c - 端口更改后 UDP 客户端服务器无法交换消息

Question

我目前正在开发一个 UDP 客户端-服务器程序，我正在逐步实现一些高于当前 UDP 功能的 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)。

我已经成功地正确设置了 3 次握手，并且在客户端和服务器之间正确地交换了消息。我使用 SYN-ACK 消息从服务器提取一个新的端口号，客户端将使用该端口号来交换数据(在本例中只是消息)。但是，当客户端完成同步并更改端口后，我无法继续进行消息交换，服务器始终无法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, 0, 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, 0, sizeof(server_data_addr));

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

    if(setsockopt(socket_data_fd, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, 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, 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, 0, (struct sockaddr*) &client_addr, &client_length);
            if (strstr(buffer, "SYN") != NULL)
            {
                memset(buffer, 0, sizeof(buffer));
                sprintf(buffer, "SYN-ACK-%i", port_data);
                sendto(socket_fd, buffer, BUFFER_SIZE, 0, (struct sockaddr*) &client_addr, sizeof(client_addr));

                recvfrom(socket_fd, buffer, BUFFER_SIZE, 0, (struct sockaddr*) & client_addr, &client_length);
                if (strstr(buffer, "ACK"))
                {
                    memset(buffer, 0, 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, buffer, BUFFER_SIZE, 0, (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, buffer, recvfrom_return, 0, (struct sockaddr*) & client_data_addr, client_data_length);
                    memset(buffer, 0, 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, char* argv[])
{
    // INITIALIZATION
    int port_sync, 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, 0, sizeof(client_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);
    }

    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, 0, sizeof(buffer));
            sprintf(buffer, "SYN");
            sendto(socket_fd, buffer, strlen(buffer), 0, (struct sockaddr*) & client_addr, sizeof(client_addr));
            recvfrom(socket_fd, buffer, BUFFER_SIZE, 0, (struct sockaddr*) & client_addr, &socket_length);
            if (strstr(buffer, "SYN-ACK") != NULL)
            {
                port_data = get_data_port(buffer);
                printf("New port: %d\n", port_data);

                memset(buffer, 0, sizeof(buffer));
                sprintf(buffer, "ACK");
                sendto(socket_fd, buffer, strlen(buffer), 0, (struct sockaddr*) & client_addr, sizeof(client_addr));
            }
            memset(buffer, 0, 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, BUFFER_SIZE, stdin);
            buffer[strcspn(buffer, "\n")] = 0;
            sendto(socket_fd, buffer, sizeof(buffer), 0, (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, buffer, sizeof(buffer), 0, (struct sockaddr*) & client_addr, &socket_length)) < 0)
            {
                perror("[-] Data reception error");
            }
            else
            {
                buffer[recvfrom_return] = 0;
                printf("Server: %s\n", buffer);
            }
        }
    }

    return 0;
}

我已经检查了许多关于如何通过套接字通信更改端口的在线示例和教程，我感觉好像我已经遵循了所有指南，但显然我遗漏了一些东西。

编辑

我的问题是，在我使用 client_addr.sin_port = htons(port_data); 更改端口后，服务器永远不会收到客户端消息。 。我检查了服务器端，代码进入第二个if(FD_ISSET...)陈述。我尚未查明导致消息未到达的原因。

提前致谢，请毫不犹豫地指出这是否重复(并链接重复的问题)!

Answer 1

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);