ietf-822
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Re: Is 8BIT ESTMP really needed

2001-05-10 08:47:54
chl(_at_)clw(_dot_)cs(_dot_)man(_dot_)ac(_dot_)uk (Charles Lindsey) writes:

Suppose your message has Content-Type: application/foo (there is never any
problem with text/plain). The body of the message is
    fooCRbarLFbazCRLF
(the naked CR and LF are a 'feature' os the application/foo protocol).
Suppose you decide to encode it in QP (maybe not the wisest choice, but
legal).

Just a note that there are real examples of this out there:

Gnus used to (or maybe it still does) encode binary attachments as
QP/B64 depending on which resulted in the smallest size.  As it
happened, PDF files often contain lots of ASCII and only a little
binary data, so it would often be encoded as QP.

And this is an entirely reasonable thing to do.

In addition of causing problems with QP-encoded binary contents in
some clients, up/down-conversion of the PDF file sometimes caused the
content to be unreadable.

Then that's a problem with the conversion. Just because it is encoded using
QP doesn't mean it is text. And you'll find precious little support for any
such view in the MIME RFCs.

So it's not only an issue of MD5 or digital
signatures, but of actually being able to transfer the data.  So in
practice QP seem to be "for text only".

I have not found this to be the case. If anything I've found that the
assumption has been anything encoded cannot be assumed to be text even if the
content type says it is. This can be annoying but doesn't cause problems in
practice.

Now, in the early days of MIME there were a variety of problems with various
encoders and decoders. For example, there was a popular base64 encoder that did
the 3-in-4 thing backwards from everyone else's. I don't recall bogus
upconversion of QP being a problem specifically, but anything is possible. But
most of these early problems have long since been fixed.

Of course it is impossible to prove a negative. And the Internet is so large
that it is quite possible for there to be aberrant behavior in various places
that few if any of us are aware of. But I can say that software I've written
uses exactly the same approach as what you say Gnus uses, that software is in
widespread use, I've personally seen every problem report ever sent to the
vendor regarding this software, and I don't recall any reports of this sort of
problem.

                                Ned