Lib/rfc822.py

"""RFC 2822 message manipulation.

Note: This is only a very rough sketch of a full RFC-822 parser; in particular
the tokenizing of addresses does not adhere to all the quoting rules.

Note: RFC 2822 is a long awaited update to RFC 822.  This module should
conform to RFC 2822, and is thus mis-named (it's not worth renaming it).  Some
effort at RFC 2822 updates have been made, but a thorough audit has not been
performed.  Consider any RFC 2822 non-conformance to be a bug.

    RFC 2822: http://www.faqs.org/rfcs/rfc2822.html
    RFC  822: http://www.faqs.org/rfcs/rfc822.html (obsolete)

Directions for use:

To create a Message object: first open a file, e.g.:

  fp = open(file, 'r')

You can use any other legal way of getting an open file object, e.g. use
sys.stdin or call os.popen().  Then pass the open file object to the Message()
constructor:

  m = Message(fp)

This class can work with any input object that supports a readline method.  If
the input object has seek and tell capability, the rewindbody method will
work; also illegal lines will be pushed back onto the input stream.  If the
input object lacks seek but has an `unread' method that can push back a line
of input, Message will use that to push back illegal lines.  Thus this class
can be used to parse messages coming from a buffered stream.

The optional `seekable' argument is provided as a workaround for certain stdio
libraries in which tell() discards buffered data before discovering that the
lseek() system call doesn't work.  For maximum portability, you should set the
seekable argument to zero to prevent that initial \code{tell} when passing in
an unseekable object such as a a file object created from a socket object.  If
it is 1 on entry -- which it is by default -- the tell() method of the open
file object is called once; if this raises an exception, seekable is reset to
0.  For other nonzero values of seekable, this test is not made.

To get the text of a particular header there are several methods:

  str = m.getheader(name)
  str = m.getrawheader(name)

where name is the name of the header, e.g. 'Subject'.  The difference is that
getheader() strips the leading and trailing whitespace, while getrawheader()
doesn't.  Both functions retain embedded whitespace (including newlines)
exactly as they are specified in the header, and leave the case of the text
unchanged.

For addresses and address lists there are functions

  realname, mailaddress = m.getaddr(name)
  list = m.getaddrlist(name)

where the latter returns a list of (realname, mailaddr) tuples.

There is also a method

  time = m.getdate(name)

which parses a Date-like field and returns a time-compatible tuple,
i.e. a tuple such as returned by time.localtime() or accepted by
time.mktime().

See the class definition for lower level access methods.

There are also some utility functions here.
"""
# Cleanup and extensions by Eric S. Raymond <esr@thyrsus.com>

import time

__all__ = ["Message","AddressList","parsedate","parsedate_tz","mktime_tz"]

_blanklines = ('\r\n', '\n')            # Optimization for islast()


class Message:
    """Represents a single RFC 2822-compliant message."""

    def __init__(self, fp, seekable = 1):
        """Initialize the class instance and read the headers."""
        if seekable == 1:
            # Exercise tell() to make sure it works
            # (and then assume seek() works, too)
            try:
                fp.tell()
            except (AttributeError, IOError):
                seekable = 0
            else:
                seekable = 1
        self.fp = fp
        self.seekable = seekable
        self.startofheaders = None
        self.startofbody = None
        #
        if self.seekable:
            try:
                self.startofheaders = self.fp.tell()
            except IOError:
                self.seekable = 0
        #
        self.readheaders()
        #
        if self.seekable:
            try:
                self.startofbody = self.fp.tell()
            except IOError:
                self.seekable = 0

    def rewindbody(self):
        """Rewind the file to the start of the body (if seekable)."""
        if not self.seekable:
            raise IOError, "unseekable file"
        self.fp.seek(self.startofbody)

    def readheaders(self):
        """Read header lines.

        Read header lines up to the entirely blank line that terminates them.
        The (normally blank) line that ends the headers is skipped, but not
        included in the returned list.  If a non-header line ends the headers,
        (which is an error), an attempt is made to backspace over it; it is
        never included in the returned list.

