Re: queriing the version of libpq

On Tue, Oct 5, 2010 at 09:33, Massa, Harald Armin <chef@ghum.de> wrote:
> With 9.0 there is the new hex encoding for BYTEA, which is activated by
> default.
> libpq BEFORE 9.0 are not able to decode that encoding.
> I am programming with Python, using psycopg2. When psycopg2 is linked with
> libpq 9.0, everything works fine with hex-encoding; if psycopg2 is linked
> with libpq < 9.0, decoding hex-encoded bytea fails (it stays hexencoded).
> This happens because in default configuration psycopg2 calls the
> libpq-decode-encoded-bytea function (which is the way it should be done).
> Now I would love to have an additional check "is the used psycopg2 linked to
> an advanced-enough libpq", to be able to set bytea_output to 'escape' if the
> libpq is not worthy.
> My question: Which way is available to query the linked libpq version?
> My other option is to select 'something_that_gets_casted_to_bytea'::bytea,
> and check the return value. BUT that requires a round-trip to the server....

You can try calling PQconninfoParse() on a connectino string that has
applicationname= in it. That will fail on anything pre-9.0. Assuming
there's a way to access that function through psycopg2.

But it does outline that fact that it wouldn't suck to have a function
in libpq returning the version so that application can check this at
runtime - clearly it would also be useful when being linked "through"
something like psycopg2.

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/