Cyzyk, Mark

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Mark Cyzyk. Book Review: Clinton Wong's Web Client Programming with Perl, inTelecommunications Electronic Reviews, v4 (8), September 1997. http://www.ala.org/ala/mgrps/divs/lita/ter/terv4n8september.cfm#wongVolume 4, Issue 8, September 1997Telecommunications Electronic Reviews (TER) is a publication of the Library andInformation Technology Association.Telecommunications Electronic Reviews (ISSN: 1075-9972) is a periodical copyright ©1997 by the American Library Association. Documents i  this issue, subject to copyrightby the American Library Association or by the authors f the documents, may bereproduced for noncommercial, educational, or scientif c purposes granted by Sections107 and 108 of the Copyright Revision Act of 1976, provided that the copyright statementand source for that material are clearly acknowledged and that the material is reproducedwithout alteration. None of these documents may be reproduced or adapted forcommercial distribution without the prior written permission of the designated copyrightholder for the specific documents.REVIEW OF: Clinton Wong. Web Client Programming wit hPerl. Sebastopol, CA: O'Reilly & Associates, 1997.by Mark CyzykThe purpose of this book is to introduce UNIX-based Webmasters to simple Web client programmingusing Perl (Practical Extraction and Report Language). It can, however, be profitably read by anyoneinterested in how Web clients work.The first third of the volume concentrates on what Web clients are and how they do what they do. Thesecond chapter, "Demystifying the Browser," examines th  anatomy of a Web client and the basicstructure of a client/server transaction. The various HTTP (Hypertext Transfer Protocol) headers thatare passed from client to server and back again are illustrated. To illustrate the text-based nature ofHTTP, Wong offers an interesting example of a manual HTTP transaction. He shows how one cansimply Telnet into a Web server and manually issue HTTP commands resulting in output from theserver. This powerful example of a simple HTTP transaction stays firmly in the reader's mind duringthe rest of the book.The third chapter, "Client Request Methods," offers a elatively in-depth discussion of HTTP itself.Although there are fully ten methods that a client can use to make a request of a server, Wong spendstime only on the seven most important: GET, HEAD, POST, PUT, DELETE, TRACE, and OPTIONS.These are the most useful request methods for the budding client programmer to understand. All CGI(Common Gateway Interface) programmers are familiar w th the GET and POST methods, butWong's discussion of the other methods is fascinating to those like myself who, when confronted withthe automatic upload features of recent versions of Netscape and other Web-based applications,wonder "How did they do that?" (Hint: they used the PUT method.) The chapter ends with a soliddiscussion of server response codes, e.g., 403 Forbidden, and what they mean, as well as acomprehensive list and select discussion of HTTP headers.For the client programmer who revels in the bits and bytes, chapter four, "The Socket Library," coversnetwork socket programming over a TCP/IP (Transmission Control Protocol/Internet Protocol)network, specifically in a UNIX environment. Though important for a comprehensive understandingof the client/server process over TCP/IP, as Wong himself states, a deep understanding of socketprogramming is not needed to create Web-based client programs. The reason for this is thatprogrammers can avail themselves of the Library of W rld Wide Web (WWW) modules for Perl(LWP) that are widely available from most Perl archives.Like any Perl library, the LWP modules exist to greatly simplify the programming process. The heartof the book is to be found in chapters five and six, "The LWP Library" and "Example LWPPrograms," where the LWP Library is discussed and its uses are illustrated. LWP is a library ofmodules for Perl 5 that allows the programmer to accomplish complex tasks (such as socketprogramming or Uniform Resource Locator parsing) in a simple and elegant manner.The library as a whole is comprised of eight discrete modules of which Wong addresses only the fourmost useful: the LWP, HTML (Hypertext Markup Languae), HTTP, and URI (Uniform ResourceIdentification) modules. Essentially, the LWP module handles socket communications between clientand server; the HTML module handles the parsing of HTML documents; the HTTP module handlesHTTP requests and responses; and the URI module handles the escaping of URIs and the relative-to-absolute translation of URLs. Within each module ar to be found several