NAME

WebFetch - Perl module to download and save information from the Web


SYNOPSIS

  use WebFetch;


DESCRIPTION

The WebFetch module is a general framework for downloading and saving information from the web, and for display on the web. It requires another module to inherit it and fill in the specifics of what and how to download. WebFetch provides a generalized interface for saving to a file while keeping the previous version as a backup. This is expected to be used for periodically-updated information which is run as a cron job.


INSTALLATION

After unpacking and the module sources from the tar file, run

perl Makefile.PL

make

make install

Or from a CPAN shell you can simply type ``install WebFetch'' and it will download, build and install it for you.

If you need help setting up a separate area to install the modules (i.e. if you don't have write permission where perl keeps its modules) then see the Perl FAQ.

To begin using the WebFetch modules, you will need to test your fetch operations manually, put them into a crontab, and then use server-side include (SSI) or a similar server configuration to include the files in a live web page.


MANUALLY TESTING A FETCH OPERATION

Select a directory which will be the storage area for files created by WebFetch. This is an important administrative decision - keep the volatile automatically-generated files in their own directory so they'll be separated from manually-maintained files.

Choose the specific WebFetch-derived modules that do the work you want. See their particular manual/web pages for details on command-line arguments. Test run them first before committing to a crontab.


SETTING UP CRONTAB ENTRIES

First of all, if you don't have crontab access or don't know what they are, contact your site's system administrator(s). Only local help will do any good on local-configuration issues. No one on the Internet can help. (If you are the administrator for your system, see the crontab(1) and crontab(5) manpages and nearly any book on Unix system administration.)

Since the WebFetch command lines are usually very long, you may prefer to make one or more scripts as front-ends so your crontab entries aren't so huge.

Do not run the crontab entries too often - be a good net.citizen and do your updates no more often than necessary. Popular sites need their users to refrain from making automated requests too often because they add up on an enormous scale on the Internet. Some sites such as Freshmeat prefer no shorter than hourly intervals. Slashdot prefers no shorter than half-hourly intervals. When in doubt, ask the site maintainers what they prefer.

(Then again, there are a very few sites like Yahoo and CNN who don't mind getting the extra hits if you're going to create links to them. Even so, more often than every 20 minutes would still be excessive to the biggest web sites.)


SETTING UP SERVER-SIDE INCLUDES

See the manual for your web server to make sure you have server-side include (SSI) enabled for the files that need it. (It's wasteful to enable it for all your files so be careful.)

When using Apache HTTPD, a line like this will include a WebFetch-generated file:

<!--#include file=``fetch/slashdot.html''-->


WebFetch FUNCTIONS

The following function definitions assume $obj is a blessed reference to a module that is derived from (inherits from) WebFetch.

Do not use the new() function directly from WebFetch.

Use the new function from a derived class, not directly from WebFetch. The WebFetch module itself is just infrastructure for the other modules, and contains none of the details needed to complete any specific fetches.

$obj->init( ... )

This is called from the new function of all WebFetch modules. It takes ``name'' => ``value'' pairs which are all placed verbatim as attributes in $obj.

$obj->run

This function is exported by standard WebFetch-derived modules as fetch_main. This handles command-line processing for some standard options, calling the module-specific fetch function and WebFetch's $obj->save function to save the contents to one or more files.

The command-line processing for some standard options are as follows:

--dir directory

(required) the directory in which to write output files

--group group

(optional) the group ID to set the output file(s) to

--mode mode

(optional) the file mode (permissions) to set the output file(s) to

--export export-file

(optional) save a portable WebFetch-export copy of the fetched info in the file named by this parameter. The contents of this file can be read by the WebFetch::General module. You may use this to export your own news to other WebFetch users. (Exports may be explicitly disabled by some WebFetch-derived modules simply by omiting the export step from their fetch() functions. Though it works with all the modules that come included with the WebFetch package itself.)

