#23745: handle duplicate MIME parameter names in new parser.

This mimics get_param's error handling for the most part.  It is slightly
better in some regards as get_param can produce some really weird results for
duplicate *0* parts.  It departs from get_param slightly in that if we have a
mix of non-extended and extended pieces for the same parameter name, the new
parser assumes they were all supposed to be extended and concatenates all the
values, whereas get_param always picks the non-extended parameter value.  All
of this error recovery is pretty much arbitrary decisions...

1 files changed, 27 insertions, 7 deletions

diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index 1806cac..a9bdf44 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -71,6 +71,7 @@ import re
 import urllib   # For urllib.parse.unquote
 from string import hexdigits
 from collections import OrderedDict
+from operator import itemgetter
 from email import _encoded_words as _ew
 from email import errors
 from email import utils
@@ -1098,15 +1099,34 @@ class MimeParameters(TokenList):
                 params[name] = []
             params[name].append((token.section_number, token))
         for name, parts in params.items():
-            parts = sorted(parts)
-            # XXX: there might be more recovery we could do here if, for
-            # example, this is really a case of a duplicate attribute name.
+            parts = sorted(parts, key=itemgetter(0))
+            first_param = parts[0][1]
+            charset = first_param.charset
+            # Our arbitrary error recovery is to ignore duplicate parameters,
+            # to use appearance order if there are duplicate rfc 2231 parts,
+            # and to ignore gaps.  This mimics the error recovery of get_param.
+            if not first_param.extended and len(parts) > 1:
+                if parts[1][0] == 0:
+                    parts[1][1].defects.append(errors.InvalidHeaderDefect(
+                        'duplicate parameter name; duplicate(s) ignored'))
+                    parts = parts[:1]
+                # Else assume the *0* was missing...note that this is different
+                # from get_param, but we registered a defect for this earlier.
             value_parts = []
-            charset = parts[0][1].charset
-            for i, (section_number, param) in enumerate(parts):
+            i = 0
+            for section_number, param in parts:
                 if section_number != i:
-                    param.defects.append(errors.InvalidHeaderDefect(
-                        "inconsistent multipart parameter numbering"))
+                    # We could get fancier here and look for a complete
+                    # duplicate extended parameter and ignore the second one
+                    # seen.  But we're not doing that.  The old code didn't.
+                    if not param.extended:
+                        param.defects.append(errors.InvalidHeaderDefect(
+                            'duplicate parameter name; duplicate ignored'))
+                        continue
+                    else:
+                        param.defects.append(errors.InvalidHeaderDefect(
+                            "inconsistent RFC2231 parameter numbering"))
+                i += 1
                 value = param.param_value
                 if param.extended:
                     try: