Web Server in C

I implemented a web server in C language using only the standard libraries and thought it would be useful for you guys if I share the code.

The server runs on Linux and includes features like handling HTTP GET request, handling content types(txt, html, jpg, zip. rar, pdf, php etc.), sending proper HTTP error codes, serving the files from a web root, change in web root in a config file, zero copy optimization using sendfile method and php file handling. A port number should be provided as a command line argument.

After the server is up and running you can request for files using a web browser like Firefox.

For an example assume port number is "9000" and if you want to request a file called "test.php" which is in the webroot, use

http://localhost:9000/test.php 

WebServer.c

/*
 * WebServer.c
 *
 *  Created on: Nov 3, 2012
 *      Author: pavithra
 *
 * A web server in C language using only the standard libraries.
 * The port number is passed as an argument.
 *
 */

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

#define EOL "\r\n"
#define EOL_SIZE 2

typedef struct {
 char *ext;
 char *mediatype;
} extn;

//Possible media types
extn extensions[] ={
 {"gif", "image/gif" },
 {"txt", "text/plain" },
 {"jpg", "image/jpg" },
 {"jpeg","image/jpeg"},
 {"png", "image/png" },
 {"ico", "image/ico" },
 {"zip", "image/zip" },
 {"gz",  "image/gz"  },
 {"tar", "image/tar" },
 {"htm", "text/html" },
 {"html","text/html" },
 {"php", "text/html" },
 {"pdf","application/pdf"},
 {"zip","application/octet-stream"},
 {"rar","application/octet-stream"},
 {0,0} };

/*
 A helper function
 */
void error(const char *msg) {
 perror(msg);
 exit(1);
}

/*
 A helper function
 */
int get_file_size(int fd) {
 struct stat stat_struct;
 if (fstat(fd, &stat_struct) == -1)
  return (1);
 return (int) stat_struct.st_size;
}

/*
 A helper function
 */
void send_new(int fd, char *msg) {
 int len = strlen(msg);
 if (send(fd, msg, len, 0) == -1) {
  printf("Error in send\n");
 }
}

/*
 This function recieves the buffer
 until an "End of line(EOL)" byte is recieved
 */
int recv_new(int fd, char *buffer) {
 char *p = buffer; // Use of a pointer to the buffer rather than dealing with the buffer directly
 int eol_matched = 0; // Use to check whether the recieved byte is matched with the buffer byte or not
 while (recv(fd, p, 1, 0) != 0) // Start receiving 1 byte at a time
 {
  if (*p == EOL[eol_matched]) // if the byte matches with the first eol byte that is '\r'
    {
   ++eol_matched;
   if (eol_matched == EOL_SIZE) // if both the bytes matches with the EOL
   {
    *(p + 1 - EOL_SIZE) = '\0'; // End the string
    return (strlen(buffer)); // Return the bytes recieved
   }
  } else {
   eol_matched = 0;
  }
  p++; // Increment the pointer to receive next byte
 }
 return (0);
}

/*
 A helper function: Returns the
 web root location.
 */
char* webroot() {
 // open the file "conf" for reading
 FILE *in = fopen("conf", "rt");
 // read the first line from the file
 char buff[1000];
 fgets(buff, 1000, in);
 // close the stream
 fclose(in);
 char* nl_ptr = strrchr(buff, '\n');
 if (nl_ptr != NULL)
  *nl_ptr = '\0';
 return strdup(buff);
}

/*
 Handles php requests
 */
void php_cgi(char* script_path, int fd) {
 send_new(fd, "HTTP/1.1 200 OK\n Server: Web Server in C\n Connection: close\n");
 dup2(fd, STDOUT_FILENO);
 char script[500];
 strcpy(script, "SCRIPT_FILENAME=");
 strcat(script, script_path);
 putenv("GATEWAY_INTERFACE=CGI/1.1");
 putenv(script);
 putenv("QUERY_STRING=");
 putenv("REQUEST_METHOD=GET");
 putenv("REDIRECT_STATUS=true");
 putenv("SERVER_PROTOCOL=HTTP/1.1");
 putenv("REMOTE_HOST=127.0.0.1");
 execl("/usr/bin/php-cgi", "php-cgi", NULL);
}

