How do I compare certain values from different XML documents?

I want to write code in Perl that compares two XML files.

A Little bit from the history... With API Documentation (get request) I get data1 form the Web Service1 and data2 from the Service2. They are presented in XML Format, but not the same.

I should compare just two elements in these files (deviceName and ipAddress), if they are the same in both files, It should be a message " WebService1 already contains DeviceName "Switch1" ". If not - I would make POST request and add this device in WebService1/WebService2.

Can you give me advice, what Modules should I use and how should I begin with this comparing?

For example (file1)

   <?xml version="1.0" ?>
   <queryResponse last="34" first="0" count="35" type="Devices" responseType="listEntityInstances" requestUrl="https://hostname/webacs/api/v1/data/Devices?.full=true" rootUrl="https://hostname/webacs/api/v1/data">
      <entity dtoType="devicesDTO" type="Devices" url="https://hostname/webacs/api/v1/data/Devices/201">
         <devicesDTO displayName="201201" id="201">
           <clearedAlarms>0</clearedAlarms>
           <collectionDetail></collectionDetail>
           <collectionTime></collectionTime>
           <creationTime></creationTime>
           <criticalAlarms>0</criticalAlarms>
           <deviceId>205571</deviceId>
           <deviceName>NEW-SW5</deviceName>
           <deviceType>Cisco Switch</deviceType>
           <informationAlarms>0</informationAlarms>
           <ipAddress>10.66.12.128</ipAddress>
         <location></location>
           <majorAlarms>0</majorAlarms>
           <managementStatus></managementStatus>
              <manufacturerPartNrs>
                  <manufacturerPartNr></manufacturerPartNr>
              </manufacturerPartNrs>
              <minorAlarms>0</minorAlarms>
              <productFamily></productFamily>
              <reachability>Reachable</reachability>
              <softwareType>IOS</softwareType>
              <softwareVersion>12.1(22)</softwareVersion>
              <warningAlarms>0</warningAlarms>
         </devicesDTO>
      </entity>
   </queryResponse>

File2

  <?xml version="1.0" encoding="utf-8" standalone="yes"?>
  <ns3:networkdevice name="NEW-SW5" id="9a6ef750-2620-11e4-81be-b83861d71f95" xmlns:ns2="ers.ise.cisco.com" xmlns:ns3="network.ers.ise.cisco.com">
  <link type="application/xml" href="https://hostname:9060/ers/config/networkdevice/123456" rel="self"/>
       <authenticationSettings>
          <enableKeyWrap>false</enableKeyWrap>
          <keyInputFormat>ASCII</keyInputFormat>
          <networkProtocol>RADIUS</networkProtocol>
          <radiusSharedSecret>******</radiusSharedSecret>
       </authenticationSettings>
       <NetworkDeviceIPList>
         <NetworkDeviceIP>
            <ipaddress>10.66.12.128</ipaddress>
            <mask>21</mask>
         </NetworkDeviceIP>
       </NetworkDeviceIPList>
       <NetworkDeviceGroupList>
         <NetworkDeviceGroup>Location#All Locations</NetworkDeviceGroup>
         <NetworkDeviceGroup>Device Type#All Device Types</NetworkDeviceGroup>
   </NetworkDeviceGroupList>
  </ns3:networkdevice>

There is smth special: In file1 my tags called: deviceName, ipAddress and they are elements.
In file2 we have one attribute (because it is staying in the main element ns3:networkdevice and it's called name what responds our deviceName from file1 ) and the other element is called ipaddress (ipAddress in file1)

Solution

You can use XML::Twig to parse both responses. Each of them needs an individual parser.

For the first one, you need to go for the two tags <deviceName> and <ipAddress>. A simple twig_handler for each of them that access the text property of the matched element is sufficient.

Those handlers can be complex, but in our case a code reference that deals with a single value is enough. We know that there is only one occurrence of each value, so we can directly assign both of them to their respective lexical variables.

use strict;
use warnings;
use XML::Twig;

my ($device_name, $ip_address);
XML::Twig->new(
    twig_handlers => {
        deviceName => sub { $device_name = $_->text },
        ipAddress => sub { $ip_address = $_->text },
    }
)->parse(\*DATA);

say $device_name;
say $ip_address;

