[fpc-pascal] TStream descendant to compress/decompress gzip data from another stream

[Flávio Etrusco]

On Thu, Mar 28, 2013 at 8:51 AM, José Mejuto <joshyfun at gmail.com> wrote:
> El 28/03/2013 1:06, Ewald escribió:
>
>
>>>> Google found an old thread on lazarus mailing list about this ("FPC,
>>>> gzip and stream") but without any solution, everything mentioned there
>>>> has either the limitations of TCompressionStream/TDecompressionStream
>>>> (no gzip format) or TGZFileStream (not able to work wit ObjectPascal
>>>> streams).
>>>
>>>
>>> Hello,
>>>
>>> .gz is a quite simple format, but it can not be implemented as a TStream
>>> (only) descendant because in a single .gz file many files could be added so
>>> something like the class to handle .zip files should be used.
>>
>>
>> Sorry to just drop in on this quite late, but isn't gzip  a compression
>> algorithm and not a file format as such? gzip (the command line utility)
>> only compresses one file and *doesn't* put this in a multi-file container.
>> To get `multi-file gzips`, you will first want to bundle the files and
>> compress this bundle (files -> tar -> gzip) or compress the files separately
>> and then bundle them together (files -> multiple separate gzipped files ->
>> tar). Or are we talking about a different gzip here?
>>
>
> Hello,
>
> Just quoting the RFC1952 about .gz format:
>
> --- http://tools.ietf.org/html/rfc1952 --------
>
> 2.2. File format
>
>       A gzip file consists of a series of "members" (compressed data
>       sets).  The format of each member is specified in the following
>       section.  The members simply appear one after another in the file,
>       with no additional information before, between, or after them.
>
> -----------------------------------------------
>
> So I think it is legal to concatenate several .gz files and get a final .gz
> with several files inside.
>
> In the other hand, yes, the usual behavior in .gz is to store only one file.
>
> --

"Members" refer to each available section according to the flags.
Re-read this whole paragraph you posted and a few following you'll
realize only one "file" is allowed in a gzip file/blob.

-Flávio