CODEWITHSUNDEEP
csockets
suiciyom
suiciyom

Reputation: 21

Socket programming problem: Is the new socket fd used only once?

I want to write basic chat program. I don't release that, I just want to learn socket programming. The chat program will be between client and server.

server code:

//bla bla code

new_socket = accept(server_fd, (struct sockaddr*)&address,(socklen_t*)&addrlen);

char server_msg[128];
char client_msg[128];

int running = 1;

while(running){
    fgets(server_msg, 64, stdin);

    send(new_socket, server_msg, strlen(server_msg), 0);

    recv(new_socket, client_msg, 128, 0);
}

client code:

char server_msg[128];
char client_msg[128];

int running = 1;

while(running){
    fgets(client_msg, 64, stdin);

    
    send(server_socket, client_msg, strlen(client_msg), 0);

    recv(server_socket, server_msg, 128, 0);
}

Questions:

  1. Is the new socket fd used only once? That means; Will I do create a new socket for each sending and receiving. Or can I use this forever?

  2. If first question answer is "FOREVER", Will I do something to new socket fd? I don't know maybe clear.

  3. The above code is not working as expected. As I expected. Actually, The code is working very well :D. How do I perform interrupt operations such as getting input, sending messages, receiving messages?

My English is not good, I'm sorry.

Upvotes: 0

Views: 80

Answers (1)

Luis Colorado
Luis Colorado

Reputation: 12668

  1. Is the new socket fd used only once? That means; Will I do create a new socket for each sending and receiving. Or can I use this forever?

you open a TCP socket connection, so, once in the connected state (the ESTABLISHED state) it remains there until one side closes it (and the other side will notice it by reading 0 bytes as result, this explanation is oversimplified to make it simpler to your case, normally you should detect the end of file in the socket, so you can close it, and accept(2) another connection)

  1. If first question answer is "FOREVER", Will I do something to new socket fd? I don't know maybe clear.

Your program is not a chat program, as the server uses the SAME socket to write what it has read, so it will return the message sent to the same client that issued it (acting more as an echo server, than a chat)

  1. The above code is not working as expected. As I expected. Actually, The code is working very well :D. How do I perform interrupt operations such as getting input, sending messages, receiving messages?

Normally, a chat server should wait for a message to arrive at several sockets (by means of the select(2) system call) and will determine which socket needs attention. As a result, the server will read(2) from that socket (probably in a non blocking way, to avoid being blocked on a read to a socket, that will not be interrupted if data enters on another socket) The chat server should write what it has read over all the other sockets it has connections from, so every other user of your chat system receives a copy of the message (sending back the message to the sender is optional, but not very elegant, the issuer of the message should do local echo of it, although, to ensure the user sees his messages interspersed between the ones from other users)

I recommend you to read the book "Unix Network Programming" from Richard Stevens. It describes perfectly how to use the sockets API and IMHO it is the best reference you can get to learn how to use the socket interface.

One final note:

Don't use plain numbers hardwired in your code, as it is error prone (you declare a buffer string to be 128 bytes, but then read only 64, making 64 unused bytes in the array, you can use sizeof buffer as to make the compiler to use the amount declared in the variable, or you can #define BUFFSIZE 128 and then declare char buffer[BUFFSIZE]; and later do a fgets(buffer, BUFFSIZE, socket_FILE_descriptor); if you use a constant to size a buffer, use a constant name to name it :) and use it everywhere, in case you decide to give it a different value, all the occurences of it will change, instead of having to reviste all places in your code where you have used the number 64.

Upvotes: 2

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