refactor(go): avoid using unsafe.Pointer for passing handles (#195)

Functions that receive a `void*` in the C world must be called with an `unsafe.Pointer` from the Go world. However, we are not really passing a pointer, but a "handle", and coercing a handle into an `unsafe.Pointer` is problematic (`go vet` complains with "possible misuse of unsafe.Pointer", and it could cause a panic as described in https://i.hsfzxjy.site/invalid-pointer-will-bite-you/).

The solution is introducing small C stub functions that receive an `uintptr_t` instead of a `void*`, and the call the original function, casting the `uintptr_t` into `void*`.

Author: plusvic

go/example_test.go

@@ -72,4 +72,4 @@ func Example_compilerAndScanner() {
 	// Output:
 	// rule foo matched
 	// rule bar matched
-}
+}

go/main.go

@@ -5,27 +5,42 @@ package yara_x
 // #cgo static_link pkg-config: --static yara_x_capi
 // #include <yara_x.h>
 //
-// static uint64_t meta_i64(void* value) {
+// static inline uint64_t meta_i64(void* value) {
 //   return ((YRX_METADATA_VALUE*) value)->i64;
 // }
 //
-// static double meta_f64(void* value) {
+// static inline double meta_f64(void* value) {
 //   return ((YRX_METADATA_VALUE*) value)->f64;
 // }
 //
-// static bool meta_bool(void* value) {
+// static inline bool meta_bool(void* value) {
 //   return ((YRX_METADATA_VALUE*) value)->boolean;
 // }
 //
-// static char* meta_str(void* value) {
+// static inline char* meta_str(void* value) {
 //   return ((YRX_METADATA_VALUE*) value)->string;
 // }
 //
-// static YRX_METADATA_BYTES* meta_bytes(void* value) {
+// static inline YRX_METADATA_BYTES* meta_bytes(void* value) {
 //   return &(((YRX_METADATA_VALUE*) value)->bytes);
 // }
 //
-// void onRule(YRX_RULE*, void*);
+// enum YRX_RESULT static inline _yrx_rules_iterate(
+// 		 struct YRX_RULES *rules,
+//     YRX_RULE_CALLBACK callback,
+//     uintptr_t user_data) {
+//   return yrx_rules_iterate(rules, callback, (void*) user_data);
+// }
+//
+// enum YRX_RESULT static inline _yrx_rules_iterate_imports(
+//   	 struct YRX_RULES *rules,
+//     YRX_IMPORT_CALLBACK callback,
+//     uintptr_t user_data) {
+//   return yrx_rules_iterate_imports(rules, callback, (void*) user_data);
+// }
+//
+//
+// void onRule(YRX_RULE*, uintptr_t);
 // void onImport(char*, void*);
 import "C"
 
@@ -157,8 +172,8 @@ func (r *Rules) Destroy() {
 // This is the callback called by yrx_rules_iterate, when Rules.GetRules is
 // called.
 //export onRule
-func onRule(rule *C.YRX_RULE, handle unsafe.Pointer) {
-	h := (cgo.Handle)(handle)
+func onRule(rule *C.YRX_RULE, handle C.uintptr_t) {
+	h := cgo.Handle(handle)
 	rules, ok := h.Value().(*[]*Rule)
 	if !ok {
 		panic("onRule didn't receive a *[]Rule")
@@ -173,10 +188,10 @@ func (r *Rules) Slice() []*Rule {
 	handle := cgo.NewHandle(&rules)
 	defer handle.Delete()
 
-	C.yrx_rules_iterate(
+	C._yrx_rules_iterate(
 		r.cRules,
 		C.YRX_RULE_CALLBACK(C.onRule),
-		unsafe.Pointer(handle))
+		C.uintptr_t(handle))
 
 	runtime.KeepAlive(r)
 	return rules
@@ -195,7 +210,7 @@ func (r *Rules) Count() int {
 // is called.
 //export onImport
 func onImport(module_name *C.char, handle unsafe.Pointer) {
-	h := (cgo.Handle)(handle)
+	h := cgo.Handle(handle)
 	imports, ok := h.Value().(*[]string)
 	if !ok {
 		panic("onImport didn't receive a *[]string")
@@ -206,13 +221,13 @@ func onImport(module_name *C.char, handle unsafe.Pointer) {
 // Count returns the total number of rules.
 func (r *Rules) Imports() []string {
 	imports := make([]string, 0)
-	handle := cgo.NewHandle(&imports)
-	defer handle.Delete()
+  handle := cgo.NewHandle(&imports)
+  defer handle.Delete()
 
-	C.yrx_rules_iterate_imports(
+	C._yrx_rules_iterate_imports(
 		r.cRules,
 		C.YRX_RULE_CALLBACK(C.onImport),
-		unsafe.Pointer(handle))
+		C.uintptr_t(handle))
 
 	runtime.KeepAlive(r)
 	return imports

go/scanner.go

@@ -2,7 +2,14 @@ package yara_x
 
 // #include <yara_x.h>
 //
-// void onMatchingRule(YRX_RULE*, void*);
+// enum YRX_RESULT static inline _yrx_scanner_on_matching_rule(
+//     struct YRX_SCANNER *scanner,
+//     YRX_RULE_CALLBACK callback,
+//     uintptr_t user_data) {
+//   return yrx_scanner_on_matching_rule(scanner, callback, (void*) user_data);
+// }
+//
+// void onMatchingRule(YRX_RULE*, uintptr_t);
 import "C"
 
 import (
@@ -19,8 +26,6 @@ import (
 	"google.golang.org/protobuf/proto"
 )
 
-
-
 // Scanner scans data with a set of compiled YARA rules.
 type Scanner struct {
 	// Pointer to C-side scanner.
@@ -55,9 +60,10 @@ func (s ScanResults) MatchingRules() []*Rule {
 }
 
 // This is the callback function called every time a YARA rule matches.
+//
 //export onMatchingRule
-func onMatchingRule(rule *C.YRX_RULE, handle unsafe.Pointer) {
-	h := (cgo.Handle)(handle)
+func onMatchingRule(rule *C.YRX_RULE, handle C.uintptr_t) {
+	h := cgo.Handle(handle)
 	scanner, ok := h.Value().(*Scanner)
 	if !ok {
 		panic("onMatchingRule didn't receive a Scanner")
@@ -76,13 +82,12 @@ func NewScanner(r *Rules) *Scanner {
 		panic("yrx_scanner_create failed")
 	}
 
-	// Create a new handle that points to the scanner.
 	s.handle = cgo.NewHandle(s)
 
-	C.yrx_scanner_on_matching_rule(
+	C._yrx_scanner_on_matching_rule(
 		s.cScanner,
 		C.YRX_RULE_CALLBACK(C.onMatchingRule),
-		unsafe.Pointer(s.handle))
+		C.uintptr_t(s.handle))
 
 	runtime.SetFinalizer(s, (*Scanner).Destroy)
 	return s
@@ -242,5 +247,6 @@ func (s *Scanner) Destroy() {
 		s.handle.Delete()
 		s.cScanner = nil
 	}
+	s.rules = nil
 	runtime.SetFinalizer(s, nil)
 }