--xml_export xml-export-file

(optional) save a generic XML copy of the fetched info into the file named by this parameter. (A module to read this XML output will be included in a near-future version of WebFetch.) For more info on XML see http://www.w3.org/XML/ or http://www.perlxml.com/faq/perl-xml-faq.html

If you choose to generate and sustain XML content on your site over the long term, you may want to have your site listed on the XML Tree at http://www.xmltree.com/

--ns_export ns-export-file

(optional) save a MyNetscape export copy of the fetched info into the file named by this parameter. If this optional parameter is used, three additional parameters become required: --ns_site_title, --ns_site_link, and --ns_site_desc. If you want to include an icon in the channel display, you should also use --ns_image_title and --ns_image_url. A URL Prefix must also be set for this to work correctly, which can be supplied via the the --url_prefix parameter or in the url-prefix line of the WebFetch::SiteNews news input file. For more info see http://my.netscape.com/publish/ and http://www.w3.org/RDF/

Note that MyNetscape uses Resource Description Framework (RDF), which is a form of XML, for its imports. Though this command-line option uses some specific RDF parameters for the MyNetscape portal, this format should be readable by any other RDF-capable and even some XML-capable sites. You should use the ".rdf" suffix on file names that use this format.

--ns_site_title site-title

(required if --ns_export is used) For exporting to MyNetscape, this sets the name of your site. It cannot be more than 40 characters

--ns_site_link site-link

(required if --ns_export is used) For exporting to MyNetscape, this is the full URL MyNetscape will use to link to your site. It cannot be more than 500 characters.

--ns_site_desc site-description

(required if --ns_export is used) For exporting to MyNetscape, this is a short description of your site. It cannot be more than 500 characters.

--ns_image_title image-title

(optional) For exporting to MyNetscape, this is the title (alt) text for the icon image.

--ns_image_url image-url

(optional) For exporting to MyNetscape, this is the URL MyNetscpae will use for your icon image. If this is present, the link on the image will be the same as your --ns_site_link parameter.

--url_prefix url-prefix

(optional) include a URL prefix to use on the saved URLs on --ns_export output files. (It could also be used in the future by other output formats that need URL prefixes.) This is considered optional by WebFetch though you will probably need it for MyNetscape to properly link to your site. This information can also be supplied via the url-prefix line of the WebFetch::SiteNews news input file. If it is set in the WebFetch::SiteNews, it will override the --url_prefix command line parameter.

--font_size number

(optional) choose a font size for generated HTML text. This will be used in a font tag so it may be relative, like ``-1'' or ``+1''.

--font_face string

(optional) choose a font face for generated HTML text. This will be used in a font tag so it may be any standard font name or a list. For example, for a sans-serif font, use ``Helvetica,Arial,sans-serif''.

--style style-name-list

(optional) select from one or more of various HTML output styles for the generated HTML text. If more than one style name is listed, they must be separated by commas (no spaces.)

para

use paragraph breaks between lines/links instead of unordered lists

notable

usually WebFetch modules generate HTML table-formatted output text but this option will disable the e of tables

bullet

use explicit bullet characters (HTML entity #149) and line breaks (br) to identify and separate each link

ul

(default) use an HTML unnumbered list (ul) block for the list of links

The para, bullet and ul styles are mutually exclusive. Others may be specified at the same time.

--quiet

(optional) suppress printed warnings for HTTP errors (applies only to modules which use the WebFetch::get() function) in case they are not desired for cron outputs

--debug

(optional) print verbose debugging outputs, only useful for developers adding new WebFetch-based modules or finding/reporting a bug in an existing module

Modules derived from WebFetch may add their own command-line options that WebFetch::run() will use by defining a variable called @Options in the calling module, using the name/value pairs defined in Perl's Getopts::Long module. Derived modules can also add to the command-line usage error message by defining a variable called $Usage with a string of the additional parameters, as they should appear in the usage message.