classes (LWP is object-oriented); Wong discusses the most important for each of the four modules.Wong offers three types of example Web clients--simple clients, periodic clients, and recursiveclients--to illustrate the many uses of the LWP library. Wong's simple client calls a URL with a customUser Agent header designating the name of the client program, thereby identifying itself to the server.His periodic client--more complex than the simple cli nt--periodically connects to the Federal ExpressWeb site, uses a tracking number to query its database, and waits to see if a package has beendelivered. The program runs until it receives notification of delivery. Such a periodic client could formthe basis of any Web-based function that needs to be performed regularly, for example, a stock tickerchecker. Wong's recursive client--by far the most cmplex--checks all the HTML pages at a specifiedWeb site for malfunctioning hyperlinks. A list of these links is then printed out.For those running X Windows, the final chapter, "Graphical Examples with Perl/Tk," illustrates howone can program a graphical user interface (GUI) for Perl text-based programs. In this manner, theprogrammer can actually program a custom GUI Web browser.As are most of the O'Reilly publications, this book is well- prepared, useful, and a pleasure to read,using the chatty style that O'Reilly authors seem to prefer. Examples throughout are relevant andclearly presented. The book as a whole proceeds in a satisfying manner, its pace easing the reader intoever deeper programming concepts and examples. For the Webmaster hoping to create custom, text-based Web clients for use in Web site administration, or for those just interested in learning moreabout how the hypertext transfer protocol functions, this book is recommended.Mark Cyzyk (mcyzyk@towson.edu) is Head of Information Technology at Albert S. Cook Library,Towson State University, in Maryland.Copyright © 1997 by Mark Cyzyk. This document may be reproduced in whole or in part fornoncommercial, educational, or scientific purposes, provided that the preceding copyright statementand source are clearly acknowledged. All other rights are reserved. For permission to reproduce oradapt this document or any part of it for commercial distribution, address requests to the author atmcyzyk@towson.edu.About TEREditor-in-Chief is Thomas C. Wilson, University of Houston (TWilson@uh.edu). Editorial BoardMembers are Marshall Breeding, Vanderbilt University (Breeding@library.vanderbilt.edu); ShawnCollins, University of Tennessee, Knoxville (scollins@utk.edu); Nancy Nuckles Colyar, LouisianaState University (lbysec@lsuvm. sncc.lsu.edu), Thomas Dowling, OhioLINK(tdowling@ohiolink.edu); Pat Ensor, University of Houston (PLEnsor@uh.edu); Martin Halbert,Emory University (mhalber@emory.edu); Elizabeth Lane Lawley, Internet Training & ConsultingServices (liz@itcs.com); Scott P. Muir, Boston College (muirs@bc.edu); and Kate Wakefield, WLN(Wake@wln.com).Technology Electronic Reviews (TER) is an irregular electronic serial publication of the Library andInformation Technology Association, a division of the American Library Association, 50 E. Huron St.,Chicago, IL 60611. The primary function of TER is to provide reviews of and pointers to a variety ofprint and electronic resources about information technology. Resources include books, articles, serials,discussion lists, training materials, bibliographies, and other items of interest to librarians andinformation technology professionals. The topics covered may include, but are not limited to,networking technologies and standards; hardware and software; operating systems; databases; specificprogramming languages; management tools and utilities; echnical project management; training andpersonnel issues; library perspectives; and research and development.Opinions expressed in this publication are those of the writers and do not necessarily represent theviewpoints of LITA, ALA, or organizations involved in the storage and/or distribution of thepublication. TER is distributed electronically via Internet. There is no subscription fee. Currently it is available viaWorld Wide Web (http://www.lita.org/ter/) and new-issue announcements are posted on the LITA-Lelectronic discussion list. To subscribe, send an email message to listproc@ala1.ala.org that says:subscribe LITA-L First-Name Last-Name. Other distribut on arrangements may be made in the future.

Book Review: Clinton Wong's Web Client Programming with Perl

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Book Review: Clinton Wong's Web Client Programming with Perl

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