zlib compression - verifying it
grarpamp
How can I verify and test that a given openssl binary
installation supports zlib compression?
Can I simply [un]compress a file with openssl and
do the reverse with gzip as a command line test?
s_client and s_server?
Are the zlib and zlib-dynamic options intended to be
exclusive?
Or is zlib-dynamic considered an optional additional
flag to the zlib option?
Guess I'm having trouble understanding this part
and finding appropriate docs. Thanks :)
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Dr. Stephen Henson
> Hello.
>
> How can I verify and test that a given openssl binary
> installation supports zlib compression?
> Can I simply [un]compress a file with openssl and
> do the reverse with gzip as a command line test?
> s_client and s_server?
>
The OpenSSL use of zlib is currently not compatible with gzip: it just uses
the raw zlib format which is suitable for use in the CMS compressed data type
and SSL/TLS compression.
If the binary supports zlib compression then
> Are the zlib and zlib-dynamic options intended to be
> exclusive?
> Or is zlib-dynamic considered an optional additional
> flag to the zlib option?
>
> Guess I'm having trouble understanding this part
> and finding appropriate docs. Thanks :)
--
Dr Stephen N. Henson. OpenSSL project core developer.
Commercial tech support now available see: http://www.openssl.org
Dr. Stephen Henson
>
> How can I verify and test that a given openssl binary
> installation supports zlib compression?
> Can I simply [un]compress a file with openssl and
> do the reverse with gzip as a command line test?
> s_client and s_server?
>
The OpenSSL use of zlib is currently not compatible with gzip: it just uses
the raw zlib format which is suitable for use in the CMS compressed data type
and SSL/TLS compression.
If the binary supports zlib compression then you can see this with the openssl
utility. If you do: openssl version -f if zlib is supported you'll see the
option -DZLIB present. If zlib-shared is set you'll also see -DZLIB_SHARED
> Are the zlib and zlib-dynamic options intended to be
> exclusive?
> Or is zlib-dynamic considered an optional additional
> flag to the zlib option?
>
> Guess I'm having trouble understanding this part
> and finding appropriate docs. Thanks :)
Well zlib-dynamic enables zlib support so using both is the same as just
specifying zlib-dynamic.
With just zlib the zlib library is statically linked into OpenSSL meaning that
there is a dependency on the zlib library.
With zlib-dynamic an attempt is made to dynamically load the zlib library and
use it. If it can't be loaded then zlib support is simply disabled. This is
useful for binary distributions where zlib may or may not be present on the
target system.
Steve.