#!/usr/bin/env python """SPF (Sender-Permitted From) implementation. Copyright (c) 2003, Terence Way This module is free software, and you may redistribute it and/or modify it under the same terms as Python itself, so long as this copyright message and disclaimer are retained in their original form. IN NO EVENT SHALL THE AUTHOR BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF THIS CODE, EVEN IF THE AUTHOR HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. THE AUTHOR SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE CODE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THERE IS NO OBLIGATION WHATSOEVER TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS. For more information about SPF, a tool against email forgery, see http://spf.pobox.com For news, bugfixes, etc. visit the home page for this implementation at http://www.wayforward.net/spf/ """ # Changes: # 9-dec-2003, v1.1, Meng Weng Wong added PTR code, THANK YOU # 11-dec-2003, v1.2, ttw added macro expansion, exp=, and redirect= # 13-dec-2003, v1.3, ttw added %{o} original domain macro, # print spf result on command line, support default=, # support localhost, follow DNS CNAMEs, cache DNS results # during query, support Python 2.2 for Mac OS X # 16-dec-2003, v1.4, ttw fixed include handling (include is a mechanism, # complete with status results, so -include: should work. # Expand macros AFTER looking for status characters ?-+ # so altavista.com SPF records work. # 17-dec-2003, v1.5, ttw use socket.inet_aton() instead of DNS.addr2bin, so # n, n.n, and n.n.n forms for IPv4 addresses work, and to # ditch the annoying Python 2.4 FutureWarning # 18-dec-2003, v1.6, Failures on Intel hardware: endianness. Use ! on # struct.pack(), struct.unpack(). # # Development taken over by Stuart Gathman since # Terrence is not responding to email. # # $Log$ # Revision 1.14 2004/08/23 02:28:24 stuart # Remove Perl usage message. # # Revision 1.13 2004/07/23 19:23:12 stuart # Always fail to match on ip6, until we support it properly. # # Revision 1.12 2004/07/23 18:48:15 stuart # Fold CID parsing into spf # # Revision 1.11 2004/07/21 21:32:01 stuart # Handle CID records (Microsoft XML format). # # Revision 1.10 2004/04/19 22:12:11 stuart # Release 0.6.9 # # Revision 1.9 2004/04/18 03:29:35 stuart # Pass most tests except -local and -rcpt-to # # Revision 1.8 2004/04/17 22:17:55 stuart # Header comment method. # # Revision 1.7 2004/04/17 18:22:48 stuart # Support default explanation. # # Revision 1.6 2004/04/06 20:18:02 stuart # Fix bug in include # # Revision 1.5 2004/04/05 22:29:46 stuart # SPF best_guess, # # Revision 1.4 2004/03/25 03:27:34 stuart # Support delegation of SPF records. # # Revision 1.3 2004/03/13 12:23:23 stuart # Expanded result codes. Tolerate common method misspellings. # __author__ = "Terence Way" __email__ = "terry@wayforward.net" __version__ = "1.6: December 18, 2003" MODULE = 'spf' USAGE = """To check an incoming mail request: % python spf.py {ip} {sender} {helo} % python spf.py 69.55.226.139 tway@optsw.com mx1.wayforward.net To test an SPF record: % python spf.py "v=spf1..." {ip} {sender} {helo} % python spf.py "v=spf1 +mx +ip4:10.0.0.1 -all" 10.0.0.1 tway@foo.com a To fetch an SPF record: % python spf.py {domain} % python spf.py wayforward.net To test this script (and to output this usage message): % python spf.py """ import re import socket # for inet_ntoa() and inet_aton() import struct # for pack() and unpack() import time # for time() import DNS # http://pydns.sourceforge.net import xml.sax # ------------------------------------------------------------------------- # Convert a MS Caller-ID entry (XML) to a SPF entry # # (c) 2004 by Ernesto Baschny # (c) 2004 Python version by Stuart Gathman # # Date: 2004-02-25 # # A complete reverse translation (SPF -> CID) might be impossible, since # there are no way to handle: # - PTR and EXISTS mechanism # - MX mechanism with an different domain as argument # - macros # # References: # http://www.microsoft.com/mscorp/twc/privacy/spam_callerid.mspx # http://spf.pobox.com/ # # Known bugs: # - Currently it won't handle the exclusions provided in the A and R # tags (prefix '!'). They will show up "as-is" in the SPF record # - I really haven't read the MS-CID specs in-depth, so there are probably # other bugs too :) # # Ernesto Baschny # class CIDParser(xml.sax.ContentHandler): "Convert a MS Caller-ID entry (XML) to a SPF entry." def __init__(self,q=None): self.spf = [] self.action = '-all' self.has_servers = None self.spf_entry = None if q: self.spf_query = q else: self.spf_query = query(i='127.0.0.1', s='localhost', h='unknown') def startElement(self,tag,attr): if tag == 'm': if self.has_servers != None and not self.has_servers: raise ValueError( "Declared and later , this CID entry is not valid." ) self.has_servers = True elif tag == 'noMailServers': if self.has_servers: raise ValueError( "Declared and later , this CID entry is not valid." ) self.has_servers = False elif tag == 'ep': if attr.has_key('testing') and attr.getValue('testing') == 'true': # A CID with 'testing' found: # From the MS-specs: # "Documents in which such attribute is present with a true # value SHOULD be entirely ignored (one should act as if the # document were absent)" # From the SPF-specs: # "Neutral (?): The SPF client MUST proceed as if a domain did # not publish SPF data." # So we set SPF action to "neutral": self.action = '?all' elif tag == 'mx': # The empty MX-tag, same as SPF's MX-mechanism self.spf.append('mx') self.tag = tag def characters(self,text): tag = self.tag # Remove starting and trailing spaces from text: text = text.strip() if tag == 'a' or tag == 'r': # The A and R tags from MS-CID are both handled by the # ipv4/6-mechanisms from SPF: if text.find(':') < 0: mechanism = 'ip4' else: mechanism = 'ip6' self.spf.append(mechanism + ':' + text) elif tag == 'indirect': # MS-CID's indirect is "sort of" the include from SPF: # Not really true, because the tag from MS-CID also # provides a fallback in case the included domain doesn't provide # _ep-records: The inbound MX-servers of the included domains # are added to the list of allowed outgoing mailservers for the # domain that declared the _ep-record with the tag. # In SPF you would use the 'mx:domain' to handle this, but this # wouldn't depend on referred domain having or not SPF-records. cid_xml = self.cid_txt(text) if cid_xml: p = CIDParser() xml.sax.parseString(cid_xml,p) if p.has_servers != False: self.spf += p.spf else: self.spf.append('mx:' + text) def cid_txt(self,domain): q = self.spf_query domain='_ep.' + domain a = q.dns_txt(domain) if not a: return None if a[0].lower().startswith(''): return ''.join(a) return None def endElement(self,tag): if tag == 'ep': # This is the end... assemble what we've got spf_entry = ['v=spf1'] if self.has_servers != False: spf_entry += self.spf spf_entry.append(self.action) self.spf_entry = ' '.join(spf_entry) def spf_txt(self,cid_xml): if not cid_xml.startswith('<'): cid_xml = self.cid_txt(cid_xml) if not cid_xml: return None # Parse the beast. Any XML-problem will be reported by xlm.sax self.spf_entry = None xml.sax.parseString(cid_xml,self) return self.spf_entry # 32-bit IPv4 address mask MASK = 0xFFFFFFFFL # Regular expression to look for modifiers RE_MODIFIER = re.compile(r'^([a-zA-Z]+)=') # Regular expression to find macro expansions RE_CHAR = re.compile(r'%(%|_|-|(\{[a-zA-Z][0-9]*r?[^\}]*\}))') # Regular expression to break up a macro expansion RE_ARGS = re.compile(r'([0-9]*)(r?)([^0-9a-zA-Z]*)') # Local parts and senders have their delimiters replaced with '.' during # macro expansion # JOINERS = {'l': '.', 's': '.'