A GNUNET_log oddity

[Alessio Vanni]

Hello,

I was recently puzzled by a behaviour which apparently has been going on
for a while, but I noticed it only now.

It seems that `GNUNET_log' (and `GNUNET_log_from') is unable to print
messages when the error level is GNUNET_ERROR_TYPE_DEBUG under certain
circumstances.

Consider this small testcase:

#include <netinet/in.h>
#include <stdbool.h>
#include <gnunet/gettext.h>
#include <gnunet/gnunet_util_lib.h>

static void
run(void *cls, char *const *args, const char *cf, const struct 
GNUNET_CONFIGURATION_Handle *cfg) {
     GNUNET_log(GNUNET_ERROR_TYPE_ERROR, "error\n");
     GNUNET_log(GNUNET_ERROR_TYPE_WARNING, "warning\n");
     GNUNET_log(GNUNET_ERROR_TYPE_INFO, "info\n");
     GNUNET_log(GNUNET_ERROR_TYPE_DEBUG, "debug\n");
     GNUNET_SCHEDULER_shutdown();
}

int main(int argc, char *argv[]) {
     const struct GNUNET_GETOPT_CommandLineOption opts[] = {
          GNUNET_GETOPT_OPTION_END,
     };
     return GNUNET_PROGRAM_run(argc, argv, "test-client", "",
                               opts, &run, NULL);
}

(To compile it just run

gcc -o <out file name> <source file name> -lgnunetutil

nothing else is required.)

If you run it with different values for the `-L' flag, you will see that
`-L DEBUG' will print only up to INFO.

Apparently, this is because of this condition check:

(GNUNET_EXTRA_LOGGING > 0) || ((GNUNET_ERROR_TYPE_DEBUG & (kind)) == 0)

Trying to understand why a message is logged only when this condition is
true, I discovered that it was introduced in a commit that simply says:

"Let the compiler not include debug strings in binary when make is not
configured with verbose"

(The commit's full hash is: 51ded2191d94c707434cc5e082c7053f9469f149)

This is somewhat in line with a section of the GNUnet Developer
Handbook, specifically about building GNUnet from source:

"If you want to be able to enable DEBUG-level log messages, add
‘--enable-logging=verbose’ to the end of the ‘./configure’ command.
‘DEBUG’-level log messages are in English only and should only be useful
for developers (or for filing really detailed bug reports)."

Because the above doesn't apply to applications not part of the GNUnet
core, there is currently no way to log DEBUG-level messages unless the
application developer knows that GNUNET_EXTRA_LOGGING has to be defined
to a value bigger than 0; it is normally set to 0 if the symbol is not
defined in "gnunet_common.h".

It's true that there is a comment briefly explaining
GNUNET_EXTRA_LOGGING and that it could be possible to change its value
to a different number when it's not defined (never happens in GNUnet
core, as configure.ac always define a value for it) in a way that
applications have DEBUG-level logging enabled by default, but should the
current behaviour be kept at all in the first place?

DEBUG-level messages, even when enabled, still require the `-L' flag to
be set to "DEBUG", so no matter how GNUnet is built users will never see
those messages unless they explicitly ask for them. Similarly, people
interested in DEBUG-level messages first will have to build GNUnet with
the appropriate "configure" flags, which might not be possible in
certain situations, and then use `-L' accordingly.

I think that at least the calls to `GNUNET_log' (and `GNUNET_log_from',
and other similar "generic" function/macros) should always try to print
something, letting the `-L' flag decide whether the user should see the
message or not, leaving the whole GNUNET_EXTRA_LOGGING stuff as
something used internally by GNUnet and nothing else (since it is used
in a few places to include or exclude some code paths.)

Thanks,
A.V.