Before there was HTTP, there
was FTP, NNTP, IMAP, POP3, and a whole alphabet soup of other protocols. Many people quickly embraced web browsers
because the browser provided an integrated program that let them check their
email, read newsgroups, transfer files, and view documents without worrying
about the details surrounding the underlying means of communication. PHP
provides functions, both natively and through PEAR, to use these other
protocols. With them, you can use PHP to create web frontend applications that
perform all sorts of network-enabled tasks, such as looking up domain names or
sending web-based email. While PHP simplifies these jobs, it is important to
understand the strengths and limitations of each protocol.
Section
17.2 to Section
17.4 cover the most popular feature of all: email. Section
17.2 shows how to send basic email messages. Section
17.3 describes MIME-encoded email, which enables you to send plain-text and
HTML-formatted messages. The IMAP and POP3 protocols, which are used to read
mailboxes, are discussed in Section
17.4.
The next two recipes discuss how to read newsgroups with NNTP.
Newsgroups are similar to mailing lists, but instead of every person on the list
receiving an email message, people can access a news server and view just the
messages they're interested in. Newsgroups also allow threaded discussions, so
its easy to trace a conversation through the archives. Section
17.5 discusses posting messages, while Section
17.6 covers retrieving messages.
Section
17.7 covers how to exchange files using FTP. FTP, or file transfer protocol, is a method for sending and
receiving files across the Internet. FTP servers can require users to log in
with a password or allow anonymous usage.
Searching LDAP servers is the topic of Section
17.8, while Section
17.9 discusses how to authenticate users against an LDAP server. LDAP
servers are used as address books and as a centralized store for user
information. They're optimized for information retrieval and can be configured
to replicate their data to ensure high reliability and quick response times.
The chapter concludes with recipes on networking. Section
17.10 covers DNS lookups, both from domain name to IP and vice versa. The
final recipe tells how to check if a host is up and accessible with PEAR's Ping
module.
Other parts of the book deal with some network protocols as
well. HTTP is covered in detail in Chapter 11. Those
recipes discuss how to fetch URLs in a variety of different ways. Protocols that
combine HTTP and XML are covered in Chapter 12. In that
chapter, along with covering DOM and XSLT, we discuss the emerging area of web
services, using the XML-RPC and SOAP protocols.
