A Very Simple HTTP Server writen in C

https://blog.abhijeetr.com/2010/04/very-simple-http-server-writen-in-c.html

/*
AUTHOR: Abhijeet Rastogi (http://www.google.com/profiles/abhijeet.1989)
This is a very simple HTTP server. Default port is 10000 and ROOT for the server is your current working directory..
You can provide command line arguments like:- $./a.aout -p [port] -r [path]
for ex.
$./a.out -p 50000 -r /home/
to start a server at port 50000 with root directory as "/home"
$./a.out -r /home/shadyabhi
starts the server at port 10000 with ROOT as /home/shadyabhi
*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<sys/socket.h>
#include<arpa/inet.h>
#include<netdb.h>
#include<signal.h>
#include<fcntl.h>
#define CONNMAX 1000
#define BYTES 1024
char *ROOT;
int listenfd, clients[CONNMAX];
void error(char *);
void startServer(char *);
void respond(int);
int main(int argc, char* argv[])
{
  struct sockaddr_in clientaddr;
  socklen_t addrlen;
  char c;
  //Default Values PATH = ~/ and PORT=10000
  char PORT[6];
  ROOT = getenv("PWD");
  strcpy(PORT,"10000");
  int slot=0;
  //Parsing the command line arguments
  while ((c = getopt (argc, argv, "p:r:")) != -1)
    switch (c)
    {
      case 'r':
        ROOT = malloc(strlen(optarg));
        strcpy(ROOT,optarg);
        break;
      case 'p':
        strcpy(PORT,optarg);
        break;
      case '?':
        fprintf(stderr,"Wrong arguments given!!!\n");
        exit(1);
      default:
        exit(1);
    }
  printf("Server started at port no. %s%s%s with root directory as %s%s%s\n","\033[92m",PORT,"\033[0m","\033[92m",ROOT,"\033[0m");
  // Setting all elements to -1: signifies there is no client connected
  int i;
  for (i=0; i<CONNMAX; i++)
    clients[i]=-1;
  startServer(PORT);
  // ACCEPT connections
  while (1)
  {
    addrlen = sizeof(clientaddr);
    clients[slot] = accept (listenfd, (struct sockaddr *) &clientaddr, &addrlen);
    if (clients[slot]<0)
      error ("accept() error");
    else
    {
      if ( fork()==0 )
      {
        respond(slot);
        exit(0);
      }
    }
    while (clients[slot]!=-1) slot = (slot+1)%CONNMAX;
  }
  return 0;
}
//start server
void startServer(char *port)
{
  struct addrinfo hints, *res, *p;
  // getaddrinfo for host
  memset (&hints, 0, sizeof(hints));
  hints.ai_family = AF_INET;
  hints.ai_socktype = SOCK_STREAM;
  hints.ai_flags = AI_PASSIVE;
  if (getaddrinfo( NULL, port, &hints, &res) != 0)
  {
    perror ("getaddrinfo() error");
    exit(1);
  }
  // socket and bind
  for (p = res; p!=NULL; p=p->ai_next)
  {
    listenfd = socket (p->ai_family, p->ai_socktype, 0);
    if (listenfd == -1) continue;
    if (bind(listenfd, p->ai_addr, p->ai_addrlen) == 0) break;
  }
  if (p==NULL)
  {
    perror ("socket() or bind()");
    exit(1);
  }
  freeaddrinfo(res);
  // listen for incoming connections
  if ( listen (listenfd, 1000000) != 0 )
  {
    perror("listen() error");
    exit(1);
  }
}
//client connection
void respond(int n)
{
  char mesg[99999], *reqline[3], data_to_send[BYTES], path[99999];
  int rcvd, fd, bytes_read;
  memset( (void*)mesg, (int)'\0', 99999 );
  rcvd=recv(clients[n], mesg, 99999, 0);
  if (rcvd<0)    // receive error
    fprintf(stderr,("recv() error\n"));
  else if (rcvd==0)    // receive socket closed
    fprintf(stderr,"Client disconnected upexpectedly.\n");
  else    // message received
  {
    printf("%s", mesg);
    reqline[0] = strtok (mesg, " \t\n");
    if ( strncmp(reqline[0], "GET\0", 4)==0 )
    {
      reqline[1] = strtok (NULL, " \t");
      reqline[2] = strtok (NULL, " \t\n");
      if ( strncmp( reqline[2], "HTTP/1.0", 8)!=0 && strncmp( reqline[2], "HTTP/1.1", 8)!=0 )
      {
        write(clients[n], "HTTP/1.0 400 Bad Request\n", 25);
      }
      else
      {
        if ( strncmp(reqline[1], "/\0", 2)==0 )
          reqline[1] = "/index.html";        //Because if no file is specified, index.html will be opened by default (like it happens in APACHE...
        strcpy(path, ROOT);
        strcpy(&path[strlen(ROOT)], reqline[1]);
        printf("file: %s\n", path);
        if ( (fd=open(path, O_RDONLY))!=-1 )    //FILE FOUND
        {
          send(clients[n], "HTTP/1.0 200 OK\n\n", 17, 0);
          while ( (bytes_read=read(fd, data_to_send, BYTES))>0 )
            write (clients[n], data_to_send, bytes_read);
        }
        else    write(clients[n], "HTTP/1.0 404 Not Found\n", 23); //FILE NOT FOUND
      }
    }
  }
  //Closing SOCKET
  shutdown (clients[n], SHUT_RDWR);         //All further send and recieve operations are DISABLED...
  close(clients[n]);
  clients[n]=-1;
}

$ gcc httpserver.c 
$ ./a.out -p 50000
Server started at port no. 50000 with root directory as /home/XXX/concurrency

http://127.0.0.1:50000/

$ ./a.out -p 50000
Server started at port no. 50000 with root directory as /home/ningluwsl/concurrency
GET / HTTP/1.1
Host: 127.0.0.1:50000
Connection: keep-alive
Cache-Control: max-age=0
sec-ch-ua: " Not A;Brand";v="99", "Chromium";v="102", "Microsoft Edge";v="102"
sec-ch-ua-mobile: ?0
sec-ch-ua-platform: "Windows"
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.5005.63 Safari/537.36 Edg/102.0.1245.30
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Sec-Fetch-Site: none
Sec-Fetch-Mode: navigate
Sec-Fetch-User: ?1
Sec-Fetch-Dest: document
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.9,en;q=0.8,en-GB;q=0.7,en-US;q=0.6
file: /home/XXX/concurrency/index.html