Manpages - HTML_Parser.3pm

HTML::Parser - HTML parser class

use strict; use warnings; use HTML::Parser (); # Create parser object my $p = 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); # … # signal end of document $p->eof; # Parse directly from file $p->parse_file(“foo.html”); # or open(my $fh, “<:utf8”, “foo.html”) || die; $p->parse_file($fh);

Objects of the 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.

HTML::Parser is 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 HTML::PullParser. This is an HTML::Parser subclass that allows a more conventional program structure.

The following method is used to construct a new HTML::Parser object:

$p = HTML::Parser->new( %options_and_handlers )

This class method creates a new HTML::Parser object and returns it. Key/value argument pairs may be provided to assign event handlers or initialize parser options. The handlers and parser options can also be set or modified later by the 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 =HTML::Parser. See the section on version 2 compatibility below for details. The 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 = 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. $p = HTML::Parser->new( api_version => 3, start_h => [ my_start, "self,tokens" ] ); This creates a new parser object with a start event handler method that receives the =$p and the tokens array. $p = 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 HTML::Parser object:

$p->parse( $string )

Parse $string as the next chunk of the HTML document. Handlers invoked should not attempt to modify the $string in-place until $p->parse returns. If an invoked event handler aborts parsing by calling $p->eof, then $p->*parse()* will return a FALSE value. Otherwise the return value is a reference to the parser object ($p).

$p->parse( $code_ref )

If a code reference is passed as the argument to be parsed, then the chunks to be parsed are obtained by invoking this function repeatedly. Parsing continues until the function returns an empty (or undefined) result. When this happens $p->eof is automatically signaled. Parsing will also abort if one of the event handlers calls $p->eof. The effect of this is the same as: while (1) { my $chunk = &$code_ref(); if (!defined($chunk) || !length($chunk)) { $p->eof; return $p; } $p->parse($chunk) || return undef; } But it is more efficient as this loop runs internally in XS code.

$p->parse_file( $file )

Parse text directly from a file. The $file argument can be a filename, an open file handle, or a reference to 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 on a file handle that is not in binary mode. If a filename is passed in, then parse_file() will open the file in binary mode.

$p->eof

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()*. After $p->eof has been called, the parse() and parse_file() methods can be invoked to feed new documents with the parser object. The return value from eof() 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:

$p->attr_encoded

$p->attr_encoded( $bool )

By default, the attr and @attr argspecs will have general entities for attribute values decoded. Enabling this attribute leaves entities alone.

$p->backquote

$p->backquote( $bool )

By default, only ’ and “ are recognized as quote characters around attribute values. MSIE also recognizes backquotes for some reason. Enabling this attribute provides compatibility with this behaviour.

$p->boolean_attribute_value( $val )

This method sets the value reported for boolean attributes inside HTML start tags. By default, the name of the attribute is also used as its value. This affects the values reported for tokens and attr argspecs.

$p->case_sensitive

$p->case_sensitive( $bool )

By default, tag names and attribute names are down-cased. Enabling this attribute leaves them as found in the HTML source document.

$p->closing_plaintext

$p->closing_plaintext( $bool )

By default, plaintext element can never be closed. Everything up to the end of the document is parsed in CDATA mode. This historical behaviour is what at least MSIE does. Enabling this attribute makes closing = </plaintext= > tag effective and the parsing process will resume after seeing this tag. This emulates early gecko-based browsers.

$p->empty_element_tags

$p->empty_element_tags( $bool )

By default, empty element tags are not recognized as such and the / before > is just treated like a normal name character (unless strict_names is enabled). Enabling this attribute make HTML::Parser recognize these tags. Empty element tags look like start tags, but end with the character sequence /> instead of >. When recognized by 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 token array will have one element containing the tag name.

$p->marked_sections

$p->marked_sections( $bool )

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 the marked section markup, but the text can be returned as skipped_text.

$p->strict_comment

$p->strict_comment( $bool )

By default, comments are terminated by the first occurrence of –>. This is the behaviour of most popular browsers (like Mozilla, Opera 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. Enabling of ’strict_comment’ also disables recognizing these forms as comments: </ comment> <! comment>

$p->strict_end

$p->strict_end( $bool )

By default, attributes and other junk are allowed to be present on end tags in a manner that emulates MSIE’s behaviour. The official behaviour is enabled with this attribute. If enabled, only whitespace is allowed between the tagname and the final >.

$p->strict_names

$p->strict_names( $bool )

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 attribute 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 Mozilla 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.

