Unix C套接字服务器不接受连接

Question

Here's the deal, I'm writing a simple tcp socket server in C (with unix system calls) that I'm not able to get to accept connections.

From what I can tell, I get through the server initialization just fine, but when I try to connect to the port that I print out (see code below) it refuses as if nothing is there.

More to the point, when I netstat that port isn't even in use. I'm not throwing any errors with my current set up, I'm all dried up for ideas.

int main(){

    int sock_fd;
    int conn_fd;
    struct sockaddr_in serv_addr;
    struct sockaddr_in cli_addr;
    socklen_t* serlen;
    socklen_t* clilen;
    clilen  = malloc(sizeof(socklen_t));
    serlen  = malloc(sizeof(socklen_t));
    *serlen = sizeof(serv_addr);
    *clilen = sizeof(cli_addr);

    /*=============================Create Socket=============================*/


        //Create Socket
        sock_fd = socket(AF_INET, SOCK_STREAM, 0);
            if(sock_fd<0){
                fprintf(stderr,"error creating socket\n");
                exit(1);}

        //Initialize Server Address Struct
        bzero((char *) &serv_addr, *serlen);
        serv_addr.sin_family = AF_INET;
        serv_addr.sin_addr.s_addr = INADDR_ANY;
        serv_addr.sin_port = 0;

    /*=============================Bind Address==============================*/

        //Bind socket to an address
        if(bind(sock_fd,(struct sockaddr*)&serv_addr,*serlen)<0){
            fprintf(stderr,"error binding\n");
            exit(1);}

        //Get socket data
        if(getsockname(sock_fd,(struct sockaddr*)&serv_addr, serlen)<0){
            fprintf(stderr,"error with socket name");
            exit(1);}

    /*=============================Server Started============================*/

        //Listen for connections
        listen(sock_fd,32);

        //Print port
        printf("%i", serv_addr.sin_port);

        conn_fd = accept(sock_fd,(struct sockaddr*)&cli_addr,clilen);

        /**Do something exciting with my new connection**/

}

Answer 1

Are you really trying to listen on port zero? Try a high port number, preferably > 1024. /etc/services will give a hint about free ports - but it only a set of comments, those port numbers are not enforced.

Edit: another hint. The port number should be in network order , so the assignment should use htons() . It could be that the "random numbers" you are getting are simple numbers that appear garbled because you might be on a little-endian machine (like Intel). When you print them, convert them back using ntohs() .

Answer 2

props to @askmish for inspiring this one

    //Print port
    printf("%i", serv_addr.sin_port);

becomes

    //Print port
    printf("%i", htons(serv_addr.sin_port));

Answer 3

In your code:

• Instead of:

   serv_addr.sin_port = 0; 

  try this:

   serv_addr.sin_port=htons(2056);//Any port no. 

• Instead of:

    listen(sock_fd,32); 

  try this:

    if(listen(sock_fd,SOMAXCONN)<0)//Just to be sure that you are considering max. no. of requests { fprintf(stderr,"error with listen"); exit(1);} 

• Also for:

    conn_fd = accept(sock_fd,(struct sockaddr*)&cli_addr,clilen); 

  Add this:

    if(conn_fd <0) { //handle the error here } 

If none of these solve your issues, then, there might be problem with the client code or your server environment.