$obj->do_actions

do_actions was added in WebFetch 0.10 as part of the WebFetch Embedding API. Upon entry to this function, $obj must contain the following attributes:

data

is a reference to a hash containing the following three (required) keys:

fields

is a reference to an array containing the names of the fetched data fields in the order they appear in the records of the data array. This is necessary to define what each field is called because any kind of data can be fetched from the web.

wk_names

is a reference to a hash which maps from a key string with a ``well-known'' (to WebFetch) field type to a field name used in this table. The well-known names are defined as follows:

title

a one-liner banner or title text (plain text, no HTML tags)

url

URL/link to the news (fully-qualified URL only, no HTML tags)

date

a date stamp, which must be program-readable by Perl's Date::Calc module in the Parse_Date() function in order to support timestamp-related comparisons and processing that some users have requested. If the date cannot be parsed by Date::Calc, either translate it when your module captures it, or do not define this ``well-known'' field because it wouldn't fit the definition. (plain text, no HTML tags)

summary

a paragraph of summary text in HTML

comments

number of comments/replies at the news site (plain text, no HTML tags)

author

a name, handle or login name representing the author of the news item (plain text, no HTML tags)

category

a word or short phrase representing the category, topic or department of the news item (plain text, no HTML tags)

location

a location associated with the news item (plain text, no HTML tags)

The field names for this table are defined in the fields array.

The hash only maps for the fields available in the table. If no field representing a given well-known name is present in the data fields, that well-known name key must not be defined in this hash.

records

an array containing the data records. Each record is itself a reference to an array of strings which are the data fields. This is effectively a two-dimensional array or a table.

Only one table-type set of data is permitted per fetch operation. If more are needed, they should be arranged as separate fetches with different parameters.

actions

is a reference to a hash. The hash keys are names for handler functions. The WebFetch core provides internal handler functions called fmt_handler_html (for HTML output), fmt_handler_xml (for XML output), fmt_handler_wf (for WebFetch::General format), fmt_handler_rdf (for MyNetscape RDF format). However, WebFetch modules may provide additional format handler functions of their own by prepending ``fmt_handler_'' to the key string used in the actions array.

The values are array references containing "action specs", which are themselves arrays of parameters that will be passed to the handler functions for generating output in a specific format. There may be more than one entry for a given format if multiple outputs with different parameters are needed.

The presence of values in this field mean that output is to be generated in the specified format. The presence of these would have been chosed by the WebFetch module that created them - possibly by default settings or by a command-line argument that directed a specific output format to be used.

For each valid action spec, a separate ``savable'' (contents to be placed in a file) will be generated from the contents of the data variable.

The valid (but all optional) keys are

html

the value must be a reference to an array which specifies all the HTML generation (html_gen) operations that will take place upon the data. Each entry in the array is itself an array reference, containing the following parameters for a call to html_gen():

filename

a file name or path string (relative to the WebFetch output directory unless a full path is given) for output of HTML text.

params

a hash reference containing optional name/value parameters for the HTML format handler.

filter_func

(optional) a reference to code that, given a reference to an entry in @{$self->{data}{records}}, returns true (1) or false (0) for whether it will be included in the HTML output. By default, all records are included.

sort_func

(optional) a reference to code that, given references to two entries in @{$self->{data}{records}}, returns the sort comparison value for the order they should be in. By default, no sorting is done and all records (subject to filtering) are accepted in order.

format_func

(optional) a refernce to code that, given a reference to an entry in @{$self->{data}{records}}, returns an HTML representation of the string. By default, a standard HTML formatting is generated using the well-known fields in the record. (This default generation fails if none of the title, url or text names are defined in %{$self->{data}{wk_names}}.

xml

the value must be a reference to an array which specifies all the XML export (xml_export) operations that will take place upon the data. Each entry in the array is itself an array reference, containing the following parameters for a call to xml_export():

filename

a file name or path string (relative to the WebFetch output directory unless a full path is given) for output of XML text.

