--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/planemo/lib/python3.7/site-packages/future/backports/email/header.py	Fri Jul 31 00:18:57 2020 -0400
@@ -0,0 +1,581 @@
+# Copyright (C) 2002-2007 Python Software Foundation
+# Author: Ben Gertzfield, Barry Warsaw
+# Contact: email-sig@python.org
+
+"""Header encoding and decoding functionality."""
+from __future__ import unicode_literals
+from __future__ import division
+from __future__ import absolute_import
+from future.builtins import bytes, range, str, super, zip
+
+__all__ = [
+    'Header',
+    'decode_header',
+    'make_header',
+    ]
+
+import re
+import binascii
+
+from future.backports import email
+from future.backports.email import base64mime
+from future.backports.email.errors import HeaderParseError
+import future.backports.email.charset as _charset
+
+# Helpers
+from future.backports.email.quoprimime import _max_append, header_decode
+
+Charset = _charset.Charset
+
+NL = '\n'
+SPACE = ' '
+BSPACE = b' '
+SPACE8 = ' ' * 8
+EMPTYSTRING = ''
+MAXLINELEN = 78
+FWS = ' \t'
+
+USASCII = Charset('us-ascii')
+UTF8 = Charset('utf-8')
+
+# Match encoded-word strings in the form =?charset?q?Hello_World?=
+ecre = re.compile(r'''
+  =\?                   # literal =?
+  (?P<charset>[^?]*?)   # non-greedy up to the next ? is the charset
+  \?                    # literal ?
+  (?P<encoding>[qb])    # either a "q" or a "b", case insensitive
+  \?                    # literal ?
+  (?P<encoded>.*?)      # non-greedy up to the next ?= is the encoded string
+  \?=                   # literal ?=
+  ''', re.VERBOSE | re.IGNORECASE | re.MULTILINE)
+
+# Field name regexp, including trailing colon, but not separating whitespace,
+# according to RFC 2822.  Character range is from tilde to exclamation mark.
+# For use with .match()
+fcre = re.compile(r'[\041-\176]+:$')
+
+# Find a header embedded in a putative header value.  Used to check for
+# header injection attack.
+_embeded_header = re.compile(r'\n[^ \t]+:')
+
+
+def decode_header(header):
+    """Decode a message header value without converting charset.
+
+    Returns a list of (string, charset) pairs containing each of the decoded
+    parts of the header.  Charset is None for non-encoded parts of the header,
+    otherwise a lower-case string containing the name of the character set
+    specified in the encoded string.
+
+    header may be a string that may or may not contain RFC2047 encoded words,
+    or it may be a Header object.
+
+    An email.errors.HeaderParseError may be raised when certain decoding error
+    occurs (e.g. a base64 decoding exception).
+    """
+    # If it is a Header object, we can just return the encoded chunks.
+    if hasattr(header, '_chunks'):
+        return [(_charset._encode(string, str(charset)), str(charset))
+                    for string, charset in header._chunks]
+    # If no encoding, just return the header with no charset.
+    if not ecre.search(header):
+        return [(header, None)]
+    # First step is to parse all the encoded parts into triplets of the form
+    # (encoded_string, encoding, charset).  For unencoded strings, the last
+    # two parts will be None.
+    words = []
+    for line in header.splitlines():
+        parts = ecre.split(line)
+        first = True
+        while parts:
+            unencoded = parts.pop(0)
+            if first:
+                unencoded = unencoded.lstrip()
+                first = False
+            if unencoded:
+                words.append((unencoded, None, None))
+            if parts:
+                charset = parts.pop(0).lower()
+                encoding = parts.pop(0).lower()
+                encoded = parts.pop(0)
+                words.append((encoded, encoding, charset))
+    # Now loop over words and remove words that consist of whitespace
+    # between two encoded strings.
+    import sys
+    droplist = []
+    for n, w in enumerate(words):
+        if n>1 and w[1] and words[n-2][1] and words[n-1][0].isspace():
+            droplist.append(n-1)
+    for d in reversed(droplist):
+        del words[d]
+
+    # The next step is to decode each encoded word by applying the reverse
+    # base64 or quopri transformation.  decoded_words is now a list of the
+    # form (decoded_word, charset).
+    decoded_words = []
+    for encoded_string, encoding, charset in words:
+        if encoding is None:
+            # This is an unencoded word.
