Lib/email/Generator.py

# Copyright (C) 2001 Python Software Foundation
# Author: barry@zope.com (Barry Warsaw)

"""Classes to generate plain text from a message object tree.
"""

import time
import re
import random

from types import ListType, StringType
from cStringIO import StringIO

EMPTYSTRING = ''
SEMISPACE = '; '
BAR = '|'
UNDERSCORE = '_'
NL = '\n'
NLTAB = '\n\t'
SEMINLTAB = ';\n\t'
SPACE8 = ' ' * 8

fcre = re.compile(r'^From ', re.MULTILINE)



class Generator:
    """Generates output from a Message object tree.

    This basic generator writes the message to the given file object as plain
    text.
    """
    #
    # Public interface
    #

    def __init__(self, outfp, mangle_from_=1, maxheaderlen=78):
        """Create the generator for message flattening.

        outfp is the output file-like object for writing the message to.  It
        must have a write() method.

        Optional mangle_from_ is a flag that, when true, escapes From_ lines
        in the body of the message by putting a `>' in front of them.

        Optional maxheaderlen specifies the longest length for a non-continued
        header.  When a header line is longer (in characters, with tabs
        expanded to 8 spaces), than maxheaderlen, the header will be broken on
        semicolons and continued as per RFC 2822.  If no semicolon is found,
        then the header is left alone.  Set to zero to disable wrapping
        headers.  Default is 78, as recommended (but not required by RFC
        2822.
        """
        self._fp = outfp
        self._mangle_from_ = mangle_from_
        self.__first = 1
        self.__maxheaderlen = maxheaderlen

    def write(self, s):
        # Just delegate to the file object
        self._fp.write(s)

    def __call__(self, msg, unixfrom=0):
        """Print the message object tree rooted at msg to the output file
        specified when the Generator instance was created.

        unixfrom is a flag that forces the printing of a Unix From_ delimiter
        before the first object in the message tree.  If the original message
        has no From_ delimiter, a `standard' one is crafted.  By default, this
        is 0 to inhibit the printing of any From_ delimiter.

        Note that for subobjects, no From_ line is printed.
        """
        if unixfrom:
            ufrom = msg.get_unixfrom()
            if not ufrom:
                ufrom = 'From nobody ' + time.ctime(time.time())
            print >> self._fp, ufrom
        self._write(msg)

    #
    # Protected interface - undocumented ;/
    #

    def _write(self, msg):
        # We can't write the headers yet because of the following scenario:
        # say a multipart message includes the boundary string somewhere in
        # its body.  We'd have to calculate the new boundary /before/ we write
        # the headers so that we can write the correct Content-Type:
        # parameter.
        #
        # The way we do this, so as to make the _handle_*() methods simpler,
        # is to cache any subpart writes into a StringIO.  The we write the
        # headers and the StringIO contents.  That way, subpart handlers can
        # Do The Right Thing, and can still modify the Content-Type: header if
        # necessary.
        oldfp = self._fp
        try:
            self._fp = sfp = StringIO()
            self._dispatch(msg)
        finally:
            self._fp = oldfp
        # Write the headers.  First we see if the message object wants to
        # handle that itself.  If not, we'll do it generically.
        meth = getattr(msg, '_write_headers', None)
        if meth is None:
            self._write_headers(msg)
        else:
            meth(self)
        self._fp.write(sfp.getvalue())

    def _dispatch(self, msg):
        # Get the Content-Type: for the message, then try to dispatch to
        # self._handle_maintype_subtype().  If there's no handler for the full
        # MIME type, then dispatch to self._handle_maintype().  If that's
        # missing too, then dispatch to self._writeBody().
        ctype = msg.get_type()
        if ctype is None:
            # No Content-Type: header so try the default handler
            self._writeBody(msg)
        else:
            # We do have a Content-Type: header.
            specific = UNDERSCORE.join(ctype.split('/')).replace('-', '_')
            meth = getattr(self, '_handle_' + specific, None)
            if meth is None:
                generic = msg.get_main_type().replace('-', '_')
                meth = getattr(self, '_handle_' + generic, None)
                if meth is None:
                    meth = self._writeBody
            meth(msg)

