Java script FAQ [was Re: :Mechanize]

Hi Andy,

Some time a ago, I sent you the text for the FAQ on Java script. There 
is a section "So what do I do". I would like to suggest that you update 
the text:

Original text:

   So what can I do?

   Since Javascript is completely visible to the client, it cannot be
   used to prevent a scraper from following links. But it can make life
   difficult, and until someone writes a Javascript interpreter for
   Perl or a Mechanize clone to control Firefox, there will be no
   general solution. But if you want to scrape specific pages, then a
   solution is always possible.

   One typical use of Javascript is to perform argument checking before
   posting to the server. The URL you want is probably just buried in
   the Javascript function. Do a regular expression match on
   |$mech->content()| to find the link that you want and |$mech->get|
   it directly (this assumes that you know what your are looking for in
   advance).

   In more difficult cases, the Javascript is used for URL mangling to
   satisfy the needs of some middleware. In this case you need to
   figure out what the Javascript is doing (why are these URLs always
   really long?). There is probably some function with one or more
   arguments which calculates the new URL. Step one: using your
   favorite browser, get the before and after URLs and save them to
   files. Edit each file, converting the the argument separators ('?',
   '&' or ';') into newlines. Now it is easy to use diff or comm to
   find out what Javascript did to the URL. Step 2 - find the function
   call which created the URL - you will need to parse and interpret
   its argument list. Using the Javascript Debugger Extension for
   Firefox may help with the analysis. At this point, it is fairly
   trivial to write your own function which emulates the Javascript for
   the pages you want to process.

Please append to it:

   An Alternative Approach (this is also an answer to the question, "It
   works in Firefox, why not in $mech?" )

   Everything the web server knows about the client is present in the
   HTTP request. If two requests are identical, the results should be
   identical. So the real question is "What is different between the
   mech request and the Firefox request?"

   I would suggest using the Firefox extension "Tamper Data" to look at
   the headers of the requests you send to the server. Compare that
   with what LWP is sending. Once the two are identical, the action of
   the server should be the same as well.

   I say "should", because this is an oversimplification - some values
   are naturally unique, e.g. a SessionID, but if a SessionID is
   present, that is probably sufficient, even though the value will be
   different between the LWP request and the Firefox request. The
   server could use the session to store information which is
   troublesome, but that's not the first place to look (and highly
   unlike to be relevant when you are requesting the login page of your
   site).

   Generally the problem is to be found in missing or incorrect
   POSTDATA arguments, Cookies, User-Agents, Accepts, etc. If you are
   using mech, then redirects and cookies should not be a problem, but
   are listed here for completeness. If you are missing headers,
   $mech->add_header can be used to add the headers that you need.

Is there a preferred way to get the request which mech is going to send? 
I was able to get it by following the code into the innards of 
HTTP::Request, but that seems like the kind of stuff a $mechanize user 
won't want to do.

Cheers,

Peter



Cahoon, Forrest wrote:
> If you're specifically looking at Yahoo! Mail, there's at least one CPAN module 
> for that:
> http://search.cpan.org/~johnsca/MailClientYahoo-1.0/lib/Mail/Client/Yahoo.pm
>
> If it's just something similar to Yahoo!, perhaps that code will give you some 
> clues.
> (I haven't used that module myself, just happened to notice it's existence.)
>
> Forrest
> not speaking for merrill corporation 
>
>   
> > -----Original Message-----
> > From: Roy Lor [mailto:roytech88@xxxxxxxxxxxx] 
> > Sent: Tuesday, April 04, 2006 8:21 AM
> > To: libwww@xxxxxxxx
> > Subject: WWW::Mechanize
> >
> > can u give me a code/script that records the information in a 
> > log-in  form with javascript..like that of mail.yahoo.com? i 
> > badly need  this..thanks
> >   
> > 		
> > ---------------------------------
> > On Yahoo!7
> >   Desperate Housewives: Sneak peeks, recaps and more. 
> >
> >     
>
>
>