Perl | Dimuthu's Blog

Last week I had an opportunity to write some CGI scripts in Perl. It is like going few years back in web development. And it gave me the answer why PHP become favorite over Perl among the web developers. It is not just PHP’s C-like friendly syntax, but also the ability to write inline script in html may have been a big factor.

In there we came across parsing following type of XML.

<ns1:person
       xmlns:ns1="http://dimuthu.org/example/perl_xml/xsd">
<ns1:name>PQR XYZ</ns1:name>
<ns1:age>25</ns1:age>
</ns1:person>

We started to use XML::Twig. And it is pretty straightforward. Here was our code.

use XML::Twig;

my $xml_str = <<E;
<ns1:person
    xmlns:ns1="http://dimuthu.org/example/perl_xml/xsd">
<ns1:name>PQR XYZ</ns1:name>
<ns1:age>25</ns1:age>
</ns1:person>
E

my $xt = XML::Twig->new();

$xt->parse($xml_str);

my $txt = $xt->root->findvalue("//ns1:name");
print $txt;

OK. It was working.

Anyway in practice we found that this is not the only way we receive the xml. That is the namespace prefix can be different. When you write an XML to an XML schema you are free to have your own prefixes for the namespaces. And in fact in practice different people, programs and vendors uses different prefixes.

So our program should be able to parse following XML too. (see the namespace prefix is changed)

<ns0:person
    xmlns:ns0="http://dimuthu.org/example/perl_xml/xsd">
<ns0:name>PQR XYZ</ns0:name>
<ns0:age>25</ns0:age>
</ns0:person>

And with the default namespace.

<person xmlns="http://dimuthu.org/example/perl_xml/xsd">
<name>PQR XYZ</name>
<age>25</age>
</person>

Both these occasions our code failed. And normally whenever there is an API to parse XPath, you can register namespaces. But XML::Twit there was no something like that. That made us to jump to use XML::LibXML. It is apparently little complicated than the simple Twig API. But it did work. (Look later for the code using XML::LibXML)

The story is actually there is a way to register namespaces in Twit, in fact it is not in XML::Twit, it is in the XML::Twit:XPath module which is hardly any documented. It just duplicate the Twit API adding some functionalities to deal with namespaces. Apparently not the most elegant way of designing an API. Anyway Here is the code that works written using XML::Twit:XPath.

use XML::Twig;
use XML::Twig::XPath;

my $xml_str = <<E;

<person xmlns="http://dimuthu.org/example/perl_xml/xsd">
<name>PQR XYZ</name>
<age>25</age>
</person>

E

my $xtp = XML::Twig::XPath->new();
$xtp->parse($xml_str);

$xtp->set_namespace('ns',
       'http://dimuthu.org/example/perl_xml/xsd');

my $txt = $xtp->root->findvalue('//ns:name');
print $txt;

Note that I have register the namespace to the prefix ‘ns’, so in xpath quires I can use this prefix to refer namespaces.

Anyway Perl is not bad, it has dozens of modules to do the same thing. So just for the reference I will note down it here,

Using XML:XPath,

use XML::XPath;
my $xml_str = <<E;

<person xmlns="http://dimuthu.org/example/perl_xml/xsd">
<name>PQR XYZ</name>
<age>25</age>
</person>

E

my $xp = XML::XPath->new(xml => $xml_str);

$xp->set_namespace('ns',
       'http://dimuthu.org/example/perl_xml/xsd');
my $txt = $xp->findvalue('//ns:name'); # get name 

print $txt;

Then Using XML::LibXML;

use XML::LibXML;

my $xml_str = <<E;

<person xmlns="http://dimuthu.org/example/perl_xml/xsd">
<name>PQR XYZ</name>
<age>25</age>
</person>

E

my $xl= XML::LibXML->new();

$xml = $xl->parse_string($xml_str);

my $xpc = XML::LibXML::XPathContext->new($xml);

$xpc->registerNs('ns',
        'http://dimuthu.org/example/perl_xml/xsd');
my $txt = $xpc->findvalue('//ns:name'); # get name 

print $txt;

So it is all for this post, And one reason I didn’t tell you earlier and so obvious why PHP is popular over Perl. Look at http://php.net/dom or http://php.net/simplexml. It has a great documentation for every function to the every needle. Whenever Perl, Ruby thinking of going pass PHP, they have to consider this aspect too more seriously.

Today I got to install wso2 wsf/perl in my Ubuntu 8.04 OS. It was really straight forward. Just follow the following steps and you are ready to do real web services in perl.

Download wsf/perl 1.1 from cpan web site. http://search.cpan.org/CPAN/authors/id/C/CH/CHINTANA/WSO2-WSF-Perl-1.1.tar.gz
Download wsf/c 1.3.0 from the oxygen tank. http://dist.wso2.org/products/wsf/c/1.3.0/wso2-wsf-c-src-1.3.0.tar.gz
First extract the wsf/c packtar xvzf wso2-wsf-c-src-1.3.0.tar.gz
Compile and install the wsf/c to a preferred directory (say /tmp/wsfc)../configure –prefix=’/tmp/wsfc’makemake install (you may need super user privileges depending on where you select to install the package)
Install the following packages from apt respositories.perl, libperl-dev, liberror-perlYou can use the following command to install themsudo apt-get install perlsudo apt-get install libperl-dev
sudo apt-get install liberror-perl
Now extract the WSO2-WSF-Perl-1.1.tar.gztar xvzf WSO2-WSF-Perl-1.1.tar.gz
Set the WSFC_HOME environment variable to where you install wsf/c. (in our example it is /tmp/wsfc)export WSFC_HOME=/tmp/wsfc (Remember you have to do this every time you open a new shell, or else put this line in the ~/.bashrc file)
Inside the WSO2-WSF-Perl-1.1 directory runperl Makefile.PLNote: This may sometime complains about missiling libraries (actually for -laxis2_minizip, -laxis2_libxml2, -lhtpwcb). Anyway this will not be a problem for your installation.
Now the last step of your installation.makesudo make install (Here you need to have super user priviledges)
Just go to the samples directory and run the echo_client.pl (You need to have a wsf/php server running to response these wsf/perl calls). Make sure it gives the expexted output.

Currently WSF/Perl have only the web services client libraries. But it is rich with features like WS-Security, WS-Reliable Messaging, MTOM and many more.

Dimuthu’s Blog

July 28th, 2008Perl XML Parsers And My Story

July 19th, 2008Installing wsf/perl in Ubuntu

Dimuthu’s Blog

July 28th, 2008Perl XML Parsers And My Story

July 19th, 2008Installing wsf/perl in Ubuntu

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