On Apr 9, 2009, at 10:38 PM, Barry Warsaw wrote:
> So, what I'm really asking is this. Let's say you agree that there
> are use cases for accessing a header value as either the raw encoded
> bytes or the decoded unicode.
As I said in the thread having nearly the same exact discussion on web-
sig, except about WSGI headers...
> What should this return:
>
> >>> message['Subject']
>
> The raw bytes or the decoded unicode?
Until you write a parser for every header, you simply cannot decode to
unicode. The only sane choices are:
1) raw bytes
2) parsed structured data
There's no "decoded to unicode but not parsed" option: that's doing
things in the wrong order. If you RFC2047-decode the header before
doing tokenization and parsing, you will just have a *broken*
implementation.
Here's an example where it matters. If you decode the RFC2047 part
before parsing, you'd decide that there's two recipients to the
message. There aren't. "<broken at example.com>, " is the display-name of
"actual at example.com", not a second recipient.
To: =?UTF-8?B?PGJyb2tlbkBleGFtcGxlLmNvbT4sIA==?= <actual at example.com>
Here's a quote from RFC2047:
> NOTE: Decoding and display of encoded-words occurs *after* a
> structured field body is parsed into tokens. It is therefore
> possible to hide 'special' characters in encoded-words which, when
> displayed, will be indistinguishable from 'special' characters in
> the surrounding text. For this and other reasons, it is NOT
> generally possible to translate a message header containing 'encoded-
> word's to an unencoded form which can be parsed by an RFC 822 mail
> reader.
And another quote for good measure:
> (2) Any header field not defined as '*text' should be parsed
> according to the syntax rules for that header field. However, any
> 'word' that appears within a 'phrase' should be treated as an
> 'encoded-word' if it meets the syntax rules in section 2. Otherwise
> it should be treated as an ordinary 'word'.
Now, I suppose there's also a third possibility:
3) US-ASCII-only strings, unmolested except for doing
a .decode('ascii'). That'll give you a string all right, but it's
really just cheating. It's not actually a text string in any
meaningful sense.
(in all this I'm assuming your question is not about the "Subject"
header in particular; that is of course just unstructured text so the
parse step doesn't actually do anything...).
James
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