PSP::HTML::Parser - HTML parser class
This is the new XS based PSP::HTML::Parser. It should be completely backwards compatible with PSP::HTML::Parser version 2.2x, but has many new features and is significantly faster.
use PSP::HTML::Parser ();
# Create parser object
$p = PSP::HTML::Parser->new( api_version => 3,
start_h => [\&start, "tagname, attr"],
end_h => [\&end, "tagname"],
marked_sections => 1,
);
# Parse document text chunk by chunk
$p->parse($chunk1);
$p->parse($chunk2);
#...
$p->eof; # signal end of document
# Parse directly from file
$p->parse_file("foo.html");
# or
open(F, "foo.html") || die;
$p->parse_file(*F);
PSP::HTML::Parser version 2 style subclassing and method callbacks:
{
package MyParser;
use base 'PSP::HTML::Parser';
sub start {
my($self, $tagname, $attr, $attrseq, $origtext) = @_;
#...
}
sub end {
my($self, $tagname, $origtext) = @_;
#...
}
sub text {
my($self, $origtext, $is_cdata) = @_;
#...
}
}
my $p = MyParser->new;
$p->parse_file("foo.html");
Objects of the PSP::HTML::Parser class will recognize markup and
separate it from plain text (alias data content) in HTML
documents. As different kinds of markup and text are recognized, the
corresponding event handlers are invoked.
PSP::HTML::Parser in not a generic SGML parser. We have tried to
make it able to deal with the HTML that is actually "out there", and
it normally parses as closely as possible to the way the popular web
browsers do it instead of strictly following one of the many HTML
specifications from W3C. Where there is disagreement there is often
an option that you can enable to get the official behaviour.
The document to be parsed may be supplied in arbitrary chunks. This makes on-the-fly parsing as documents are received from the network possible.
If event driven parsing does not feel right for your application, you
might want to use PSP::HTML::TokeParser. It is a
PSP::HTML::Parser subclass that allows a more conventional program
structure.
The following method is used to construct a new PSP::HTML::Parser object:
This class method creates a new PSP::HTML::Parser object and
returns it. Key/value pair arguments may be provided to assign event
handlers or initialize parser options. The handlers and parser
options can also be set or modified later by method calls described below.
If a top level key is in the form "<event>_h" (e.g., "text_h"} then it assigns a handler to that event, otherwise it initializes a parser option. The event handler specification value must be an array reference. Multiple handlers may also be assigned with the 'handlers => [%handlers]' option. See examples below.
If new() is called without any arguments, it will create a parser that
uses callback methods compatible with version 2 of PSP::HTML::Parser.
See the section on "version 2 compatibility" below for details.
Special constructor option 'api_version => 2' can be used to initialize version 2 callbacks while still setting other options and handlers. The 'api_version => 3' option can be used if you don't want to set any options and don't want to fall back to v2 compatible mode.
Examples:
$p = PSP::HTML::Parser->new(api_version => 3,
text_h => [ sub {...}, "dtext" ]);
This creates a new parser object with a text event handler subroutine that receives the original text with general entities decoded.
$p = PSP::HTML::Parser->new(api_version => 3, start_h => [ 'my_start', "self,tokens" ]);
This creates a new parser object with a start event handler method that receives the $p and the tokens array.
$p = PSP::HTML::Parser->new(api_version => 3,
handlers => { text => [\@array, "event,text"],
comment => [\@array, "event,text"],
});
This creates a new parser object that stores the event type and the original text in @array for text and comment events.
The following methods feed the HTML document
to the PSP::HTML::Parser object:
Parse $string as the next chunk of the HTML document. The return value is normally a reference to the parser object (i.e. $p). Handlers invoked should not attempt modify the $string in-place until $p->parse returns.
If an invoked event handler aborts parsing by calling $p->eof, then $p->parse() will return a FALSE value.
Parse text directly from a file. The $file argument can be a filename, an open file handle, or a reference to a an open file handle.
If $file contains a filename and the file can't be opened, then the method returns an undefined value and $! tells why it failed. Otherwise the return value is a reference to the parser object.
If a file handle is passed as the $file argument, then the file will normally be read until EOF, but not closed.
