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3edd22ac95
This new interface will also allow for future planned enhancements in control over the parser/generator without requiring any additional complexity in the parser/generator API. Patch reviewed by Éric Araujo and Barry Warsaw.
474 lines
18 KiB
Python
474 lines
18 KiB
Python
# Copyright (C) 2001-2010 Python Software Foundation
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# Author: Barry Warsaw
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# Contact: email-sig@python.org
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"""Classes to generate plain text from a message object tree."""
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__all__ = ['Generator', 'DecodedGenerator']
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import re
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import sys
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import time
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import random
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import warnings
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from io import StringIO, BytesIO
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from email import policy
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from email.header import Header
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from email.message import _has_surrogates
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import email.charset as _charset
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UNDERSCORE = '_'
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NL = '\n' # XXX: no longer used by the code below.
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fcre = re.compile(r'^From ', re.MULTILINE)
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class Generator:
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"""Generates output from a Message object tree.
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This basic generator writes the message to the given file object as plain
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text.
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"""
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#
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# Public interface
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#
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def __init__(self, outfp, mangle_from_=True, maxheaderlen=None, *,
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policy=policy.default):
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"""Create the generator for message flattening.
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outfp is the output file-like object for writing the message to. It
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must have a write() method.
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Optional mangle_from_ is a flag that, when True (the default), escapes
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From_ lines in the body of the message by putting a `>' in front of
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them.
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Optional maxheaderlen specifies the longest length for a non-continued
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header. When a header line is longer (in characters, with tabs
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expanded to 8 spaces) than maxheaderlen, the header will split as
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defined in the Header class. Set maxheaderlen to zero to disable
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header wrapping. The default is 78, as recommended (but not required)
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by RFC 2822.
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The policy keyword specifies a policy object that controls a number of
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aspects of the generator's operation. The default policy maintains
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backward compatibility.
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"""
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self._fp = outfp
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self._mangle_from_ = mangle_from_
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self._maxheaderlen = (maxheaderlen if maxheaderlen is not None else
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policy.max_line_length)
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self.policy = policy
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def write(self, s):
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# Just delegate to the file object
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self._fp.write(s)
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def flatten(self, msg, unixfrom=False, linesep=None):
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r"""Print the message object tree rooted at msg to the output file
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specified when the Generator instance was created.
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unixfrom is a flag that forces the printing of a Unix From_ delimiter
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before the first object in the message tree. If the original message
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has no From_ delimiter, a `standard' one is crafted. By default, this
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is False to inhibit the printing of any From_ delimiter.
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Note that for subobjects, no From_ line is printed.
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linesep specifies the characters used to indicate a new line in
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the output. The default value is determined by the policy.
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"""
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# We use the _XXX constants for operating on data that comes directly
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# from the msg, and _encoded_XXX constants for operating on data that
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# has already been converted (to bytes in the BytesGenerator) and
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# inserted into a temporary buffer.
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self._NL = linesep if linesep is not None else self.policy.linesep
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self._encoded_NL = self._encode(self._NL)
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self._EMPTY = ''
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self._encoded_EMTPY = self._encode('')
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if unixfrom:
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ufrom = msg.get_unixfrom()
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if not ufrom:
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ufrom = 'From nobody ' + time.ctime(time.time())
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self.write(ufrom + self._NL)
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self._write(msg)
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def clone(self, fp):
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"""Clone this generator with the exact same options."""
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return self.__class__(fp, self._mangle_from_, self._maxheaderlen)
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#
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# Protected interface - undocumented ;/
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#
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# Note that we use 'self.write' when what we are writing is coming from
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# the source, and self._fp.write when what we are writing is coming from a
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# buffer (because the Bytes subclass has already had a chance to transform
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# the data in its write method in that case). This is an entirely
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# pragmatic split determined by experiment; we could be more general by
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# always using write and having the Bytes subclass write method detect when
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# it has already transformed the input; but, since this whole thing is a
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# hack anyway this seems good enough.
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# Similarly, we have _XXX and _encoded_XXX attributes that are used on
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# source and buffer data, respectively.