} RESULTS = {'+': 'pass', '-': 'fail', '?': 'neutral', '~': 'softfail', 'pass': 'pass', 'fail': 'fail', 'unknown': 'unknown', 'neutral': 'neutral', 'softfail': 'softfail', 'none': 'none', 'deny': 'fail' } EXPLANATIONS = {'pass': 'sender SPF verified', 'fail': 'access denied', 'unknown': 'SPF unknown', 'softfail': 'domain in transition', 'neutral': 'access neither permitted nor denied', 'none': '' } # if set to a domain name, search _spf.domain namespace if no SPF record # found in source domain. DELEGATE = None # support pre 2.2.1.... try: bool, True, False = bool, True, False except NameError: False, True = 0, 1 def bool(x): return not not x # ...pre 2.2.1 # standard default SPF record DEFAULT_SPF = 'v=spf1 a/24 mx/24 ptr' def check(i, s, h,local=None): """Test an incoming MAIL FROM:, from a client with ip address i. h is the HELO/EHLO domain name. Returns (result, mta-status-code, explanation) where result in ['pass', 'unknown', 'fail', 'error', 'softfail', 'none', 'neutral' ]. Example: >>> check(i='127.0.0.1', s='terry@wayforward.net', h='localhost') ('pass', 250, 'local connections always pass') #>>> check(i='61.51.192.42', s='liukebing@bcc.com', h='bmsi.com') """ return query(i=i, s=s, h=h,local=local).check() class query(object): """A query object keeps the relevant information about a single SPF query: i: ip address of SMTP client s: sender declared in MAIL FROM:<> l: local part of sender s d: current domain, initially domain part of sender s h: EHLO/HELO domain v: 'in-addr' for IPv4 clients and 'ip6' for IPv6 clients t: current timestamp p: SMTP client domain name o: domain part of sender s This is also, by design, the same variables used in SPF macro expansion. Also keeps cache: DNS cache. """ def __init__(self, i, s, h,local=None): self.i, self.s, self.h = i, s, h self.l, self.o = split_email(s, h) self.t = str(int(time.time())) self.v = 'in-addr' self.d = self.o self.p = None self.cache = {} self.exps = dict(EXPLANATIONS) self.local = local # local policy def set_default_explanation(self,exp): exps = self.exps for i in 'softfail','fail','unknown': exps[i] = exp def getp(self): if not self.p: p = self.dns_ptr(self.i) if len(p) > 0: self.p = p[0] else: self.p = self.i return self.p def best_guess(self,spf=DEFAULT_SPF): """Return a best guess based on a default SPF record""" return self.check(spf) def check(self, spf=None): """ Returns (result, mta-status-code, explanation) where result in ['fail', 'softfail', 'neutral' 'unknown', 'pass', 'error'] """ if self.i.startswith('127.'): return ('pass', 250, 'local connections always pass') try: if not spf: spf = self.dns_spf(self.d) if self.local and spf: spf += ' ' + self.local return self.check1(spf, self.d, 0) except DNS.DNSError: return ('error', 450, 'SPF DNS Error') def check1(self, spf, domain, recursion): # spf rfc: 3.7 Processing Limits # if recursion > 20: self.prob = 'Mechanisms used too many DNS lookups' return ('unknown', 250, 'SPF recursion limit exceeded') try: tmp, self.d = self.d, domain return self.check0(spf, recursion) finally: self.d = tmp def check0(self, spf, recursion): """Test this query information against SPF text. Returns (result, mta-status-code, explanation) where result in ['fail', 'unknown', 'pass', 'none'] """ if not spf: return ('none', 250, EXPLANATIONS['none']) # split string by whitespace, drop the 'v=spf1' # spf = spf.split()[1:] # copy of explanations to be modified by exp= exps = self.exps redirect = None # no mechanisms at all cause unknown result, unless # overridden with 'default=' modifier # default = 'neutral' self.mech = [] # unknown mechanisms # Look for modifiers # for m in spf: m = RE_MODIFIER.split(m)[1:] if len(m) != 2: continue if m[0] == 'exp': exps['fail'] = exps['unknown'] = \ self.get_explanation(m[1]) elif m[0] == 'redirect': redirect = self.expand(m[1]) elif m[0] == 'default': # default=- is the same as default=fail default = RESULTS.get(m[1], default) # spf rfc: 3.6 Unrecognized Mechanisms and Modifiers # Look for mechanisms # for mech in spf: if RE_MODIFIER.match(mech): continue m, arg, cidrlength = parse_mechanism(mech, self.d) # map '?' '+' or '-' to 'unknown' 'pass' or 'fail' result = RESULTS.get(m[0]) if result: # eat '?' '+' or '-' m = m[1:] else: # default pass result = 'pass' if m in ['a', 'mx', 'ptr', 'exists', 'include']: arg = self.expand(arg) if m == 'include': if arg != self.d: res,code,txt = self.check1(self.dns_spf(arg), arg, recursion + 1) if res == 'pass': break if res in ('fail','neutral','softfail'): continue if res == 'none': self.prob = \ 'Could not find a valid SPF record' res = 'unknown' return res,code,txt else: self.prob = 'Required option is missing' self.mech.append(mech) return ('unknown', 250, 'missing SPF option') elif m == 'all': break elif m == 'exists': if len(self.dns_a(arg)) > 0: break elif m == 'a': if cidrmatch(self.i, self.dns_a(arg), cidrlength): break elif m == 'mx': if cidrmatch(self.i, self.dns_mx(arg), cidrlength): break elif m in ('ip4', 'ipv4', 'ip') and arg != self.d: if cidrmatch(self.i, [arg], cidrlength): break elif m == 'ip6': # Until we support IPV6, we should never # get an IPv6 connection. So this mech # will never match. pass elif m in ('ptr', 'prt'): if domainmatch(self.validated_ptrs(self.i), arg): break else: # unknown mechanisms cause immediate unknown # abort results self.mech.append(mech) self.prob = 'Unknown mechanism found' return ('unknown',250,'unknown SPF mechanism') else: # no matches if redirect: return self.check1(self.dns_spf(redirect), redirect, recursion+1) else: result = default if result == 'fail': return (result, 550, exps[result]) else: return (result, 250, exps[result]) def get_explanation(self, spec): """Expand an explanation.""" if spec: return self.expand(''.join(self.dns_txt(self.expand(spec)))) else: return 'explanation : Required option is missing' def expand(self, str): """Do SPF RFC macro expansion. Examples: >>> q = query(s='strong-bad@email.example.com', ... h='mx.example.org', i='192.0.2.3') >>> q.p = 'mx.example.org' >>> q.expand('%{d}') 'email.example.com' >>> q.expand('%{d4}') 'email.example.com' >>> q.expand('%{d3}') 'email.example.com' >>> q.expand('%{d2}') 'example.com' >>> q.expand('%{d1}') 'com' >>> q.expand('%{p}') 'mx.example.org' >>> q.expand('%{p2}') 'example.org' >>> q.expand('%{dr}') 'com.example.email' >>> q.expand('%{d2r}') 'example.email' >>> q.expand('%{l}') 'strong-bad' >>> q.expand('%{l-}') 'strong.bad' >>> q.expand('%{lr}') 'strong-bad' >>> q.expand('%{lr-}') 'bad.strong' >>> q.expand('%{l1r-}') 'strong' >>> q.expand('%{ir}.%{v}._spf.%{d2}') '3.2.0.192.in-addr._spf.example.com' >>> q.expand('%{lr-}.lp._spf.%{d2}') 'bad.strong.lp._spf.example.com' >>> q.expand('%{lr-}.lp.%{ir}.%{v}._spf.%{d2}') 'bad.strong.lp.3.2.0.192.in-addr._spf.example.com' >>> q.expand('%{ir}.%{v}.%{l1r-}.lp._spf.%{d2}') '3.2.0.192.in-addr.strong.lp._spf.example.com' >>> q.expand('%{p2}.trusted-domains.example.net') 'example.org.trusted-domains.example.net' >>> q.expand('%{p2}.trusted-domains.example.net') 'example.org.trusted-domains.example.net' """ end = 0 result = '' for i in RE_CHAR.finditer(str): result += str[end:i.start()] macro = str[i.start():i.end()] if macro == '%%': result += '%' elif macro == '%_': result += ' ' elif macro == '%-': result += '%20' else: letter = macro[2].lower() if letter == 'p': self.getp() expansion = getattr(self, letter, '') if expansion: result += expand_one(expansion, macro[3:-1], JOINERS.get(letter)) end = i.end() return result + str[end:] def dns_spf(self, domain): """Get the SPF record recorded in DNS for a specific domain name. Returns None if not found, or if more than one record is found. """ a = [t for t in self.dns_txt(domain) if t.startswith('v=spf1')] if not a: if DELEGATE: a = [t for t in self.dns_txt(domain+'._spf.'