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README

NAME
     HTML::Transmorgify - HTML transformation compiler

SYNOPSIS
     use HTML::Transmorgify;

     my $magic = HTML::Transmorgify->new(xml_quoting => 1);

     $magic->mixin('HTML::Transmorgify::Metatags');
     $magic->mixin('HTML::Transmorgify::FormDefaults');

     my $output = $magic->process($input_text, { %options }, %variables);
     my %output_by_type = $magic->process($input_text, { %options }, %variables);

DESCRIPTION
    HTML::Transmorgify is an HTML compiler framework. It transforms HTML
    into a arrays of static text and CODE callbacks. The arrays can be
    turned into customized HTML very quickly. The compilation process is
    quick and the runtime process is even quicker. It is designed for sites
    that will dynamically generate all their content.

    By itself, HTML::Transmorgify doesn't do anything useful: it is just a
    framework. Most users will want to use one or more of the addon modules
    for HTML::Transmorgify:

    HTML::Transmorgify::Metatags
        Provides a template language processor with macros, control flow,
        and basic functions.

    HTML::Transmorgify::FormChecksum
        Adds cryptographic checksums to forms so that users cannot add
        additional elements, change or remove hidden values, or set
        dropdowns or radio buttons to values that were not provided.

    HTML::Transmorgify::FormDefault
        Overrides the default values in the form definition so that the
        end-user's prior input is remembered when re-displaying the form.

    HTML::Transmorgify::Crumbs
        Adds cookie crumbs to URLs to and forms so to protect against
        cross-site scripting attacks that direct a logged-in user back to a
        page that will do something naughty.

    HTML::Transmorgify::Images
        Changes multiple <img> tags into <div> tags with background
        attributes that point into shared composite image. This decreases
        page load time because many fewer items need to be fetched.

        It also adds "height" and "width" attributes to images that don't
        have them yet.

        It notices roll-over images and adds javascript to display them.

        As of January 2011, this addon is not yet complete.

    Additional modules can be added to the framework.

USING HTML::Transmorgify
    By itself, HTML::Transmorgify doesn't do anything useful. You need to
    blend in one of the addon modules or write your own.

    You invoke HTML::Transmorgify with:

     my $output = $magic->process($input_text, { %options }, %variables);

    or

     my %output_by_type = $magic->process($input_text, { %options }, %variables);

    In array context, the results from processing templates are returned as
    a hash, mapping the type of result to the result string. Two result
    types are always present: "text" and "script". Other result types may be
    added by add-on modules.

    Currently, all of the options in "{ %options }" are made available to
    addon modules via the $invocation_options variable. In additon the
    following items are singled out and have defined meanings:

    query_param    A reference to a CGI.pm-style query parameters hash.

    input_file     The filename from which the $input_text came from.

    input_line     A line-number offset from the beginning of the input_file
                   so that error messages can refer to the line number of
                   the error.

    The %variables are used by HTML::Transmorgify::Metatags as pre-defined
    macro values. They can be strings, hashes, arrays, or objects. If
    they're objects, they should inherit from
    HTML::Transmorgify::ObjectGlue.

WRITING ADDON MODULES
    HTML::Transmorgify compiles HTML. It compiles HTML into an array of
    callbacks and literals. It then executes the compiled array. Compilation
    output from an input string is cached for reuse. Files are compiled
    separately.

    When you write an addon module, you register to be called back for
    particular HTML tags. When you are called back, you need to generate
    strings to be appended to the the final document or callbacks to be
    called at runtime.

    The runtime program is an array: @$HTML::Transmorgify::rbuf. There is a
    little function for appending to that array: "rbuf()".

    Addon modules generally start the same:

     package HTML::Transmorgify::MODULE_NAME;

     use HTML::Transmorgify qw(continue_compile capture_compile run queue_intercept rbuf postbuf);

     our @ISA = qw(HTML::Transmorgify Exporter);

     sub add_tags
     {
            my ($self, $tobj) = @_;
            $self->intercept_exclusive($tobj, __PACKAGE__, A_NUMBER, %EXCLUSIVE_TAGS)
            $self->intercept_shared($tobj, __PACKAGE__, A_NUMBER, %SHARED_TAGS);
     }

    Where "A_NUMBER" is a priority number for choosing which callbacks get
    called first (lower is earlier); %EXCLUSIVE_TAGS maps HTML tags to
    callbacks that compile that HTML tag; and %SHARED_TAGS maps HTML tags to
    callbacks that participate in compiling that HTML tag.