        The variable self.status is set to the empty string if all went well,
        otherwise it is an error message.  The variable self.headers is a
        completely uninterpreted list of lines contained in the header (so
        printing them will reproduce the header exactly as it appears in the
        file).
        """
        self.dict = {}
        self.unixfrom = ''
        self.headers = list = []
        self.status = ''
        headerseen = ""
        firstline = 1
        startofline = unread = tell = None
        if hasattr(self.fp, 'unread'):
            unread = self.fp.unread
        elif self.seekable:
            tell = self.fp.tell
        while 1:
            if tell:
                try:
                    startofline = tell()
                except IOError:
                    startofline = tell = None
                    self.seekable = 0
            line = self.fp.readline()
            if not line:
                self.status = 'EOF in headers'
                break
            # Skip unix From name time lines
            if firstline and line.startswith('From '):
                self.unixfrom = self.unixfrom + line
                continue
            firstline = 0
            if headerseen and line[0] in ' \t':
                # It's a continuation line.
                list.append(line)
                x = (self.dict[headerseen] + "\n " + line.strip())
                self.dict[headerseen] = x.strip()
                continue
            elif self.iscomment(line):
                # It's a comment.  Ignore it.
                continue
            elif self.islast(line):
                # Note! No pushback here!  The delimiter line gets eaten.
                break
            headerseen = self.isheader(line)
            if headerseen:
                # It's a legal header line, save it.
                list.append(line)
                self.dict[headerseen] = line[len(headerseen)+1:].strip()
                continue
            else:
                # It's not a header line; throw it back and stop here.
                if not self.dict:
                    self.status = 'No headers'
                else:
                    self.status = 'Non-header line where header expected'
                # Try to undo the read.
                if unread:
                    unread(line)
                elif tell:
                    self.fp.seek(startofline)
                else:
                    self.status = self.status + '; bad seek'
                break

    def isheader(self, line):
        """Determine whether a given line is a legal header.

        This method should return the header name, suitably canonicalized.
        You may override this method in order to use Message parsing on tagged
        data in RFC 2822-like formats with special header formats.
        """
        i = line.find(':')
        if i > 0:
            return line[:i].lower()
        else:
            return None

    def islast(self, line):
        """Determine whether a line is a legal end of RFC 2822 headers.

        You may override this method if your application wants to bend the
        rules, e.g. to strip trailing whitespace, or to recognize MH template
        separators ('--------').  For convenience (e.g. for code reading from
        sockets) a line consisting of \r\n also matches.
        """
        return line in _blanklines

    def iscomment(self, line):
        """Determine whether a line should be skipped entirely.

        You may override this method in order to use Message parsing on tagged
        data in RFC 2822-like formats that support embedded comments or
        free-text data.
        """
        return None

    def getallmatchingheaders(self, name):
        """Find all header lines matching a given header name.

        Look through the list of headers and find all lines matching a given
        header name (and their continuation lines).  A list of the lines is
        returned, without interpretation.  If the header does not occur, an
        empty list is returned.  If the header occurs multiple times, all
        occurrences are returned.  Case is not important in the header name.
        """
        name = name.lower() + ':'
        n = len(name)
        list = []
        hit = 0
        for line in self.headers:
            if line[:n].lower() == name:
                hit = 1
            elif not line[:1].isspace():
                hit = 0
            if hit:
                list.append(line)
        return list

    def getfirstmatchingheader(self, name):
        """Get the first header line matching name.

        This is similar to getallmatchingheaders, but it returns only the
        first matching header (and its continuation lines).
        """
        name = name.lower() + ':'
        n = len(name)
        list = []
        hit = 0
        for line in self.headers:
            if hit:
                if not line[:1].isspace():
                    break
            elif line[:n].lower() == name:
                hit = 1
            if hit:
                list.append(line)
        return list

    def getrawheader(self, name):
        """A higher-level interface to getfirstmatchingheader().

        Return a string containing the literal text of the header but with the
        keyword stripped.  All leading, trailing and embedded whitespace is
        kept in the string, however.  Return None if the header does not
        occur.
        """

        list = self.getfirstmatchingheader(name)
        if not list:
            return None
        list[0] = list[0][len(name) + 1:]
        return ''.join(list)

    def getheader(self, name, default=None):
        """Get the header value for a name.

