Re: [GENERAL] Querying libpq compile time options

Martijn van Oosterhout wrote:
-- Start of PGP signed section.
> On Fri, May 12, 2006 at 08:38:07PM -0400, Bruce Momjian wrote:
> > Is this like detecting of libpq is SSL-enabled?  I see PQgetssl().  Do
> > we need to add a libpq function to return true/false for threading?
> > Slony requires a threaded libpq, so it could do the test to prevent
> > wrong configurations.  It would be nice to enabled threading by default,
> > but it is like SSL in that not all operating systems support it.
>
> PQgetssl() doesn't tell you if SSL is supported, it tells you if the
> *current connection* is using OpenSSL, which is similar but not the
> same.
>
> There is AFAIK no way to tell if SSL support is compiled in. Part of
> the patch I posted for GnuTLS support answered this question also
> (PQgettlsinfo()).

I thought about this.  Attached is a patch you can use to
popen("pg_config") and then look for the thread flag to configure.  One
idea would be to add this sample to our libpq documentation.  The
problem with the example is popen() overhead, pg_config not in $PATH, or
pg_config's version not matching libpq's version.

A more comprehensive idea would be to embed the configure string in
libpq, like we do for pg_config, and allow that to be returned to the
caller so they can do a strstr() to see if a certain flag was used.

Having per-configure flag functions, like for threading, seems like it
could be a mess because there is a lot more application programmers might
care about in addition to threading, like SSL, multi-byte, etc.

--
  Bruce Momjian   http://candle.pha.pa.us
  EnterpriseDB    http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +
/*
 *    This function queries pg_config to check for specific
 *    configure flags used to build PostgreSQL.  It can be
 *    easily modified to return true/false to the caller.
 *    This example tests thread safety.
 */
#include <stdio.h>
#include <string.h>


#define PG_CONFIG_CMD    "pg_config --configure"
/*
 *    pg_config's output should fit in one string because we don't want
 *    the search string to split across reads.
 */
#define POPEN_READ        8192

int
main(int argc, char *argv[])
{
    FILE    *p;
    char    str[POPEN_READ];

    if ((p = popen(PG_CONFIG_CMD, "r")) == NULL ||
        fgets(str, POPEN_READ, p) == NULL)
    {
        fprintf(stderr, "Cannot run \"%s\", perhaps incorrect $PATH", PG_CONFIG_CMD);
        if (p)
            pclose(p);
        exit(2);
    }

    pclose(p);

    if (strstr(str, "--enable-thread-safety") != NULL)
    {
        puts("threading enabled");
        return 0;
    }
    else
    {
        puts("threading not enabled");
        return 1;
    }
}