/*
 This function parses the HTTP requests,
 arrange resource locations,
 check for supported media types,
 serves files in a web root,
 sends the HTTP error codes.
 */
int connection(int fd) {
 char request[500], resource[500], *ptr;
 int fd1, length;
 if (recv_new(fd, request) == 0) {
  printf("Recieve Failed\n");
 }
 printf("%s\n", request);
 // Check for a valid browser request
 ptr = strstr(request, " HTTP/");
 if (ptr == NULL) {
  printf("NOT HTTP !\n");
 } else {
  *ptr = 0;
  ptr = NULL;

  if (strncmp(request, "GET ", 4) == 0) {
   ptr = request + 4;
  }
  if (ptr == NULL) {
   printf("Unknown Request ! \n");
  } else {
   if (ptr[strlen(ptr) - 1] == '/') {
    strcat(ptr, "index.html");
   }
   strcpy(resource, webroot());
   strcat(resource, ptr);
   char* s = strchr(ptr, '.');
   int i;
   for (i = 0; extensions[i].ext != NULL; i++) {
    if (strcmp(s + 1, extensions[i].ext) == 0) {
     fd1 = open(resource, O_RDONLY, 0);
     printf("Opening \"%s\"\n", resource);
     if (fd1 == -1) {
      printf("404 File not found Error\n");
      send_new(fd, "HTTP/1.1 404 Not Found\r\n");
      send_new(fd, "Server : Web Server in C\r\n\r\n");
      send_new(fd, "<html><head><title>404 Not Found</head></title>");
      send_new(fd, "<body><p>404 Not Found: The requested resource could not be found!</p></body></html>");
      //Handling php requests
     } else if (strcmp(extensions[i].ext, "php") == 0) {
      php_cgi(resource, fd);
      sleep(1);
      close(fd);
      exit(1);
     } else {
      printf("200 OK, Content-Type: %s\n\n",
        extensions[i].mediatype);
      send_new(fd, "HTTP/1.1 200 OK\r\n");
      send_new(fd, "Server : Web Server in C\r\n\r\n");
      if (ptr == request + 4) // if it is a GET request
        {
       if ((length = get_file_size(fd1)) == -1)
        printf("Error in getting size !\n");
       size_t total_bytes_sent = 0;
       ssize_t bytes_sent;
       while (total_bytes_sent < length) {
        //Zero copy optimization
        if ((bytes_sent = sendfile(fd, fd1, 0,
          length - total_bytes_sent)) <= 0) {
         if (errno == EINTR || errno == EAGAIN) {
          continue;
         }
         perror("sendfile");
         return -1;
        }
        total_bytes_sent += bytes_sent;
       }

      }
     }
     break;
    }
    int size = sizeof(extensions) / sizeof(extensions[0]);
    if (i == size - 2) {
     printf("415 Unsupported Media Type\n");
     send_new(fd, "HTTP/1.1 415 Unsupported Media Type\r\n");
     send_new(fd, "Server : Web Server in C\r\n\r\n");
     send_new(fd, "<html><head><title>415 Unsupported Media Type</head></title>");
     send_new(fd, "<body><p>415 Unsupported Media Type!</p></body></html>");
    }
   }

   close(fd);
  }
 }
 shutdown(fd, SHUT_RDWR);
}

int main(int argc, char *argv[]) {
 int sockfd, newsockfd, portno, pid;
 socklen_t clilen;
 struct sockaddr_in serv_addr, cli_addr;

 if (argc < 2) {
  fprintf(stderr, "ERROR, no port provided\n");
  exit(1);
 }
 sockfd = socket(AF_INET, SOCK_STREAM, 0);
 if (sockfd < 0)
  error("ERROR opening socket");
 bzero((char *) &serv_addr, sizeof(serv_addr));
 portno = atoi(argv[1]);
 serv_addr.sin_family = AF_INET;
 serv_addr.sin_addr.s_addr = INADDR_ANY;
 serv_addr.sin_port = htons(portno);
 if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
  error("ERROR on binding");
 listen(sockfd, 5);
 clilen = sizeof(cli_addr);
 /*
  Server runs forever, forking off a separate
  process for each connection.
  */
 while (1) {
  newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
  if (newsockfd < 0)
   error("ERROR on accept");
  pid = fork();
  if (pid < 0)
   error("ERROR on fork");
  if (pid == 0) {
   close(sockfd);
   connection(newsockfd);
   exit(0);
  } else
   close(newsockfd);
 } /* end of while */
 close(sockfd);
 return 0; /* we never get here */
}

Make sure you have installed php and there's exist a "conf" file consisted of the webroot before running this.

Enjoy!

