[NNTP] NNTP Compression
murch at andrew.cmu.edu
Sat Jan 23 08:29:47 PST 2010
Julien ÉLIE wrote:
> Does MODE COMPRESS do the same thing as COMPRESS? I see an explanation
> but as I do not know zlib APIs, I am unsure it does the same thing.
I'd have to look at the zlib docs and the actual Diablo code (which I
have no desire to do), but tt looks like MODE COMPRESS is actually
putting a gzip header on each chunk of compressed data. The COMPRESS
command as standardized by IMAP/NNTP COMPRESS doesn't bother putting an
unnecessary header on the data. That's why IMAP/NNTP COMPRESS uses
[de|in]flatInit2() calls rather than the simpler [de|in]flateInit(), so
it can specify more params rather than using defaults.
>> * The text referring to attachments needs work. Should we discuss yEnc
>> and/or uuencode? I'm not sure the text regarding binary form even applies
>> to NNTP.
> When you say:
> > A very simple strategy is to change the level to 0 at the start of
> > a multi-line data block provided the first two bytes are either
> > 0x1F 0x8B (as in deflate-compressed files) or 0xFF 0xD8 (JPEG),
> > and to keep it at 1-5 the rest of the time.
> It would apply to BODY only (at the start of a multi-line data block).
It would also apply to ARTICLE, POST, IHAVE, TAKETHIS.
> But we usually have a MIME message or yEnc. Not a binary file.
Correct, so this text can probably be removed. IMAP has the ability to
fetch individual MIME parts, and an extension to do so with any CTE
> Maybe yEnc and uuencode should be mentioned, yes.
yEnc and uuencode most likely would be similar to base64 in terms of how
to handle them.
> Besides, in Section 3 about compression efficiency, can another type
> of data be mentioned? I think about overview data (OVER), HDR and
> LIST answers. Maybe also NEWNEWS answers.
All NNTP data other than large article bodies fall into the same
category, so I don't think we need to mention all of them specifically.
>> In order to increase interoperability, it is desirable to have as few
>> different compression algorithms as possible, so this document specifies
>> only one.
> Why couldn't we define several algorithms (some are more efficient than
> DEFLATE, for instance LZMA or LZMA2) and say that DEFLATE *MUST* be
> implemented when COMPRESS is implemented?
Well, IMAP/NNTP COMPRESS are really just stop-gaps until existing TLS
implementations support compression. As mentioned in the text TLS
really should be the preferred way to negotiate compression. So I don't
see the need to add more algorithms to NNTP COMPRESS.
>> Second [...] Third
>> independent of the order
> Isn't it better to use "Secondly", "Thirdly"/"Finally", "independently of"?
This text was already approved by the LEMONADE WG and the RFC editor, so
I don't see any need to change it.
>> Example of a server failing to activate compression:
>> [C] CAPABILITIES
>> [S] 101 Capability list:
>> [S] VERSION 2
>> [S] COMPRESS DEFLATE
>> [S] .
> That example is weird: a news server that requires compression to show
> other commands. Maybe IHAVE and STREAMING should also be advertised?
> (case of a transit-only server)
Yes, you're right. I was trying to keep extra clutter out of the
examples, but I do need to add reader and/or feeder commands.
> Are there SASL mechanisms that negotiate a compression layer? I think not,
> but better ask...
No currently. Again, TLS is the preferred method for negotiating
Carnegie Mellon University
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