    #
    # Default handlers
    #

    def _write_headers(self, msg):
        for h, v in msg.items():
            # We only write the MIME-Version: header for the outermost
            # container message.  Unfortunately, we can't use same technique
            # as for the Unix-From above because we don't know when
            # MIME-Version: will occur.
            if h.lower() == 'mime-version' and not self.__first:
                continue
            # RFC 2822 says that lines SHOULD be no more than maxheaderlen
            # characters wide, so we're well within our rights to split long
            # headers.
            text = '%s: %s' % (h, v)
            if self.__maxheaderlen > 0 and len(text) > self.__maxheaderlen:
                text = self._split_header(text)
            print >> self._fp, text
        # A blank line always separates headers from body
        print >> self._fp

    def _split_header(self, text):
        maxheaderlen = self.__maxheaderlen
        # Find out whether any lines in the header are really longer than
        # maxheaderlen characters wide.  There could be continuation lines
        # that actually shorten it.  Also, replace hard tabs with 8 spaces.
        lines = [s.replace('\t', SPACE8) for s in text.split('\n')]
        for line in lines:
            if len(line) > maxheaderlen:
                break
        else:
            # No line was actually longer than maxheaderlen characters, so
            # just return the original unchanged.
            return text
        rtn = []
        for line in text.split('\n'):
            # Short lines can remain unchanged
            if len(line.replace('\t', SPACE8)) <= maxheaderlen:
                rtn.append(line)
                SEMINLTAB.join(rtn)
            else:
                oldlen = len(text)
                # Try to break the line on semicolons, but if that doesn't
                # work, try to split on folding whitespace.
                while len(text) > maxheaderlen:
                    i = text.rfind(';', 0, maxheaderlen)
                    if i < 0:
                        break
                    rtn.append(text[:i])
                    text = text[i+1:].lstrip()
                if len(text) <> oldlen:
                    # Splitting on semis worked
                    rtn.append(text)
                    return SEMINLTAB.join(rtn)
                # Splitting on semis didn't help, so try to split on
                # whitespace.
                parts = re.split(r'(\s+)', text)
                # Watch out though for "Header: longnonsplittableline"
                if parts[0].endswith(':') and len(parts) == 3:
                    return text
                first = parts.pop(0)
                sublines = [first]
                acc = len(first)
                while parts:
                    len0 = len(parts[0])
                    len1 = len(parts[1])
                    if acc + len0 + len1 < maxheaderlen:
                        sublines.append(parts.pop(0))
                        sublines.append(parts.pop(0))
                        acc += len0 + len1
                    else:
                        # Split it here, but don't forget to ignore the
                        # next whitespace-only part
                        rtn.append(EMPTYSTRING.join(sublines))
                        del parts[0]
                        first = parts.pop(0)
                        sublines = [first]
                        acc = len(first)
                rtn.append(EMPTYSTRING.join(sublines))
                return NLTAB.join(rtn)

    #
    # Handlers for writing types and subtypes
    #

    def _handle_text(self, msg):
        payload = msg.get_payload()
        if payload is None:
            return
        if not isinstance(payload, StringType):
            raise TypeError, 'string payload expected: %s' % type(payload)
        if self._mangle_from_:
            payload = fcre.sub('>From ', payload)
        self._fp.write(payload)

    # Default body handler
    _writeBody = _handle_text

    def _handle_multipart(self, msg, isdigest=0):
        # The trick here is to write out each part separately, merge them all
        # together, and then make sure that the boundary we've chosen isn't
        # present in the payload.
        msgtexts = []
        for part in msg.get_payload():
            s = StringIO()
            g = self.__class__(s, self._mangle_from_, self.__maxheaderlen)
            g(part, unixfrom=0)
            msgtexts.append(s.getvalue())
        # Now make sure the boundary we've selected doesn't appear in any of
        # the message texts.
        alltext = NL.join(msgtexts)
        # BAW: What about boundaries that are wrapped in double-quotes?
        boundary = msg.get_boundary(failobj=_make_boundary(alltext))
        # If we had to calculate a new boundary because the body text
        # contained that string, set the new boundary.  We don't do it
        # unconditionally because, while set_boundary() preserves order, it
        # doesn't preserve newlines/continuations in headers.  This is no big
        # deal in practice, but turns out to be inconvenient for the unittest
        # suite.
        if msg.get_boundary() <> boundary:
            msg.set_boundary(boundary)
        # Write out any preamble
        if msg.preamble is not None:
            self._fp.write(msg.preamble)
        # First boundary is a bit different; it doesn't have a leading extra
        # newline.
        print >> self._fp, '--' + boundary
        if isdigest:
            print >> self._fp
        # Join and write the individual parts
        joiner = '\n--' + boundary + '\n'
        if isdigest:
            # multipart/digest types effectively add an extra newline between
            # the boundary and the body part.
            joiner += '\n'
        self._fp.write(joiner.join(msgtexts))
        print >> self._fp, '\n--' + boundary + '--',
        # Write out any epilogue
        if msg.epilogue is not None:
            if not msg.epilogue.startswith('\n'):
                print >> self._fp
            self._fp.write(msg.epilogue)