wf

the value must be a reference to an array which specifies all the WebFetch export (wf_export) operations that will take place upon the data. Each entry in the array is itself an array reference, containing the following parameters for a call to wf_export():

filename

a file name or path string (relative to the WebFetch output directory unless a full path is given) for output of the WebFetch::General export format.

rdf

the value must be a reference to an array which specifies all the Resource Description Framework (RDF) export (ns_export, used by MyNetscape) operations that will take place upon the data. Each entry in the array is itself an array reference, containing the following parameters for a call to ns_export():

filename

a file name or path string (relative to the WebFetch output directory unless a full path is given) for output of RDF format, for the MyNetscape portal or other sites that can use RDF.

site_title

For exporting to MyNetscape, this sets the name of your site. It cannot be more than 40 characters

site_link

For exporting to MyNetscape, this is the full URL MyNetscape will use to link to your site. It cannot be more than 500 characters.

site_desc

For exporting to MyNetscape, this is a short description of your site. It cannot be more than 500 characters.

image_title

(optional) For exporting to MyNetscape, this is the title (alt) text for the icon image.

image_url

(optional) For exporting to MyNetscape, this is the URL MyNetscpae will use for your icon image. If this is present, the link on the image will be the same as your $site_link parameter.

Additional valid keys may be created by modules that inherit from WebFetch by supplying a method/function named with ``fmt_handler_'' preceding the string used for the key. For example, for an ``xyz'' format, the handler function would be fmt_handler_xyz. The value (the ``action spec'') of the hash entry must be an array reference. Within that array are ``action spec entries'', each of which is a reference to an array containing the list of parameters that will be passed verbatim to the fmt_handler_xyz function.

When the format handler function returns, it is expected to have created entries in the $obj->{savables} array (even if they only contain error messages explaining a failure), which will be used by $obj->save() to save the files and print the error messages.

For coding examples, use the fmt_handler_* functions in WebFetch.pm itself.

$obj->fetch

This function must be provided by each derived module to perform the fetch operaton specific to that module. It will be called from new() so you should not call it directly. Your fetch function should extract some data from somewhere and place of it in HTML or other meaningful form in the ``savable'' array.

Upon entry to this function, $obj must contain the following attributes:

dir

The name of the directory to save in. (If called from the command-line, this will already have been provided by the required --dir parameter.)

savable

a reference to an array where the ``savable'' items will be placed by the $obj->fetch function. (You only need to provide an array reference - other WebFetch functions can write to it.)

In WebFetch 0.10 and later, this parameter should no longer be supplied by the fetch function (unless you wish to use 0.09 backward compatibility) because it is filled in by the do_actions after the fetch function is completed based on the data and actions variables that are set in the fetch function. (See below.)

Each entry of the savable array is a hash reference with the following attributes:

file

file name to save in

content

scalar w/ entire text or raw content to write to the file

group

(optional) group setting to apply to file

mode

(optional) file permissions to apply to file

Contents of savable items may be generated directly by derived modules or with WebFetch's html_gen, html_savable or raw_savable functions. These functions will set the group and mode parameters from the object's own settings, which in turn could have originated from the WebFetch command-line if this was called that way.

Note that the fetch functions requirements changed in WebFetch 0.10. The old requirement (0.09 and earlier) is supported for backward compatibility.

In WebFetch 0.09 and earlier, upon exit from this function, the $obj->savable array must contain one entry for each file to be saved. More than one array entry means more than one file to save. The WebFetch infrastructure will save them, retaining backup copies and setting file modes as needed.

Beginning in WebFetch 0.10, the ``WebFetch embedding'' capability was introduced. In order to do this, the captured data of the fetch function had to be externalized where other Perl routines could access it. So the fetch function now only populates data structures (including code references necessary to process the data.)

Upon exit from the function, the following variables must be set in $obj:

data

is a reference to a hash which will be used by the do_actions function. (See above.)

actions

is a reference to a hash which will be used by the do_actions function. (See above.)

