Beginning Web Development With Perl : From Novice to ... - Nabo

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CHAPTER 5 ■ LWP MODULES 101which parameters, if any, are required, and the corresponding values for them. Of course,since this is Perl, it’s common to substitute variables for the parameter values themselves.So instead of hard-coding the zip code, you might want to set $zip as a scalar variable thatchanges for the web form. Naturally, what you do with the POSTed data is up to you and theform itself.Handling CookiesAs explained in Chapter 1, cookies are used by web sites to track state and other informationabout the visiting browser or user agent. It’s up to you to work with the cookies that are set andexpected by the web site.The LWP’s cookie_jar attribute is used with sites that set and read browser cookies. Usingthe cookie_jar attribute, you can store cookies both in memory or out to a file. When I monitoreda site to win a gaming console (as I described earlier in the chapter), I used an existingcookie store. Since that site required authentication using a cookie, I was able to use the cookiesfile from Firefox to successfully authenticate to the site from within the script.The cookie_jar attribute can read cookies based solely in memory, or it can use cookiesin a file. If the cookies are based in memory, they exist only as long as the life of the user agentobject created within the program itself. If the cookies are based in a file, they become persistentand can be saved and read between multiple user agents and multiple executions of theprogram itself.You can create a temporary cookie store in memory by invoking the HTTP::Cookies object.For example, assume a browser object named $browser. Creating a memory-based cookie storewould look like this:$browser->cookie_jar(HTTP::Cookies->new);On the other hand, using a file would look like this:use LWP;my $browser = LWP::UserAgent->new( );my $cookie_jar = HTTP::Cookies->new('file' => '/home/suehring/cookies.txt');$browser->cookie_jar($cookie_jar);Handling Password-Protected SitesSome sites require authentication through a username and password in order to sign in anduse the resources found there. This authentication is provided or indicated by a 401 AuthorizationRequired HTTP response. Normally, a dialog box prompting for authentication pops up,as opposed to a username and password web page. The LWP includes attributes to work withsites that use basic authentication. Using the credentials() method, you add these attributesto a given browser object programmatically. The credentials() method looks like this:$browser->credentials('server:port','realm','username'=>'password');For example, the site www.example.com has a subscribers area for which you must supplycredentials. This site uses a realm of Subscribers.
102CHAPTER 5 ■ LWP MODULES$browser->credentials('www.example.com:80','Subscribers','suehring' => 'badpassword');Now when the $browser object is used to access a URL within the www.example.com domainthat prompts for credentials, the credentials specified in the example will be sent.The credentials themselves die at the end of the browser object’s life. You can store asmany credentials inside a browser object as you need, based on the server name and realmname for the protected resource.Mirroring a Web SiteEarlier in this chapter, I mentioned LWP::Simple’s mirror() function, as well as the lwp-mirrorprogram. Both of these work well for mirroring an entire web site. The browser object also hasa mirror() method that enables a site to be mirrored, while taking advantage of the extra powerof the object’s interface.The lwp-mirror program does an excellent job of mirroring a site in a sane, easy-tounderstandmanner. I recommend the lwp-mirror program for nearly all mirroringoperations. lwp-mirror is called from your shell and accepts a URL and an output file asarguments:lwp-mirror Here is an example:lwp-mirror http://www.braingia.org/ local_braingia_index.htmlThe mirror() method on the browser object has two requirements as well: the URL andthe output file. Here is an example of using this method:$browser->mirror('http://www.braingia.org','local_braingia_index.html');Handling ProxiesProxies are sometimes required to access Internet services. The LWP includes a set of methodsfor working with proxies that enable you to set a proxy for a given protocol or set of protocols.When a proxy is required on a given system, it’s not uncommon for it to be set among the differentenvironment variables in the shell. The LWP can use the shell environment variable forproxy. A call to the env_proxy() method will look for environment variables that indicate theproxy server to use, such as http_proxy, as in the following example:$browser->env_proxy();It doesn’t hurt to call this method if nothing is set for the proxy environment variable—theproxy value for the browser object will still be empty.The proxy() method accepts two arguments: the protocol and the actual proxy to use.Here is its format:$browser->proxy(protocol, proxy_server);
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Beginning Web Development with Perl
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PART 5 ■ ■ ■ Creating Web Tem
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■CONTENTSvii■CHAPTER 4 System I
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■CONTENTSixCreating a SOAP Listen
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■CONTENTSxiTemplate Toolkit Synta
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About the Author■STEVE SUEHRING i