        This is the normal interface: it returns a stripped version of the
        header value for a given header name, or None if it doesn't exist.
        This uses the dictionary version which finds the *last* such header.
        """
        try:
            return self.dict[name.lower()]
        except KeyError:
            return default
    get = getheader

    def getheaders(self, name):
        """Get all values for a header.

        This returns a list of values for headers given more than once; each
        value in the result list is stripped in the same way as the result of
        getheader().  If the header is not given, return an empty list.
        """
        result = []
        current = ''
        have_header = 0
        for s in self.getallmatchingheaders(name):
            if s[0].isspace():
                if current:
                    current = "%s\n %s" % (current, s.strip())
                else:
                    current = s.strip()
            else:
                if have_header:
                    result.append(current)
                current = s[s.find(":") + 1:].strip()
                have_header = 1
        if have_header:
            result.append(current)
        return result

    def getaddr(self, name):
        """Get a single address from a header, as a tuple.

        An example return value:
        ('Guido van Rossum', 'guido@cwi.nl')
        """
        # New, by Ben Escoto
        alist = self.getaddrlist(name)
        if alist:
            return alist[0]
        else:
            return (None, None)

    def getaddrlist(self, name):
        """Get a list of addresses from a header.

        Retrieves a list of addresses from a header, where each address is a
        tuple as returned by getaddr().  Scans all named headers, so it works
        properly with multiple To: or Cc: headers for example.
        """
        raw = []
        for h in self.getallmatchingheaders(name):
            if h[0] in ' \t':
                raw.append(h)
            else:
                if raw:
                    raw.append(', ')
                i = h.find(':')
                if i > 0:
                    addr = h[i+1:]
                raw.append(addr)
        alladdrs = ''.join(raw)
        a = AddrlistClass(alladdrs)
        return a.getaddrlist()

    def getdate(self, name):
        """Retrieve a date field from a header.

        Retrieves a date field from the named header, returning a tuple
        compatible with time.mktime().
        """
        try:
            data = self[name]
        except KeyError:
            return None
        return parsedate(data)

    def getdate_tz(self, name):
        """Retrieve a date field from a header as a 10-tuple.

        The first 9 elements make up a tuple compatible with time.mktime(),
        and the 10th is the offset of the poster's time zone from GMT/UTC.
        """
        try:
            data = self[name]
        except KeyError:
            return None
        return parsedate_tz(data)


    # Access as a dictionary (only finds *last* header of each type):

    def __len__(self):
        """Get the number of headers in a message."""
        return len(self.dict)

    def __getitem__(self, name):
        """Get a specific header, as from a dictionary."""
        return self.dict[name.lower()]

    def __setitem__(self, name, value):
        """Set the value of a header.

        Note: This is not a perfect inversion of __getitem__, because any
        changed headers get stuck at the end of the raw-headers list rather
        than where the altered header was.
        """
        del self[name] # Won't fail if it doesn't exist
        self.dict[name.lower()] = value
        text = name + ": " + value
        lines = text.split("\n")
        for line in lines:
            self.headers.append(line + "\n")

    def __delitem__(self, name):
        """Delete all occurrences of a specific header, if it is present."""
        name = name.lower()
        if not self.dict.has_key(name):
            return
        del self.dict[name]
        name = name + ':'
        n = len(name)
        list = []
        hit = 0
        for i in range(len(self.headers)):
            line = self.headers[i]
            if line[:n].lower() == name:
                hit = 1
            elif not line[:1].isspace():
                hit = 0
            if hit:
                list.append(i)
        list.reverse()
        for i in list:
            del self.headers[i]

    def get(self, name, default=""):
        name = name.lower()
        if self.dict.has_key(name):
            return self.dict[name]
        else:
            return default

    def setdefault(self, name, default=""):
        lowername = name.lower()
        if self.dict.has_key(lowername):
            return self.dict[lowername]
        else:
            text = name + ": " + default
            lines = text.split("\n")
            for line in lines:
                self.headers.append(line + "\n")
            self.dict[lowername] = default
            return default

    def has_key(self, name):
        """Determine whether a message contains the named header."""
        return self.dict.has_key(name.lower())

    def keys(self):
        """Get all of a message's header field names."""
        return self.dict.keys()

    def values(self):
        """Get all of a message's header field values."""
        return self.dict.values()

    def items(self):
        """Get all of a message's headers.

