Avoid crash in "postgres -C guc" for a GUC with a null string value.

Emit "(null)" instead, which was the behavior all along on platforms
that don't crash, eg OS X.  Per report from Jehan-Guillaume de Rorthais.
Back-patch to 9.2 where -C option was introduced.

Michael Paquier

Report: <20160615204036.2d35d86a@firost>

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 6421c8601bc25729d841ef517c862c0442940250..e350dd2925298540fc52488f42134a13b9b80937 100644 (file)
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -827,10 +827,14 @@ PostmasterMain(int argc, char *argv[])
    if (output_config_variable != NULL)
    {
        /*
-        * permission is handled because the user is reading inside the data
-        * dir
+        * "-C guc" was specified, so print GUC's value and exit.  No extra
+        * permission check is needed because the user is reading inside the
+        * data dir.
         */
-       puts(GetConfigOption(output_config_variable, false, false));
+       const char *config_val = GetConfigOption(output_config_variable,
+                                                false, false);
+
+       puts(config_val ? config_val : "(null)");
        ExitPostmaster(0);
    }