+            decoded_words.append((encoded_string, charset))
+        elif encoding == 'q':
+            word = header_decode(encoded_string)
+            decoded_words.append((word, charset))
+        elif encoding == 'b':
+            paderr = len(encoded_string) % 4   # Postel's law: add missing padding
+            if paderr:
+                encoded_string += '==='[:4 - paderr]
+            try:
+                word = base64mime.decode(encoded_string)
+            except binascii.Error:
+                raise HeaderParseError('Base64 decoding error')
+            else:
+                decoded_words.append((word, charset))
+        else:
+            raise AssertionError('Unexpected encoding: ' + encoding)
+    # Now convert all words to bytes and collapse consecutive runs of
+    # similarly encoded words.
+    collapsed = []
+    last_word = last_charset = None
+    for word, charset in decoded_words:
+        if isinstance(word, str):
+            word = bytes(word, 'raw-unicode-escape')
+        if last_word is None:
+            last_word = word
+            last_charset = charset
+        elif charset != last_charset:
+            collapsed.append((last_word, last_charset))
+            last_word = word
+            last_charset = charset
+        elif last_charset is None:
+            last_word += BSPACE + word
+        else:
+            last_word += word
+    collapsed.append((last_word, last_charset))
+    return collapsed
+
+
+def make_header(decoded_seq, maxlinelen=None, header_name=None,
+                continuation_ws=' '):
+    """Create a Header from a sequence of pairs as returned by decode_header()
+
+    decode_header() takes a header value string and returns a sequence of
+    pairs of the format (decoded_string, charset) where charset is the string
+    name of the character set.
+
+    This function takes one of those sequence of pairs and returns a Header
+    instance.  Optional maxlinelen, header_name, and continuation_ws are as in
+    the Header constructor.
+    """
+    h = Header(maxlinelen=maxlinelen, header_name=header_name,
+               continuation_ws=continuation_ws)
+    for s, charset in decoded_seq:
+        # None means us-ascii but we can simply pass it on to h.append()
+        if charset is not None and not isinstance(charset, Charset):
+            charset = Charset(charset)
+        h.append(s, charset)
+    return h
+
+
+class Header(object):
+    def __init__(self, s=None, charset=None,
+                 maxlinelen=None, header_name=None,
+                 continuation_ws=' ', errors='strict'):
+        """Create a MIME-compliant header that can contain many character sets.
+
+        Optional s is the initial header value.  If None, the initial header
+        value is not set.  You can later append to the header with .append()
+        method calls.  s may be a byte string or a Unicode string, but see the
+        .append() documentation for semantics.
+
+        Optional charset serves two purposes: it has the same meaning as the
+        charset argument to the .append() method.  It also sets the default
+        character set for all subsequent .append() calls that omit the charset
+        argument.  If charset is not provided in the constructor, the us-ascii
+        charset is used both as s's initial charset and as the default for
+        subsequent .append() calls.
+
+        The maximum line length can be specified explicitly 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 78 as recommended
+        by RFC 2822.
+
+        continuation_ws must be RFC 2822 compliant folding whitespace (usually
+        either a space or a hard tab) which will be prepended to continuation
+        lines.
+
+        errors is passed through to the .append() call.
+        """
+        if charset is None:
+            charset = USASCII
+        elif not isinstance(charset, Charset):
+            charset = Charset(charset)
+        self._charset = charset
+        self._continuation_ws = continuation_ws
+        self._chunks = []
+        if s is not None:
+            self.append(s, charset, errors)
+        if maxlinelen is None:
+            maxlinelen = MAXLINELEN
+        self._maxlinelen = maxlinelen
+        if header_name is None:
+            self._headerlen = 0
+        else:
+            # Take the separating colon and space into account.
+            self._headerlen = len(header_name) + 2
+
+    def __str__(self):
+        """Return the string value of the header."""
+        self._normalize()
+        uchunks = []
+        lastcs = None
+        lastspace = None
+        for string, charset in self._chunks:
+            # We must preserve spaces between encoded and non-encoded word
+            # boundaries, which means for us we need to add a space when we go
+            # from a charset to None/us-ascii, or from None/us-ascii to a
+            # charset.  Only do this for the second and subsequent chunks.