        Returns a list of name, value tuples.
        """
        return self.dict.items()

    def __str__(self):
        str = ''
        for hdr in self.headers:
            str = str + hdr
        return str


# Utility functions
# -----------------

# XXX Should fix unquote() and quote() to be really conformant.
# XXX The inverses of the parse functions may also be useful.


def unquote(str):
    """Remove quotes from a string."""
    if len(str) > 1:
        if str[0] == '"' and str[-1:] == '"':
            return str[1:-1]
        if str[0] == '<' and str[-1:] == '>':
            return str[1:-1]
    return str


def quote(str):
    """Add quotes around a string."""
    return str.replace('\\', '\\\\').replace('"', '\\"')


def parseaddr(address):
    """Parse an address into a (realname, mailaddr) tuple."""
    a = AddrlistClass(address)
    list = a.getaddrlist()
    if not list:
        return (None, None)
    else:
        return list[0]


class AddrlistClass:
    """Address parser class by Ben Escoto.

    To understand what this class does, it helps to have a copy of
    RFC 2822 in front of you.

    http://www.faqs.org/rfcs/rfc2822.html

    Note: this class interface is deprecated and may be removed in the future.
    Use rfc822.AddressList instead.
    """

    def __init__(self, field):
        """Initialize a new instance.

        `field' is an unparsed address header field, containing one or more
        addresses.
        """
        self.specials = '()<>@,:;.\"[]'
        self.pos = 0
        self.LWS = ' \t'
        self.CR = '\r\n'
        self.atomends = self.specials + self.LWS + self.CR
        # Note that RFC 2822 now specifies `.' as obs-phrase, meaning that it
        # is obsolete syntax.  RFC 2822 requires that we recognize obsolete
        # syntax, so allow dots in phrases.
        self.phraseends = self.atomends.replace('.', '')
        self.field = field
        self.commentlist = []

    def gotonext(self):
        """Parse up to the start of the next address."""
        while self.pos < len(self.field):
            if self.field[self.pos] in self.LWS + '\n\r':
                self.pos = self.pos + 1
            elif self.field[self.pos] == '(':
                self.commentlist.append(self.getcomment())
            else: break

    def getaddrlist(self):
        """Parse all addresses.

        Returns a list containing all of the addresses.
        """
        ad = self.getaddress()
        if ad:
            return ad + self.getaddrlist()
        else: return []

    def getaddress(self):
        """Parse the next address."""
        self.commentlist = []
        self.gotonext()

        oldpos = self.pos
        oldcl = self.commentlist
        plist = self.getphraselist()

        self.gotonext()
        returnlist = []

        if self.pos >= len(self.field):
            # Bad email address technically, no domain.
            if plist:
                returnlist = [(' '.join(self.commentlist), plist[0])]

        elif self.field[self.pos] in '.@':
            # email address is just an addrspec
            # this isn't very efficient since we start over
            self.pos = oldpos
            self.commentlist = oldcl
            addrspec = self.getaddrspec()
            returnlist = [(' '.join(self.commentlist), addrspec)]

        elif self.field[self.pos] == ':':
            # address is a group
            returnlist = []

            fieldlen = len(self.field)
            self.pos = self.pos + 1
            while self.pos < len(self.field):
                self.gotonext()
                if self.pos < fieldlen and self.field[self.pos] == ';':
                    self.pos = self.pos + 1
                    break
                returnlist = returnlist + self.getaddress()

        elif self.field[self.pos] == '<':
            # Address is a phrase then a route addr
            routeaddr = self.getrouteaddr()

            if self.commentlist:
                returnlist = [(' '.join(plist) + ' (' + \
                         ' '.join(self.commentlist) + ')', routeaddr)]
            else: returnlist = [(' '.join(plist), routeaddr)]

        else:
            if plist:
                returnlist = [(' '.join(self.commentlist), plist[0])]
            elif self.field[self.pos] in self.specials:
                self.pos = self.pos + 1

        self.gotonext()
        if self.pos < len(self.field) and self.field[self.pos] == ',':
            self.pos = self.pos + 1
        return returnlist

    def getrouteaddr(self):
        """Parse a route address (Return-path value).