$p->unbroken_text

$p->unbroken_text( $bool )

By default, blocks of text are given to the text handler as soon as possible (but the parser takes care always to break text at a boundary between whitespace and non-whitespace so single words and entities can always be decoded safely). This might create breaks that make it hard to do transformations on the text. When this attribute is enabled, blocks of text are always reported in one piece. This will delay the text event until the following (non-text) event has been recognized by the parser. Note that the offset argspec will give you the offset of the first segment of text and length is the combined length of the segments. Since there might be ignored tags in between, these numbers can’t be used to directly index in the original document file.

$p->utf8_mode

$p->utf8_mode( $bool )

Enable this option when parsing raw undecoded UTF-8. This tells the parser that the entities expanded for strings reported by attr, @attr and dtext should be expanded as decoded UTF-8 so they end up compatible with the surrounding text. If utf8_mode is enabled then it is an error to pass strings containing characters with code above 255 to the parse() method, and the parse() method will croak if you try. Example: The Unicode character \x{2665} is \xE2\x99\xA5 when UTF-8 encoded. The character can also be represented by the entity &hearts; or &#x2665. If we feed the parser: $p->parse(“\xE2\x99\xA5&hearts;”); then dtext will be reported as \xE2\x99\xA5\x{2665} without utf8_mode enabled, but as \xE2\x99\xA5\xE2\x99\xA5 when enabled. The later string is what you want. This option is only available with perl-5.8 or better.

$p->xml_mode

$p->xml_mode( $bool )

Enabling this attribute changes the parser to allow some XML constructs. This enables the behaviour controlled by individually by the case_sensitive, empty_element_tags, strict_names and xml_pic attributes and also suppresses special treatment of elements that are parsed as CDATA for HTML.

$p->xml_pic

$p->xml_pic( $bool )

By default, processing instructions are terminated by >. When this attribute is enabled, processing instructions are terminated by ?> instead.

As markup and text is recognized, handlers are invoked. The following method is used to set up handlers for different events:

$p->handler( event => \&subroutine, $argspec )

$p->handler( event => $method_name, $argspec )

$p->handler( event => \@accum, $argspec )

$p->handler( event => “” );

$p->handler( event => undef );

$p->handler( event );

This method assigns a subroutine, method, or array to handle an event. Event is one of text, start, end, declaration, comment, process, start_document, end_document or default. The \&subroutine is a reference to a subroutine which is called to handle the event. The $method_name is the name of a method of $p which is called to handle the event. The @accum is an 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. The $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. The return value from $p->handler is the old callback routine or a reference to the accumulator array. Any 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 the $p->*parse()* or $p->*parse_file()* method. An exception will be raised if it tries. 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=]. $p->handler(start => ""); This causes 'start' events to be ignored. It also suppresses invocations of any default handler for start events. It is in most cases equivalent to =$p->handler(start > sub {}), but is more efficient. It is different from the empty-sub-handler in that =skipped_text is not reset by it. $p->handler(start => undef); This causes no handler to be associated with start events. If there is a default handler it will be invoked.

Filters based on tags can be set up to limit the number of events reported. The main bottleneck during parsing is often the huge number of callbacks made from the parser. Applying filters can improve performance significantly.

The following methods control filters:

$p->ignore_elements( @tags )

Both the start event and the end event as well as any events that would be reported in between are suppressed. The ignored elements can contain nested occurrences of itself. Example: $p->ignore_elements(qw(script style)); The script and style tags will always nest properly since their content is parsed in CDATA mode. For most other tags ignore_elements must be used with caution since HTML is often not well formed.

$p->ignore_tags( @tags )

Any start and end events involving any of the tags given are suppressed. To reset the filter (i.e. don’t suppress any start and end events), call ignore_tags without an argument.

$p->report_tags( @tags )

Any start and end events involving any of the tags not given are suppressed. To reset the filter (i.e. report all start and end events), call report_tags without an argument.

Internally, the system has two filter lists, one for report_tags and one for ignore_tags, and both filters are applied. This effectively gives ignore_tags precedence over report_tags.

Examples:

$p->ignore_tags(qw(style)); $p->report_tags(qw(script style));

results in only script events being reported.

When an HTML::Parser object is constructed with no arguments, a set of handlers is automatically provided that is compatible with the old 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” );

Setting up these handlers can also be requested with the api_version => 2 constructor option.

The HTML::Parser class is able to be subclassed. Parser objects are plain hashes and 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 HTML::Parser; HTML::Parser->new( default_h => [sub { print shift }, text], comment_h => [“”], )->parse_file(shift || die) || die $!;

An alternative implementation is:

use HTML::Parser; HTML::Parser->new( end_document_h => [sub { print shift }, skipped_text], comment_h => [“”], )->parse_file(shift || die)

die $!;

This will in most cases be much more efficient since only a single callback will be made.

