Get-WhoIs.ps1

function Get-WhoIs {
    <#
    .SYNOPSIS
        Get a WhoIs record using servers published via whois-servers.net.
    .DESCRIPTION
        For IP lookups, Get-WhoIs uses whois.arin.net as a starting point, chasing referrals within the record to get to an authoritative answer.
    
        For name lookups, Get-WhoIs uses the whois-servers.net service to attempt to locate a whois server for the top level domain (TLD).
        
        Get-WhoIs connects directly to whois servers using TCP/43.
    .INPUTS
        System.String
    .EXAMPLE
        Get-WhoIs indented.co.uk
    .EXAMPLE
        Get-WhoIs 10.0.0.1
    #>

    [CmdletBinding()]
    [OutputType([String])]
    param (
        # The name or IP address to locate the WhoIs record for.
        [Parameter(Mandatory, ValueFromPipeline)]
        [String]$Name,

        # A WhoIs server to use for the query. Discovered, but can be overridden.
        [String]$WhoIsServer,

        # A command to execute on the WhoIs server if the server requires a command prefixing before the query.
        [String]$Command
    )
 
    process {
        if (-not $WhoIsServer) {
            if ([IPAddress]::TryParse($Name, [Ref]$null) -or $Name.EndsWith("arpa")) {
                $WhoIsServer = $whoIsServerName = "whois.arin.net"
                $Command = "n "
            } else {
                $WhoIsServer = $whoIsServerName = '{0}.whois-servers.net' -f $Name.Split('.')[-1]
            }
        }
        if (-not ([IPAddress]::TryParse($WhoIsServer, [Ref]$null))) {
            $whoIsServerRecord = [System.Net.Dns]::GetHostEntry($WhoIsServer) |
                Select-Object -Expand AddressList |
                Select-Object -First 1
            $WhoIsServer = $whoIsServerRecord
        }

        if ($WhoIsServer) {
            Write-Debug ('Get-WhoIs: Asking {0} ({1}) for {2} using command {3}{4}' -f $whoIsServerName, $WhoIsServer, $Name, $Command, $Name)

            $socket = [System.Net.Sockets.Socket]::new('Stream', 'Tcp')
            try {
                $socket.Connect($WhoIsServer, 43)
            } catch [System.Net.Sockets.SocketException] {
                $errorRecord = [System.Management.Automation.ErrorRecord]::new(
                    [System.Net.Sockets.SocketException]::new($_.Exception.InnerException.NativeErrorCode),
                    'ConnectionFailed',
                    [System.Management.Automation.ErrorCategory]::ConnectionError,
                    $WhoIsServer
                )
                Write-Error -ErrorRecord $errorRecord
            }

            [Byte[]]$buffer = [System.Text.Encoding]::UTF8.GetBytes("$Command$Name`r`n")
            $null = $socket.Send($buffer)

            $receivedBytes = do {
                $buffer = [Byte[]]::new(4096)
                $receivedCount = $socket.Receive($buffer)
                if ($receivedCount -gt 0) {
                    [Array]::Resize([Ref]$buffer, $receivedCount - 1)
                    $buffer
                }

                Write-Debug ('Get-WhoIs: Received {0} bytes from {1}' -f $receivedCount, $socket.RemoteEndPoint.Address)
            } until ($receivedCount -eq 0)

            $socket.Close()

            $whoIsRecord = [System.Text.Encoding]::UTF8.GetString($receivedBytes)
            if ($whoIsRecord -match 'ReferralServer: whois://(.+):') {
                Write-Debug ('Get-WhoIs: Following referral for {0} to {1}' -f $Name, $matches[1])

                Get-WhoIs $Name -WhoIsServer $matches[1]
            } else {
                $whoIsRecord
            }
        }
    }
}