email.header.decode_header makes mistakes

[a7220865-50c5-40ed-8425-d0c4c0e25af6]

BPO	8132
Nosy	@bitdancer

^{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: ```python assignee = None closed_at = created_at = labels = ['invalid', 'type-bug', 'library'] title = 'email.header.decode_header makes mistakes' updated_at = user = 'https://bugs.python.org/grmtz' ``` bugs.python.org fields: ```python activity = actor = 'r.david.murray' assignee = 'none' closed = True closed_date = closer = 'r.david.murray' components = ['Library (Lib)'] creation = creator = 'grmtz' dependencies = [] files = [] hgrepos = [] issue_num = 8132 keywords = [] message_count = 2.0 messages = ['101004', '101039'] nosy_count = 2.0 nosy_names = ['r.david.murray', 'grmtz'] pr_nums = [] priority = 'normal' resolution = 'not a bug' stage = 'resolved' status = 'closed' superseder = None type = 'behavior' url = 'https://bugs.python.org/issue8132' versions = ['Python 2.6'] ```

[a7220865-50c5-40ed-8425-d0c4c0e25af6]

Examples:

s = '=?UTF-8?B?QWNjdXPDqSBkZSByw6ljZXB0aW9uIChhZmZpY2jDqSkgLSA=?=Arobase !' decode_header(s) ---> [('=?UTF-8?B?QWNjdXPDqSBkZSByw6ljZXB0aW9uIChhZmZpY2jDqSkgLSA=?=Arobase !', None)] which seems bad... but ss ='=?UTF-8?B?QWNjdXPDqSBkZSByw6ljZXB0aW9uIChhZmZpY2jDqSkgLSA=?= Arobase !' decode_header(ss) ---> [('Accus\xc3\xa9 de r\xc3\xa9ception (affich\xc3\xa9) - ', 'utf-8'), ('Arobase !', None)] which seems good...

[bitdancer]

Per the RFC, this is the correct behavior. An encoded word *must* begin and end either at the field boundary or with whitespace. So ...?=Arobase, with no whitespace between the = and Arobase, makes your first example into an invalid encoded word, and thus it is returned as if it were plain ASCII.

One could argue that email could be smarter and interpret this string as an encoded word anyway, following the Postel principle (be generous in what you accept), but it currently does not do so, and not doing so is not a bug.

email6 will handle such non-RFC compliant examples better, if all goes well.