refactor(capi): yrx_rule_patterns returns null when the rule doesn'…

…t have any patterns.

capi/include/yara_x.h

@@ -283,7 +283,8 @@ void yrx_metadata_destroy(struct YRX_METADATA *metadata);
 // object that must be destroyed with [`yrx_patterns_destroy`] when not needed
 // anymore.
 //
-// This function returns a null pointer when `rule` is null.
+// This function returns a null pointer when `rule` is null or when the rule
+// doesn't have any patterns.
 struct YRX_PATTERNS *yrx_rule_patterns(const struct YRX_RULE *rule);
 
 // Destroys a [`YRX_PATTERNS`] object.

capi/src/lib.rs

@@ -629,7 +629,8 @@ pub unsafe extern "C" fn yrx_metadata_destroy(metadata: *mut YRX_METADATA) {
 /// object that must be destroyed with [`yrx_patterns_destroy`] when not needed
 /// anymore.
 ///
-/// This function returns a null pointer when `rule` is null.
+/// This function returns a null pointer when `rule` is null or the rule doesn't
+/// have any patterns.
 #[no_mangle]
 pub unsafe extern "C" fn yrx_rule_patterns(
     rule: *const YRX_RULE,
@@ -640,6 +641,10 @@ pub unsafe extern "C" fn yrx_rule_patterns(
         return std::ptr::null_mut();
     };
 
+    if patterns_iter.len() == 0 {
+        return std::ptr::null_mut();
+    }
+
     let mut patterns = Vec::with_capacity(patterns_iter.len());
 
     for pattern in patterns_iter {

go/main.go

@@ -274,7 +274,9 @@ func newRule(cRule *C.YRX_RULE) *Rule {
 }
 
 func (r *Rule) destroy() {
-	C.yrx_patterns_destroy(r.cPatterns)
+	if r.cPatterns != nil {
+		C.yrx_patterns_destroy(r.cPatterns)
+	}
 	if r.cMetadata != nil {
 		C.yrx_metadata_destroy(r.cMetadata)
 	}
@@ -359,6 +361,13 @@ func (r *Rule) Patterns() []Pattern {
 		return r.patterns
 	}
 
+	// if cPatterns is nil the rule doesn't have any patterns, return an
+	// empty list.
+	if r.cPatterns == nil {
+		r.patterns = make([]Pattern, 0)
+		return r.patterns
+	}
+
 	numPatterns := int(r.cPatterns.num_patterns)
 	cPatterns := unsafe.Slice(r.cPatterns.patterns, numPatterns)
 	r.patterns = make([]Pattern, numPatterns)