+DELEGATE) if t.startswith('v=spf1') ] if not a: # No SPF record: convert and return CID if present p = CIDParser(q=self) return p.spf_txt(domain) if len(a) == 1: return a[0] else: return None def dns_txt(self, domainname): "Get a list of TXT records for a domain name." if domainname: return [t for a in self.dns(domainname, 'TXT') for t in a] return [] def dns_mx(self, domainname): """Get a list of IP addresses for all MX exchanges for a domain name. """ return [a for mx in self.dns(domainname, 'MX') \ for a in self.dns_a(mx[1])] def dns_a(self, domainname): """Get a list of IP addresses for a domainname.""" return self.dns(domainname, 'A') def dns_aaaa(self, domainname): """Get a list of IPv6 addresses for a domainname.""" return self.dns(domainname, 'AAAA') def validated_ptrs(self, i): """Figure out the validated PTR domain names for a given IP address. """ return [p for p in self.dns_ptr(i) if i in self.dns_a(p)] def dns_ptr(self, i): """Get a list of domain names for an IP address.""" return self.dns(reverse_dots(i) + ".in-addr.arpa", 'PTR') def dns(self, name, qtype): """DNS query. If the result is in cache, return that. Otherwise pull the result from DNS, and cache ALL answers, so additional info is available for further queries later. CNAMEs are followed. If there is no data, [] is returned. pre: qtype in ['A', 'AAAA', 'MX', 'PTR', 'TXT', 'SPF'] post: isinstance(__return__, types.ListType) """ result = self.cache.get( (name, qtype) ) cname = None if not result: req = DNS.DnsRequest(name, qtype=qtype) resp = req.req() for a in resp.answers: # key k: ('wayforward.net', 'A'), value v k, v = (a['name'], a['typename']), a['data'] if k == (name, 'CNAME'): cname = v self.cache.setdefault(k, []).append(v) result = self.cache.get( (name, qtype), []) if not result and cname: result = self.dns(cname, qtype) return result def get_header(self,res,receiver): if res in ('pass','fail'): return '%s (%s: %s) client-ip=%s; envelope-from=%s; helo=%s;' % ( res,receiver,self.get_header_comment(res),self.i, self.l + '@' + self.o, self.h) if res == 'unknown': return '%s (%s: %s)' % (' '.join([res] + self.mech), receiver,self.get_header_comment(res)) return '%s (%s: %s)' % (res,receiver,self.get_header_comment(res)) def get_header_comment(self,res): """Return comment for Received-SPF header. """ sender = self.o if res == 'pass': if self.i.startswith('127.'): return "localhost is always allowed." else: return \ "domain of %s designates %s as permitted sender" \ % (sender,self.i) elif res == 'softfail': return \ "transitioning domain of %s does not designate %s as permitted sender" \ % (sender,self.i) elif res == 'neutral': return \ "%s is neither permitted nor denied by domain of %s" \ % (self.i,sender) elif res == 'none': return \ "%s is neither permitted nor denied by domain of %s" \ % (self.i,sender) #"%s does not designate permitted sender hosts" % sender elif res == 'unknown': return \ "error in processing during lookup of domain of %s: %s" \ % (sender, self.prob) elif res == 'error': return \ "error in processing during lookup of %s" % sender elif res == 'fail': return \ "domain of %s does not designate %s as permitted sender" \ % (sender,self.i) raise ValueError("invalid SPF result for header comment: "+res) def split_email(s, h): """Given a sender email s and a HELO domain h, create a valid tuple (l, d) local-part and domain-part. Examples: >>> split_email('', 'wayforward.net') ('postmaster', 'wayforward.net') >>> split_email('foo.com', 'wayforward.net') ('postmaster', 'foo.com') >>> split_email('terry@wayforward.net', 'optsw.com') ('terry', 'wayforward.net') """ if not s: return 'postmaster', h else: parts = s.split('@', 1) if len(parts) == 2: return tuple(parts) else: return 'postmaster', s def parse_mechanism(str, d): """Breaks A, MX, IP4, and PTR mechanisms into a (name, domain, cidr) tuple. The domain portion defaults to d if not present, the cidr defaults to 32 if not present. Examples: >>> parse_mechanism('a', 'foo.com') ('a', 'foo.com', 32) >>> parse_mechanism('a:bar.com', 'foo.com') ('a', 'bar.com', 32) >>> parse_mechanism('a/24', 'foo.com') ('a', 'foo.com', 24) >>> parse_mechanism('a:bar.com/16', 'foo.com') ('a', 'bar.com', 16) """ a = str.split('/') if len(a) == 2: a, port = a[0], int(a[1]) else: a, port = str, 32 b = a.split(':') if len(b) == 2: return b[0], b[1], port else: return a, d, port def reverse_dots(name): """Reverse dotted IP addresses or domain names. Example: >>> reverse_dots('192.168.0.145') '145.0.168.192' >>> reverse_dots('email.example.com') 'com.example.email' """ a = name.split('.') a.reverse() return '.'