nmap

Makefile

CFLAGS := -Wall -Werror

server: server.c

server.c

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

int main(int argc, char const *argv[])
{
    if (argc < 2)
    {
        fprintf(stderr, "error: too few arguments\n");
        fprintf(stderr, "usage: %s port\n", basename((char *)argv[0]));
        exit(1);
    }

    int port = atoi(argv[1]);
    if (((port == 0) && (argv[1][0] != '0')) || (port < 0) || (port > 65536))
    {
        fprintf(stderr, "error: invalid port %s\n", argv[1]);
        exit(1);
    }

    int fd, peer_fd;
    struct sockaddr_in addr, bind_addr, peer_addr;
    socklen_t sockaddr_len = sizeof(struct sockaddr_in);

    char buf[1024];
    char peer_name[INET6_ADDRSTRLEN + 1 + 5]; // <ip>:65536

    if ((fd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        perror("socket");
        exit(1);
    }

    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_port = htons(port);

    if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) == -1)
    {
        perror("bind");
        exit(1);
    }
    if (listen(fd, 10) == -1)
    {
        perror("listen");
        exit(1);
    }

    if (getsockname(fd, (struct sockaddr *)&bind_addr, &sockaddr_len) == -1)
    {
        perror("getsockname");
        exit(1);
    }
    fprintf(stdout, "listen of port: %d\n", ntohs(bind_addr.sin_port));
    fflush(stdout);

    while (1)
    {
        if ((peer_fd = accept(fd, (struct sockaddr *)NULL, NULL)) == -1)
        {
            perror("accept");
            exit(1);
        }

        memset(&peer_name, 0, sizeof(peer_name));
        if (getpeername(peer_fd, (struct sockaddr *)&peer_addr, &sockaddr_len) == 0)
        {
            switch (peer_addr.sin_family)
            {
            case AF_INET:
            {
                inet_ntop(AF_INET, &peer_addr.sin_addr, peer_name, INET_ADDRSTRLEN);
                break;
            }
            case AF_INET6:
            {
                inet_ntop(AF_INET6, &(((struct sockaddr_in6 *)&peer_addr)->sin6_addr), peer_name, INET6_ADDRSTRLEN);
                break;
            }
            default:
                break;
            }
        }
        else
        {
            sprintf(peer_name, "[unknown]");
        }

        fprintf(stdout, "accepted peer: %s:%d\n", peer_name, ntohs(peer_addr.sin_port));
        fflush(stdout);

        ssize_t count = 0;
        do
        {
            count = read(peer_fd, buf, sizeof(buf));
            if (count == 0)
            {
                fprintf(stdout, "peer closed stdin\n");
                fflush(stdout);
            }
            if (count > 0)
            {
                fprintf(stdout, "read %ld byte(s) from peer: [", count);
                {
                    fprintf(stdout, "%d", buf[0]);
                    for (int i = 1; i < count; i++)
                    {
                        fprintf(stdout, ",%hhu", buf[i]);
                    }
                    fprintf(stdout, "]\n");
                }
                fflush(stdout);
            }
            else
            {
                fprintf(stderr, "errno: %d, strerror: %s\n", errno, strerror(errno));
            }
        } while (count > 0);

        if (close(peer_fd) == -1)
        {
            perror("close");
            exit(1);
        }
        fprintf(stdout, "closed\n");
        fflush(stdout);
    }

    return 0;
}