perror("[-] setsockopt error");
        exit(1);
    }

    server_addr.sin_family = DOMAIN;
    server_addr.sin_port = htons(port_sync);
    server_addr.sin_addr.s_addr = INADDR_ANY;

    int socket_length = sizeof(server_addr);

    // SYNCHRONIZATION SOCKET BIND
    if (bind(socket_fd,(struct sockaddr*) &server_addr,sizeof(server_addr)) < 0)
    {
        perror("[-] Bind error");
        exit(1);
    }
    printf("[+] Binded successfully to port %d.\n",port_sync);

    // DATA SOCKET
    struct sockaddr_in server_data_addr;
    memset((char*)&server_data_addr,sizeof(server_data_addr));

    int socket_data_fd;
    if ((socket_data_fd = socket(DOMAIN,PROTOCOL)) < 0)
    {
        perror("[-] Connection error");
        exit(1);
    }
    printf("[+] Data socket created.\n");

    if(setsockopt(socket_data_fd,sizeof(opt)) < 0)
    {
        perror("[-] setsockopt error");
        exit(1);
    }

    server_data_addr.sin_family = DOMAIN;
    server_data_addr.sin_port = htons(port_data);
    server_data_addr.sin_addr.s_addr = INADDR_ANY;

    int socket_data_length = sizeof(server_data_addr);

    // DATA SOCKET BIND
    if (bind(socket_data_fd,(struct sockaddr*) &server_data_addr,sizeof(server_data_addr)) < 0)
    {
        perror("[-] Bind error");
        exit(1);
    }
    printf("[+] Binded successfully to port %d.\n",port_data);

    // CLIENT SYNCHRONIZATION
    struct sockaddr_in client_addr;
    socklen_t client_length;

    // CLIENT DATA
    struct sockaddr_in client_data_addr;
    socklen_t client_data_length;
    char* client_data_IP;
    int client_data_port;

    // CONNECTION
    int online = 1;
    int sync_done = 0;
    char buffer[BUFFER_SIZE];

    while(online)
    {
        FD_ZERO(&read_fd_set);
        if (!sync_done)
        {
            FD_SET(socket_fd,&read_fd_set);
        }
        FD_SET(socket_data_fd,&read_fd_set);

        if (((select_return = select(10,&read_fd_set,NULL,NULL))) < 0 && (errno!=EINTR))
        {
            perror("[-] Select error\n");
            exit(1);
        }

        if (FD_ISSET(socket_fd,&read_fd_set))
        {
            client_length = sizeof(client_addr);
            bzero(buffer,sizeof(buffer));
            recvfrom(socket_fd,buffer,BUFFER_SIZE,(struct sockaddr*) &client_addr,&client_length);
            if (strstr(buffer,"SYN") != NULL)
            {
                memset(buffer,sizeof(buffer));
                sprintf(buffer,"SYN-ACK-%i",port_data);
                sendto(socket_fd,sizeof(client_addr));

                recvfrom(socket_fd,(struct sockaddr*) & client_addr,&client_length);
                if (strstr(buffer,"ACK"))
                {
                    memset(buffer,sizeof(buffer));
                }
            }

            printf("Finished synchronization\n");
            FD_CLR(socket_fd,&read_fd_set);
            sync_done = 1;
        }

        if (FD_ISSET(socket_data_fd,&read_fd_set))
        {
            int recvfrom_return = recvfrom(socket_data_fd,(struct sockaddr*) & client_data_addr,&client_data_length);
            if (strcmp(buffer,"") != 0)
            {
                client_data_IP = inet_ntoa(client_data_addr.sin_addr);
                client_data_port = ntohs(client_data_addr.sin_port);

                if (strcmp(buffer,":exit") == 0)
                {
                    printf("[-] Disconnected from %s:%d\n",client_data_IP,client_data_port);
                    close(socket_data_fd);
                    break;
                }
                else
                {
                    printf("UDP Client: %s\n",buffer);
                    sendto(socket_data_fd,recvfrom_return,client_data_length);
                    memset(buffer,sizeof(buffer));
                    bzero(buffer,sizeof(buffer));
                }
            }
        }
    }

