html-parser
Description
A permissive, scalable HTML parser.
Author
Repository
This egg is hosted on the CHICKEN Subversion repository:
https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/html-parser
If you want to check out the source code repository of this egg and you are not familiar with Subversion, see this page.
Documentation
html-parser is intended as a permissive HTML parser for people who prefer the scalable interface described in Oleg Kiselyov's SSAX parser, as well as providing simple convenience utilities. It correctly handles all invalid HTML, inserting "virtual" starting and closing tags as needed to maintain the proper tree structure needed for the foldts down/up logic. A major goal of this parser is bug-for-bug compatibility with the way common web browsers parse HTML.
Main interface
make-html-parser
[procedure] (make-html-parser . keys)Returns a procedure of two arguments, an initial seed and an optional input port, which parses the HTML document from the port with the callbacks specified in the plist KEYS (using normal, quoted symbols, for portability and to avoid making this a macro). The following callbacks are recognized:
START: TAG ATTRS SEED VIRTUAL?
fdown in foldts, called when a start-tag is encountered.
TAG: tag name
ATTRS: tag attributes as a alist
SEED: current seed value
VIRTUAL?: #t iff this start tag was inserted to fix the HTML tree
END: TAG ATTRS PARENT-SEED SEED VIRTUAL?
fup in foldts, called when an end-tag is encountered.
TAG: tag name
ATTRS: tag attributes of the corresponding start tag
PARENT-SEED: parent seed value (i.e. seed passed to the start tag)
SEED: current seed value
VIRTUAL?: #t iff this end tag was inserted to fix the HTML tree
TEXT: TEXT SEED
fhere in foldts, called when any text is encountered. May be
called multiple times between a start and end tag, so you need
to string-append yourself if desired.
TEXT: entity-decoded text
SEED: current seed value
COMMENT: TEXT SEED
fhere on comment data
DECL: NAME ATTRS SEED
fhere on declaration data
PROCESS: LIST SEED
fhere on process-instruction data
In addition, entity-mappings may be overriden with the ENTITIES: keyword.
Convenience functions
html->sxml
[procedure] (html->sxml [port])Returns the SXML representation of the document from PORT, using the default parsing options.
html-strip
[procedure] (html-strip [port])Returns a string representation of the document from PORT with all tags removed. No whitespace reduction or other rendering is done.
Misc
make-string-reader/ci
[procedure] (make-string-reader/ci str)Generates a KMP reader that works on ports, returning the text read up until the search string (or the entire port if the search string isn't found). This is O(n) in the length of the string returned, as opposed to the find-string-from-port? in SSAX which uses backtracking for an O(nm) algorithm. This is hard-coded to case-insensitively match, since that's what we need for HTML. A more general utility would abstract the character matching predicate and possibly provide a limit on the length of the string read.
html-display-escaped-string
[procedure] (html-display-escaped-string str out)Writes a HTML escaped string to the output port, replacing the characters <>&"' with the appropriate HTML entities.
html-escape
[procedure] (html-escape str)Returns a HTML escaped string. Equivalent to using html-display-escaped-string with a string output port.
html-attr->string
[procedure] (html-attr->string attr)Format an attribute pair as string. Both (name . "value") and (name "value") are supported and are turned into "name=\"value\"".
html-tag->string
[procedure] (html-tag->string tag attrs)Format tag and attribute list as string. The tag must be a symbol, the attribute list is processed using html-attr->string. For example (html-tag->string 'a '((href "#"))) is turned into "<a href=\"#\">".
sxml-display-as-html
[procedure] (sxml-display-as-html sxml [port])Write the HTML representation of sxml, with the optional port argument defaulting to (current-output-port). Processing instructions, declarations, comments, top nodes and regular nodes are handled.
sxml->html
[procedure] (sxml->html sxml)Convert the HTML representation of sxml to a string. Equivalent to using sxml-display-as-html with a string output port.
Examples
This is the definition of the html->sxml convenience function included in the egg:
(define html->sxml
(let ((parse
(make-html-parser
'start: (lambda (tag attrs seed virtual?) '())
'end: (lambda (tag attrs parent-seed seed virtual?)
`((,tag ,@(if (pair? attrs)
`((@ ,@attrs) ,@(reverse seed))
(reverse seed)))
,@parent-seed))
'decl: (lambda (tag attrs seed) `((*DECL* ,tag ,@attrs) ,@seed))
'process: (lambda (attrs seed) `((*PI* ,@attrs) ,@seed))
'comment: (lambda (text seed) `((*COMMENT* ,text) ,@seed))
'text: (lambda (text seed) (cons text seed))
)))
(lambda o
(reverse (apply parse '() o)))))
The parser for html-strip could be defined as:
(make-html-parser
'start: (lambda (tag attrs seed virtual?) seed)
'end: (lambda (tag attrs parent-seed seed virtual?) seed)
'text: (lambda (text seed) (display text)))
Changelog
- 0.3 Add meta and link tag handling
- 0.2 ported to CHICKEN 5 (by felix)
- 0.1 Import upstream as of 2009-01-25
License
BSD-style license: http://synthcode.com/license.txt.