    def _handle_multipart_digest(self, msg):
        self._handle_multipart(msg, isdigest=1)

    def _handle_message_delivery_status(self, msg):
        # We can't just write the headers directly to self's file object
        # because this will leave an extra newline between the last header
        # block and the boundary.  Sigh.
        blocks = []
        for part in msg.get_payload():
            s = StringIO()
            g = self.__class__(s, self._mangle_from_, self.__maxheaderlen)
            g(part, unixfrom=0)
            text = s.getvalue()
            lines = text.split('\n')
            # Strip off the unnecessary trailing empty line
            if lines and lines[-1] == '':
                blocks.append(NL.join(lines[:-1]))
            else:
                blocks.append(text)
        # Now join all the blocks with an empty line.  This has the lovely
        # effect of separating each block with an empty line, but not adding
        # an extra one after the last one.
        self._fp.write(NL.join(blocks))

    def _handle_message(self, msg):
        s = StringIO()
        g = self.__class__(s, self._mangle_from_, self.__maxheaderlen)
        # A message/rfc822 should contain a scalar payload which is another
        # Message object.  Extract that object, stringify it, and write that
        # out.
        g(msg.get_payload(), unixfrom=0)
        self._fp.write(s.getvalue())



class DecodedGenerator(Generator):
    """Generator a text representation of a message.

    Like the Generator base class, except that non-text parts are substituted
    with a format string representing the part.
    """
    def __init__(self, outfp, mangle_from_=1, maxheaderlen=78, fmt=None):
        """Like Generator.__init__() except that an additional optional
        argument is allowed.

        Walks through all subparts of a message.  If the subpart is of main
        type `text', then it prints the decoded payload of the subpart.

        Otherwise, fmt is a format string that is used instead of the message
        payload.  fmt is expanded with the following keywords (in
        %(keyword)s format):

        type       : Full MIME type of the non-text part
        maintype   : Main MIME type of the non-text part
        subtype    : Sub-MIME type of the non-text part
        filename   : Filename of the non-text part
        description: Description associated with the non-text part
        encoding   : Content transfer encoding of the non-text part

        The default value for fmt is None, meaning

        [Non-text (%(type)s) part of message omitted, filename %(filename)s]
        """
        Generator.__init__(self, outfp, mangle_from_, maxheaderlen)
        if fmt is None:
            fmt = ('[Non-text (%(type)s) part of message omitted, '
                   'filename %(filename)s]')
        self._fmt = fmt

    def _dispatch(self, msg):
        for part in msg.walk():
            maintype = part.get_main_type('text')
            if maintype == 'text':
                print >> self, part.get_payload(decode=1)
            elif maintype == 'multipart':
                # Just skip this
                pass
            else:
                print >> self, self._fmt % {
                    'type'       : part.get_type('[no MIME type]'),
                    'maintype'   : part.get_main_type('[no main MIME type]'),
                    'subtype'    : part.get_subtype('[no sub-MIME type]'),
                    'filename'   : part.get_filename('[no filename]'),
                    'description': part.get('Content-Description',
                                            '[no description]'),
                    'encoding'   : part.get('Content-Transfer-Encoding',
                                            '[no encoding]'),
                    }



# Helper
def _make_boundary(self, text=None):
    # Craft a random boundary.  If text is given, ensure that the chosen
    # boundary doesn't appear in the text.
    boundary = ('=' * 15) + repr(random.random()).split('.')[1] + '=='
    if text is None:
        return boundary
    b = boundary
    counter = 0
    while 1:
        cre = re.compile('^--' + re.escape(b) + '(--)?$', re.MULTILINE)
        if not cre.search(text):
            break
        b = boundary + '.' + str(counter)
        counter += 1
    return b