Lib/sgmllib.py

"""A parser for SGML, using the derived class as a static DTD."""

# XXX This only supports those SGML features used by HTML.

# XXX There should be a way to distinguish between PCDATA (parsed
# character data -- the normal case), RCDATA (replaceable character
# data -- only char and entity references and end tags are special)
# and CDATA (character data -- only end tags are special).


import re
import string

__all__ = ["SGMLParser"]

# Regular expressions used for parsing

interesting = re.compile('[&<]')
incomplete = re.compile('&([a-zA-Z][a-zA-Z0-9]*|#[0-9]*)?|'
                           '<([a-zA-Z][^<>]*|'
                              '/([a-zA-Z][^<>]*)?|'
                              '![^<>]*)?')

entityref = re.compile('&([a-zA-Z][-.a-zA-Z0-9]*)[^a-zA-Z0-9]')
charref = re.compile('&#([0-9]+)[^0-9]')

starttagopen = re.compile('<[>a-zA-Z]')
shorttagopen = re.compile('<[a-zA-Z][-.a-zA-Z0-9]*/')
shorttag = re.compile('<([a-zA-Z][-.a-zA-Z0-9]*)/([^/]*)/')
piopen = re.compile('<\?')
piclose = re.compile('>')
endtagopen = re.compile('</[<>a-zA-Z]')
endbracket = re.compile('[<>]')
special = re.compile('<![^<>]*>')
commentopen = re.compile('<!--')
commentclose = re.compile(r'--\s*>')
tagfind = re.compile('[a-zA-Z][-.a-zA-Z0-9]*')
attrfind = re.compile(
    r'\s*([a-zA-Z_][-.a-zA-Z_0-9]*)(\s*=\s*'
    r'(\'[^\']*\'|"[^"]*"|[-a-zA-Z0-9./:;+*%?!&$\(\)_#=~]*))?')

declname = re.compile(r'[a-zA-Z][-_.a-zA-Z0-9]*\s*')
declstringlit = re.compile(r'(\'[^\']*\'|"[^"]*")\s*')


class SGMLParseError(RuntimeError):
    """Exception raised for all parse errors."""
    pass


# SGML parser base class -- find tags and call handler functions.
# Usage: p = SGMLParser(); p.feed(data); ...; p.close().
# The dtd is defined by deriving a class which defines methods
# with special names to handle tags: start_foo and end_foo to handle
# <foo> and </foo>, respectively, or do_foo to handle <foo> by itself.
# (Tags are converted to lower case for this purpose.)  The data
# between tags is passed to the parser by calling self.handle_data()
# with some data as argument (the data may be split up in arbitrary
# chunks).  Entity references are passed by calling
# self.handle_entityref() with the entity reference as argument.

class SGMLParser:

    # Interface -- initialize and reset this instance
    def __init__(self, verbose=0):
        self.verbose = verbose
        self.reset()

    # Interface -- reset this instance.  Loses all unprocessed data
    def reset(self):
        self.rawdata = ''
        self.stack = []
        self.lasttag = '???'
        self.nomoretags = 0
        self.literal = 0

    # For derived classes only -- enter literal mode (CDATA) till EOF
    def setnomoretags(self):
        self.nomoretags = self.literal = 1

    # For derived classes only -- enter literal mode (CDATA)
    def setliteral(self, *args):
        self.literal = 1

    # Interface -- feed some data to the parser.  Call this as
    # often as you want, with as little or as much text as you
    # want (may include '\n').  (This just saves the text, all the
    # processing is done by goahead().)
    def feed(self, data):
        self.rawdata = self.rawdata + data
        self.goahead(0)

