A LinuxJunky Blog: A Very Simple HTTP Server writen in C

This is a part of the semester assignment. I felt like sharing it because I couldnt find any simple code like this on internet..

I have just edited the code to meet my requirements, originally it was made by my friend.. This code simply creates a web server with root in the current working directory and default port as 10000..

Can handle a maximum of 1000 clients.. fork() is used to handle each clients. Not a very efficient way if the number of clients increase but its a basic example to how you how to implement a simple HTTP Server.
/*
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;
}