        This method just skips all the route stuff and returns the addrspec.
        """
        if self.field[self.pos] != '<':
            return

        expectroute = 0
        self.pos = self.pos + 1
        self.gotonext()
        adlist = None
        while self.pos < len(self.field):
            if expectroute:
                self.getdomain()
                expectroute = 0
            elif self.field[self.pos] == '>':
                self.pos = self.pos + 1
                break
            elif self.field[self.pos] == '@':
                self.pos = self.pos + 1
                expectroute = 1
            elif self.field[self.pos] == ':':
                self.pos = self.pos + 1
                expectaddrspec = 1
            else:
                adlist = self.getaddrspec()
                self.pos = self.pos + 1
                break
            self.gotonext()

        return adlist

    def getaddrspec(self):
        """Parse an RFC 2822 addr-spec."""
        aslist = []

        self.gotonext()
        while self.pos < len(self.field):
            if self.field[self.pos] == '.':
                aslist.append('.')
                self.pos = self.pos + 1
            elif self.field[self.pos] == '"':
                aslist.append('"%s"' % self.getquote())
            elif self.field[self.pos] in self.atomends:
                break
            else: aslist.append(self.getatom())
            self.gotonext()

        if self.pos >= len(self.field) or self.field[self.pos] != '@':
            return ''.join(aslist)

        aslist.append('@')
        self.pos = self.pos + 1
        self.gotonext()
        return ''.join(aslist) + self.getdomain()

    def getdomain(self):
        """Get the complete domain name from an address."""
        sdlist = []
        while self.pos < len(self.field):
            if self.field[self.pos] in self.LWS:
                self.pos = self.pos + 1
            elif self.field[self.pos] == '(':
                self.commentlist.append(self.getcomment())
            elif self.field[self.pos] == '[':
                sdlist.append(self.getdomainliteral())
            elif self.field[self.pos] == '.':
                self.pos = self.pos + 1
                sdlist.append('.')
            elif self.field[self.pos] in self.atomends:
                break
            else: sdlist.append(self.getatom())
        return ''.join(sdlist)

    def getdelimited(self, beginchar, endchars, allowcomments = 1):
        """Parse a header fragment delimited by special characters.

        `beginchar' is the start character for the fragment.  If self is not
        looking at an instance of `beginchar' then getdelimited returns the
        empty string.

        `endchars' is a sequence of allowable end-delimiting characters.
        Parsing stops when one of these is encountered.

        If `allowcomments' is non-zero, embedded RFC 2822 comments are allowed
        within the parsed fragment.
        """
        if self.field[self.pos] != beginchar:
            return ''

        slist = ['']
        quote = 0
        self.pos = self.pos + 1
        while self.pos < len(self.field):
            if quote == 1:
                slist.append(self.field[self.pos])
                quote = 0
            elif self.field[self.pos] in endchars:
                self.pos = self.pos + 1
                break
            elif allowcomments and self.field[self.pos] == '(':
                slist.append(self.getcomment())
            elif self.field[self.pos] == '\\':
                quote = 1
            else:
                slist.append(self.field[self.pos])
            self.pos = self.pos + 1

        return ''.join(slist)

    def getquote(self):
        """Get a quote-delimited fragment from self's field."""
        return self.getdelimited('"', '"\r', 0)

    def getcomment(self):
        """Get a parenthesis-delimited fragment from self's field."""
        return self.getdelimited('(', ')\r', 1)

    def getdomainliteral(self):
        """Parse an RFC 2822 domain-literal."""
        return '[%s]' % self.getdelimited('[', ']\r', 0)

    def getatom(self, atomends=None):
        """Parse an RFC 2822 atom.