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AcknowledgmentsThanks to James Lee
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xx■INTRODUCTIONThis book will use
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CHAPTER 1■ ■ ■The CGI ModuleT
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CHAPTER 1 ■ THE CGI MODULE 5for t
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CHAPTER 1 ■ THE CGI MODULE 9exit;
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CHAPTER 1 ■ THE CGI MODULE 27No m
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CHAPTER 1 ■ THE CGI MODULE 33Also
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CHAPTER 2■ ■ ■Popular CGI Mod
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CHAPTER 2 ■ POPULAR CGI MODULES 3
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Page 66 and 67: 50CHAPTER 3 ■ DATABASES AND PERLT
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Page 104 and 105: CHAPTER 5■ ■ ■LWP ModulesLWP
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Page 122 and 123: 108CHAPTER 6 ■ NET:: TOOLSCreatin
Page 124 and 125: 110CHAPTER 6 ■ NET:: TOOLSThe out
Page 126 and 127: 112CHAPTER 6 ■ NET:: TOOLSmy $pop
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Page 148 and 149: PART 3■ ■ ■XML and RSS
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154CHAPTER 8 ■ PERL AND RSSFigure
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156CHAPTER 8 ■ PERL AND RSShttp:/
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158CHAPTER 8 ■ PERL AND RSSDebugg
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160CHAPTER 8 ■ PERL AND RSS$rsswr
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162CHAPTER 8 ■ PERL AND RSSListin
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CHAPTER 9■ ■ ■XML Parsing wit
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CHAPTER 9 ■ XML PARSING WITH PERL
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PART 4■ ■ ■PerformanceEnhance
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184CHAPTER 10 ■ APACHE AND MOD_PE
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202CHAPTER 11 ■ DEVELOPMENT WITH
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CHAPTER 12■ ■ ■The Template T
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CHAPTER 12 ■ THE TEMPLATE TOOLKIT
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CHAPTER 13■ ■ ■Perl Web Sites
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CHAPTER 13 ■ PERL WEB SITES WITH
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284APPENDIX ■ PERL BASICSKeywords
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286APPENDIX ■ PERL BASICS$ perl n
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288APPENDIX ■ PERL BASICSAnd line
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290APPENDIX ■ PERL BASICSCan you
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292APPENDIX ■ PERL BASICSBy defau
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294APPENDIX ■ PERL BASICS#!/usr/b
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296APPENDIX ■ PERL BASICSThe last
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298APPENDIX ■ PERL BASICSThe NOT
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300APPENDIX ■ PERL BASICSprint "S
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302APPENDIX ■ PERL BASICSthe syst
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304APPENDIX ■ PERL BASICS$ perl s
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306APPENDIX ■ PERL BASICSThis cod
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308APPENDIX ■ PERL BASICS$a = 6 *
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310APPENDIX ■ PERL BASICS$a = "A9
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312APPENDIX ■ PERL BASICS#!/usr/b
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314APPENDIX ■ PERL BASICSmy $name
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316APPENDIX ■ PERL BASICSis short
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318APPENDIX ■ PERL BASICSLet’s
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320APPENDIX ■ PERL BASICSOther Te
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322APPENDIX ■ PERL BASICS}}}actio
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324APPENDIX ■ PERL BASICSNotice t
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326APPENDIX ■ PERL BASICSLooping
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328APPENDIX ■ PERL BASICSuse stri
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330APPENDIX ■ PERL BASICSuntil ($
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332APPENDIX ■ PERL BASICSuse stri
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334APPENDIX ■ PERL BASICSdoneAll
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336APPENDIX ■ PERL BASICS$ perl r
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338APPENDIX ■ PERL BASICSSummaryT
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340■INDEXmethods for retrieving r
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342■INDEXdo() method for, 62dumpi
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344■INDEXhello option for Net::SM
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346■INDEXNet::DNS module, 125-128
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348■INDEXrecord with Net::DNS mod
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350■INDEXstoring mail server in e
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352■INDEXlogging based on, 229pri
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