c - Why bind function is returning -1

Question

So i am following the book of UNIX network programming, and tried to write a simple daytime server from chapter 1 and client but the bind function is always returning an error, what I'm doing wrong can anyone help??

server.c

/*
 * Daytime Server
*/

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <arpa/inet.h>

void printError(char *str)
{
    printf("%s", str);
    exit(0);
}

int main(int argc, char **argv)
{
    int listenfd, connfd;
    struct sockaddr_in servaddr;
    char buff[4096];
    time_t ticks;

    if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printError("Error at line 32 socket fuct.");
    }

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(13);

    if (bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
    {
        printError("Error at bind function");
    }
    

    if (listen(listenfd, 1024) < 0)
    {
        printError("Error at listen fuct.");
    }

    while (1)
    {
        if ((connfd = accept(listenfd, (struct sockaddr *)NULL, NULL)) < 0)
        {
            printError("Error at accept fuct.");
        }

        ticks = time(NULL);
        snprintf(buff, sizeof(buff), "%.24s
", ctime(&ticks));

        if (write(connfd, buff, strlen(buff)) < 0)
        {
            printError("Error at write fuct.");
        }

        close(connfd);
    }

    return EXIT_SUCCESS;
}

client.c

/*
 * Daytime Client
*/

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

void printError(char *str)
{
    printf("%s", str);
    exit(0);
}

int main(int argc, char **argv)
{
    int socketfd, n;
    char recvline[4097];
    struct sockaddr_in servaddr;

    if (argc != 2)
    {
        printError("Requires ip address of the server");
    }

    if ((socketfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printError("Unable to create a Connection");
    }

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_port = htons(13);
    servaddr.sin_family = AF_INET;

    if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)
    {
        printError("Not valid IP");
    }

    if (connect(socketfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
    {
        printError("Connection Error");
    }

    while ((n = read(socketfd, recvline, 4096)) > 0)
    {
        recvline[n] = 0;
        if (fputs(recvline, stdout) == EOF)
        {
            printError("Fputs Error");
        }
    }

    if (n < 0)
    {
        printError("Not readable");
    }

    return EXIT_SUCCESS;
}

Running server is always returning -1 on bind function. and running client always prints connection error.

Thank you in advance for help.

question from:https://stackoverflow.com/questions/65946404/why-bind-function-is-returning-1

Answer 1

You should check with errno to find out WHY bind() is failing when it returns -1. You can use perror() to print a human-readable description of errno to the console, or at least strerror() to get that description in a string buffer that you can then do whatever you want with.

But the most likely reason for WHY bind() is failing is that you are trying to bind() your server to port 13. On most systems, ports 0-1023 are reserved for system services, so you would need to run your app with admin rights to listen on those ports.