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_encoded_EMPTY = ''
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def _new_buffer(self):
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# BytesGenerator overrides this to return BytesIO.
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return StringIO()
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def _encode(self, s):
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# BytesGenerator overrides this to encode strings to bytes.
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return s
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def _write(self, msg):
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# We can't write the headers yet because of the following scenario:
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# say a multipart message includes the boundary string somewhere in
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# its body. We'd have to calculate the new boundary /before/ we write
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# the headers so that we can write the correct Content-Type:
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# parameter.
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#
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# The way we do this, so as to make the _handle_*() methods simpler,
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# is to cache any subpart writes into a buffer. The we write the
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# headers and the buffer contents. That way, subpart handlers can
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# Do The Right Thing, and can still modify the Content-Type: header if
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# necessary.
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oldfp = self._fp
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try:
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self._fp = sfp = self._new_buffer()
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self._dispatch(msg)
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finally:
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self._fp = oldfp
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# Write the headers. First we see if the message object wants to
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# handle that itself. If not, we'll do it generically.
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meth = getattr(msg, '_write_headers', None)
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if meth is None:
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self._write_headers(msg)
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else:
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meth(self)
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self._fp.write(sfp.getvalue())
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def _dispatch(self, msg):
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# Get the Content-Type: for the message, then try to dispatch to
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# self._handle_<maintype>_<subtype>(). If there's no handler for the
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# full MIME type, then dispatch to self._handle_<maintype>(). If
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# that's missing too, then dispatch to self._writeBody().
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main = msg.get_content_maintype()
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sub = msg.get_content_subtype()
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specific = UNDERSCORE.join((main, sub)).replace('-', '_')
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meth = getattr(self, '_handle_' + specific, None)
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if meth is None:
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generic = main.replace('-', '_')
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meth = getattr(self, '_handle_' + generic, None)
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if meth is None:
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meth = self._writeBody
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meth(msg)
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#
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# Default handlers
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#
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def _write_headers(self, msg):
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for h, v in msg.items():
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self.write('%s: ' % h)
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if isinstance(v, Header):
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self.write(v.encode(
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maxlinelen=self._maxheaderlen, linesep=self._NL)+self._NL)
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else:
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# Header's got lots of smarts, so use it.
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header = Header(v, maxlinelen=self._maxheaderlen,
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header_name=h)
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self.write(header.encode(linesep=self._NL)+self._NL)
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# A blank line always separates headers from body
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self.write(self._NL)
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#
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# Handlers for writing types and subtypes
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#
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def _handle_text(self, msg):
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payload = msg.get_payload()
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if payload is None:
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return
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if not isinstance(payload, str):
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raise TypeError('string payload expected: %s' % type(payload))
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if _has_surrogates(msg._payload):
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charset = msg.get_param('charset')
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if charset is not None:
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del msg['content-transfer-encoding']
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msg.set_payload(payload, charset)
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payload = msg.get_payload()
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if self._mangle_from_:
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payload = fcre.sub('>From ', payload)
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self.write(payload)
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# Default body handler
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_writeBody = _handle_text
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def _handle_multipart(self, msg):
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# The trick here is to write out each part separately, merge them all
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# together, and then make sure that the boundary we've chosen isn't
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# present in the payload.
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msgtexts = []
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subparts = msg.get_payload()
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if subparts is None:
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subparts = []
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elif isinstance(subparts, str):
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# e.g. a non-strict parse of a message with no starting boundary.
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self.write(subparts)
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return
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elif not isinstance(subparts, list):
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# Scalar payload
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subparts = [subparts]
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for part in subparts:
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s = self._new_buffer()
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g = self.clone(s)
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g.flatten(part, unixfrom=False, linesep=self._NL)
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msgtexts.append(s.getvalue())
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# BAW: What about boundaries that are wrapped in double-quotes?
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boundary = msg.get_boundary()
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if not boundary:
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# Create a boundary that doesn't appear in any of the
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# message texts.
