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Teach this class about "highest-level syntactic breaks" but only for 

headers with no charset or 'us-ascii' charsets.  Actually this is only
partially true: we know about semicolons (but not true parameters) and
we know about whitespace (but not technically folding whitespace).
Still it should be good enough for all practical purposes.

Other changes include:

__init__(): Add a continuation_ws argument, which defaults to a single
space.  Set this to change the whitespace used for continuation lines
when a header must be split.  Also, changed the way header line
lengths are calculated, so that they take into account continuation_ws
(when tabs-expanded) and any provided header_name parameter.  This
should do much better on returning split headers for which the first
and subsequent lines must fit into a specified width.

guess_maxlinelen(): Removed.  I don't think we need this method as
part of the public API.

encode_chunks() -> _encode_chunks(): I don't think we need this one as
part of the public API either.
This commit is contained in:
Barry Warsaw 2002-06-28 23:46:53 +00:00
parent 062749ac57
commit 766125080f
1 changed files with 152 additions and 59 deletions
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209
Lib/email/Header.py
View File

@ -16,7 +16,9 @@ except SyntaxError:
CRLFSPACE = '\r\n '
CRLF = '\r\n'
NLSPACE = '\n '
NL = '\n'
SPACE8 = ' ' * 8
EMPTYSTRING = ''
MAXLINELEN = 76
@ -92,11 +94,12 @@ def decode_header(header):
class Header:
def __init__(self, s, charset=None, maxlinelen=None, header_name=None):
def __init__(self, s, charset=None, maxlinelen=None, header_name=None,
continuation_ws=' '):
"""Create a MIME-compliant header that can contain many languages.
Specify the initial header value in s. Specify its character set as a
Charset object in the charset argument. If none, a default Charset
Charset object in the charset argument. If None, a default Charset
instance will be used.
You can later append to the header with append(s, charset) below;
@ -104,43 +107,41 @@ class Header:
here. In fact, it's optional, and if not given, defaults to the
charset specified in the constructor.
The maximum line length can be specified explicitly via maxlinelen.
You can also pass None for maxlinelen and the name of a header field
(e.g. "Subject") to let the constructor guess the best line length to
use. The default maxlinelen is 76.
The maximum line length can be specified explicit via maxlinelen. For
splitting the first line to a shorter value (to account for the field
header which isn't included in s, e.g. `Subject') pass in the name of
the field in header_name. The default maxlinelen is 76.
continuation_ws must be RFC 2822 compliant folding whitespace (usually
either a space or a hard tab) which will be prepended to continuation
lines.
"""
if charset is None:
charset = Charset()
self._charset = charset
self._continuation_ws = continuation_ws
cws_expanded_len = len(continuation_ws.replace('\t', SPACE8))
# BAW: I believe `chunks' and `maxlinelen' should be non-public.
self._chunks = []
self.append(s, charset)
if maxlinelen is None:
maxlinelen = MAXLINELEN
if header_name is None:
self._maxlinelen = MAXLINELEN
# We don't know anything about the field header so the first line
# is the same length as subsequent lines.
self._firstlinelen = maxlinelen
else:
self.guess_maxlinelen(header_name)
else:
self._maxlinelen = maxlinelen
# The first line should be shorter to take into account the field
# header. Also subtract off 2 extra for the colon and space.
self._firstlinelen = maxlinelen - len(header_name) - 2
# Second and subsequent lines should subtract off the length in
# columns of the continuation whitespace prefix.
self._maxlinelen = maxlinelen - cws_expanded_len
def __str__(self):
"""A synonym for self.encode()."""
return self.encode()
def guess_maxlinelen(self, s=None):
"""Guess the maximum length to make each header line.
Given a header name (e.g. "Subject"), set this header's maximum line
length to an appropriate length to avoid line wrapping. If s is not
given, return the previous maximum line length and don't set it.
Returns the new maximum line length.
"""
# BAW: is this semantic necessary?
if s is not None:
self._maxlinelen = MAXLINELEN - len(s) - 2
return self._maxlinelen
def append(self, s, charset=None):
"""Append string s with Charset charset to the MIME header.
@ -150,7 +151,7 @@ class Header:
charset = self._charset
self._chunks.append((s, charset))
def _split(self, s, charset):
def _split(self, s, charset, firstline=0):
# Split up a header safely for use with encode_chunks. BAW: this
# appears to be a private convenience method.
splittable = charset.to_splittable(s)
@ -159,6 +160,20 @@ class Header:
if elen <= self._maxlinelen:
return [(encoded, charset)]
# BAW: I'm not sure what the right test here is. What we're trying to
# do is be faithful to RFC 2822's recommendation that ($2.2.3):
#
# "Note: Though structured field bodies are defined in such a way that
# folding can take place between many of the lexical tokens (and even
# within some of the lexical tokens), folding SHOULD be limited to
# placing the CRLF at higher-level syntactic breaks."
#
# For now, I can only imagine doing this when the charset is us-ascii,
# although it's possible that other charsets may also benefit from the
# higher-level syntactic breaks.
#
elif charset == 'us-ascii':
