Validating email addresses

Question: Can I a DNS lookup inside an RPGLE or CL program?

Yes you can. The following code does it the reverse way, finding the host name for a given IP address.

You could change the gethostbyaddr() function to gethostbynam() and make the needed changes.

   PGM        PARM(&IP)
   DCL        VAR(&IP) TYPE(*CHAR) LEN(15)
   DCL        VAR(&HOST) TYPE(*CHAR) LEN(64)
   CALL       PGM(GETHOST1) PARM(&IP &HOST)
   SNDPGMMSG  MSG('The host name for TCP/IP address ' || +
                &IP *BCAT 'is ' || &HOST)
   ENDPGM
      
*===================================================================
*  Bryan Dietz       Some of the code borrowed from others         
*
*  3X Corp.                                                        
*
*  bdietz@3x.com                                                   
*
*==================================================================*
     hdebug dftactgrp( *no ) bnddir( 'QC2LE' )
     Dinet_addr        PR            10U 0 ExtProc('inet_addr')
     D  IPAddr                         *   Value

     DGetHostByAddr    PR              *   ExtProc('gethostbyaddr')
     D  HostEnt                        *   Value
     D  AddrLen                       5I 0 Value
     D  AddrType                      5I 0 Value

     DSysInfDS        SDS
     D CurDevice             244    253

     DRcvVar           DS
     D  Protocol             859    859
     D  IPAddress            878    892

     DRcvLen           S              9B 0
     DFormat           S              8
     DDevice           S             10
     DIPAddr           S               *
     DHostEnt          S               *
     DHostAddr         S               *
     DAddrLen          S              5I 0
     DAddrType         S              5I 0

     DHostEntS         DS                  Based(HostEntP)
     D  HostNPtr                       *

     DHostName         S             64    Based(HostNameP)

     DHostAddrS        DS                  Based(HostAddrP)
     D  IP32Addr                     10U 0

     DAF_INET          S              5I 0 Inz(2)
     DSpaces           S             64    Inz(*Blanks)

     DAPIError         DS
     D  NbrBytes               1      4B 0 Inz(15)
     D  CPFID                  9     15
      *****************************************************************
     C     *Entry        PList
     C                   Parm                    P#IPAddress      15
     C                   Parm                    P#IPName         64

      * Get IP-name
     c                   Eval      IPAddress = P#IPAddress
     C                   Eval      HostEntP  = %Addr(HostEnt)

     C                   Eval      HostAddrP = %Addr(HostAddr)
     C                   Eval      IP32Addr  = inet_addr(%Addr(IPAddress))
     C                   Eval      AddrLen   = %Size(HostAddrS)
     C                   Eval      AddrType  = AF_INET

     C                   Eval      HostEntP  = GetHostByAddr(HostAddrP:
     C                                                       AddrLen:
     C                                                       AddrType)

     C     HostEntP      IfEq      *NULL
     C                   Eval      P#IPName  = Spaces
     C                   Else
     C                   Eval      HostNameP = HostNPtr
     C                   Eval      P#IPName  = HostName

     C     X'00':X'40'   XLate     P#IPName      P#IPName

     C                   EndIf

      * Return parameters
     C                   Eval      P#IPAddress = IPAddress

     C                   SetOn                                        Lr
     C                   Return

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