        Optional atomends specifies a different set of end token delimiters
        (the default is to use self.atomends).  This is used e.g. in
        getphraselist() since phrase endings must not include the `.' (which
        is legal in phrases)."""
        atomlist = ['']
        if atomends is None:
            atomends = self.atomends

        while self.pos < len(self.field):
            if self.field[self.pos] in atomends:
                break
            else: atomlist.append(self.field[self.pos])
            self.pos = self.pos + 1

        return ''.join(atomlist)

    def getphraselist(self):
        """Parse a sequence of RFC 2822 phrases.

        A phrase is a sequence of words, which are in turn either RFC 2822
        atoms or quoted-strings.  Phrases are canonicalized by squeezing all
        runs of continuous whitespace into one space.
        """
        plist = []

        while self.pos < len(self.field):
            if self.field[self.pos] in self.LWS:
                self.pos = self.pos + 1
            elif self.field[self.pos] == '"':
                plist.append(self.getquote())
            elif self.field[self.pos] == '(':
                self.commentlist.append(self.getcomment())
            elif self.field[self.pos] in self.phraseends:
                break
            else:
                plist.append(self.getatom(self.phraseends))

        return plist

class AddressList(AddrlistClass):
    """An AddressList encapsulates a list of parsed RFC 2822 addresses."""
    def __init__(self, field):
        AddrlistClass.__init__(self, field)
        if field:
            self.addresslist = self.getaddrlist()
        else:
            self.addresslist = []

    def __len__(self):
        return len(self.addresslist)

    def __str__(self):
        return ", ".join(map(dump_address_pair, self.addresslist))

    def __add__(self, other):
        # Set union
        newaddr = AddressList(None)
        newaddr.addresslist = self.addresslist[:]
        for x in other.addresslist:
            if not x in self.addresslist:
                newaddr.addresslist.append(x)
        return newaddr

    def __iadd__(self, other):
        # Set union, in-place
        for x in other.addresslist:
            if not x in self.addresslist:
                self.addresslist.append(x)
        return self

    def __sub__(self, other):
        # Set difference
        newaddr = AddressList(None)
        for x in self.addresslist:
            if not x in other.addresslist:
                newaddr.addresslist.append(x)
        return newaddr

    def __isub__(self, other):
        # Set difference, in-place
        for x in other.addresslist:
            if x in self.addresslist:
                self.addresslist.remove(x)
        return self

    def __getitem__(self, index):
        # Make indexing, slices, and 'in' work
        return self.addresslist[index]

def dump_address_pair(pair):
    """Dump a (name, address) pair in a canonicalized form."""
    if pair[0]:
        return '"' + pair[0] + '" <' + pair[1] + '>'
    else:
        return pair[1]

# Parse a date field

_monthnames = ['jan', 'feb', 'mar', 'apr', 'may', 'jun', 'jul',
               'aug', 'sep', 'oct', 'nov', 'dec',
               'january', 'february', 'march', 'april', 'may', 'june', 'july',
               'august', 'september', 'october', 'november', 'december']
_daynames = ['mon', 'tue', 'wed', 'thu', 'fri', 'sat', 'sun']

# The timezone table does not include the military time zones defined
# in RFC822, other than Z.  According to RFC1123, the description in
# RFC822 gets the signs wrong, so we can't rely on any such time
# zones.  RFC1123 recommends that numeric timezone indicators be used
# instead of timezone names.

_timezones = {'UT':0, 'UTC':0, 'GMT':0, 'Z':0,
              'AST': -400, 'ADT': -300,  # Atlantic (used in Canada)
              'EST': -500, 'EDT': -400,  # Eastern
              'CST': -600, 'CDT': -500,  # Central
              'MST': -700, 'MDT': -600,  # Mountain
              'PST': -800, 'PDT': -700   # Pacific
              }


def parsedate_tz(data):
    """Convert a date string to a time tuple.