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alltext = self._encoded_NL.join(msgtexts)
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boundary = self._make_boundary(alltext)
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msg.set_boundary(boundary)
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# If there's a preamble, write it out, with a trailing CRLF
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if msg.preamble is not None:
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self.write(msg.preamble + self._NL)
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# dash-boundary transport-padding CRLF
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self.write('--' + boundary + self._NL)
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# body-part
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if msgtexts:
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self._fp.write(msgtexts.pop(0))
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# *encapsulation
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# --> delimiter transport-padding
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# --> CRLF body-part
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for body_part in msgtexts:
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# delimiter transport-padding CRLF
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self.write(self._NL + '--' + boundary + self._NL)
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# body-part
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self._fp.write(body_part)
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# close-delimiter transport-padding
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self.write(self._NL + '--' + boundary + '--')
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if msg.epilogue is not None:
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self.write(self._NL)
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self.write(msg.epilogue)
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def _handle_multipart_signed(self, msg):
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# The contents of signed parts has to stay unmodified in order to keep
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# the signature intact per RFC1847 2.1, so we disable header wrapping.
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# RDM: This isn't enough to completely preserve the part, but it helps.
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old_maxheaderlen = self._maxheaderlen
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try:
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self._maxheaderlen = 0
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self._handle_multipart(msg)
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finally:
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self._maxheaderlen = old_maxheaderlen
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def _handle_message_delivery_status(self, msg):
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# We can't just write the headers directly to self's file object
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# because this will leave an extra newline between the last header
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# block and the boundary. Sigh.
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blocks = []
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for part in msg.get_payload():
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s = self._new_buffer()
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g = self.clone(s)
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g.flatten(part, unixfrom=False, linesep=self._NL)
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text = s.getvalue()
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lines = text.split(self._encoded_NL)
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# Strip off the unnecessary trailing empty line
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if lines and lines[-1] == self._encoded_EMPTY:
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blocks.append(self._encoded_NL.join(lines[:-1]))
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else:
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blocks.append(text)
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# Now join all the blocks with an empty line. This has the lovely
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# effect of separating each block with an empty line, but not adding
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# an extra one after the last one.
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self._fp.write(self._encoded_NL.join(blocks))
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def _handle_message(self, msg):
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s = self._new_buffer()
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g = self.clone(s)
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# The payload of a message/rfc822 part should be a multipart sequence
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# of length 1. The zeroth element of the list should be the Message
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# object for the subpart. Extract that object, stringify it, and
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# write it out.
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# Except, it turns out, when it's a string instead, which happens when
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# and only when HeaderParser is used on a message of mime type
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# message/rfc822. Such messages are generated by, for example,
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# Groupwise when forwarding unadorned messages. (Issue 7970.) So
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# in that case we just emit the string body.
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payload = msg._payload
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if isinstance(payload, list):
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g.flatten(msg.get_payload(0), unixfrom=False, linesep=self._NL)
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payload = s.getvalue()
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else:
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payload = self._encode(payload)
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self._fp.write(payload)
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# This used to be a module level function; we use a classmethod for this
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# and _compile_re so we can continue to provide the module level function
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# for backward compatibility by doing
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# _make_boudary = Generator._make_boundary
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# at the end of the module. It *is* internal, so we could drop that...
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@classmethod
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def _make_boundary(cls, text=None):
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# Craft a random boundary. If text is given, ensure that the chosen
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# boundary doesn't appear in the text.
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token = random.randrange(sys.maxsize)
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boundary = ('=' * 15) + (_fmt % token) + '=='
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if text is None:
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return boundary
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b = boundary
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counter = 0
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while True:
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cre = cls._compile_re('^--' + re.escape(b) + '(--)?$', re.MULTILINE)
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if not cre.search(text):
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break
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b = boundary + '.' + str(counter)
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counter += 1
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return b
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@classmethod
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def _compile_re(cls, s, flags):
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return re.compile(s, flags)
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class BytesGenerator(Generator):
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"""Generates a bytes version of a Message object tree.
