"""Retrieves Microsoft SQL Server instance information by querying the SQL Browser
service.
"""
import argparse
import sys
import socket
from collections import OrderedDict


SQL_BROWSER_DEFAULT_PORT = 1434
BUFFER_SIZE = 4096
TIMEOUT = 4

def get_instance_info(host, instance=None, sql_browser_port=SQL_BROWSER_DEFAULT_PORT,
                    buffer_size=BUFFER_SIZE, timeout=TIMEOUT):
    """Gets Microsoft SQL Server instance information by querying the SQL Browser service.

    Args:
        host (str): Hostname or IP address of the SQL Server to query for information.
        instance (str): The name of the instance to query for information.
                        All instances are included if none.
        sql_browser_port (int): SQL Browser port number to query.
        buffer_size (int): Buffer size for the UDP request.
        timeout (int): timeout for the query.

    Returns:
        dict: A dictionary with the server name as the key and a dictionary of the
            server information as the value.

    """
    # Create a UDP socket
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    # Set a timeout
    sock.settimeout(timeout)

    server_address = (host, sql_browser_port)

    if instance:
        # The message is a CLNT_UCAST_INST packet to get a single instance
        # https://msdn.microsoft.com/en-us/library/cc219746.aspx
        message = '\x04%s\x00' % instance
        # Encode the message as a bytesarray
    else:
        # The message is a CLNT_UCAST_EX packet to get all instances
        # https://msdn.microsoft.com/en-us/library/cc219745.aspx
        message = '\x03'

    # Encode the message as a bytesarray
    message = message.encode()

    # Send data
    sock.sendto(message, server_address)

    # Receive response
    data, server = sock.recvfrom(buffer_size)

    results = []

    # Loop through the server data
    for server in data[3:].decode().split(';;'):
        server_info = OrderedDict()
        chunk = server.split(';')

        if len(chunk) > 1:
            for i in range(1, len(chunk), 2):
                server_info[chunk[i - 1]] = chunk[i]

            results.append(server_info)

    # Close socket
    sock.close()

    return results


def main():
    """Main program logic if called as a script."""

    parser = argparse.ArgumentParser(description=__doc__)

    parser.add_argument('host',
                        help='hostname or IP address of the SQL Server to query for information')
    parser.add_argument('-i', '--instance', default=None, required=False,
                        help='name of the instance to query for information')
    parser.add_argument('-p', '--port', default=SQL_BROWSER_DEFAULT_PORT, required=False,
                        help='SQL Browser port')

    arguments = parser.parse_args()

    try:
        instance_info = get_instance_info(arguments.host, instance=arguments.instance,
                                        sql_browser_port=arguments.port)
    except socket.error as error:
        sys.stderr.write('Connection to %s failed: %s' % (arguments.host, error))
        sys.exit(1)

    for i in instance_info:
        print('')

        for key, value in i.items():
            print('%s: %s' % (key, value))


if __name__ == '__main__':
    main()

C:\Scripts\mssql_info>python mssql_info.py mssqlserver1

ServerName: mssqlserver1
InstanceName: instance1
IsClustered: Yes
Version: 12.0.5000.0
tcp: 1442
np: \\mssqlserver1\pipe\MSSQL$instance1\sql\query

ServerName: mssqlserver2
InstanceName: instance2
IsClustered: Yes
Version: 13.0.4001.0
tcp: 1440
np: \\mssqlserver2\pipe\MSSQL$instance2\sql\query

ServerName: mssqlserver3
InstanceName: instance3
IsClustered: Yes
Version: 11.0.6020.0
tcp: 1448
np: \\mssqlserver3\pipe\MSSQL$instance3\sql\query

C:\Scripts\mssql_info>python mssql_info.py mssqlserver1 -i instance1

ServerName: mssqlserver1
InstanceName: instance1
IsClustered: Yes
Version: 12.0.5000.0
tcp: 1442
np: \\mssqlserver1\pipe\MSSQL$instance1\sql\query

C:\Scripts\mssql_info>