Chapter 18. Internet Services - Perl Cd Bookshelf [Electronic resources] نسخه متنی

Chapter 18. Internet Services

Contents:

Introduction

Simple DNS Lookups

Being an FTP Client

Sending Mail

Reading and Posting Usenet News Messages

Reading Mail with POP3

Simulating Telnet from a Program

Pinging a Machine

Accessing an LDAP Server

Sending Attachments in Mail

Extracting Attachments from Mail

Writing an XML-RPC Server

Writing an XML-RPC Client

Writing a SOAP Server

Writing a SOAP Client

Program: rfrm

Program: expn and vrfy

Western Union internal memo, 1876

This "telephone" has too many shortcomings to be seriously considered
as a means of communication. The device is inherently of no value to
us.

18.0. Introduction

Correct use of sockets is only part of
writing programs that communicate over the network. Once you have a
way for two programs to talk, you still need a
protocol for communication. This protocol lets
each party know when to talk, and it precisely defines who is
responsible for which part of the service.

Common Internet protocols are listed in Table
18-1.

Table 18-1. Common Internet protocols

Even something as relatively simple as connecting to a remote
computer requires intricate negotiations between client and server.
If you had to write the Perl code to implement these protocols each
time you wanted to use a network service, you'd probably end up
writing a lot of buggy programs, trying to get demoted into a
management position, or both.

Fortunately, Perl has modules for these protocols. Most modules
implement the client side of the protocol rather than the server
side. This is because most clients make one query at a time, whereas
a server must be prepared to deal with multiple clients and that code
can get quite tricky. That said, there are FTP (Net::FTPServer), HTTP
(HTTP::Daemon, POE::Component::Server::HTTP), SMTP
(POE::Component:Server::SMTP), and IRC (POE::Component::Server::IRC)
servers on CPAN.

Most of these modules fall under the Net:: hierarchy, a common subset
of which has been included standard with Perl since v5.8. We use
Net::FTP to send and receive files using FTP, Net::NNTP to read and
post Usenet news, Net::Telnet (from CPAN) to simulate a connection to
another machine, Net::Ping to check whether a machine is alive, and
Net::POP3 and Mail::Mailer (from CPAN) to receive and send mail. We
cover the CGI protocol in Chapter 19, and with HTTP
in Chapter 20.

Recent years have seen a growth in web services,
i.e., services offered through the web's HTTP protocol. Chapter 19, Chapter 20, and Chapter 21 address the Web in more detail, but we cover
web services in this chapter. The three main ways of offering web
services are XML-RPC, SOAP, and REST.

XML-RPC is a simple way to make remote
procedure calls. You can transport XML-RPC requests ("I want to call
this method with these arguments") and responses ("this fault
occurred" or "this is what the method returned") across protocols
like HTTP, SMTP, Jabber, and so on. The XMLRPC::Lite modules handle
translation between Perl function calls and the XML representation
that goes across the wire.

SOAP is more
complex than XML-RPC, providing more OO and exception support. It
also offers a "document mode," where the response is an XML document
rather than an encoded data structure; for example, you might submit
an order and get back an XML receipt. SOAP has more built-in data
types than XML-RPC and lets you define custom data types using W3C
Schema. Like XML-RPC, SOAP runs over a variety of protocols. Both
SOAP and XML-RPC are implemented in the SOAP-Lite distribution.

Representational State
Transfer (REST) is a different way of viewing web services. Rather
than writing remote procedure calls and encoding arguments, which
exposes the implementation, REST offers a way to separate
implementation from how the client accesses a particular resource. In
REST, a URL is an object's address. You can use GET, POST, PUT, and
DELETE methods to fetch, change state, create, update, and delete.
Because it's more a design philosophy than an API or encoding, we
don't cover it here. The book Programming Web Services with
Perl, by Randy Ray and Pavel Kulchenko (O'Reilly), gives
an introduction to REST.

You can thank Graham Barr, whose IO::Socket modules we used for
low-level network communication in Chapter 17, for
most of these modules. He also wrote Net::FTP, Net::NNTP, Net::POP3,
and Mail::Mailer. Jay Rogers wrote Net::Telnet, and Paul Kulchenko
developed the SOAP-Lite toolkit. Thank these folks that you don't
have to reinvent these tricky wheels!

17.21. Program: fwdport		18.1. Simple DNS Lookups

Copyright © 2003 O'Reilly & Associates. All rights reserved.