    # Interface -- handle the remaining data
    def close(self):
        self.goahead(1)

    # Internal -- handle data as far as reasonable.  May leave state
    # and data to be processed by a subsequent call.  If 'end' is
    # true, force handling all data as if followed by EOF marker.
    def goahead(self, end):
        rawdata = self.rawdata
        i = 0
        n = len(rawdata)
        while i < n:
            if self.nomoretags:
                self.handle_data(rawdata[i:n])
                i = n
                break
            match = interesting.search(rawdata, i)
            if match: j = match.start(0)
            else: j = n
            if i < j: self.handle_data(rawdata[i:j])
            i = j
            if i == n: break
            if rawdata[i] == '<':
                if starttagopen.match(rawdata, i):
                    if self.literal:
                        self.handle_data(rawdata[i])
                        i = i+1
                        continue
                    k = self.parse_starttag(i)
                    if k < 0: break
                    i = k
                    continue
                if endtagopen.match(rawdata, i):
                    k = self.parse_endtag(i)
                    if k < 0: break
                    i =  k
                    self.literal = 0
                    continue
                if commentopen.match(rawdata, i):
                    if self.literal:
                        self.handle_data(rawdata[i])
                        i = i+1
                        continue
                    k = self.parse_comment(i)
                    if k < 0: break
                    i = i+k
                    continue
                if piopen.match(rawdata, i):
                    if self.literal:
                        self.handle_data(rawdata[i])
                        i = i+1
                        continue
                    k = self.parse_pi(i)
                    if k < 0: break
                    i = i+k
                    continue
                match = special.match(rawdata, i)
                if match:
                    if self.literal:
                        self.handle_data(rawdata[i])
                        i = i+1
                        continue
                    # This is some sort of declaration; in "HTML as
                    # deployed," this should only be the document type
                    # declaration ("<!DOCTYPE html...>").
                    k = self.parse_declaration(i)
                    if k < 0: break
                    i = k
                    continue
            elif rawdata[i] == '&':
                match = charref.match(rawdata, i)
                if match:
                    name = match.group(1)
                    self.handle_charref(name)
                    i = match.end(0)
                    if rawdata[i-1] != ';': i = i-1
                    continue
                match = entityref.match(rawdata, i)
                if match:
                    name = match.group(1)
                    self.handle_entityref(name)
                    i = match.end(0)
                    if rawdata[i-1] != ';': i = i-1
                    continue
            else:
                raise SGMLParseError('neither < nor & ??')
            # We get here only if incomplete matches but
            # nothing else
            match = incomplete.match(rawdata, i)
            if not match:
                self.handle_data(rawdata[i])
                i = i+1
                continue
            j = match.end(0)
            if j == n:
                break # Really incomplete
            self.handle_data(rawdata[i:j])
            i = j
        # end while
        if end and i < n:
            self.handle_data(rawdata[i:n])
            i = n
        self.rawdata = rawdata[i:]
        # XXX if end: check for empty stack

    # Internal -- parse comment, return length or -1 if not terminated
    def parse_comment(self, i):
        rawdata = self.rawdata
        if rawdata[i:i+4] != '<!--':
            raise SGMLParseError('unexpected call to parse_comment()')
        match = commentclose.search(rawdata, i+4)
        if not match:
            return -1
        j = match.start(0)
        self.handle_comment(rawdata[i+4: j])
        j = match.end(0)
        return j-i

    # Internal -- parse declaration.
    def parse_declaration(self, i):
        rawdata = self.rawdata
        j = i + 2
        # in practice, this should look like: ((name|stringlit) S*)+ '>'
        while 1:
            c = rawdata[j:j+1]
            if c == ">":
                # end of declaration syntax
                self.handle_decl(rawdata[i+2:j])
                return j + 1
            if c in "\"'":
                m = declstringlit.match(rawdata, j)
                if not m:
                    # incomplete or an error?
                    return -1
                j = m.end()
            elif c in "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ":
                m = declname.match(rawdata, j)
                if not m:
                    # incomplete or an error?
                    return -1
                j = m.end()
            elif i == len(rawdata):
                # end of buffer between tokens
                return -1
            else:
                raise SGMLParseError(
                    "unexpected char in declaration: %s" % `rawdata[i]`)
        assert 0, "can't get here!"