+            # Don't add a space if the None/us-ascii string already has
+            # a space (trailing or leading depending on transition)
+            nextcs = charset
+            if nextcs == _charset.UNKNOWN8BIT:
+                original_bytes = string.encode('ascii', 'surrogateescape')
+                string = original_bytes.decode('ascii', 'replace')
+            if uchunks:
+                hasspace = string and self._nonctext(string[0])
+                if lastcs not in (None, 'us-ascii'):
+                    if nextcs in (None, 'us-ascii') and not hasspace:
+                        uchunks.append(SPACE)
+                        nextcs = None
+                elif nextcs not in (None, 'us-ascii') and not lastspace:
+                    uchunks.append(SPACE)
+            lastspace = string and self._nonctext(string[-1])
+            lastcs = nextcs
+            uchunks.append(string)
+        return EMPTYSTRING.join(uchunks)
+
+    # Rich comparison operators for equality only.  BAW: does it make sense to
+    # have or explicitly disable <, <=, >, >= operators?
+    def __eq__(self, other):
+        # other may be a Header or a string.  Both are fine so coerce
+        # ourselves to a unicode (of the unencoded header value), swap the
+        # args and do another comparison.
+        return other == str(self)
+
+    def __ne__(self, other):
+        return not self == other
+
+    def append(self, s, charset=None, errors='strict'):
+        """Append a string to the MIME header.
+
+        Optional charset, if given, should be a Charset instance or the name
+        of a character set (which will be converted to a Charset instance).  A
+        value of None (the default) means that the charset given in the
+        constructor is used.
+
+        s may be a byte string or a Unicode string.  If it is a byte string
+        (i.e. isinstance(s, str) is false), then charset is the encoding of
+        that byte string, and a UnicodeError will be raised if the string
+        cannot be decoded with that charset.  If s is a Unicode string, then
+        charset is a hint specifying the character set of the characters in
+        the string.  In either case, when producing an RFC 2822 compliant
+        header using RFC 2047 rules, the string will be encoded using the
+        output codec of the charset.  If the string cannot be encoded to the
+        output codec, a UnicodeError will be raised.
+
+        Optional `errors' is passed as the errors argument to the decode
+        call if s is a byte string.
+        """
+        if charset is None:
+            charset = self._charset
+        elif not isinstance(charset, Charset):
+            charset = Charset(charset)
+        if not isinstance(s, str):
+            input_charset = charset.input_codec or 'us-ascii'
+            if input_charset == _charset.UNKNOWN8BIT:
+                s = s.decode('us-ascii', 'surrogateescape')
+            else:
+                s = s.decode(input_charset, errors)
+        # Ensure that the bytes we're storing can be decoded to the output
+        # character set, otherwise an early error is raised.
+        output_charset = charset.output_codec or 'us-ascii'
+        if output_charset != _charset.UNKNOWN8BIT:
+            try:
+                s.encode(output_charset, errors)
+            except UnicodeEncodeError:
+                if output_charset!='us-ascii':
+                    raise
+                charset = UTF8
+        self._chunks.append((s, charset))
+
+    def _nonctext(self, s):
+        """True if string s is not a ctext character of RFC822.
+        """
+        return s.isspace() or s in ('(', ')', '\\')
+
+    def encode(self, splitchars=';, \t', maxlinelen=None, linesep='\n'):
+        r"""Encode a message header into an RFC-compliant format.
+
+        There are many issues involved in converting a given string for use in
+        an email header.  Only certain character sets are readable in most
+        email clients, and as header strings can only contain a subset of
+        7-bit ASCII, care must be taken to properly convert and encode (with
+        Base64 or quoted-printable) header strings.  In addition, there is a
+        75-character length limit on any given encoded header field, so
+        line-wrapping must be performed, even with double-byte character sets.
+
+        Optional maxlinelen specifies the maximum length of each generated
+        line, exclusive of the linesep string.  Individual lines may be longer
+        than maxlinelen if a folding point cannot be found.  The first line
+        will be shorter by the length of the header name plus ": " if a header
+        name was specified at Header construction time.  The default value for
+        maxlinelen is determined at header construction time.
+
+        Optional splitchars is a string containing characters which should be
+        given extra weight by the splitting algorithm during normal header
+        wrapping.  This is in very rough support of RFC 2822's `higher level
+        syntactic breaks':  split points preceded by a splitchar are preferred
+        during line splitting, with the characters preferred in the order in
+        which they appear in the string.  Space and tab may be included in the
+        string to indicate whether preference should be given to one over the
+        other as a split point when other split chars do not appear in the line
+        being split.  Splitchars does not affect RFC 2047 encoded lines.
