Lib/robotparser.py

""" robotparser.py

    Copyright (C) 2000  Bastian Kleineidam

    You can choose between two licenses when using this package:
    1) GNU GPLv2
    2) PSF license for Python 2.2

    The robots.txt Exclusion Protocol is implemented as specified in
    http://info.webcrawler.com/mak/projects/robots/norobots-rfc.html
"""
import urlparse,urllib

__all__ = ["RobotFileParser"]

debug = 0

def _debug(msg):
    if debug: print(msg)


class RobotFileParser:
    """ This class provides a set of methods to read, parse and answer
    questions about a single robots.txt file.

    """

    def __init__(self, url=''):
        self.entries = []
        self.default_entry = None
        self.disallow_all = False
        self.allow_all = False
        self.set_url(url)
        self.last_checked = 0

    def mtime(self):
        """Returns the time the robots.txt file was last fetched.

        This is useful for long-running web spiders that need to
        check for new robots.txt files periodically.

        """
        return self.last_checked

    def modified(self):
        """Sets the time the robots.txt file was last fetched to the
        current time.

        """
        import time
        self.last_checked = time.time()

    def set_url(self, url):
        """Sets the URL referring to a robots.txt file."""
        self.url = url
        self.host, self.path = urlparse.urlparse(url)[1:3]

    def read(self):
        """Reads the robots.txt URL and feeds it to the parser."""
        opener = URLopener()
        f = opener.open(self.url)
        lines = []
        line = f.readline()
        while line:
            lines.append(line.strip())
            line = f.readline()
        self.errcode = opener.errcode
        if self.errcode == 401 or self.errcode == 403:
            self.disallow_all = True
            _debug("disallow all")
        elif self.errcode >= 400:
            self.allow_all = True
            _debug("allow all")
        elif self.errcode == 200 and lines:
            _debug("parse lines")
            self.parse(lines)

    def _add_entry(self, entry):
        if "*" in entry.useragents:
            # the default entry is considered last
            self.default_entry = entry
        else:
            self.entries.append(entry)

    def parse(self, lines):
        """parse the input lines from a robots.txt file.
           We allow that a user-agent: line is not preceded by
           one or more blank lines."""
        state = 0
        linenumber = 0
        entry = Entry()

        for line in lines:
            linenumber = linenumber + 1
            if not line:
                if state==1:
                    _debug("line %d: warning: you should insert"
                           " allow: or disallow: directives below any"
                           " user-agent: line" % linenumber)
                    entry = Entry()
                    state = 0
                elif state==2:
                    self._add_entry(entry)
                    entry = Entry()
                    state = 0
            # remove optional comment and strip line
            i = line.find('#')
            if i>=0:
                line = line[:i]
            line = line.strip()
            if not line:
                continue
            line = line.split(':', 1)
            if len(line) == 2:
                line[0] = line[0].strip().lower()
                line[1] = urllib.unquote(line[1].strip())
                if line[0] == "user-agent":
                    if state==2:
                        _debug("line %d: warning: you should insert a blank"
                               " line before any user-agent"
                               " directive" % linenumber)
                        self._add_entry(entry)
                        entry = Entry()
                    entry.useragents.append(line[1])
                    state = 1
                elif line[0] == "disallow":
                    if state==0:
                        _debug("line %d: error: you must insert a user-agent:"
                               " directive before this line" % linenumber)
                    else:
                        entry.rulelines.append(RuleLine(line[1], False))
                        state = 2
                elif line[0] == "allow":
                    if state==0:
                        _debug("line %d: error: you must insert a user-agent:"
                               " directive before this line" % linenumber)
                    else:
                        entry.rulelines.append(RuleLine(line[1], True))
                else:
                    _debug("line %d: warning: unknown key %s" % (linenumber,
                               line[0]))
            else:
                _debug("line %d: error: malformed line %s"%(linenumber, line))
        if state==2:
            self.entries.append(entry)
        _debug("Parsed rules:\n%s" % str(self))


    def can_fetch(self, useragent, url):
        """using the parsed robots.txt decide if useragent can fetch url"""
        _debug("Checking robots.txt allowance for:\n  user agent: %s\n  url: %s" %
               (useragent, url))
        if self.disallow_all:
            return False
        if self.allow_all:
            return True
        # search for given user agent matches
        # the first match counts
        url = urllib.quote(urlparse.urlparse(urllib.unquote(url))[2]) or "/"
        for entry in self.entries:
            if entry.applies_to(useragent):
                return entry.allowance(url)
        # try the default entry last
        if self.default_entry:
            return self.default_entry.allowance(url)
        # agent not found ==> access granted
        return True