    # Internal -- parse processing instr, return length or -1 if not terminated
    def parse_pi(self, i):
        rawdata = self.rawdata
        if rawdata[i:i+2] != '<?':
            raise SGMLParseError('unexpected call to parse_pi()')
        match = piclose.search(rawdata, i+2)
        if not match:
            return -1
        j = match.start(0)
        self.handle_pi(rawdata[i+2: j])
        j = match.end(0)
        return j-i

    __starttag_text = None
    def get_starttag_text(self):
        return self.__starttag_text

    # Internal -- handle starttag, return length or -1 if not terminated
    def parse_starttag(self, i):
        self.__starttag_text = None
        start_pos = i
        rawdata = self.rawdata
        if shorttagopen.match(rawdata, i):
            # SGML shorthand: <tag/data/ == <tag>data</tag>
            # XXX Can data contain &... (entity or char refs)?
            # XXX Can data contain < or > (tag characters)?
            # XXX Can there be whitespace before the first /?
            match = shorttag.match(rawdata, i)
            if not match:
                return -1
            tag, data = match.group(1, 2)
            self.__starttag_text = '<%s/' % tag
            tag = tag.lower()
            k = match.end(0)
            self.finish_shorttag(tag, data)
            self.__starttag_text = rawdata[start_pos:match.end(1) + 1]
            return k
        # XXX The following should skip matching quotes (' or ")
        match = endbracket.search(rawdata, i+1)
        if not match:
            return -1
        j = match.start(0)
        # Now parse the data between i+1 and j into a tag and attrs
        attrs = []
        if rawdata[i:i+2] == '<>':
            # SGML shorthand: <> == <last open tag seen>
            k = j
            tag = self.lasttag
        else:
            match = tagfind.match(rawdata, i+1)
            if not match:
                raise SGMLParseError('unexpected call to parse_starttag')
            k = match.end(0)
            tag = rawdata[i+1:k].lower()
            self.lasttag = tag
        while k < j:
            match = attrfind.match(rawdata, k)
            if not match: break
            attrname, rest, attrvalue = match.group(1, 2, 3)
            if not rest:
                attrvalue = attrname
            elif attrvalue[:1] == '\'' == attrvalue[-1:] or \
                 attrvalue[:1] == '"' == attrvalue[-1:]:
                attrvalue = attrvalue[1:-1]
            attrs.append((attrname.lower(), attrvalue))
            k = match.end(0)
        if rawdata[j] == '>':
            j = j+1
        self.__starttag_text = rawdata[start_pos:j]
        self.finish_starttag(tag, attrs)
        return j

    # Internal -- parse endtag
    def parse_endtag(self, i):
        rawdata = self.rawdata
        match = endbracket.search(rawdata, i+1)
        if not match:
            return -1
        j = match.start(0)
        tag = rawdata[i+2:j].strip().lower()
        if rawdata[j] == '>':
            j = j+1
        self.finish_endtag(tag)
        return j

    # Internal -- finish parsing of <tag/data/ (same as <tag>data</tag>)
    def finish_shorttag(self, tag, data):
        self.finish_starttag(tag, [])
        self.handle_data(data)
        self.finish_endtag(tag)

    # Internal -- finish processing of start tag
    # Return -1 for unknown tag, 0 for open-only tag, 1 for balanced tag
    def finish_starttag(self, tag, attrs):
        try:
            method = getattr(self, 'start_' + tag)
        except AttributeError:
            try:
                method = getattr(self, 'do_' + tag)
            except AttributeError:
                self.unknown_starttag(tag, attrs)
                return -1
            else:
                self.handle_starttag(tag, method, attrs)
                return 0
        else:
            self.stack.append(tag)
            self.handle_starttag(tag, method, attrs)
            return 1