+
+        Optional linesep is a string to be used to separate the lines of
+        the value.  The default value is the most useful for typical
+        Python applications, but it can be set to \r\n to produce RFC-compliant
+        line separators when needed.
+        """
+        self._normalize()
+        if maxlinelen is None:
+            maxlinelen = self._maxlinelen
+        # A maxlinelen of 0 means don't wrap.  For all practical purposes,
+        # choosing a huge number here accomplishes that and makes the
+        # _ValueFormatter algorithm much simpler.
+        if maxlinelen == 0:
+            maxlinelen = 1000000
+        formatter = _ValueFormatter(self._headerlen, maxlinelen,
+                                    self._continuation_ws, splitchars)
+        lastcs = None
+        hasspace = lastspace = None
+        for string, charset in self._chunks:
+            if hasspace is not None:
+                hasspace = string and self._nonctext(string[0])
+                import sys
+                if lastcs not in (None, 'us-ascii'):
+                    if not hasspace or charset not in (None, 'us-ascii'):
+                        formatter.add_transition()
+                elif charset not in (None, 'us-ascii') and not lastspace:
+                    formatter.add_transition()
+            lastspace = string and self._nonctext(string[-1])
+            lastcs = charset
+            hasspace = False
+            lines = string.splitlines()
+            if lines:
+                formatter.feed('', lines[0], charset)
+            else:
+                formatter.feed('', '', charset)
+            for line in lines[1:]:
+                formatter.newline()
+                if charset.header_encoding is not None:
+                    formatter.feed(self._continuation_ws, ' ' + line.lstrip(),
+                                   charset)
+                else:
+                    sline = line.lstrip()
+                    fws = line[:len(line)-len(sline)]
+                    formatter.feed(fws, sline, charset)
+            if len(lines) > 1:
+                formatter.newline()
+        if self._chunks:
+            formatter.add_transition()
+        value = formatter._str(linesep)
+        if _embeded_header.search(value):
+            raise HeaderParseError("header value appears to contain "
+                "an embedded header: {!r}".format(value))
+        return value
+
+    def _normalize(self):
+        # Step 1: Normalize the chunks so that all runs of identical charsets
+        # get collapsed into a single unicode string.
+        chunks = []
+        last_charset = None
+        last_chunk = []
+        for string, charset in self._chunks:
+            if charset == last_charset:
+                last_chunk.append(string)
+            else:
+                if last_charset is not None:
+                    chunks.append((SPACE.join(last_chunk), last_charset))
+                last_chunk = [string]
+                last_charset = charset
+        if last_chunk:
+            chunks.append((SPACE.join(last_chunk), last_charset))
+        self._chunks = chunks
+
+
+class _ValueFormatter(object):
+    def __init__(self, headerlen, maxlen, continuation_ws, splitchars):
+        self._maxlen = maxlen
+        self._continuation_ws = continuation_ws
+        self._continuation_ws_len = len(continuation_ws)
+        self._splitchars = splitchars
+        self._lines = []
+        self._current_line = _Accumulator(headerlen)
+
+    def _str(self, linesep):
+        self.newline()
+        return linesep.join(self._lines)
+
+    def __str__(self):
+        return self._str(NL)
+
+    def newline(self):
+        end_of_line = self._current_line.pop()
+        if end_of_line != (' ', ''):
+            self._current_line.push(*end_of_line)
+        if len(self._current_line) > 0:
+            if self._current_line.is_onlyws():
+                self._lines[-1] += str(self._current_line)
+            else:
+                self._lines.append(str(self._current_line))
+        self._current_line.reset()
+
+    def add_transition(self):
+        self._current_line.push(' ', '')
+
+    def feed(self, fws, string, charset):
+        # If the charset has no header encoding (i.e. it is an ASCII encoding)
+        # then we must split the header 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 commas, then
+        # whitespace.  Eventually, this should be pluggable.
+        if charset.header_encoding is None:
+            self._ascii_split(fws, string, self._splitchars)
+            return
+        # Otherwise, we're doing either a Base64 or a quoted-printable
+        # encoding which means we don't need to split the line on syntactic
+        # breaks.  We can basically just find enough characters to fit on the
+        # current line, minus the RFC 2047 chrome.  What makes this trickier
+        # though is that we have to split at octet boundaries, not character
+        # boundaries but it's only safe to split at character boundaries so at
+        # best we can only get close.
