ietf-822
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Re: A Kinder, Gentler New Draft

1991-04-23 10:03:06
One of the more common Content-Encodings I'm seeing right now is
uuencoded-compressed.  Would this be Content-Encoding "BASE64"?  How
does one talk about the compression?  Or is it simply not a valid
encoding?

No, the encoding table specified for Base64 does not match the encoding
table which uuencode uses.  The technique is extraordinarily similar,
however.  It would be a Very Good thing if uuencode were included in
the standard, regardless of its warts (using trailing blanks for
instance).  Specifying that the uuencode used be the version which does
a checksum for each line avoids the trailing blank problem and provides
a bit more assurance that "it worked" ...

As for compression .. It belongs in either Content-Encoding:  or
Content-Type:.  What you really have is a sequence of possible
encodings which can be placed on a file, as we all know.  It would be
good to be able to specify a sequence of encodings which were applied
to the data.  We might as well seperate the ultimate data type from the
encodings used, as the end-user is going to be mainly interested in
that and rather uninterested in what magic was performed to get it to
him/her.

Suggestion:

        Content-Type := type [ ";" ver-num [ ";" 1#resource-ref ]]
                [In other words, unchanged from before]

        Content-Encoding := 1#content-encoding-type

        content-encoding-type := "Base64" /
                                 "UUENCODE" /
                                 "UUENCODE-CRC" /
                                 "HEXADECIMAL" /
                                 "QUOTED-PRINTABLE" /
                                 "8BIT" / "BINARY" /
                                 "7BIT" /
                                 "LZW-COMPRESS" /
                                 "HUFF-COMPRESS" /
                                 "other-COMPRESS" /
                                 "X-"atom

Example:

        Content-Type: PPM
        Content-Encoding: uuencode-crc lzw-compress


I am having a hard time coming up with an example which would include
more levels of encoding.  But why limit ourselves needlessly?

The Content-Encoding: likely should be a comma-seperated list.  This
is to allow for richer encoding types.  Repeating the example above:


        Content-Type: PPM
        Content-Encoding: uuencode crc, lzw-compress 12bit





                                David


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