    return 0;
}

这是客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define DOMAIN AF_INET
#define TYPE SOCK_DGRAM
#define PROTOCOL 0
#define BUFFER_SIZE 1025
#define TIMEOUT_SECONDS 1
#define TIMEOUT_micrO 0

int get_data_port(char* buffer)
{
    char delim[] = "-";
    char port[20];
    char* ptr = strtok(buffer,delim); // ptr = "SYN"
    ptr = strtok(NULL,delim);      // ptr = "ACK"
    ptr = strtok(NULL,delim);      // ptr = port_data
    strcpy(port,ptr);
    int port_data = atoi(port);
    return port_data;
}

int main(int argc,port_data;
    char addr[15];
    if (argc < 3)
    {
        printf("Too few arguments given.\n");
        printf("Format: ./client <adresseIP> <port>\n");
        exit(1);
    }
    else if (argc > 3)
    {
        printf("Too many arguments given.\n");
        printf("Format: ./client <adresseIP> <port>\n");
        exit(1);
    }
    else
    {
        strcpy(addr,argv[1]);
        port_sync = atoi(argv[2]);
    }

    // SOCKET OPTION
    int opt = 1;

    // SYNCHRONIZATION SOCKET
    struct sockaddr_in client_addr;
    memset((char*)&client_addr,sizeof(client_addr));

    int socket_fd;
    if ((socket_fd = socket(DOMAIN,sizeof(opt)) < 0)
    {
        perror("[-] setsockopt error");
        exit(1);
    }

    client_addr.sin_family = DOMAIN;
    client_addr.sin_port = htons(port_sync);
    client_addr.sin_addr.s_addr = INADDR_ANY;

    socklen_t socket_length = sizeof(client_addr);

    // CONNECTION
    int online = 1;
    int sync_done = 0;
    char buffer[BUFFER_SIZE];

    while (online)
    {
        if (!sync_done)
        {
            memset(buffer,sizeof(buffer));
            sprintf(buffer,"SYN");
            sendto(socket_fd,strlen(buffer),sizeof(client_addr));
            recvfrom(socket_fd,&socket_length);
            if (strstr(buffer,"SYN-ACK") != NULL)
            {
                port_data = get_data_port(buffer);
                printf("New port: %d\n",port_data);

                memset(buffer,"ACK");
                sendto(socket_fd,sizeof(client_addr));
            }
            memset(buffer,sizeof(buffer));
            printf("Finished synchronization\n");
            client_addr.sin_port = htons(port_data);
            sync_done = 1;
            socket_length = sizeof(client_addr);
        }
        else
        {       
            printf("UDP Client: ");
            fgets(buffer,stdin);
            buffer[strcspn(buffer,"\n")] = 0;
            sendto(socket_fd,sizeof(buffer),(struct sockaddr*)& client_addr,sizeof(client_addr));

            if (strcmp(buffer,":exit") == 0)
            {
                close(socket_fd);
                printf("[-] Disconnected from server\n");
                exit(1);
            }
            int recvfrom_return;
            if ((recvfrom_return = recvfrom(socket_fd,&socket_length)) < 0)
            {
                perror("[-] Data reception error");
            }
            else
            {
                buffer[recvfrom_return] = 0;
                printf("Server: %s\n",buffer);
            }
        }
    }

    return 0;
}

我检查了许多在线示例和教程，以了解如何通过套接字通信更改端口，我觉得我已经遵循了所有指南，但是显然我缺少了一些东西。

编辑

我的问题是，我用client_addr.sin_port = htons(port_data);更改端口后，服务器再也没有收到客户端消息。我已经检查了服务器端，并且代码输入了第二条if(FD_ISSET...)语句。我还没有查明是什么原因导致消息无法到达。

在此先感谢您，并且会毫不犹豫地指出这是否是重复项（并也链接重复的问题）！

moon_zero 回答：UDP客户端服务器在端口更改后无法交换消息

我需要初始化两个地址长度，如下所示：

socklen_t client_length = sizeof(client_addr);

socklen_t client_data_length = sizeof(client_data_addr);

cportsocketsudp
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