option.bif: Short-circuit option changes when terminating

Due to the asynchronous behavior of the input framework and broker
communication, change handlers were previously called even after
zeek_done() event processing completed and also broker shutdown.

Accessing broker store handles within change handlers this late
triggered invalid Broker store handle messages:

    error in ././my_option_store.zeek, line 13: invalid Broker store handle (Broker::put(Test::store, to_any_coercemy_option, to_any_coerceTest::new_value, 0 secs) and broker::store::{})

Fixes #2010

NEWS

@@ -41,6 +41,10 @@ Changed Functionality
 - The default logging directory is now set globally across all log
   writers through ``Log::default_logdir``.
 
+- Calling `Option::set()` when Zeek is terminating is now a noop and returns `F`.
+  This prevents callbacks into script-land through change handlers when parts
+  of the environment have already been torn down.
+
 Deprecated Functionality
 ------------------------
 

src/option.bif

@@ -10,6 +10,11 @@ module Option;
 static bool call_option_handlers_and_set_value(zeek::StringVal* name, const zeek::detail::IDPtr& i,
                                                zeek::ValPtr val, zeek::StringVal* location)
 	{
+	// when shutting down, don't call back into script land handlers as
+	// these may use resources that have already been shutdown.
+	if ( zeek::run_state::terminating )
+		return false;
+
 	if ( i->HasOptionHandlers() )
 		{
 		for ( auto handler_function : i->GetOptionHandlers() )

testing/btest/Baseline/core.option-zeek-done/.stdout

@@ -0,0 +1,7 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+Initial value, T
+Value of testbool changed from T to F (zeek_is_terminating=F)
+Next value, F
+Next changed, T
+Final value, F
+Final changed, F

testing/btest/core/option-zeek-done.zeek

@@ -0,0 +1,29 @@
+# @TEST-DOC: Ensure change handlers do not run when terminating by trying to change an option during zeek_done()
+# @TEST-EXEC: zeek -b %INPUT
+# @TEST-EXEC: btest-diff .stdout
+
+export {
+	option testbool: bool = T;
+}
+
+function option_changed(ID: string, new_value: bool): bool {
+	print fmt("Value of %s changed from %s to %s (zeek_is_terminating=%s)", ID, testbool, new_value, zeek_is_terminating());
+	return new_value;
+}
+
+event zeek_init()
+	{
+	print "Initial value", testbool;
+	Option::set_change_handler("testbool", option_changed);
+	local changed = Option::set("testbool", F);
+	print "Next value", testbool;
+	print "Next changed", changed;
+	}
+
+event zeek_done()
+	{
+	local changed = Option::set("testbool", T);
+	print "Final value", testbool;
+	print "Final changed", changed;
+	}
+