• Tom Lane's avatar
    Make printf("%s", NULL) print "(null)" instead of crashing. · 89ad14cd
    Tom Lane authored
    We previously took a hard-line attitude that callers should never print
    a null string pointer, and doing so is worthy of an assertion failure
    or crash.  However, we've long since flushed out any easy-to-find bugs
    of that nature.  What remains is a lot of code that perhaps could fail
    that way in hard-to-reach corner cases.  For example, in something as
    simple as
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("constraint \"%s\" for table \"%s\" does not exist",
                        conname, get_rel_name(relid))));
    one must wonder whether it's completely guaranteed that get_rel_name
    cannot return NULL in this context.  If such a situation did occur,
    the existing policy converts what might be a pretty minor bug into
    a server crash condition.  This is not good for robustness.
    
    Hence, let's follow the lead of glibc and print "(null)" instead
    of failing.  We should, of course, still consider it a bug if that
    behavior is reachable in ordinary use; but crashing seems less
    desirable than not crashing.
    
    This fix works across-the-board in v12 and up, where we always use
    src/port/snprintf.c.  Before that, on most platforms we're at the mercy
    of the local libc, but it appears that Solaris 10 is the only supported
    platform where we'd still get a crash.  Most other platforms such as
    *BSD, macOS, and Solaris 11 have adopted glibc's behavior at some
    point.  (AIX and HPUX just print "" not "(null)", but that's close
    enough.)  I've not checked what Windows' native printf would do, but
    it doesn't matter because we've long used snprintf.c on that platform.
    
    In v12 and up, also const-ify related code so that we're not casting
    away const on the constant string.  This is just neatnik-ism, since
    next to no compilers will warn about that.
    
    Discussion: https://postgr.es/m/17098-b960f3616c861f83@postgresql.org
    89ad14cd
snprintf.c 34.8 KB