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# Copyright (C) 2001-2010 Python Software Foundation
# Author: Barry Warsaw
# Contact:
"""Classes to generate plain text from a message object tree."""
__all__ = ['Generator', 'DecodedGenerator', 'BytesGenerator']
import re
import sys
import time
import random
from copy import deepcopy
from io import StringIO, BytesIO
from email.utils import _has_surrogates
NL = '\n' # XXX: no longer used by the code below.
NLCRE = re.compile(r'\r\n|\r|\n')
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
# Public interface
def __init__(self, outfp, mangle_from_=None, maxheaderlen=None, *,
"""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 (the default if policy
is not set), 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 split as
defined in the Header class. Set maxheaderlen to zero to disable
header wrapping. The default is 78, as recommended (but not required)
by RFC 2822.
The policy keyword specifies a policy object that controls a number of
aspects of the generator's operation. If no policy is specified,
the policy associated with the Message object passed to the
flatten method is used.
if mangle_from_ is None:
mangle_from_ = True if policy is None else policy.mangle_from_
self._fp = outfp
self._mangle_from_ = mangle_from_
self.maxheaderlen = maxheaderlen
self.policy = policy
def write(self, s):
# Just delegate to the file object
def flatten(self, msg, unixfrom=False, linesep=None):
r"""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 False to inhibit the printing of any From_ delimiter.
Note that for subobjects, no From_ line is printed.
linesep specifies the characters used to indicate a new line in
the output. The default value is determined by the policy specified
when the Generator instance was created or, if none was specified,
from the policy associated with the msg.
# We use the _XXX constants for operating on data that comes directly
# from the msg, and _encoded_XXX constants for operating on data that
# has already been converted (to bytes in the BytesGenerator) and
# inserted into a temporary buffer.
policy = msg.policy if self.policy is None else self.policy
if linesep is not None:
policy = policy.clone(linesep=linesep)
if self.maxheaderlen is not None:
policy = policy.clone(max_line_length=self.maxheaderlen)
self._NL = policy.linesep
self._encoded_NL = self._encode(self._NL)
self._EMPTY = ''
self._encoded_EMPTY = self._encode(self._EMPTY)
# Because we use clone (below) when we recursively process message
# subparts, and because clone uses the computed policy (not None),
# submessages will automatically get set to the computed policy when
# they are processed by this code.
old_gen_policy = self.policy
old_msg_policy = msg.policy
self.policy = policy
msg.policy = policy
if unixfrom:
ufrom = msg.get_unixfrom()
if not ufrom:
ufrom = 'From nobody ' + time.ctime(time.time())
self.write(ufrom + self._NL)
self.policy = old_gen_policy
msg.policy = old_msg_policy
def clone(self, fp):
"""Clone this generator with the exact same options."""
return self.__class__(fp,
None, # Use policy setting, which we've adjusted
# Protected interface - undocumented ;/
# Note that we use 'self.write' when what we are writing is coming from
# the source, and self._fp.write when what we are writing is coming from a
# buffer (because the Bytes subclass has already had a chance to transform
# the data in its write method in that case). This is an entirely
# pragmatic split determined by experiment; we could be more general by
# always using write and having the Bytes subclass write method detect when
# it has already transformed the input; but, since this whole thing is a
# hack anyway this seems good enough.
def _new_buffer(self):
# BytesGenerator overrides this to return BytesIO.
return StringIO()
def _encode(self, s):
# BytesGenerator overrides this to encode strings to bytes.
return s
def _write_lines(self, lines):
# We have to transform the line endings.
if not lines:
lines = NLCRE.split(lines)
for line in lines[:-1]:
if lines[-1]:
# XXX logic tells me this else should be needed, but the tests fail
# with it and pass without it. (NLCRE.split ends with a blank element
# if and only if there was a trailing newline.)
# self.write(self._NL)
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 buffer. The we write the
# headers and the buffer contents. That way, subpart handlers can
# Do The Right Thing, and can still modify the Content-Type: header if
# necessary.
oldfp = self._fp
self._munge_cte = None
self._fp = sfp = self._new_buffer()
self._fp = oldfp
munge_cte = self._munge_cte
del self._munge_cte
# If we munged the cte, copy the message again and re-fix the CTE.
if munge_cte:
msg = deepcopy(msg)
msg.replace_header('content-transfer-encoding', munge_cte[0])
msg.replace_header('content-type', munge_cte[1])
# 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:
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().
main = msg.get_content_maintype()
sub = msg.get_content_subtype()
specific = UNDERSCORE.join((main, sub)).replace('-', '_')
meth = getattr(self, '_handle_' + specific, None)
if meth is None:
generic = main.replace('-', '_')
meth = getattr(self, '_handle_' + generic, None)
if meth is None:
meth = self._writeBody
# Default handlers
def _write_headers(self, msg):
for h, v in msg.raw_items():
self.write(self.policy.fold(h, v))
# A blank line always separates headers from body
# Handlers for writing types and subtypes
def _handle_text(self, msg):
payload = msg.get_payload()
if payload is None:
if not isinstance(payload, str):
raise TypeError('string payload expected: %s' % type(payload))
if _has_surrogates(msg._payload):
charset = msg.get_param('charset')
if charset is not None:
# XXX: This copy stuff is an ugly hack to avoid modifying the
# existing message.
msg = deepcopy(msg)
del msg['content-transfer-encoding']
msg.set_payload(payload, charset)
payload = msg.get_payload()
self._munge_cte = (msg['content-transfer-encoding'],
if self._mangle_from_:
payload = fcre.sub('>From ', payload)
# Default body handler
_writeBody = _handle_text
def _handle_multipart(self, msg):
# 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 = []
subparts = msg.get_payload()
if subparts is None:
subparts = []
elif isinstance(subparts, str):