Synchronous Cilent Server application in java

Client code

Client.java

This program creates a socket connection with the server running on port 9050 on localhost and gets the input stream from the socket by chaining the BufferedReader with the InputStreamReader.

package clientserver;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;
import java.net.UnknownHostException;

public class client {

 public static void main(String args[]) {

  try {
   Socket s = new Socket("127.0.0.1", 9050);

   InputStreamReader streamreader = new InputStreamReader(
     s.getInputStream());
   BufferedReader br = new BufferedReader(streamreader);

   String number = br.readLine();

   System.out.println("Today's number is " + number);
   br.close();

  } catch (UnknownHostException e) {
   e.printStackTrace();
  } catch (IOException e) {
   e.printStackTrace();
  }

 }

}

Server code

Server.java

This program makes a ServerSocket and waits for client Requests. When a client tries to connect the server creates a new socket in a random port(using accept() method), which knows about the ip address and the port number of the client and makes the connection to the client. Also here server uses PrintWriter to sned messages to client.

package mainserver;

import java.io.IOException;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Random;

public class Server {

 public static void main(String args[]) {

  try {
   ServerSocket serverSock = new ServerSocket(9050);

   while (true) {

    Socket sock = serverSock.accept();
    PrintWriter pw = new PrintWriter(sock.getOutputStream());
    String TodayNum = new Server().getNumber();
    pw.println(TodayNum);
    pw.close();
    System.out.println(TodayNum);

   }

  } catch (IOException e) {
   e.printStackTrace();
  }

 }

 public String getNumber() {

  Random rg = new Random();
  int num = rg.nextInt(100);
  String numb = Integer.toString(num);
  return numb;

 }

}

Output

System.Net.Sockets.Socket Class

System.Net.Sockets.Socket Class provides the basic functionality of a socket application.

• Some important properties of System.Net.Sockets.Socket

Property	Description
AddressFamily	Gets the address family of the socket-the value is from the Socket.AddressFamily enumeration
Available	Returns the amount of available data to read
Blocking	Gets or sets the value which indicates whether the socket is in blocking mode or not
Connected	Returns the value that informs whether the socket is still connected with the remote host
LocalEndPoint	Gets the local endpoint
ProtocolType	Get the protocol type of the socket
RemoteEndPoint	Gets the remote endpoint of a socket
SocketType	Gets the type of the socket

• Some important methods of System.Net.Sockets.Socket

Method	Description
Accept()	Creates a new socket to handle the incoming connection request.
Bind()	Associates a socket with the local endpoint for listening to incoming connections.
Close()	Forces the socket to close itself.
Connect()	Establishes a connection with the remote host.
GetSocketOption()	Returns the value of a SocketOption.
IOControl()	Sets low-level operating modes for the socket. This method provides low-level access to the underlying socket instance of the Socket class.
Listen()	Places the socket in listening mode. This method is exclusive to server applications.
Receive()	Receives data from a connected socket.
Poll()	Determines the status of the socket.
Select()	Checks the status of one or more sockets.
Send()	Sends data to the connected socket.
SetSocketOption()	Sets a SocketOption.
Shutdown()	Disables send and receive on a socket.

Sockets

Sockets

• Socket is one end of a two way communication link between two programs running on a network.
• Data can be passed between different processes by connecting the two sockets together

Basic socket types

• Stream Socket
  
  • Connection oriented sockets
    
  • Consists of a stream of bytes that can be bi-directional
    
  • Usage of stream sockets is a more reliable method than the usage of datagram sockets
    
• Datagram sockets
  
  • AKA Connectionless sockets, no explicit connection is established
    
  • A message is sent to a specified socket and can be received appropriately from the specified socket
    
  • Usage of datagram sockets is reducing the overhead incurred by establishing an explicit connection
    

Row sockets

• Generalized form of sockets called row sockets
• Packet is passed directly to the application that needs it bypassing the mechanism by which the computer handles TCP/IP

Ports

• Defined to solve the problem of communicating with multiple operations simultaneously

Sockets composed of

• IP address of the machine
• Port no used by TCP application

Socket numbers are unique across the entire internet as IP address is unique across the internet and the port no is unique on the individual machine. This enables process to communicate with another process across network based entirely on socket number.

Client Server applications uses sockets

• Server waits for the connection from the client
  
• Client initiates the connection with the server
• Server should be already running before client tries to connect
• Client must know the target address and the port no, tries to establish a connection with the server
• Server accepts the connection
• Server application creates a new socket to deal specifically with the connected client
• Server and client communicate by reading from and writing to their respective sockets