+        encoded_lines = charset.header_encode_lines(string, self._maxlengths())
+        # The first element extends the current line, but if it's None then
+        # nothing more fit on the current line so start a new line.
+        try:
+            first_line = encoded_lines.pop(0)
+        except IndexError:
+            # There are no encoded lines, so we're done.
+            return
+        if first_line is not None:
+            self._append_chunk(fws, first_line)
+        try:
+            last_line = encoded_lines.pop()
+        except IndexError:
+            # There was only one line.
+            return
+        self.newline()
+        self._current_line.push(self._continuation_ws, last_line)
+        # Everything else are full lines in themselves.
+        for line in encoded_lines:
+            self._lines.append(self._continuation_ws + line)
+
+    def _maxlengths(self):
+        # The first line's length.
+        yield self._maxlen - len(self._current_line)
+        while True:
+            yield self._maxlen - self._continuation_ws_len
+
+    def _ascii_split(self, fws, string, splitchars):
+        # The RFC 2822 header folding algorithm is simple in principle but
+        # complex in practice.  Lines may be folded any place where "folding
+        # white space" appears by inserting a linesep character in front of the
+        # FWS.  The complication is that not all spaces or tabs qualify as FWS,
+        # and we are also supposed to prefer to break at "higher level
+        # syntactic breaks".  We can't do either of these without intimate
+        # knowledge of the structure of structured headers, which we don't have
+        # here.  So the best we can do here is prefer to break at the specified
+        # splitchars, and hope that we don't choose any spaces or tabs that
+        # aren't legal FWS.  (This is at least better than the old algorithm,
+        # where we would sometimes *introduce* FWS after a splitchar, or the
+        # algorithm before that, where we would turn all white space runs into
+        # single spaces or tabs.)
+        parts = re.split("(["+FWS+"]+)", fws+string)
+        if parts[0]:
+            parts[:0] = ['']
+        else:
+            parts.pop(0)
+        for fws, part in zip(*[iter(parts)]*2):
+            self._append_chunk(fws, part)
+
+    def _append_chunk(self, fws, string):
+        self._current_line.push(fws, string)
+        if len(self._current_line) > self._maxlen:
+            # Find the best split point, working backward from the end.
+            # There might be none, on a long first line.
+            for ch in self._splitchars:
+                for i in range(self._current_line.part_count()-1, 0, -1):
+                    if ch.isspace():
+                        fws = self._current_line[i][0]
+                        if fws and fws[0]==ch:
+                            break
+                    prevpart = self._current_line[i-1][1]
+                    if prevpart and prevpart[-1]==ch:
+                        break
+                else:
+                    continue
+                break
+            else:
+                fws, part = self._current_line.pop()
+                if self._current_line._initial_size > 0:
+                    # There will be a header, so leave it on a line by itself.
+                    self.newline()
+                    if not fws:
+                        # We don't use continuation_ws here because the whitespace
+                        # after a header should always be a space.
+                        fws = ' '
+                self._current_line.push(fws, part)
+                return
+            remainder = self._current_line.pop_from(i)
+            self._lines.append(str(self._current_line))
+            self._current_line.reset(remainder)
+
+
+class _Accumulator(list):
+
+    def __init__(self, initial_size=0):
+        self._initial_size = initial_size
+        super().__init__()
+
+    def push(self, fws, string):
+        self.append((fws, string))
+
+    def pop_from(self, i=0):
+        popped = self[i:]
+        self[i:] = []
+        return popped
+
+    def pop(self):
+        if self.part_count()==0:
+            return ('', '')
+        return super().pop()
+
+    def __len__(self):
+        return sum((len(fws)+len(part) for fws, part in self),
+                   self._initial_size)
+
+    def __str__(self):
+        return EMPTYSTRING.join((EMPTYSTRING.join((fws, part))
+                                for fws, part in self))
+
+    def reset(self, startval=None):
+        if startval is None:
+            startval = []
+        self[:] = startval
+        self._initial_size = 0
+
+    def is_onlyws(self):
+        return self._initial_size==0 and (not self or str(self).isspace())
+
+    def part_count(self):
+        return super().__len__()