    Generally you want an exclusive tag when the tag isn't actually part of
    HTML like when you are creating a template language like what is done in
    HTML::Transmorgify::Metatags.

    For situations where you are making an adjustment to regular HTML tags,
    you usually want a shared tag. For example,
    HTML::Transmorgify::FormChecksum and HTML::Transmorgify::FormDefault
    both modify forms and attach callbacks to the <input> tags.

    Shared tags must be handled carefully so that the multiple modules that
    are acting on a tag do not get in each other's way. Not everything can
    be handled by with a shared tag For example, the <foreach> tag defined
    in HTML::Transmorgify::Metatags is an exclusive tag.

    All callbacks are invoked with the following arguments:

    $attr   A HTML::Transmorgify::Attributes object representing the a tag
            and its attributes.

    $closed Closed if this is an end-tag or self-contained tag like <hr />.

  Shared Tags
    The return value from a shared tag callback is ignored unless the return
    value is a CODE ref. The callbacks are called at compile time. Any CODE
    refs returned by the callback will be invoked at runtime BEFORE the tag
    is interpolated into the results.

    Shared tags are always interpolated into the results.

    The usual form of a shared tag is something like:

     $SHARED_TAGS{img} = \&img_tag;
     sub img_tag {
        my ($attr, $closed) = @_;
        return 1 unless $attr->raw('alt');
        $attr->eval_at_runtime(1);
        rbuf(sub {
            my $text = $attr->get('src');
            $text =~ s{.*/}{};
            $text =~ s/([a-z])([A-Z])/$1 $2/g;
            $text =~ s/_/ /g;
            $attr->set(alt => $text);
        });
        return 1;
     }

    This example transformation will try to turn the image file name into an
    <alt> tag.

    It uses "rbuf()" to add a callback that will run just before the <img>
    tag is added to the output stream.

    It calls

        $attr->eval_at_runtime(1);

    to make sure that the <img> tag is evaluated at runtime rather than
    added as a literal string at compile time.

    It returns a value of 1 to indicate that the <img> tag should be
    included in the output stream.

  Exclusive Tags
    The return value from an exclusive tag indicates whether the tag should
    be included in the resulting text or not. A true value will cause the
    tag to be inclucd; a false value will not.

  APIs for Callback Writers
    rbuf()
        The tiny rbuf function pushes its arguments on the
        "HTML::Transmorgify::rbuf" array. This array represents the output
        from compiling the HTML. It can conntain the following elements:

        strings        Plain scalars will be interpolated into the final
                       output unchanged.

        CODE refs      Code references will be called. For them to add to
                       the final output, they need to append to the strings
                       in @$HTML::Transmorgify::result. The first of these,
                       $$HTML::Transmorgify::result[0] is used for regular
                       results. If additional types of output are needed,
                       the array indexes should be allocated by calling
                       "allocate_result_type".

    postbuf()
        Pushes its arguments onto @HTML::Transmorgify::post_intercept_push.
        This is used during shared tag callback processing. The contents of
        @HTML::Transmorgify::post_intercept_push is pushed onto
        "HTML::Transmorgify::rbuf" after the rest of the shared tag callback
        processing is done.

    allocate_result_type()
        Alocates another "key" for the results array. The predefined keys
        are: "text" and "script".

        Keys can be looked up in %HTML::Transmorgify::result_index.

    boolean()
        The boolean function returns false if it's argument is: "false",
        "no", "off", 0, or undefined. Otherwise it returns true.

    run($buf, $results)
        The run function "executes" the compiled HTML in @$buf. Literal
        strings will be added to $$results[0], code references will be
        invoked.

        If $results is not specified, it will default to
        $HTML::Transmorgify::results.

    eat_cr()
        *Exclusive tag callbacks only.* Advance the input parsing position
        "pos($$HTML::Transmorgify::textref)" past a newline.

