fix: typed array offset

NativeScript/runtime/NSDataAdapter.mm

@@ -41,8 +41,12 @@ - (void*)mutableBytes {
 
     Local<ArrayBufferView> bufferView = obj.As<ArrayBufferView>();
     if (bufferView->HasBuffer()) {
-        void* data = bufferView->Buffer()->GetBackingStore()->Data();
-        return data;
+        uint8_t* data = static_cast<uint8_t*>(bufferView->Buffer()->GetBackingStore()->Data());
+        if (data == nullptr) {
+            return nullptr;
+        }
+
+        return data + bufferView->ByteOffset();
     }
 
     size_t length = bufferView->ByteLength();

TestFixtures/Marshalling/TNSObjCTypes.h

@@ -36,6 +36,7 @@ typedef int (^NumberReturner)(int, int, int);
 - (id)methodWithNSArrayWrappingDictionary:(id)array;
 - (NSDictionary*)methodWithNSDictionary:(NSDictionary*)dictionary;
 - (NSData*)methodWithNSData:(NSData*)data;
+- (NSMutableData*)methodWithNSMutableData:(NSMutableData*)data;
 - (NSDecimalNumber*)methodWithNSDecimalNumber:(NSDecimalNumber*)number;
 - (NSNumber*)methodWithNSCFBool;
 - (NSNull*)methodWithNSNull;

TestFixtures/Marshalling/TNSObjCTypes.m

@@ -115,6 +115,15 @@ - (NSData*)methodWithNSData:(NSData*)data {
     return data;
 }
 
+- (NSMutableData*)methodWithNSMutableData:(NSMutableData*)data {
+    if (data.length > 0) {
+        uint8_t* bytes = (uint8_t*)data.mutableBytes;
+        bytes[0] = 'A';
+    }
+
+    return data;
+}
+
 - (NSDecimalNumber*)methodWithNSDecimalNumber:(NSDecimalNumber*)number {
     TNSLog([number stringValue]);
     return number;

TestRunner/app/tests/Marshalling/ObjCTypesTests.js

@@ -263,6 +263,31 @@ describe(module.id, function () {
         TNSClearOutput();
     });
 
+    it("should respect ArrayBufferView byteOffset when wrapping in NSData", function () {
+        var source = new Uint8Array([48, 49, 50, 51, 52, 53]);
+        var view = new Uint8Array(source.buffer, 1, 4);
+
+        var wrappedArrayBufferViewData = TNSObjCTypes.alloc().init().methodWithNSData(view);
+
+        expect(TNSGetOutput()).toBe('1234');
+        expect(wrappedArrayBufferViewData).toBe(view);
+        TNSClearOutput();
+    });
+
+    it("should respect ArrayBufferView byteOffset when mutating NSMutableData", function () {
+        var source = new Uint8Array([48, 49, 50, 51, 52]);
+        var view = new Uint8Array(source.buffer, 2, 2);
+
+        var wrappedArrayBufferViewData = TNSObjCTypes.alloc().init().methodWithNSMutableData(view);
+
+        expect(wrappedArrayBufferViewData).toBe(view);
+        expect(source[0]).toEqual(48);
+        expect(source[1]).toEqual(49);
+        expect(source[2]).toEqual(65);
+        expect(source[3]).toEqual(51);
+        expect(source[4]).toEqual(52);
+    });
+
     it("should be possible to wrap NSData in an ArrayBuffer", function () {
         var data = NSString.stringWithString("test").dataUsingEncoding(NSUTF8StringEncoding);