c - 套接字连接被拒绝，但客户端和服务器都独立工作

Question

我用 C 语言实现了一个网络聊天客户端，如下所示:

#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "stdbool.h"
#include "sys/socket.h"
#include "sys/types.h"
#include "netdb.h"
#include "netinet/in.h"
#include "pthread.h"
#include "errno.h"

#define MESSAGE_BUFFER 500
#define USERNAME_BUFFER 10

typedef struct {
    char* prompt;
    int socket;
} thread_data;


// Connect to server
void * connect_to_server(int socket_fd, struct sockaddr_in *address) {
    int response = connect(socket_fd, (struct sockaddr *) address, sizeof *address);
    if (response < 0) {
        fprintf(stderr, "socket() failed: %s\n", strerror(errno));
        printf("Failed to connect\n");
        exit(1);
    } else {
      printf("Connected\n");
    }
}

// Get message from stdin and send to server
void * send_message(char prompt[USERNAME_BUFFER+4], int socket_fd, struct sockaddr_in *address) {
  printf("%s", prompt);
  char message[MESSAGE_BUFFER];
  char final_message[MESSAGE_BUFFER+USERNAME_BUFFER+1];
  while (fgets(message, MESSAGE_BUFFER, stdin) != NULL) {
      memset(final_message,0,strlen(final_message)); // Clear final message buffer
      strcat(final_message, prompt);
      strcat(final_message, message);
      printf("\n%s", prompt);
      if (strncmp(message, "/quit", 5) == 0) {
        printf("Closing connection...\n");
        exit(0);
      }
      sendto(socket_fd, final_message, MESSAGE_BUFFER+USERNAME_BUFFER+1, 0, (struct sockaddr *) &address, sizeof address);
  }
}

void * receive(void * threadData) {
    int socket_fd, response;
    char message[MESSAGE_BUFFER];
    thread_data* pData = (thread_data*)threadData;
    socket_fd = pData->socket;
    char* prompt = pData->prompt;
    memset(message, 0, MESSAGE_BUFFER); // Clear message buffer

    // Print received message
    while(true) {
        response = recvfrom(socket_fd, message, MESSAGE_BUFFER, 0, NULL, NULL);
        if (response) {
            printf("\nServer> %s", message);
            printf("%s", prompt);
            fflush(stdout); // Make sure "User>" gets printed
        }
    }
}

int main(int argc, char**argv) {
    long port = strtol(argv[2], NULL, 10);
    struct sockaddr_in address, cl_addr;
    char * server_address;
    int socket_fd, response;
    char prompt[USERNAME_BUFFER+4];
    char username[USERNAME_BUFFER];
    pthread_t thread;

    // Check for required arguments
    if (argc < 3) {
        printf("Usage: client ip_address port_number\n");
        exit(1);
    }

    // Get user handle
    printf("Enter your user name: ");
    fgets(username, USERNAME_BUFFER, stdin);
    username[strlen(username) - 1] = 0; // Remove newline char from end of string
    strcpy(prompt, username);
    strcat(prompt, "> ");

    server_address = argv[1];
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = inet_addr(server_address);
    address.sin_port = port;
    socket_fd = socket(AF_INET, SOCK_STREAM, 0);

    connect_to_server(socket_fd, &address);

    // Create data struct for new thread
    thread_data data;
    data.prompt = prompt;
    data.socket = socket_fd;

    // Create new thread to receive messages
    pthread_create(&thread, NULL, receive, (void *) &data);

    // Send message
    send_message(prompt, socket_fd, &address);

    // Close socket and kill thread
    close(socket_fd);
    pthread_exit(NULL);
    return 0;
}

这与我为其编写的服务器完美配合。然而，当我尝试让它与另一种语言的服务器或其他人编写的服务器很好地配合时，事情就会崩溃，我无法建立连接。这些不应该彼此独立工作吗？据我所知，如果两者单独工作，那么它们应该一起工作。

例如，如果我尝试在this question的答案中将我的客户端与服务器一起使用，事情不再有效。我已经测试了它们两个，它们单独工作得很好，只是不能一起工作。我查看了连接时 stderr 的输出，但得到的只是一个 Connectionrejected 错误，没有更多信息。

在尝试让这些一起工作时，我是否遗漏了一些明显的东西？如果有人可以演示我的客户端如何与示例服务器一起工作，那将非常有帮助。

Answer 1

address.sin_port = port;

问题就出在这里。应该是

address.sin_port = htons(port);

在客户端和服务器中。

还有其他问题。

fprintf(stderr, "socket() failed: %s\n", strerror(errno));

这应该是

fprintf(stderr, "connect() failed: %s\n", strerror(errno));

然后:

sendto(socket_fd, final_message, MESSAGE_BUFFER+USERNAME_BUFFER+1, 0, (struct sockaddr *) &address, sizeof address);

这应该是:

send(socket_fd, final_message, strlen(final_message)+1, 0);

您不需要 sendto()，因为您已经连接，并且不需要发送除尾随 null 之外的任何内容。事实上，您可以将整个方法简化为:

void * send_message(char prompt[USERNAME_BUFFER+4], int socket_fd, struct sockaddr_in *address) {
  printf("%s", prompt);
  char message[MESSAGE_BUFFER];
  while (fgets(message, MESSAGE_BUFFER, stdin) != NULL) {
      if (strncmp(message, "/quit", 5) == 0) {
        printf("Closing connection...\n");
        close(socket_fd);
        exit(0);
      }
      send(socket_fd, prompt, strlen(prompt), 0);
      send(socket_fd, message, strlen(message)+1, 0);
      printf("\n%s", prompt);
  }

}

然后:

  if (response) {
        printf("\nServer> %s", message);
        printf("%s", prompt);
        fflush(stdout); // Make sure "User>" gets printed
    }

应该是:

  if (response == -1) {
    fprintf(stderr, "recv() failed: %s\n", strerror(errno));
    break;
  } else if (response == 0) {
        printf("\nPeer disconnected\n");
        break;
  } else {
        printf("\nServer> %s", message);
        printf("%s", prompt);
        fflush(stdout); // Make sure "User>" gets printed
  }