    $rbuf = compile($cacheline, $textref)
        Compiles $$textref and returns the results. Results are are cached
        so compiling the same string ($$textref) in the same context will
        result in a cached result. Do not modify the returned array (@$rbuf)
        as since it can be handed out again from another call to compile.

        The $cacheline argument specifies the caching context for the input
        string. For compiling things in the normal context where all
        currently active transformations can apply, use the context
        $HTML::Transmorgify::modules.

    ($rbuf, $deferred) = capture_compile($tag, $starting_attr, $opts, %tags)
        *Exclusive tag callbacks only.* Continues to compile the current
        $HTML::Transmorgify::textref (as passed to compile()) until a
        closing "</$tag>" is reached. For better error messages, the
        HTML::Transmorgify::Attributes for the opening tag ($starting_attr)
        is passed in.

        The callbacks for multiple tags may be overridden with the %tags
        argument. Since these may be shared callbacks, only the callbacks
        for the module doing the overridding should be modified. That should
        be specified as: $$opts{tag_package}.

        The call to capture_returns after the input pointer has moved past
        "</$tag>". No "</$tag>". is pushed into the compile output buffer
        "HTML::Transmorgify::rbuf" and the callbacks requested for "</$tag>"
        have not been called. To invoke them, simply run:

         $deferred->doit();

        This will also push a "</$tag>" into the output stream.

    continue_compile($tag, $starting_attr, $opts, %tags)
        *Exclusive tag callbacks only.* continue_compile() is very much like
        "capture_compile()" except that the output from the compilation
        process is appended to the existing "HTML::Transmorgify::rbuf" array
        and there is no return value from the function.

        The purpose of continue_compile() is to allow the normal compilation
        process to continue for a while. The function returns after
        "</$tag>" has been rpocessed. Tag callbacks may be temporarily
        overridden for the duration of the call.

        If $tag is undef, the compilation will continue until the end of
        $$textref is reached or until a "HTML::Transmorgify::CloseTag"
        callback is invoked.

    local($HTML::Transmorgify::dispatch{"/$tag"}) =
    HTML::Transmorgify::ClosedTag->new($HTML::Transmorgify::dispatch{"/$tag"
    });
        This will override the callbacks for "</$tag>" so that
        continue_compile or capture_compile will stop when "</$tag>" is
        reached. This is normally done automatically but this invocation is
        needed if stopping for more than one tag.

    queue_capture($coderef)
        *Shared tag callbacks only.* Shared tag callbacks cannot use
        capture_compile() and continue_compile(): they can use
        queue_capture() instead. The function that handles calling all the
        shared tag callbacks will do a capture_compile(), looking for the
        close tag to match the current tag if any of the shared tag
        callbacks uses queue_capture().

        After the $coderefs are invoked (they receive the $rbuf from
        capture_compile() as their only argument) the temporary $rbuf
        compile buffer will be appended to the main compile buffer. After
        that, the deferred callbacks from the close tag will be invoked.

    queue_intercept($tag_pkg, %tags)
        *Shared tag callbacks only.* Shared tag callbacks cannot use
        capture_compile() and continue_compile(): they can use
        queue_capture() instead. The function that handles calling all the
        shared tag callbacks will do a continue_compile(), looking for the
        close tag to match the current tag if any of the shared tag
        callbacks uses queue_intercept(). If queue_capture is also used by a
        tag callback, then capture_compile() will be used instead.

        For the duration of the continue_compile() (or capture_compile())
        tag callbacks will be overridden by %tags. $tag_pkg should be set to
        the name of the invoking package (__PACKAGE__).

NAMING
    Calvin & Hobbs used to transmogrify not transmorgify things. This module
    will be renamed to fix my spelling mistake soon. Other API changes may
    still be made. Please contact the author if you want to be included in
    dicussions of this module's future.

SEE ALSO
    Other modules that do similar things: HTML::Seamstreess

AUTHOR
    David Muir Sharnoff <muir at idiom dot org>

    Development of this module is hosted on github:
    <https://github.com/muir/HTML-Transmorgify>.

    Some parts of this module are Copyright (C) Google, Inc.

LICENSE
    Your choice of LGPL or Artistic License.

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