Some invalid email address groups cause an IndexError instead of a HeaderParseError

[mtorromeo]

BPO	32178
Nosy	@warsaw, @bitdancer, @maxking, @csabella, @mtorromeo, @miss-islington
PRs	bpo-32178: Fix IndexError on invalid email group header parsing #4642 bpo-32178: Fix IndexError trying to parse 'To' header starting with ':'. #15044 [3.8] bpo-32178: Fix IndexError trying to parse 'To' header starting with ':'. (GH-15044) #15213 [3.7] bpo-32178: Fix IndexError trying to parse 'To' header starting with ':'. (GH-15044) #15214

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-08-11.21:09:42.939>
created_at = <Date 2017-11-30.10:40:34.903>
labels = ['3.8', 'type-bug', '3.7', 'expert-email', '3.9']
title = 'Some invalid email address groups cause an IndexError instead of a HeaderParseError'
updated_at = <Date 2019-08-11.21:09:42.931>
user = 'https://github.com/mtorromeo'

bugs.python.org fields:

activity = <Date 2019-08-11.21:09:42.931>
actor = 'maxking'
assignee = 'none'
closed = True
closed_date = <Date 2019-08-11.21:09:42.939>
closer = 'maxking'
components = ['email']
creation = <Date 2017-11-30.10:40:34.903>
creator = 'mtorromeo'
dependencies = []
files = []
hgrepos = []
issue_num = 32178
keywords = ['patch']
message_count = 9.0
messages = ['307285', '307291', '307293', '345627', '347248', '347585', '349407', '349408', '349409']
nosy_count = 6.0
nosy_names = ['barry', 'r.david.murray', 'maxking', 'cheryl.sabella', 'mtorromeo', 'miss-islington']
pr_nums = ['4642', '15044', '15213', '15214']
priority = 'normal'
resolution = None
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32178'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[mtorromeo]

With some malformed email address list, the parser for email groups raises an IndexError instead of the correct HeaderParseError.

This results in a complete failure to parse the email while it is still preferable to just ignore the malformed header.

An example of such a malformed list is this:
To: :Foo <foo@example.com> <bar@example.com>

[mtorromeo]

In case an address email header contains and empty string, the tokenizer return a BareQuotedString
which is also a TokenList, but this list is empty and the parser fails to check this and insteads raises an IndexError.

For example an email with this header will trigger the IndexError:
ReplyTo: ""

[mtorromeo]

Disregard my last message, I posted it in the wrong bug report by mistake.
Sorry about the noise

[maxking]

I don't think this is an issue anymore, I guess this was fixed as a part of some other PR.

I tested this out on a recent branch:

   >>> import email
   >>> msg = email.message_from_string('From: Abhilash <maxking@email.com> <Another@some.com>')
   >>> msg['From'] 
   'Abhilash <maxking@email.com> <Another@some.com>'

@david, @barry: I think we can close this issue.

[csabella]

Based on @maxking's comment, I'm going to close this issue. Thank you!

[bitdancer]

The fact that the original report mentions HeaderParserError implies that the new API is being used, though the report didn't make that clear. The problem still exists:

>>> m = message_from_string("To: :Foo <foo@example.com> <bar@example.com>\n\n", policy=default)
>>> m['To']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/rdmurray/python/p38/Lib/email/message.py", line 391, in __getitem__
    return self.get(name)
  File "/home/rdmurray/python/p38/Lib/email/message.py", line 471, in get
    return self.policy.header_fetch_parse(k, v)
  File "/home/rdmurray/python/p38/Lib/email/policy.py", line 163, in header_fetch_parse
    return self.header_factory(name, value)
  File "/home/rdmurray/python/p38/Lib/email/headerregistry.py", line 602, in __call__
    return self[name](name, value)
  File "/home/rdmurray/python/p38/Lib/email/headerregistry.py", line 197, in __new__
    cls.parse(value, kwds)
  File "/home/rdmurray/python/p38/Lib/email/headerregistry.py", line 343, in parse
    groups.append(Group(addr.display_name,
  File "/home/rdmurray/python/p38/Lib/email/_header_value_parser.py", line 315, in display_name
    return self[0].display_name
  File "/home/rdmurray/python/p38/Lib/email/_header_value_parser.py", line 382, in display_name
    return self[0].display_name
  File "/home/rdmurray/python/p38/Lib/email/_header_value_parser.py", line 564, in display_name
    if res[0].token_type == 'cfws':
IndexError: list index out of range

[miss-islington]

New changeset 09a1872 by Miss Islington (bot) (Abhilash Raj) in branch 'master':
bpo-32178: Fix IndexError trying to parse 'To' header starting with ':'. (GH-15044)
09a1872

[miss-islington]

New changeset 9500bbe by Miss Islington (bot) in branch '3.8':
bpo-32178: Fix IndexError trying to parse 'To' header starting with ':'. (GH-15044)
9500bbe

[miss-islington]

New changeset dec231a by Miss Islington (bot) in branch '3.7':
bpo-32178: Fix IndexError trying to parse 'To' header starting with ':'. (GH-15044)
dec231a