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Perl Lecture Notes - June 15, 2002 - XML take 3

• Questions

• RPC in general
  • We already do this.
  • Just use a script to hit someone's web form and parse the result. Voila.
  • So what's wrong with this picture?
  • Coming soon to an internet near you: Web Services

• SOAP::Lite
  • Go look at the first example before wading through this summary.
  • Also check the acronyms for RPC, XML-RPC, SOAP, WSDL, XSD, UDDI, REST, .NET
  • Overall it's just like Perl:
    • Extremely simple to do simple stuff - even in one line.
    • Multiple syntax options for nearly everything.
    • Many ways to configure and use
    • Details of XML envelopes : possible but harder.
    • It can hide all the SOAP XML from you.
    • It can even turn remote perl objects (packages) into persistent objects that appear to be local.
    • Very cool.
  • Capabilities:
    • Support for SOAP clients and servers.
    • Support for XML-RPC clients and servers
    • Support for many transport protocols.
    • Examples of connecting to/from .NET and COM service/clients
    • Support for reading .wsdl files to define service.
    • Supports compression for HTTP messages
    • No support for creating .wsdl files.
    • Limited support for queries to UDDI servers.
  • Data types
    • SOAP is strongly typed. Perl is not.
    • Getting arguments back is usually fine - they're just converted into something appropriate. Multiple argument returns turn into key-value hashes, for example.
    • Sending out arguments can be a bit trickier. SOAP::Lite will try to guess the type (number or string, say), or you can specify data types and keys within a SOAP::Data structure, and send that structure as the argument.
  • Caveats
    • Many fine examples; however, details are often hazy.
    • Various SOAP server/clients expect various specifics in the SOAP envelope. Getting SOAP::Lite to fit other's expectations may take some massaging of SOAP::Data or SOAPAction. But there are many examples as well as debugging tools.
    • The documentation can be a bit spotty.
    • Parts (UDDI, WSDL, some docs) feel like a work in progress.
  • One (albeit long) liner:
    perl "-MSOAP::Lite service=>'http://www.xmethods.net/sd/StockQuoteService.wsdl'" -le "print getQuote('MSFT')"

  • Examples
    These command line clients can be on any machine.
    As usual .pl and .cgi files will have pretty formatting if you append
    • dns lookup - client to look up DNS, defined from WSDL.
      • client-dns.pl - client source code
      • client-dns.out - details of SOAP and HTTP transaction
      • NSLookup.wsdl - the WSDL service definition. (I fetched this with "wget".)
    • names/ - server and several clients with XML/header trace
      • ExamineNames.pm
      • test.pl
      • server-ExamineNames.cgi
      • client1.pl
      • trace-client-output.txt - shows a simple SOAP XML envelope
      • client2.pl - using WSDL
      • ExamineNames.wsdl - Jim's by-hand WSDL for this service
      • client3.pl - autodispatch
      • aside - format-xml.pl, xml pretty printing with SAX using XML::Handler::YAWriter
    • isbn_price_quote/ , two clients with data types
    • NET-Example/, another book price quote
    • htaccess/ iterator, encapsulated perl object instance
    • persistent server object with soap.deamon server
    • xmlrpc client with XML/header trace
    • uddi, a rather lame example

• paraphrased from "What's Next" conference
  • "SOAP is friendly to a firewalls the way a bullet is friendly to a skull."
  • "HTML/JavaScript is the universal client;
    HTTP is the universal transport;
    CGI is the universal server."
  • Future is rich clients (Flash etc) and web services.
  • A big question - trust and security.
    (Many options, though: see SOAP::Lite Cookbook)

• Resources and Documentation
  • This week's acronyms
  • soaplite.com
    • guide
    • cookbook includes a number of security (SSL, cookies, tickets, ...) examples
    • perl.com Quick Start part 1, part 2
  • SOAP-Lite-0.55 distribution, local copy
    • SOAP-Lite-0.55/examples/
  • CPAN SOAP-Lite docs
  • http://www.xmethods.net/ - listing of public SOAP services
  • http://www.xmlrpc.com/ - listing of some XMLRPC services
  • SOAP security article on XML.com, Leigh Dodds
  • w3.org Technical Reports
    • SOAP at w3.org
    • WSDML at w3.org

• Assignmnent
  • Reading
    • Browse the SOAP site documentation and tutorials.
  • Writing
    • Use SOAP::Lite to turn a piece of one of your CGI websites into a SOAP service.
    • Write a client that accesses your service.
    • Create a webpage that gives a brief description of your service.

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