gistfile1.txt

/* Example socket code - find a free port
 * [email protected]
 * 10/2/2015
 * Example only - not production tested
 */
#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>

#define STARTPORT 8081 /* Start port range to check for a free port */
#define ENDPOINT 8090

int bind_open_port(int sock);

int main()
{
        int sock;
        uint16_t port;
        /* Generic socket creation, ipv4, TCP */
        sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
        if (sock < 0) {
                perror("Failed to create socket");
                exit(EXIT_FAILURE);
        }

        port = bind_open_port(sock);
        printf("Successfully bound to socket %d\n", port);
        (void)close(sock);

        return 0;
}

/* Cycles from STARTPORT to ENDPORT, looking for a port that is
 * available for bind().
 * int sock: Valid socket
 * Returns: port number, or -1 for error
 */

int bind_open_port(int sock)
{
        struct sockaddr_in servAddr;
        uint16_t port;

        for(port = STARTPORT; port <= ENDPOINT; port++) {
                memset(&servAddr, 0, sizeof(servAddr));
                servAddr.sin_family = AF_INET;
                servAddr.sin_addr.s_addr = htonl(INADDR_ANY);
                servAddr.sin_port = htons(port);
                if (bind(sock, (struct sockaddr *) &servAddr,
                                        sizeof(servAddr)) < 0) {
                        if(errno == EADDRINUSE) {
                                /* This is the "port in use" error */
                                printf("Port %d is in use\n", port);
                                continue;
                        }
                        /* Reaching here indicates a different error */
                        perror("Failed to bind");
                        return(-1);
                }
                return port;
        }
        printf("Unable to find a valid port");
        return(-1);
}