bytes substring optimization

gjson.go

@@ -2,6 +2,7 @@
 package gjson
 
 import (
+	"reflect"
 	"strconv"
 	"unsafe"
 
@@ -1140,9 +1141,28 @@ func GetBytes(json []byte, path string) Result {
 	if json != nil {
 		// unsafe cast to string
 		result = Get(*(*string)(unsafe.Pointer(&json)), path)
-		// copy of string data for safety
-		result.Raw = string(*(*[]byte)(unsafe.Pointer(&result.Raw)))
-		result.Str = string(*(*[]byte)(unsafe.Pointer(&result.Str)))
+		// copy of string data for safety.
+		rawh := *(*reflect.SliceHeader)(unsafe.Pointer(&result.Raw))
+		strh := *(*reflect.SliceHeader)(unsafe.Pointer(&result.Str))
+		if strh.Data == 0 {
+			if rawh.Data == 0 {
+				result.Raw = ""
+			} else {
+				result.Raw = string(*(*[]byte)(unsafe.Pointer(&result.Raw)))
+			}
+			result.Str = ""
+		} else if rawh.Data == 0 {
+			result.Raw = ""
+			result.Str = string(*(*[]byte)(unsafe.Pointer(&result.Str)))
+		} else if strh.Data >= rawh.Data && strh.Len <= rawh.Len {
+			// Str is a substring of Raw.
+			result.Raw = string(*(*[]byte)(unsafe.Pointer(&result.Raw)))
+			start := int(strh.Data - rawh.Data)
+			result.Str = result.Raw[start : start+strh.Len]
+		} else {
+			result.Raw = string(*(*[]byte)(unsafe.Pointer(&result.Raw)))
+			result.Str = string(*(*[]byte)(unsafe.Pointer(&result.Str)))
+		}
 	}
 	return result
 }

gjson_test.go

@@ -128,11 +128,15 @@ var basicJSON = `{"age":100, "name":{"here":"B\\\"R"},
 var basicJSONB = []byte(basicJSON)
 
 func TestByteSafety(t *testing.T) {
-	jsonb := []byte(`{"name":"Janet"}`)
+	jsonb := []byte(`{"name":"Janet","age":38}`)
 	mtok := GetBytes(jsonb, "name")
 	if mtok.String() != "Janet" {
 		t.Fatalf("expected %v, got %v", "Jason", mtok.String())
 	}
+	mtok2 := GetBytes(jsonb, "age")
+	if mtok2.Raw != "38" {
+		t.Fatalf("expected %v, got %v", "Jason", mtok2.Raw)
+	}
 	jsonb[9] = 'T'
 	jsonb[12] = 'd'
 	jsonb[13] = 'y'