__DATA__
<?xml version="1.0" ?>
<queryResponse last="34" first="0" count="35" type="Devices" responseType="listEntityInstances" requestUrl="https://hostname/webacs/api/v1/data/Devices?.full=true" rootUrl="https://hostname/webacs/api/v1/data">
   <entity dtoType="devicesDTO" type="Devices" url="https://hostname/webacs/api/v1/data/Devices/201">
      <devicesDTO displayName="201201" id="201">
        <clearedAlarms>0</clearedAlarms>
        <collectionDetail></collectionDetail>
        <collectionTime></collectionTime>
        <creationTime></creationTime>
        <criticalAlarms>0</criticalAlarms>
        <deviceId>205571</deviceId>
        <deviceName>NEW-SW5</deviceName>
        <deviceType>Cisco Switch</deviceType>
        <informationAlarms>0</informationAlarms>
        <ipAddress>10.66.12.128</ipAddress>
      <location></location>
        <majorAlarms>0</majorAlarms>
        <managementStatus></managementStatus>
           <manufacturerPartNrs>
               <manufacturerPartNr></manufacturerPartNr>
           </manufacturerPartNrs>
           <minorAlarms>0</minorAlarms>
           <productFamily></productFamily>
           <reachability>Reachable</reachability>
           <softwareType>IOS</softwareType>
           <softwareVersion>12.1(22)</softwareVersion>
           <warningAlarms>0</warningAlarms>
      </devicesDTO>
   </entity>
</queryResponse>

For the second one you need to use att() to get the name attribute of one of the elements, but that's also straight-forward.

use strict;
use warnings;
use XML::Twig;

my ($device_name, $ip_address);
XML::Twig->new(
    twig_handlers => {
        'ns3:networkdevice' => sub { $device_name = $_->att('name') },
        ipaddress => sub { $ip_address = $_->text },
    }
)->parse(\*DATA);

say $device_name;
say $ip_address;
__DATA__
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<ns3:networkdevice name="NEW-SW5" id="9a6ef750-2620-11e4-81be-b83861d71f95" xmlns:ns2="ers.ise.cisco.com" xmlns:ns3="network.ers.ise.cisco.com">
<link type="application/xml" href="https://hostname:9060/ers/config/networkdevice/123456" rel="self"/>
     <authenticationSettings>
        <enableKeyWrap>false</enableKeyWrap>
        <keyInputFormat>ASCII</keyInputFormat>
        <networkProtocol>RADIUS</networkProtocol>
        <radiusSharedSecret>******</radiusSharedSecret>
     </authenticationSettings>
     <NetworkDeviceIPList>
       <NetworkDeviceIP>
          <ipaddress>10.66.12.128</ipaddress>
          <mask>21</mask>
       </NetworkDeviceIP>
     </NetworkDeviceIPList>
     <NetworkDeviceGroupList>
       <NetworkDeviceGroup>Location#All Locations</NetworkDeviceGroup>
       <NetworkDeviceGroup>Device Type#All Device Types</NetworkDeviceGroup>
 </NetworkDeviceGroupList>
</ns3:networkdevice>

Now you that you have both of these, you can combine that. I suggest to create a function for each of them, pass in the response XML and make them return the $device_name and $ip_address.

use strict;
use warnings;
use XML::Twig;

sub parse_response_1 {
    my $xml = shift;

    my ( $device_name, $ip_address );
    XML::Twig->new(
        twig_handlers => {
            deviceName => sub { $device_name = $_->text },
            ipAddress  => sub { $ip_address  = $_->text },
        }
    )->parse($xml);

    return $device_name, $ip_address;
}

sub parse_response_2 {
    my $xml = shift;

    my ( $device_name, $ip_address );
    XML::Twig->new(
        twig_handlers => {
            'ns3:networkdevice' => sub { $device_name = $_->att('name') },
            ipaddress           => sub { $ip_address  = $_->text },
        }
    )->parse($xml);

    return $device_name, $ip_address;
}

Of course my names parse_response_1 and parse_response_2 are not the best choice. Don't use the numbers, use the names of the services that returned the responses instead.

With those two functions we now have the means to retrieve exactly the information that we want. All that's left is to check them.

sub check {
    my ( $response_1, $response_2 ) = @_;

    my ( $device_name_1, $ip_address_1 ) = parse_response_1($response_1);
    my ( $device_name_2, $ip_address_2 ) = parse_response_2($response_2);

    return $device_name_1 eq $device_name_2 && $ip_address_1 eq $ip_address_2;
}

Again, the names of the variables could be better. Now you just need to call that with your two response XMLs and it will return a truthy value, or not.