This code is a Python program that uses sockets to query the whois information of any domain name entered by the user. Here is a line-by-line explanation of what the code does:

• The first line imports the socket module, which provides access to the low-level network interface in Python.

• The second line asks the user to enter a domain name, such as python.org, and converts it to lowercase.

  

  Cleaning the domain name

>>> import socket
>>> domain = input("Domain : ").lower()
# Remove unwanted characters from the domain name
>>> domain = domain.strip("http://").strip("https://").strip("www.").strip()
# Get the top-level domain (TLD) of the domain name
>>> tld = domain.split(".")[-1]
# Use a dictionary to store the mapping between TLDs and whois servers
>>> whois_servers = {
    "org": "whois.pir.org",
    "com": "whois.verisign-grs.com",
    "net": "whois.verisign-grs.com",
    # Add more TLDs and whois servers as needed
}
# Get the whois server for the TLD, or use a default value if not found
>>> whois_server = whois_servers.get(tld, "whois.iana.org")

• The next four lines remove any unwanted characters from the domain name, such as http://, https://, or www., which are not part of the domain name itself.
• The next line splits the domain name by the dot (.) character and takes the last element, which is the top-level domain (TLD) of the domain name, such as org, com, or net.

  Defining the whois server dictionary

• The next six lines define a dictionary that maps some common TLDs to their corresponding whois servers, which are the servers that store the whois information for those domains. For example, the whois server for org domains is whois.pir.org, and the whois server for com and net domains is whois.verisign-grs.com. The dictionary also has a default value of whois.iana.org, which is the whois server for the Internet Assigned Numbers Authority (IANA).
• The next line uses the get method of the dictionary to find the whois server for the given TLD, or use the default value if the TLD is not in the dictionary.

  Screenshot of the code

• The next line creates a socket object, which is an endpoint of a network communication. The socket object is initialized with two parameters: socket.AF_INET and socket.SOCK_STREAM. The first parameter specifies the address family of the socket, which is AF_INET for IPv4 addresses. The second parameter specifies the socket type, which is SOCK_STREAM for TCP sockets.

  Handling socket errors

• The next four lines use a try-except block to handle any errors that may occur during the socket operation. The try block contains the code that performs the socket communication, and the except block handles the socket.error exception, which is raised when a socket error occurs.

• The first line in the try block uses the connect method of the socket object to establish a connection to the whois server on port 43, which is the standard port for whois protocol. The connect method takes a tuple as an argument, which contains the host name and the port number of the server.

  Creating a socket object

• The next line uses the send method of the socket object to send the domain name to the whois server, followed by a carriage return (\r) and a newline (\n) characters, which indicate the end of the request. The send method takes a bytes object as an argument, so the domain name is encoded using utf-8 encoding before sending.

• The next line initializes an empty bytes object, which will store the received data from the whois server.

• The next five lines use a while loop to receive all the data from the whois server until the socket is closed. The loop condition is True, which means it will run indefinitely until a break statement is executed.

• The first line in the loop uses the recv method of the socket object to receive up to 4096 bytes of data at a time from the whois server. The recv method takes an integer as an argument, which specifies the maximum number of bytes to receive. The recv method returns a bytes object, which is assigned to the variable data.

• The next line checks if the data variable is empty, which means no more data is available from the server. If this is the case, the loop is terminated by a break statement.

  Decoding the message object

• The next line appends the received data to the msg object, which accumulates all the data from the server.

• The next line in the try block uses the close method of the socket object to close the connection to the whois server. This is a good practice to free up the resources used by the socket.

• The next line decodes the msg object to a string using utf-8 encoding, which is the standard encoding for whois information. The decoded string is assigned to the same variable msg.

  Printing the whois information

• The next line prints the msg string to the standard output, which is the console by default. The msg string contains the whois information of the domain name, such as the registrant, the registrar, the creation date, the expiration date, the name servers, and other details.

• The first line in the except block prints the socket.error exception to the standard output, which contains the error message and the error code of the socket error.

  Installation in Windows

• A prerequisite for working with a domain is to install whois:

  https://learn.microsoft.com/en-us/sysinternals/downloads/whois

  Installation on Linux

• Update your .deb repos by running:

$ sudo apt update

• Apply any pending security or apps updates to your Linux box:

$ sudo apt upgrade

• Then install the whois client on Debian or Ubuntu Linux using the apt command or apt-get command:

$ sudo apt install whois

• Test it using the whois command for IP address lookup. For example:

whois ip-address
whois 8.8.8.8

• Then you can also do the domain name lookup. For instance:

whois -h whois.server.com domainname
whois -h whois.verisign-grs.com google.com
whois -h whois.registrar.com domainname
whois -h whois.markmonitor.com google.com

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