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 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 = 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; the program htextsub shows how to edit 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.

You can browse the eg/ directory online from the [Browse] link on the http://search.cpan.org/~gaas/HTML-Parser/ page.

The <style> and <script> sections do not end with the first </, but need the complete corresponding end tag. The standard behaviour is not really practical.

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 respectively.

NET tags, e.g. code/…/ are not recognized. This is SGML shorthand for <code>…</code>.

Incomplete start or end tags, e.g. <tt<b>…</b</tt> are not recognized.

The following messages may be produced by HTML::Parser. The notation in this listing is the same as used in perldiag:

Not a reference to a hash

(F) The object blessed into or subclassed from HTML::Parser is not a hash as required by the HTML::Parser methods.

Bad signature in parser state object at %p

(F) The _hparser_xs_state element does not refer to a valid state structure. Something must have changed the internal value stored in this hash element, or the memory has been overwritten.

_hparser_xs_state element is not a reference

(F) The _hparser_xs_state element has been destroyed.

Can’t find ’_hparser_xs_state’ element in HTML::Parser hash

(F) The _hparser_xs_state element is missing from the parser hash. It was either deleted, or not created when the object was created.

API version %s not supported by HTML::Parser %s

(F) The constructor option ’api_version’ with an argument greater than or equal to 4 is reserved for future extensions.

Bad constructor option ’%s’

(F) An unknown constructor option key was passed to the new() or init() methods.

Parse loop not allowed

(F) A handler invoked the parse() or parse_file() method. This is not permitted.

marked sections not supported

(F) The $p->*marked_sections()* method was invoked in a HTML::Parser module that was compiled without support for marked sections.

Unknown boolean attribute (%d)

(F) Something is wrong with the internal logic that set up aliases for boolean attributes.

Only code or array references allowed as handler

(F) The second argument for $p->handler must be either a subroutine reference, then name of a subroutine or method, or a reference to an array.

No handler for %s events

(F) The first argument to $p->handler must be a valid event name; i.e. one of start, end, text, process, declaration or comment.

Unrecognized identifier %s in argspec

(F) The identifier is not a known argspec name. Use one of the names mentioned in the argspec section above.

Literal string is longer than 255 chars in argspec

(F) The current implementation limits the length of literals in an argspec to 255 characters. Make the literal shorter.

Backslash reserved for literal string in argspec

(F) The backslash character \ is not allowed in argspec literals. It is reserved to permit quoting inside a literal in a later version.

Unterminated literal string in argspec

(F) The terminating quote character for a literal was not found.

Bad argspec (%s)

(F) Only identifier names, literals, spaces and commas are allowed in argspecs.

Missing comma separator in argspec

(F) Identifiers in an argspec must be separated with ,.

(no term)

Parsing of undecoded UTF-8 will give garbage when decoding entities :: (W) The first chunk parsed appears to contain undecoded UTF-8 and one or more argspecs that decode entities are used for the callback handlers. The result of decoding will be a mix of encoded and decoded characters for any entities that expand to characters with code above 127. This is not a good thing. The recommended solution is to apply Encode::decode_utf8() on the data before feeding it to the $p->*parse()*. For $p->*parse_file()* pass a file that has been opened in :utf8 mode. The alternative solution is to enable the utf8_mode and not decode before passing strings to $p->*parse()*. The parser can process raw undecoded UTF-8 sanely if the utf8_mode is enabled, or if the attr, @attr or dtext argspecs are avoided.

Parsing string decoded with wrong endian selection

(W) The first character in the document is U+FFFE. This is not a legal Unicode character but a byte swapped BOM. The result of parsing will likely be garbage.

Parsing of undecoded UTF-32

(W) The parser found the Unicode UTF-32 BOM signature at the start of the document. The result of parsing will likely be garbage.

Parsing of undecoded UTF-16

(W) The parser found the Unicode UTF-16 BOM signature at the start of the document. The result of parsing will likely be garbage.

HTML::Entities, HTML::PullParser, HTML::TokeParser, HTML::HeadParser, HTML::LinkExtor, HTML::Form

HTML::TreeBuilder (part of the HTML-Tree distribution)

http://www.w3.org/TR/html4/

More information about marked sections and processing instructions may be found at http://www.is-thought.co.uk/book/sgml-8.htm.

Copyright 1996-2016 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.