    Accounts for military timezones.
    """
    data = data.split()
    if data[0][-1] in (',', '.') or data[0].lower() in _daynames:
        # There's a dayname here. Skip it
        del data[0]
    if len(data) == 3: # RFC 850 date, deprecated
        stuff = data[0].split('-')
        if len(stuff) == 3:
            data = stuff + data[1:]
    if len(data) == 4:
        s = data[3]
        i = s.find('+')
        if i > 0:
            data[3:] = [s[:i], s[i+1:]]
        else:
            data.append('') # Dummy tz
    if len(data) < 5:
        return None
    data = data[:5]
    [dd, mm, yy, tm, tz] = data
    mm = mm.lower()
    if not mm in _monthnames:
        dd, mm = mm, dd.lower()
        if not mm in _monthnames:
            return None
    mm = _monthnames.index(mm)+1
    if mm > 12: mm = mm - 12
    if dd[-1] == ',':
        dd = dd[:-1]
    i = yy.find(':')
    if i > 0:
        yy, tm = tm, yy
    if yy[-1] == ',':
        yy = yy[:-1]
    if not yy[0].isdigit():
        yy, tz = tz, yy
    if tm[-1] == ',':
        tm = tm[:-1]
    tm = tm.split(':')
    if len(tm) == 2:
        [thh, tmm] = tm
        tss = '0'
    elif len(tm) == 3:
        [thh, tmm, tss] = tm
    else:
        return None
    try:
        yy = int(yy)
        dd = int(dd)
        thh = int(thh)
        tmm = int(tmm)
        tss = int(tss)
    except ValueError:
        return None
    tzoffset = None
    tz = tz.upper()
    if _timezones.has_key(tz):
        tzoffset = _timezones[tz]
    else:
        try:
            tzoffset = int(tz)
        except ValueError:
            pass
    # Convert a timezone offset into seconds ; -0500 -> -18000
    if tzoffset:
        if tzoffset < 0:
            tzsign = -1
            tzoffset = -tzoffset
        else:
            tzsign = 1
        tzoffset = tzsign * ( (tzoffset/100)*3600 + (tzoffset % 100)*60)
    tuple = (yy, mm, dd, thh, tmm, tss, 0, 0, 0, tzoffset)
    return tuple


def parsedate(data):
    """Convert a time string to a time tuple."""
    t = parsedate_tz(data)
    if type(t) == type( () ):
        return t[:9]
    else: return t


def mktime_tz(data):
    """Turn a 10-tuple as returned by parsedate_tz() into a UTC timestamp."""
    if data[9] is None:
        # No zone info, so localtime is better assumption than GMT
        return time.mktime(data[:8] + (-1,))
    else:
        t = time.mktime(data[:8] + (0,))
        return t - data[9] - time.timezone

def formatdate(timeval=None):
    """Returns time format preferred for Internet standards.

    Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
    """
    if timeval is None:
        timeval = time.time()
    return "%s" % time.strftime('%a, %d %b %Y %H:%M:%S GMT',
                                time.gmtime(timeval))


# When used as script, run a small test program.
# The first command line argument must be a filename containing one
# message in RFC-822 format.

if __name__ == '__main__':
    import sys, os
    file = os.path.join(os.environ['HOME'], 'Mail/inbox/1')
    if sys.argv[1:]: file = sys.argv[1]
    f = open(file, 'r')
    m = Message(f)
    print 'From:', m.getaddr('from')
    print 'To:', m.getaddrlist('to')
    print 'Subject:', m.getheader('subject')
    print 'Date:', m.getheader('date')
    date = m.getdate_tz('date')
    tz = date[-1]
    date = time.localtime(mktime_tz(date))
    if date:
        print 'ParsedDate:', time.asctime(date),
        hhmmss = tz
        hhmm, ss = divmod(hhmmss, 60)
        hh, mm = divmod(hhmm, 60)
        print "%+03d%02d" % (hh, mm),
        if ss: print ".%02d" % ss,
        print
    else:
        print 'ParsedDate:', None
    m.rewindbody()
    n = 0
    while f.readline():
        n = n + 1
    print 'Lines:', n
    print '-'*70
    print 'len =', len(m)
    if m.has_key('Date'): print 'Date =', m['Date']
    if m.has_key('X-Nonsense'): pass
    print 'keys =', m.keys()
    print 'values =', m.values()
    print 'items =', m.items()