$obj->get

This WebFetch utility function will get a URL and return a reference to a scalar with the retrieved contents. Upon entry to this function, $obj must contain the following attributes:

url

the URL to get

quiet

a flag which, when set to a non-zero (true) value, suppresses printing of HTTP request errors on STDERR

$obj->wf_export ( $filename, $fields, $links, [ $comment, [ $param ]] )

In WebFetch 0.10 and later, this should be used only in format handler functions. See do_handlers() for details.

This WebFetch utility function generates contents for a WebFetch export file, which can be placed on a web server to be read by other WebFetch sites. The WebFetch::General module reads this format. $obj->wf_export has the following parameters:

$filename

the file to save the WebFetch export contents to; this will be placed in the savable record with the contents so the save function knows were to write them

$fields

a reference to an array containing a list of the names of the data fields (in each entry of the @$lines array)

$lines

a reference to an array of arrays; the outer array contains each line of the exported data; the inner array is a list of the fields within that line corresponding in index number to the field names in the @$fields array

$comment

(optional) a Human-readable string comment (probably describing the purpose of the format and the definitions of the fields used) to be placed at the top of the exported file

$param

(optional) a reference to a hash of global parameters for the exported data. This is currently unused but reserved for future versions of WebFetch.

$obj->ns_export ( $filename, $lines, $site_title, $site_link, $site_desc, $image_title, $image_url)

In WebFetch 0.10 and later, this should be used only in format handler functions. See do_handlers() for details.

This WebFetch utility function generates contents for a MyNetscape export file, which can be placed on a web server to be read by the MyNetscape site (my.netscape.com) if you create a ``channel'' for your site at MyNetscape.

Of the modules included with WebFetch, only WebFetch::SiteNews and WebFetch::Genercal call $obj->ns_export(). The others will ignore it (because they're just obtaining data from other sites themselves.) You may use $obj->ns_export() in your own modules which inherit from WebFetch. For more info see http://my.netscape.com/publish/

$obj->ns_export has the following parameters:

$filename

(required) the file to save the WebFetch export contents to; this will be placed in the savable record with the contents so the save function knows were to write them

$lines

(required) a reference to an array of arrays; the outer array contains each line of the exported data; the inner array is a list of two fields within that line consisting of a text title string in one entry and a URL in the second entry.

$site_title

(required) For exporting to MyNetscape, this sets the name of your site. It cannot be more than 40 characters

$site_link

(required) For exporting to MyNetscape, this is the full URL MyNetscape will use to link to your site. It cannot be more than 500 characters.

$site_desc

(required) For exporting to MyNetscape, this is a short description of your site. It cannot be more than 500 characters.

$image_title

(optional) For exporting to MyNetscape, this is the title (alt) text for the icon image.

$image_url

(optional) For exporting to MyNetscape, this is the URL MyNetscpae will use for your icon image. If this is present, the link on the image will be the same as your $site_link parameter.

$obj->html_gen( $filename, $format_func, $links )

In WebFetch 0.10 and later, this should be used only in format handler functions. See do_handlers() for details.

This WebFetch utility function generates some common formats of HTML output used by WebFetch-derived modules. The HTML output is stored in the $obj->{savable} array, for which all the files in that array can later be saved by the $obj->save function. It has the following parameters:

$filename

the file name to save the generated contents to; this will be placed in the savable record with the contents so the save function knows were to write them

$format_func

a refernce to code that formats each entry in @$links into a line of HTML

$links

a reference to an array of arrays of parameters for &$format_func; each entry in the outer array is contents for a separate HTML line and a separate call to &$format_func

Upon entry to this function, $obj must contain the following attributes:

num_links

number of lines/links to display

savable

reference to an array of hashes which this function will use as storage for filenames and contents to save (you only need to provide an array reference - the function will write to it)

See $obj->fetch for details on the contents of the savable parameter

table_sections

(optional) if present, this specifies the number of table columns to use; the number of links from num_links will be divided evenly between the columns

style

(optional) a hash reference with style parameter names/values that can modify the behavior of the funciton to use different HTML styles. The recognized values are enumerated with WebFetch's --style command line option. (When they reach this point, they are no longer a comma-delimited string - WebFetch or another module has parsed them into a hash with the style name as the key and the integer 1 for the value.)