If an invoked event handler aborts parsing by calling $p->eof, then $p->parse_file() may not have read the entire file.
On systems with multi-byte line terminators, the values passed for the offset and length argspecs may be too low if parse_file is called with a file handle that is not in binary mode.
Signals the end of the HTML document. Calling the $p->eof method
outside a handler callback will flush any remaining buffered text
(which triggers the text event if there is any remaining text).
Calling $p->eof inside a handler will terminate parsing at that point and cause $p->parse to return a FALSE value. This also terminates parsing by $p->parse_file().
The return value is a reference to the parser object.
Most parser options are controlled by boolean attributes. Each boolean attribute is enabled by calling the corresponding method with a TRUE argument and disabled with a FALSE argument. The attribute value is left unchanged if no argument is given. The return value from each method is the old attribute value.
Methods that can be used to get and/or set parser options are:
By default, comments are terminated by the first occurrence of "-->". This is the behaviour of most popular browsers (like Netscape and MSIE), but it is not correct according to the official HTML standard. Officially, you need an even number of "--" tokens before the closing ">" is recognized and there may not be anything but whitespace between an even and an odd "--".
The official behaviour is enabled by enabling this attribute.
By default, almost anything is allowed in tag and attribute names. This is the behaviour of most popular browsers and allows us to parse some broken tags with invalid attr values like:
<IMG SRC=newprevlstGr.gif ALT=[PREV LIST] BORDER=0>
By default, "LIST]" is parsed as a boolean attribute, not as part of the ALT value as was clearly intended. This is also what Netscape sees.
The official behaviour is enabled by enabling this attribute. If enabled, it will cause the tag above to be reported as text since "LIST]" is not a legal attribute name.
tokens and attr
argspecs.
Enabling this attribute changes the parser to allow some XML
constructs such as empty element tags and XML processing
instructions. It disables forcing tag and attribute names to lower
case when they are reported by the tagname and attr argspecs,
and suppress special treatment of elements that are parsed as CDATA
for HTML.
Empty element tags look like start tags, but end with the character
sequence "/>". When recognized by PSP::HTML::Parser they cause an
artificial end event in addition to the start event. The text for
the artificial end event will be empty and the tokenpos array will
be undefined even though the only element in the token array will have
the correct tag name.
XML processing instructions are terminated by "?>" instead of a simple ">" as is the case for HTML.
By default, section markings like <![CDATA[...]]> are treated like ordinary text. When this attribute is enabled section markings are honoured.
There are currently no events associated with marked section elements.
As markup and text is recognized, handlers are invoked. The following method is used to set up handlers for different events:
This method assigns a subroutine, method, or array to handle an event.
Event is one of text, start, end, declaration, comment,
process or default.
Subroutine is a reference to a subroutine which is called to handle the event.
Method_name is the name of a method of $p which is called to handle the event.
Accum is a array that will hold the event information as sub-arrays.
If the second argument is "", the event is ignored. If it is undef, the default handler is invoked for the event.
Argspec is a string that describes the information to be reported
for the event. Any requested information that does not apply to a
specific event is passed as undef. If argspec is omitted, then it
is left unchanged since last update.
The return value from $p->handle is the old callback routine or a reference to the accumulator array.
Return values from handler callback routines/methods are always ignored. A handler callback can request parsing to be aborted by invoking the $p->eof method. A handler callback is not allowed to invoke $p->parse() or $p->parse_file().
Examples:
$p->handler(start => "start", 'self, attr, attrseq, text' );
This causes the "start" method of object $p to be called for 'start' events. The callback signature is $p->start(\%attr, \@attr_seq, $text).
$p->handler(start => \&start, 'attr, attrseq, text' );
This causes subroutine start() to be called for 'start' events. The callback signature is start(\%attr, \@attr_seq, $text).
$p->handler(start => \@accum, '"S", attr, attrseq, text' );
This causes 'start' event information to be saved in @accum. The array elements will be ['S', \%attr, \@attr_seq, $text].
$p->handler(start => "");
This causes 'start' events to be ignored. It also supresses invokations of any default handler for start events. It is equivalent to $p->handler(start => sub {}), but is more efficient.