# e.g. a non-strict parse of a message with no starting boundary.
elif not isinstance(subparts, list):
# Scalar payload
subparts = [subparts]
for part in subparts:
s = self._new_buffer()
g = self.clone(s)
g.flatten(part, unixfrom=False, linesep=self._NL)
# BAW: What about boundaries that are wrapped in double-quotes?
boundary = msg.get_boundary()
if not boundary:
# Create a boundary that doesn't appear in any of the
# message texts.
alltext = self._encoded_NL.join(msgtexts)
boundary = self._make_boundary(alltext)
# If there's a preamble, write it out, with a trailing CRLF
if msg.preamble is not None:
if self._mangle_from_:
preamble = fcre.sub('>From ', msg.preamble)
preamble = msg.preamble
# dash-boundary transport-padding CRLF
self.write('--' + boundary + self._NL)
# body-part
if msgtexts:
# *encapsulation
# --> delimiter transport-padding
# --> CRLF body-part
for body_part in msgtexts:
# delimiter transport-padding CRLF
self.write(self._NL + '--' + boundary + self._NL)
# body-part
# close-delimiter transport-padding
self.write(self._NL + '--' + boundary + '--' + self._NL)
if msg.epilogue is not None:
if self._mangle_from_:
epilogue = fcre.sub('>From ', msg.epilogue)
epilogue = msg.epilogue
def _handle_multipart_signed(self, msg):
# The contents of signed parts has to stay unmodified in order to keep
# the signature intact per RFC1847 2.1, so we disable header wrapping.
# RDM: This isn't enough to completely preserve the part, but it helps.
p = self.policy
self.policy = p.clone(max_line_length=0)
self.policy = p
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 = self._new_buffer()
g = self.clone(s)
g.flatten(part, unixfrom=False, linesep=self._NL)
text = s.getvalue()
lines = text.split(self._encoded_NL)
# Strip off the unnecessary trailing empty line
if lines and lines[-1] == self._encoded_EMPTY:
# 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.
def _handle_message(self, msg):
s = self._new_buffer()
g = self.clone(s)
# The payload of a message/rfc822 part should be a multipart sequence
# of length 1. The zeroth element of the list should be the Message
# object for the subpart. Extract that object, stringify it, and
# write it out.
# Except, it turns out, when it's a string instead, which happens when
# and only when HeaderParser is used on a message of mime type
# message/rfc822. Such messages are generated by, for example,
# Groupwise when forwarding unadorned messages. (Issue 7970.) So
# in that case we just emit the string body.
payload = msg._payload
if isinstance(payload, list):
g.flatten(msg.get_payload(0), unixfrom=False, linesep=self._NL)
payload = s.getvalue()
payload = self._encode(payload)
# This used to be a module level function; we use a classmethod for this
# and _compile_re so we can continue to provide the module level function
# for backward compatibility by doing
# _make_boundary = Generator._make_boundary
# at the end of the module. It *is* internal, so we could drop that...
def _make_boundary(cls, text=None):
# Craft a random boundary. If text is given, ensure that the chosen
# boundary doesn't appear in the text.
token = random.randrange(sys.maxsize)
boundary = ('=' * 15) + (_fmt % token) + '=='
if text is None:
return boundary
b = boundary
counter = 0
while True:
cre = cls._compile_re('^--' + re.escape(b) + '(--)?$', re.MULTILINE)
if not
b = boundary + '.' + str(counter)
counter += 1
return b
def _compile_re(cls, s, flags):
return re.compile(s, flags)
class BytesGenerator(Generator):
"""Generates a bytes version of a Message object tree.
Functionally identical to the base Generator except that the output is
bytes and not string. When surrogates were used in the input to encode
bytes, these are decoded back to bytes for output. If the policy has
cte_type set to 7bit, then the message is transformed such that the
non-ASCII bytes are properly content transfer encoded, using the charset
The outfp object must accept bytes in its write method.
def write(self, s):
self._fp.write(s.encode('ascii', 'surrogateescape'))
def _new_buffer(self):
return BytesIO()
def _encode(self, s):
return s.encode('ascii')
def _write_headers(self, msg):
# This is almost the same as the string version, except for handling
# strings with 8bit bytes.
for h, v in msg.raw_items():
self._fp.write(self.policy.fold_binary(h, v))
# A blank line always separates headers from body
def _handle_text(self, msg):
# If the string has surrogates the original source was bytes, so
# just write it back out.
if msg._payload is None:
if _has_surrogates(msg._payload) and not self.policy.cte_type=='7bit':
if self._mangle_from_:
msg._payload = fcre.sub(">From ", msg._payload)
# Default body handler
_writeBody = _handle_text
def _compile_re(cls, s, flags):
return re.compile(s.encode('ascii'), flags)
_FMT = '[Non-text (%(type)s) part of message omitted, filename %(filename)s]'
class DecodedGenerator(Generator):
"""Generates 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_=None, maxheaderlen=None, 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:
self._fmt = _FMT
self._fmt = fmt
def _dispatch(self, msg):
for part in msg.walk():
maintype = part.get_content_maintype()
if maintype == 'text':
print(part.get_payload(decode=False), file=self)
elif maintype == 'multipart':
# Just skip this
print(self._fmt % {
'type' : part.get_content_type(),
'maintype' : part.get_content_maintype(),
'subtype' : part.get_content_subtype(),
'filename' : part.get_filename('[no filename]'),
'description': part.get('Content-Description',
'[no description]'),
'encoding' : part.get('Content-Transfer-Encoding',
'[no encoding]'),
}, file=self)
# Helper used by Generator._make_boundary
_width = len(repr(sys.maxsize-1))
_fmt = '%%0%dd' % _width
# Backward compatibility
_make_boundary = Generator._make_boundary