return self._ascii_split(s, charset, firstline)
# BAW: should we use encoded?
elif elen == len(s):
# We can split on _maxlinelen boundaries because we know that the
@ -166,13 +181,119 @@ class Header:
splitpnt = self._maxlinelen
first = charset.from_splittable(splittable[:splitpnt], 0)
last = charset.from_splittable(splittable[splitpnt:], 0)
return self._split(first, charset) + self._split(last, charset)
else:
# Divide and conquer.
halfway = _floordiv(len(splittable), 2)
first = charset.from_splittable(splittable[:halfway], 0)
last = charset.from_splittable(splittable[halfway:], 0)
return self._split(first, charset) + self._split(last, charset)
# Do the split
return self._split(first, charset, firstline) + \
self._split(last, charset)
def _ascii_split(self, s, charset, firstline):
# Attempt to split the line at the highest-level syntactic break
# possible. Note that we don't have a lot of smarts about field
# syntax; we just try to break on semi-colons, then whitespace.
rtn = []
lines = s.splitlines()
while lines:
line = lines.pop(0)
if firstline:
maxlinelen = self._firstlinelen
firstline = 0
else:
line = line.lstrip()
maxlinelen = self._maxlinelen
# Short lines can remain unchanged
if len(line.replace('\t', SPACE8)) <= maxlinelen:
rtn.append(line)
else:
oldlen = len(line)
# Try to break the line on semicolons, but if that doesn't
# work, try to split on folding whitespace.
while len(line) > maxlinelen:
i = line.rfind(';', 0, maxlinelen)
if i < 0:
break
rtn.append(line[:i] + ';')
line = line[i+1:]
# Is the remaining stuff still longer than maxlinelen?
if len(line) <= maxlinelen:
# Splitting on semis worked
rtn.append(line)
continue
# Splitting on semis didn't finish the job. If it did any
# work at all, stick the remaining junk on the front of the
# `lines' sequence and let the next pass do its thing.
if len(line) <> oldlen:
lines.insert(0, line)
continue
# Otherwise, splitting on semis didn't help at all.
parts = re.split(r'(\s+)', line)
if len(parts) == 1 or (len(parts) == 3 and
parts[0].endswith(':')):
# This line can't be split on whitespace. There's now
# little we can do to get this into maxlinelen. BAW:
# We're still potentially breaking the RFC by possibly
# allowing lines longer than the absolute maximum of 998
# characters. For now, let it slide.
#
# len(parts) will be 1 if this line has no `Field: '
# prefix, otherwise it will be len(3).
rtn.append(line)
continue
# There is whitespace we can split on.
first = parts.pop(0)
sublines = [first]
acc = len(first)
while parts:
len0 = len(parts[0])
len1 = len(parts[1])
if acc + len0 + len1 <= maxlinelen:
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
if first <> '':
rtn.append(EMPTYSTRING.join(sublines))
del parts[0]
first = parts.pop(0)
sublines = [first]
acc = len(first)
rtn.append(EMPTYSTRING.join(sublines))
return [(chunk, charset) for chunk in rtn]
def _encode_chunks(self):
"""MIME-encode a header with many different charsets and/or encodings.
Given a list of pairs (string, charset), return a MIME-encoded string
suitable for use in a header field. Each pair may have different
charsets and/or encodings, and the resulting header will accurately
reflect each setting.
Each encoding can be email.Utils.QP (quoted-printable, for ASCII-like
character sets like iso-8859-1), email.Utils.BASE64 (Base64, for
non-ASCII like character sets like KOI8-R and iso-2022-jp), or None
(no encoding).
Each pair will be represented on a separate line; the resulting string
will be in the format:
"=?charset1?q?Mar=EDa_Gonz=E1lez_Alonso?=\n
=?charset2?b?SvxyZ2VuIEL2aW5n?="
"""
chunks = []
for header, charset in self._chunks:
if charset is None or charset.header_encoding is None:
# There's no encoding for this chunk's charsets
_max_append(chunks, header, self._maxlinelen)
else:
_max_append(chunks, charset.header_encode(header, 0),
self._maxlinelen, ' ')
joiner = NL + self._continuation_ws
return joiner.join(chunks)
def encode(self):
"""Encode a message header, possibly converting charset and encoding.
@ -194,34 +315,6 @@ class Header:
"""
newchunks = []
for s, charset in self._chunks:
newchunks += self._split(s, charset)
newchunks += self._split(s, charset, 1)
self._chunks = newchunks
return self.encode_chunks()
def encode_chunks(self):
"""MIME-encode a header with many different charsets and/or encodings.
Given a list of pairs (string, charset), return a MIME-encoded string
suitable for use in a header field. Each pair may have different
charsets and/or encodings, and the resulting header will accurately
reflect each setting.
Each encoding can be email.Utils.QP (quoted-printable, for ASCII-like
character sets like iso-8859-1), email.Utils.BASE64 (Base64, for
non-ASCII like character sets like KOI8-R and iso-2022-jp), or None
(no encoding).
Each pair will be represented on a separate line; the resulting string
will be in the format:
"=?charset1?q?Mar=EDa_Gonz=E1lez_Alonso?=\n
=?charset2?b?SvxyZ2VuIEL2aW5n?="
"""
chunks = []
for header, charset in self._chunks:
if charset is None:
_max_append(chunks, header, self._maxlinelen, ' ')
else:
_max_append(chunks, charset.header_encode(header, 0),
self._maxlinelen, ' ')
return NLSPACE.join(chunks)
return self._encode_chunks()