$p->handler(start => undef);
This causes no handler to be assosiated with start events. If there is a default handler it will be invoked.
Argspec is a string containing a comma separated list that describes the information reported by the event. The following argspec identifier names can be used:
self
tokens
Tokens causes a reference to an array of token strings to be passed. The strings are exactly as they were found in the original text, no decoding or case changes are applied.
For declaration events, the array contains each word, comment, and
delimited string starting with the declaration type.
For comment events, this contains each sub-comment. If
$p->strict_comments is disabled, there will be only one sub-comment.
For start events, this contains the original tag name followed by
the attribute name/value pairs. The value of boolean attributes will
be either the value set by $p->boolean_attribute_value or the
attribute name if no value has been set by
$p->boolean_attribute_value.
For end events, this contains the original tag name (one token
only).
For process events, this contains the process instructions (one
token only).
This passes undef for text events.
tokenpos
Tokenpos causes a reference to an array of token positions to be
passed. For each string that appears in tokens, this array
contains two numbers. The first number is the offset of the start of
the token in the original text and the second number is the length
of the token.
Boolean attributes in a start event will have (0,0) for the
attribute value offset and length.
This passes undef if there are no tokens in the event (e.g., text)
and for artifical end events triggered by empty element tags.
If you are using these offsets and lengths to modify text, you
should either work from right to left, or be very careful to calculate
the changes to the offsets.
token0
Token0 causes the original text of the first token string to be passed. This should always be the same as $tokens->[0].
For declaration events, this is the declaration type.
For start and end events, this is the tag name.
For process and non-strict comment events, this is everything
inside the tag.
This passes undef if there are no tokens in the event.
tagname
This is the element name (or generic identifier in SGML jargon) for start and end tags. Since HTML is case insensitive this name is forced to lower case to ease string matching.
Since XML is case sensitive, the tagname case is not
changed when xml_mode is enabled.
The declaration type of declaration elements is also passed as a tagname,
even if that is a bit strange.
In fact, in the current implementation tagname is
identical to token0 except that the name may be forced to lower case.
attr
Attr causes a reference to a hash of attribute name/value pairs to be passed.
Boolean attributes' values are either the value set by $p->boolean_attribute_value or the attribute name if no value has been set by $p->boolean_attribute_value.
This passes undef except for start events.
Unless xml_mode is enabled, the attribute names are forced to
lower case.
General entities are decoded in the attribute values and one layer of matching quotes enclosing the attribute values are removed.
attrseq
Attrseq causes a reference to an array of attribute names to be
passed. This can be useful if you want to walk the attr hash in
the original sequence.
This passes undef except for start events.
Unless xml_mode is enabled, the attribute names are forced to lower
case.
text
dtext
Dtext causes the decoded text to be passed. General entities are
automatically decoded unless the event was inside a CDATA section or
was between literal start and end tags (script, style, xmp,
and plaintext).
The ISO 8859-1 character set (aka Latin1) is assumed for entity decoding.
It is planned that PSP::HTML::Parser will get an utf8 option
at some point that will affect the byte sequence that characters with
codes greater than 127 will decode into.
This passes undef except for text events.
is_cdata
Is_cdata causes a TRUE value to be passed if the event is inside a CDATA
section or is between literal start and end tags (script,
style, xmp, and plaintext).
When the flag is FALSE for a text event, then you should normally
either use dtext or decode the entities yourself before the text is
processed further.
offset
length
event
Event causes the event name to be passed.
The event name is one of text, start, end, declaration,
comment, process or default.
line
Note: This is not supported yet!
Line causes the line number of the start of the event to be passed. The first line in the document is 1. Line counting doesn't start until at least one handler requests this value.
'...'
undef
Handlers for the following events can be registered:
text
This event is triggered when plain text is recognized. The text may contain multiple lines. A sequence of text may be broken between several text events unless $p->unbroken_text is enabled.
The parser will make sure that it does not break a word or a sequence of whitespace between two text events.
start
This event is triggered when a start tag is recognized.
Example:
<A HREF="http://www.perl.com/">
end
This event is triggered when an end tag is recognized.
Example:
</A>
declaration
This event is triggered when a markup declaration is recognized.
For typical HTML documents, the only declaration you are likely to find is <!DOCTYPE ...>.
