HTTP server using only system sockets in C

build.sh

#!/bin/sh

set -xe

cc -Wall -Werror -std=c11 -pedantic -c common.c
cc -Wall -Werror -std=c11 -pedantic -o main main.c common.o

common.c

#include "common.h"

void err_n_die(const char *fmt, ...) {
  int errno_save = errno;
  va_list ap;

  va_start(ap, fmt);

  vfprintf(stderr, fmt, ap);
  fprintf(stderr, "\n");
  fflush(stderr);

  if (errno_save != 0) {
    fprintf(stderr, "(errno = %d): %s\n", errno_save, strerror(errno_save));
    fprintf(stderr, "\n");
    fflush(stderr);
  }

  va_end(ap);

  exit(1);
}

char *bin2hex(const unsigned char *input, size_t len) {
  char *result;
  char *hexits = "0123456789ABCDEF";

  if (input == NULL || len <= 0) {
    return NULL;
  }

  int resultlength = (len * 3) + 1;

  result = malloc(resultlength);
  bzero(result, resultlength);

  for (size_t i = 0; i < len; i++) {
    int idx = i * 3;

    result[idx] = hexits[input[i] >> 4];
    result[idx + 1] = hexits[input[i] & 0x0F];
    result[idx + 2] = ' ';
  }

  return result;
}

common.h

#ifndef _COMMON_H_
#define _COMMON_H_

#include <sys/socket.h>
#include <sys/types.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <stdarg.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <netdb.h>

#define SERVER_PORT 18000

#define MAXLINE 4096

void err_n_die(const char *fmt, ...);
char *bin2hex(const unsigned char *input, size_t len);

#endif /* _COMMON_H_ */

main.c

#include "common.h"

#define USE_TCP 0
#define CONNECTIONS_QUEUE_SIZE 10

int main(void) {
  int listenfd;
  int connfd;
  int n;
  struct sockaddr_in servaddr;
  uint8_t buff[MAXLINE + 1];
  uint8_t recvline[MAXLINE + 1];

  if ((listenfd = socket(AF_INET, SOCK_STREAM, USE_TCP)) < 0) {
    err_n_die("socket error");
  }

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

  if ((bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr))) < 0) {
    err_n_die("bind error.");
  }

  if ((listen(listenfd, CONNECTIONS_QUEUE_SIZE)) < 0 ) {
    err_n_die("listen error.");
  }

  while (1) {
    printf("Waiting for a connection on port %d", SERVER_PORT);
    fflush(stdout);

    connfd = accept(listenfd, (struct sockaddr *) NULL, NULL);

    memset(recvline, 0, MAXLINE);

    while ((n = read(connfd, recvline, MAXLINE - 1)) > 0) {
      fprintf(stdout, "\n%s\n\n%s", bin2hex(recvline, n), recvline);

      if (recvline[n - 1] == '\n') {
        break;
      }

      memset(recvline, 0, MAXLINE);
    }

    if (n < 0) {
      err_n_die("read error.");
    }

    snprintf((char *) buff, sizeof(buff), "HTTP/1.0 200 OK\r\n\r\nHello");

    write(connfd, (char *) buff, strlen((char *) buff));
    close(connfd);
  }

  return 0;
}