On 2013-10-9 6:22 pm, Andreas Schmidt wrote:
> Hi,
>
> I recently had to inflate a malformed compressed (RFC1950) string. The
> zlib magicbytes as well as the adler32-crc were missing.
> I tried different ways to inflate the string. First I prepended the zlib
> magic byte "\x78\x01" without success. 2nd I used the Zlib::Inflate
> object and pipedin the magicbytes which worked to my surprise.
> Can anybody tell me the difference of the internal behaviour of zlib, or
> is it a bug?
You'll probably need to check zlib more than in Ruby... but my _guess_
is that when you add the bytes and call inflate, it expects the data to
be well-formed incl the CRC.
However, when you stream it in, it is probably deflating the stream as
it gets it but when you don't supply the CRC, it is able to return what
was inflated, but is unable to confirm if the data is actually correct
since the CRC has not been verified.
In fact, if you see this function at https://www.zlib.net/manual.html:
ZEXTERN int ZEXPORT inflate(z_streamp strm, int flush);
> inflate decompresses as much data as possible, and stops when the
input buffer becomes empty or the output buffer becomes full. It may
introduce some output latency (reading input without producing any
output) except when forced to flush.
It adds:
> If a preset dictionary is needed after this call (see
inflateSetDictionary below), inflate sets strm->adler to the Adler-32
checksum of the dictionary chosen by the compressor and returns
Z_NEED_DICT; otherwise it sets strm->adler to the Adler-32 checksum of
all output produced so far (that is, total_out bytes) and returns Z_OK,
Z_STREAM_END or an error code as described below.
> At the end of the stream, inflate() checks that its computed Adler-32
checksum is equal to that saved by the compressor and returns
Z_STREAM_END only if the checksum is correct.
So, if it does not know that the stream has ended, it does not confirm
that checksum but returns data up to that point (till the end, in your
case).
Hope this helps.
Best regards,
Mohit.
sexp_processor version 4.17.4 has been released!
* home: <https://github.com/seattlerb/sexp_processor>
* rdoc: <http://docs.seattlerb.org/sexp_processor>
sexp_processor branches from ParseTree bringing all the generic sexp
processing tools with it. Sexp, SexpProcessor, Environment, etc... all
for your language processing pleasure.
Changes:
### 4.17.4 / 2025-09-02
This release was brought to you by ScotRail free WiFi!
* 1 minor enhancement:
* Added 3.4 to pt_testcase.rb.