.join(a) def domainmatch(ptrs, domainsuffix): """grep for a given domain suffix against a list of validated PTR domain names. Examples: >>> domainmatch(['FOO.COM'], 'foo.com') 1 >>> domainmatch(['moo.foo.com'], 'FOO.COM') 1 >>> domainmatch(['moo.bar.com'], 'foo.com') 0 """ domainsuffix = domainsuffix.lower() for ptr in ptrs: ptr = ptr.lower() if ptr == domainsuffix or ptr.endswith('.' + domainsuffix): return True return False def cidrmatch(i, ipaddrs, cidr_length = 32): """Match an IP address against a list of other IP addresses. Examples: >>> cidrmatch('192.168.0.45', ['192.168.0.44', '192.168.0.45']) 1 >>> cidrmatch('192.168.0.43', ['192.168.0.44', '192.168.0.45']) 0 >>> cidrmatch('192.168.0.43', ['192.168.0.44', '192.168.0.45'], 24) 1 """ c = cidr(i, cidr_length) for ip in ipaddrs: if cidr(ip, cidr_length) == c: return True return False def cidr(i, n): """Convert an IP address string with a CIDR mask into a 32-bit integer. i must be a string of numbers 0..255 separated by dots '.':: pre: forall([0 <= int(p) < 256 for p in i.split('.')]) n is a number of bits to mask:: pre: 0 <= n <= 32 Examples: >>> bin2addr(cidr('192.168.5.45', 32)) '192.168.5.45' >>> bin2addr(cidr('192.168.5.45', 24)) '192.168.5.0' >>> bin2addr(cidr('192.168.0.45', 8)) '192.0.0.0' """ return ~(MASK >> n) & MASK & addr2bin(i) def addr2bin(str): """Convert a string IPv4 address into an unsigned integer. Examples:: >>> addr2bin('127.0.0.1') 2130706433L >>> addr2bin('127.0.0.1') == socket.INADDR_LOOPBACK 1 >>> addr2bin('255.255.255.254') 4294967294L >>> addr2bin('192.168.0.1') 3232235521L Unlike DNS.addr2bin, the n, n.n, and n.n.n forms for IP addresses are handled as well:: >>> addr2bin('10.65536') 167837696L >>> 10 * (2 ** 24) + 65536 167837696 >>> addr2bin('10.93.512') 173867520L >>> 10 * (2 ** 24) + 93 * (2 ** 16) + 512 173867520 """ return struct.unpack("!L", socket.inet_aton(str))[0] def bin2addr(addr): """Convert a numeric IPv4 address into string n.n.n.n form. Examples:: >>> bin2addr(socket.INADDR_LOOPBACK) '127.0.0.1' >>> bin2addr(socket.INADDR_ANY) '0.0.0.0' >>> bin2addr(socket.INADDR_NONE) '255.255.255.255' """ return socket.inet_ntoa(struct.pack("!L", addr)) def expand_one(expansion, str, joiner): if not str: return expansion len, reverse, delimiters = RE_ARGS.split(str)[1:4] if not delimiters: delimiters = '.' expansion = split(expansion, delimiters, joiner) if reverse: expansion.reverse() if len: expansion = expansion[-int(len)*2+1:] return ''.join(expansion) def split(str, delimiters, joiner=None): """Split a string into pieces by a set of delimiter characters. The resulting list is delimited by joiner, or the original delimiter if joiner is not specified. Examples: >>> split('192.168.0.45', '.') ['192', '.', '168', '.', '0', '.', '45'] >>> split('terry@wayforward.net', '@.') ['terry', '@', 'wayforward', '.', 'net'] >>> split('terry@wayforward.net', '@.', '.') ['terry', '.', 'wayforward', '.', 'net'] """ result, element = [], '' for c in str: if c in delimiters: result.append(element) element = '' if joiner: result.append(joiner) else: result.append(c) else: element += c result.append(element) return result def _test(): import doctest, spf return doctest.testmod(spf) DNS.DiscoverNameServers() # Fails on Mac OS X? Add domain to /etc/resolv.conf if __name__ == '__main__': import sys if len(sys.argv) == 1: print USAGE _test() elif len(sys.argv) == 2: q = query(i='127.0.0.1', s='localhost', h='unknown') print q.dns_spf(sys.argv[1]) elif len(sys.argv) == 4: print check(i=sys.argv[1], s=sys.argv[2], h=sys.argv[3]) elif len(sys.argv) == 5: i, s, h = sys.argv[2:] q = query(i=i, s=s, h=h) print q.check(sys.argv[1]) else: print USAGE