    def __str__(self):
        ret = ""
        for entry in self.entries:
            ret = ret + str(entry) + "\n"
        return ret


class RuleLine:
    """A rule line is a single "Allow:" (allowance==True) or "Disallow:"
       (allowance==False) followed by a path."""
    def __init__(self, path, allowance):
        if path == '' and not allowance:
            # an empty value means allow all
            allowance = True
        self.path = urllib.quote(path)
        self.allowance = allowance

    def applies_to(self, filename):
        return self.path=="*" or filename.startswith(self.path)

    def __str__(self):
        return (self.allowance and "Allow" or "Disallow")+": "+self.path


class Entry:
    """An entry has one or more user-agents and zero or more rulelines"""
    def __init__(self):
        self.useragents = []
        self.rulelines = []

    def __str__(self):
        ret = ""
        for agent in self.useragents:
            ret = ret + "User-agent: "+agent+"\n"
        for line in self.rulelines:
            ret = ret + str(line) + "\n"
        return ret

    def applies_to(self, useragent):
        """check if this entry applies to the specified agent"""
        # split the name token and make it lower case
        useragent = useragent.split("/")[0].lower()
        for agent in self.useragents:
            if agent=='*':
                # we have the catch-all agent
                return True
            agent = agent.lower()
            if agent in useragent:
                return True
        return False

    def allowance(self, filename):
        """Preconditions:
        - our agent applies to this entry
        - filename is URL decoded"""
        for line in self.rulelines:
            _debug((filename, str(line), line.allowance))
            if line.applies_to(filename):
                return line.allowance
        return True

class URLopener(urllib.FancyURLopener):
    def __init__(self, *args):
        urllib.FancyURLopener.__init__(self, *args)
        self.errcode = 200

    def http_error_default(self, url, fp, errcode, errmsg, headers):
        self.errcode = errcode
        return urllib.FancyURLopener.http_error_default(self, url, fp, errcode,
                                                        errmsg, headers)

def _check(a,b):
    if not b:
        ac = "access denied"
    else:
        ac = "access allowed"
    if a!=b:
        print("failed")
    else:
        print("ok (%s)" % ac)
    print()

def _test():
    global debug
    rp = RobotFileParser()
    debug = 1

    # robots.txt that exists, gotten to by redirection
    rp.set_url('http://www.musi-cal.com/robots.txt')
    rp.read()

    # test for re.escape
    _check(rp.can_fetch('*', 'http://www.musi-cal.com/'), 1)
    # this should match the first rule, which is a disallow
    _check(rp.can_fetch('', 'http://www.musi-cal.com/'), 0)
    # various cherry pickers
    _check(rp.can_fetch('CherryPickerSE',
                       'http://www.musi-cal.com/cgi-bin/event-search'
                       '?city=San+Francisco'), 0)
    _check(rp.can_fetch('CherryPickerSE/1.0',
                       'http://www.musi-cal.com/cgi-bin/event-search'
                       '?city=San+Francisco'), 0)
    _check(rp.can_fetch('CherryPickerSE/1.5',
                       'http://www.musi-cal.com/cgi-bin/event-search'
                       '?city=San+Francisco'), 0)
    # case sensitivity
    _check(rp.can_fetch('ExtractorPro', 'http://www.musi-cal.com/blubba'), 0)
    _check(rp.can_fetch('extractorpro', 'http://www.musi-cal.com/blubba'), 0)
    # substring test
    _check(rp.can_fetch('toolpak/1.1', 'http://www.musi-cal.com/blubba'), 0)
    # tests for catch-all * agent
    _check(rp.can_fetch('spam', 'http://www.musi-cal.com/search'), 0)
    _check(rp.can_fetch('spam', 'http://www.musi-cal.com/Musician/me'), 1)
    _check(rp.can_fetch('spam', 'http://www.musi-cal.com/'), 1)
    _check(rp.can_fetch('spam', 'http://www.musi-cal.com/'), 1)

    # robots.txt that does not exist
    rp.set_url('http://www.lycos.com/robots.txt')
    rp.read()
    _check(rp.can_fetch('Mozilla', 'http://www.lycos.com/search'), 1)

if __name__ == '__main__':
    _test()