$obj->html_savable( $filename, $content )

In WebFetch 0.10 and later, this should be used only in format handler functions. See do_handlers() for details.

This WebFetch utility function stores pre-generated HTML in a new entry in the $obj->{savable} array, for later writing to a file. It's basically a simple wrapper that puts HTML comments warning that it's machine-generated around the provided HTML text. This is generally a good idea so that neophyte webmasters (and you know there are a lot of them in the world :-) will see the warning before trying to manually modify your automatically-generated text.

See $obj->fetch for details on the contents of the savable parameter

$obj->raw_savable( $filename, $content )

In WebFetch 0.10 and later, this should be used only in format handler functions. See do_handlers() for details.

This WebFetch utility function stores any raw content and a filename in the $obj->{savable} array, in preparation for writing to that file. (The actual save operation may also automatically include keeping backup files and setting the group and mode of the file.)

See $obj->fetch for details on the contents of the savable parameter

$obj->save

This WebFetch utility function goes through all the entries in the $obj->{savable} array and saves their contents, providing several services such as keeping backup copies, and setting the group and mode of the file, if requested to do so.

If you call a WebFetch-derived module from the command-line run() or fetch_main() functions, this will already be done for you. Otherwise you will need to call it after populating the savable array with one entry per file to save.

Upon entry to this function, $obj must contain the following attributes:

dir

directory to save files in

savable

names and contents for files to save

See $obj->fetch for details on the contents of the savable parameter

WRITING NEW WebFetch-DERIVED MODULES

The easiest way to make a new WebFetch-derived module is to start from the module closest to your fetch operation and modify it. Make sure to change all of the following:

fetch function

The fetch function is the meat of the operation. Get the desired info from a local file or remote site and place the contents that need to be saved in the savable parameter.

module name

Be sure to catch and change them all.

file names

The code and documentation may refer to output files by name.

module parameters

Change the URL, number of links, etc as necessary.

command-line parameters

If you need to add command-line parameters, modify both the @Options and $Usage variables. Don't forget to add documentation for your command-line options and remove old documentation for any you removed.

When adding documentation, if the existing formatting isn't enough for your changes, there's more information about Perl's POD (``plain old documentation'') embedded documentation format at http://www.cpan.org/doc/manual/html/pod/perlpod.html

authors

Add yourself as an author if you added any significant functionality. But if you used anyone else's code, retain the existing author credits in any module you modify to make a new one.

export function

If it's appropriate for users of your module to be able to export its data to other sites, add an export() function. Use the one in WebFetch::SiteNews as an example if you need to.

Please consider contributing any useful changes back to the WebFetch project at maint@webfetch.org.

AUTHOR

WebFetch was written by Ian Kluft for the Silicon Valley Linux User Group (SVLUG). Send patches, bug reports, suggestions and questions to maint@webfetch.org.

WebFetch is Open Source software distributed via the Comprehensive Perl Archive Network (CPAN), a worldwide network of Perl web mirror sites. WebFetch may be copied under the same terms and licensing as Perl itelf. A current copy of the source code and documentation may be found at http://www.webfetch.org/

SEE ALSO

perl(1), WebFetch::CNETnews, WebFetch::CNNsearch, WebFetch::COLA, WebFetch::DebianNews, WebFetch::Freshmeat, WebFetch::LinuxDevNet, WebFetch::LinuxTelephony, WebFetch::LinuxToday, WebFetch::ListSubs, WebFetch::PerlStruct, WebFetch::SiteNews, WebFetch::Slashdot, WebFetch::32BitsOnline, WebFetch::YahooBiz.