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Functionally identical to the base Generator except that the output is
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bytes and not string. When surrogates were used in the input to encode
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bytes, these are decoded back to bytes for output. If the policy has
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must_be_7bit set true, then the message is transformed such that the
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non-ASCII bytes are properly content transfer encoded, using the
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charset unknown-8bit.
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The outfp object must accept bytes in its write method.
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"""
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# Bytes versions of this constant for use in manipulating data from
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# the BytesIO buffer.
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_encoded_EMPTY = b''
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def write(self, s):
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self._fp.write(s.encode('ascii', 'surrogateescape'))
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def _new_buffer(self):
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return BytesIO()
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def _encode(self, s):
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return s.encode('ascii')
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def _write_headers(self, msg):
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# This is almost the same as the string version, except for handling
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# strings with 8bit bytes.
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for h, v in msg._headers:
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self.write('%s: ' % h)
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if isinstance(v, str):
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if _has_surrogates(v):
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if not self.policy.must_be_7bit:
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# If we have raw 8bit data in a byte string, we have no idea
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# what the encoding is. There is no safe way to split this
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# string. If it's ascii-subset, then we could do a normal
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# ascii split, but if it's multibyte then we could break the
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# string. There's no way to know so the least harm seems to
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# be to not split the string and risk it being too long.
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self.write(v+NL)
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continue
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h = Header(v, charset=_charset.UNKNOWN8BIT, header_name=h)
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else:
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h = Header(v, header_name=h)
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self.write(h.encode(linesep=self._NL,
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maxlinelen=self._maxheaderlen)+self._NL)
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# A blank line always separates headers from body
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self.write(self._NL)
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def _handle_text(self, msg):
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# If the string has surrogates the original source was bytes, so
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# just write it back out.
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if msg._payload is None:
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return
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if _has_surrogates(msg._payload) and not self.policy.must_be_7bit:
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self.write(msg._payload)
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else:
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super(BytesGenerator,self)._handle_text(msg)
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@classmethod
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def _compile_re(cls, s, flags):
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return re.compile(s.encode('ascii'), flags)
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_FMT = '[Non-text (%(type)s) part of message omitted, filename %(filename)s]'
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class DecodedGenerator(Generator):
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"""Generates a text representation of a message.
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Like the Generator base class, except that non-text parts are substituted
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with a format string representing the part.
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"""
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def __init__(self, outfp, mangle_from_=True, maxheaderlen=78, fmt=None):
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"""Like Generator.__init__() except that an additional optional
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argument is allowed.
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Walks through all subparts of a message. If the subpart is of main
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type `text', then it prints the decoded payload of the subpart.
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Otherwise, fmt is a format string that is used instead of the message
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payload. fmt is expanded with the following keywords (in
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%(keyword)s format):
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type : Full MIME type of the non-text part
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maintype : Main MIME type of the non-text part
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subtype : Sub-MIME type of the non-text part
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filename : Filename of the non-text part
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description: Description associated with the non-text part
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encoding : Content transfer encoding of the non-text part
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The default value for fmt is None, meaning
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[Non-text (%(type)s) part of message omitted, filename %(filename)s]
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"""
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Generator.__init__(self, outfp, mangle_from_, maxheaderlen)
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if fmt is None:
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self._fmt = _FMT
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else:
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self._fmt = fmt
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def _dispatch(self, msg):
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for part in msg.walk():
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maintype = part.get_content_maintype()
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if maintype == 'text':
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print(part.get_payload(decode=False), file=self)
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elif maintype == 'multipart':
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# Just skip this
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pass
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else:
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print(self._fmt % {
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'type' : part.get_content_type(),
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'maintype' : part.get_content_maintype(),
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'subtype' : part.get_content_subtype(),
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'filename' : part.get_filename('[no filename]'),
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'description': part.get('Content-Description',
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'[no description]'),
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'encoding' : part.get('Content-Transfer-Encoding',
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'[no encoding]'),
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}, file=self)
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# Helper used by Generator._make_boundary
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_width = len(repr(sys.maxsize-1))
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_fmt = '%%0%dd' % _width
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# Backward compatibility
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_make_boundary = Generator._make_boundary
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