Guess whoami : RTTI

Hi guys,

This time we will explore the technique used to determine the type of objects at runtime using Run Time Type Identification(RTTI) in C++.

Basically there are two common ways to achieve this:
1. Use a virtual function in base class and override that method in derived class:

output:

And when you use base class pointer or reference to hold object you may use bptr->typeOf() to detemine the type of object at run time.

2. Another approach which is built into language library is to use typeid() method. This method returns const object of typeinfo type.
For example,

We can also use Explicit Typecasting in C++ using :

dynamic_cast:

 It is used to ensure that the object returned after cast is complete object of requested type. If its not so it returns bad_cast exception in case of references and returns null pointer in case of pointers.

Consider non-polymorphic base class and its derived class:

This will not even clear the compilation phase. It will give this error:

Lets convert base class to polymorphic by adding virtual keyword for hello method in base class and check again. This time it clears compilation and the type is checked at run time. This is purely based on RTTI support by compiler.

static_cast: 

In this cast operator it is not checked that object returned after casting is actually a type of requested object. It is not type safe. Thus it is upto developers to take care when dereferencing. This works for:

• Implicit conversions
• Narrowing conversions
• Conversions from void *
• base class pointer to derived class pointer 
• derived class pointer to base class pointer

For example:

This will yield:

const_cast:

This cast is useful to convert const to non-const objects. This is used as another alternative to change const objects in a class without using mutable keyword.

For example,

output:

reinterpret_cast: 

This cast is used to convert any pointer type to any other pointer type, even for unrelated classes. It can also be used to convert int to pointer and other way round.

For example,

This will yield:

I hope this helps you understand basic typecasting mechanism present in C++. Stay tuned for more fun !

Simple HTTP Web server in C Language

Hi Guys !

This post helps you to write your own simple HTTP Web server in C language. This will give you a direction on how to proceed with writing web server using Berkeley Sockets( part of Berkeley Software Distribution). Berkeley sockets (or BSD sockets) is a computing library with an application programming interface (API) for internet sockets and Unix domain sockets, used for inter-process communication (IPC). We will get in details of socket in further section.

Lets discuss about traditional client-server architecture. Server is a process/layer which is listening on a port for requests to serve resources. Client is a process/layer which is requesting for the service or resource hosted on the server.

Server listens on a specific port for requests and respond to request on same connection. A socket is basically combination of IP and port number i.e. [IP,port number] defines a socket. As per TCP/IP software stack we can have TCP connection as well as UDP connections. Each have specific purpose. TCP is a connection oriented protocol and UDP is not connection oriented.i.e it send packets independent of each other. UDP does not guarantee delivery of packets.

Lets consider the flow of socket communication between client and server : The diagram shown below describes sequence of function call made to establish socket connection and exchange data.

 Server:

1. Invoke socket() function to get socket identifier. set options for socket if required using setsockopt()

2. Invoke bind() function to bind server to a specific IP and port number.

3. Invoke listen() function to make server listen on port for incoming requests.

4. Invoke accept() function whenever incoming request is received.

5. Exchange data using send() and recv() functions.

6. Terminate the socket connection using close() function.

Client:

1. Invoke socket() function to get socket identifier. set options for socket if required using setsockopt().

2. Invoke connect() function to connect to a server listening for requests at specific IP and port.

3. Once connection is established, exchange data using send() and recv() functions.

4. Terminate the socket connection using close() function.

I have shared the code for HTTP server written in C Language which returns HTML data on GET request at 8080 port:

/*
/*
Simple HTTP Web Server 
By : Kartik Kumar Perisetla(kartik.peri@gmail.com)
hosted for http://kperisetla.blogspot.com
*/

//for windows 
#include<winsock2.h>

// for POSIX based systems use- #include<sock.h> in place of #include<winsock2.h>

#include<sys/types.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#pragma comment(lib, "Ws2_32.lib")


//function specific for Windows-to be called before invoking call to socket()
int init()
{
 WSADATA wsaData;
 int iResult;

 // Initialize Winsock
 iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
 if (iResult != 0) 
 {
  printf("WSAStartup failed: %d\n", iResult);
  return 1;
 }

}

//function specific for windows-to be called after all socket communication is complete
void clean()
{
 WSACleanup();
}
int main()
{


 while(1)
 {
  init();
  server();
  clean();
 }
  
    return 0;
} 

void server()
{
 
        int sock, connected, bytes_recieved , true = 1;  
        char send_data [1024] , recv_data[1024];       

        struct sockaddr_in server_addr,client_addr;    
        int sin_size;
        
        if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
            perror("Socket");
            exit(1);
        }

        if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&true,sizeof(int)) == -1) {
            perror("Setsockopt");
            exit(1);
        }
        
        server_addr.sin_family = AF_INET;         
        server_addr.sin_port = htons(8080);     
        server_addr.sin_addr.s_addr = INADDR_ANY; 
        //bzero(&(server_addr.sin_zero),8); --This is for POSIX based systems
  memset(&(server_addr.sin_zero),0,8);
        if (bind(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr))== -1) 
    {
            perror("Unable to bind");
            exit(1);
        }

        if (listen(sock, 5) == -1) 
  {
            perror("Listen");
            exit(1);
        }
  
  printf("\n\nMyHTTPServer waiting on port 8080");
        fflush(stdout);
        

            sin_size = sizeof(struct sockaddr_in);

            connected = accept(sock, (struct sockaddr *)&client_addr,&sin_size);

           // printf("\n I got a connection from (%s , %d)",
                //   inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));

   char kk[9999];
   recv(connected,kk,sizeof(kk),0);
   printf("\n Received:%s",kk); 
   
   char xx[9999];
   strcpy(xx,"HTTP/1.1 200 OK\nContent-length: 47\nContent-Type: text/html\n\n<html><body><H1>Hello Kartik</H1></body></html>");
   
   int c=send(connected,&xx,sizeof(xx),0);
   printf("\nSTATUS:%d",c);
     
   printf("\nSent : %s\n",xx);
   
            close(sock);
   WSACleanup();
}

After writing this code, compile it and run it. I compiled this code using GCC compiler version 4.5.2.
GCC comes within Linux OS. For windows systems you can download minGW which consists of gcc, g++,etc.


Once you start the server by double clicking server.exe file you will see like this:

Now open up browser and navigate to URL : http://127.0.0.1:8080 and see the server responding to your request with web page. i.e HTML data:

and in the server console you can see the request structure and response returned:

I hope this post helps you in understanding the concept of socket communication and writing a simple HTTP web server in C language. 

Cheers !