接收多消息套接字编程C

Question

Hi I new to socket programming C. Now I working on chat program and I successful can sending and receiving message but the problem is when client request to send list of user that client online and once server send message back to client the message is successful print the list of current connected client but once it display it not going out of loop. below is only one section of the code.

server side (server.c)

pthread_mutex_lock(&list_mutex);
   for(i =0; i < NotEndOfList; i++)
   {

    sprintf(message_replay, "Server: %s \n", usersList[i].name); 
    write(sock , message_replay , strlen(message_replay));  

  }
  pthread_mutex_unlock(&list_mutex);

Client side (Client.c)

int i =0;
          while(i < NotEndOfList)
         {
            if( recv(sock , server_reply , 2000 , 0) < 0)
            {
              puts("recv failed");
              break;
            }
         i++;

        puts(server_reply);
      }

Sample Output

    User A -->:
    //List 
    User A
    User B
    User C
    // Loop

Correct Sample Output

User A -->:
//List
User A
User B
User C
User A -->:

Thank you very much

Answer 1

This solution can be used if all messages are the same size. I don't know the size of your message_replay , lets just say its of type char[256] .

At the server

Instead of using strlen() you can always send 256 bytes. The client will just ignore all trailing characters after the null terminator.

write(sock , message_replay, 256); // or sizeof(message_replay) if it's static

At the client

Client should then expect all messages to be 256 bytes long. A loop runs untill all 256 characters have been received, and appends to receive_buffer[] every loop. Counters keep track of how many bytes we have received and how many we are short of.

for (int i = 0; i < NotEndOFList; i++) {
    char receive_buffer[256];
    int received_bytes = 0;
    int remaining_bytes = sizeof(receive_buffer);

    while (remaining_bytes > 0) {
        int res = recv(sock , &receive_buffer[received_bytes] , remaining_bytes, 0);
        if (res < 0) {
            puts("recv failed");
            break;
        }
        received_bytes += res;
        remaining_bytes -= res;
    }

    puts(receive_buffer);
}

PS! I've not tested, let me know how it runs if you decide to use it.