Example:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html40/strict.dtd">
DTDs inside <!DOCTYPE ...> will confuse PSP::HTML::Parser.
comment
This event is triggered when a markup comment is recognized.
Example:
<!-- This is a comment -- -- So is this -->
process
This event is triggered when a processing instructions markup is recognized.
The format and content of processing instructions is system and application dependent.
Examples:
<? HTML processing instructions > <? XML processing instructions ?>
default
When an PSP::HTML::Parser object is constructed with no arguments, a set
of handlers is automatically provided that is compatible with the old
PSP::HTML::Parser version 2 callback methods.
This is equivalent to the following method calls:
$p->handler(start => "start", "self, tagname, attr, attrseq, text");
$p->handler(end => "end", "self, tagname, text");
$p->handler(text => "text", "self, text, is_cdata");
$p->handler(process => "process", "self, token0, text");
$p->handler(comment =>
sub {
my($self, $tokens) = @_;
for (@$tokens) {$self->comment($_);}},
"self, tokens");
$p->handler(declaration =>
sub {
my $self = shift;
$self->declaration(substr($_[0], 2, -1));},
"self, text");
Setup of these handlers can also be requested with the "api_version => 2" constructor option.
The PSP::HTML::Parser class is subclassable. Parser objects are plain
hashes and PSP::HTML::Parser reserves only hash keys that start with
"_hparser". The parser state can be set up by invoking the init()
method which takes the same arguments as new().
The first simple example shows how you might strip out comments from an HTML document. We achieve this by setting up a comment handler that does nothing and a default handler that will print out anything else:
use PSP::HTML::Parser;
PSP::HTML::Parser->new(default_h => [sub { print shift }, 'text'],
comment_h => [""],
)->parse_file(shift || die) || die $!;
The next example prints out the text that is inside the <title> element of an HTML document. Here we start by setting up a start handler. When it sees the title start tag it enables a text handler that prints any text found and an end handler that will terminate parsing as soon as the title end tag is seen:
use PSP::HTML::Parser ();
sub start_handler
{
return if shift ne "title";
my $self = shift;
$self->handler(text => sub { print shift }, "dtext");
$self->handler(end => sub { shift->eof if shift eq "title"; },
"tagname,self");
}
my $p = PSP::HTML::Parser->new(api_version => 3);
$p->handler( start => \&start_handler, "tagname,self");
$p->parse_file(shift || die) || die $!;
print "\n";
More examples are found in the "eg/" directory of the HTML-Parser
distribution; the program hrefsub shows how you can edit all links
found in a document and htextsub how to edid the text only; the
program hstrip shows how you can strip out certain tags/elements
and/or attributes; and the program htext show how to obtain the
plain text, but not any script/style content.
PSP::HTML::Parser will leave <plaintext> mode when it sees </plaintext>.
Plaintext mode should not really be escapeable.
The <style> and <script> sections do not end with the first "</", but need the complete corresponding end tag.
When the strict_comment option is enabled, we still recognize comments where there is something other than whitespace between even and odd "--" markers.
Once $p->boolean_attribute_value has been set, there is no way to restore the default behaviour.
There is currently no way to get both quote characters into the same literal argspec.
Empty tags, e.g. "<>" and "</>", are not recognized. SGML allows them to repeat the previous start tag or close the previous start tag respecitvely.
NET tags, e.g. "code/.../" are not recognized. This is an SGML shorthand for "<code>...</code>".
Unclosed start or end tags, e.g. "<tt<b>...</b</tt>" are not recognized.
The following messages may be produced by PSP::HTML::Parser. The notation in this listing is the same as used in perldiag:
PSP::HTML::Entities, PSP::HTML::TokeParser, PSP::HTML::HeadParser, PSP::HTML::LinkExtor, PSP::HTML::Form
HTML::TreeBuilder (part of the HTML-Tree distribution)
http://www.w3.org/TR/REC-html40
More information about marked sections and processing instructions may
be found at http://www.sgml.u-net.com/book/sgml-8.htm.
Copyright 1996-2000 Gisle Aas. All rights reserved. Copyright 1999-2000 Michael A. Chase. All rights reserved.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.