    # Internal -- finish processing of end tag
    def finish_endtag(self, tag):
        if not tag:
            found = len(self.stack) - 1
            if found < 0:
                self.unknown_endtag(tag)
                return
        else:
            if tag not in self.stack:
                try:
                    method = getattr(self, 'end_' + tag)
                except AttributeError:
                    self.unknown_endtag(tag)
                else:
                    self.report_unbalanced(tag)
                return
            found = len(self.stack)
            for i in range(found):
                if self.stack[i] == tag: found = i
        while len(self.stack) > found:
            tag = self.stack[-1]
            try:
                method = getattr(self, 'end_' + tag)
            except AttributeError:
                method = None
            if method:
                self.handle_endtag(tag, method)
            else:
                self.unknown_endtag(tag)
            del self.stack[-1]

    # Overridable -- handle start tag
    def handle_starttag(self, tag, method, attrs):
        method(attrs)

    # Overridable -- handle end tag
    def handle_endtag(self, tag, method):
        method()

    # Example -- report an unbalanced </...> tag.
    def report_unbalanced(self, tag):
        if self.verbose:
            print '*** Unbalanced </' + tag + '>'
            print '*** Stack:', self.stack

    # Example -- handle character reference, no need to override
    def handle_charref(self, name):
        try:
            n = int(name)
        except ValueError:
            self.unknown_charref(name)
            return
        if not 0 <= n <= 255:
            self.unknown_charref(name)
            return
        self.handle_data(chr(n))

    # Definition of entities -- derived classes may override
    entitydefs = \
            {'lt': '<', 'gt': '>', 'amp': '&', 'quot': '"', 'apos': '\''}

    # Example -- handle entity reference, no need to override
    def handle_entityref(self, name):
        table = self.entitydefs
        if table.has_key(name):
            self.handle_data(table[name])
        else:
            self.unknown_entityref(name)
            return

    # Example -- handle data, should be overridden
    def handle_data(self, data):
        pass

    # Example -- handle comment, could be overridden
    def handle_comment(self, data):
        pass

    # Example -- handle declaration, could be overridden
    def handle_decl(self, decl):
        pass

    # Example -- handle processing instruction, could be overridden
    def handle_pi(self, data):
        pass

    # To be overridden -- handlers for unknown objects
    def unknown_starttag(self, tag, attrs): pass
    def unknown_endtag(self, tag): pass
    def unknown_charref(self, ref): pass
    def unknown_entityref(self, ref): pass


class TestSGMLParser(SGMLParser):

    def __init__(self, verbose=0):
        self.testdata = ""
        SGMLParser.__init__(self, verbose)

    def handle_data(self, data):
        self.testdata = self.testdata + data
        if len(`self.testdata`) >= 70:
            self.flush()

    def flush(self):
        data = self.testdata
        if data:
            self.testdata = ""
            print 'data:', `data`

    def handle_comment(self, data):
        self.flush()
        r = `data`
        if len(r) > 68:
            r = r[:32] + '...' + r[-32:]
        print 'comment:', r

    def unknown_starttag(self, tag, attrs):
        self.flush()
        if not attrs:
            print 'start tag: <' + tag + '>'
        else:
            print 'start tag: <' + tag,
            for name, value in attrs:
                print name + '=' + '"' + value + '"',
            print '>'

    def unknown_endtag(self, tag):
        self.flush()
        print 'end tag: </' + tag + '>'

    def unknown_entityref(self, ref):
        self.flush()
        print '*** unknown entity ref: &' + ref + ';'

    def unknown_charref(self, ref):
        self.flush()
        print '*** unknown char ref: &#' + ref + ';'

    def close(self):
        SGMLParser.close(self)
        self.flush()


def test(args = None):
    import sys

    if not args:
        args = sys.argv[1:]

    if args and args[0] == '-s':
        args = args[1:]
        klass = SGMLParser
    else:
        klass = TestSGMLParser

    if args:
        file = args[0]
    else:
        file = 'test.html'

    if file == '-':
        f = sys.stdin
    else:
        try:
            f = open(file, 'r')
        except IOError, msg:
            print file, ":", msg
            sys.exit(1)

    data = f.read()
    if f is not sys.stdin:
        f.close()

    x = klass()
    for c in data:
        x.feed(c)
    x.close()


if __name__ == '__main__':
    test()