Don't return null for non-nullable Blobs in Java (#935)

Updated JNI conversion function for non-nullable Blobs to avoid returning `null` when the C++ function returns a null
shared pointer.

Having a null shared pointer coming from C++ when the type is specified as non-nullable in the IDL is a violation of
contract. The correct fix for this issue would be to change `Blob` representation from `shared_ptr<vector>` to something
that cannot be `null`. However, this would be a breaking change, so it has to be done later (#934). For now it's just
the small JNI workaround.

Resolves: #929
Signed-off-by: Daniel Kamkha <[email protected]>

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Gluecodium project Release Notes
 
+## Unreleased
+### Bug fixes:
+  * Fixed runtime issues in Java when a 'null' is returned from C++ for a non-nullable `Blob`.
+
 ## 9.1.0
 Release date: 2021-05-31
 ### Features:

functional-tests/functional/CMakeLists.txt

@@ -86,10 +86,10 @@ feature(MethodOverloading cpp android swift dart SOURCES
 )
 
 feature(Blob cpp android swift dart SOURCES
-    input/src/cpp/ArraysByteBuffer.cpp
+    input/src/cpp/Blobs.cpp
     input/src/cpp/StaticByteArrayMethods.cpp
 
-    input/lime/ArraysByteBuffer.lime
+    input/lime/Blobs.lime
     input/lime/StaticByteArrayMethods.lime
 )
 

functional-tests/functional/android/src/test/java/com/here/android/test/ArraysByteBufferTest.java → functional-tests/functional/android/src/test/java/com/here/android/test/BlobsTest.java

@@ -32,7 +32,7 @@
 
 @RunWith(RobolectricTestRunner.class)
 @Config(sdk = Build.VERSION_CODES.M, application = RobolectricApplication.class)
-public class ArraysByteBufferTest {
+public class BlobsTest {
 
   @Test
   public void methodWithByteBuffer_emptyArray() {
@@ -167,4 +167,19 @@ public void methodWithExplicitArrayInStruct_reversesArray() {
     assertNotNull(resultStruct);
     assertEquals(java.util.Arrays.asList((short) 3, (short) 2, (short) 1), resultStruct.image);
   }
+
+  @Test
+  public void blobNullsBreakingNull() {
+    byte[] resultBuffer = BlobNulls.getBreakingNull();
+
+    assertNotNull(resultBuffer);
+    assertEquals(0, resultBuffer.length);
+  }
+
+  @Test
+  public void blobNullsValidNull() {
+    byte[] resultBuffer = BlobNulls.getValidNull();
+
+    assertNull(resultBuffer);
+  }
 }

functional-tests/functional/input/lime/ArraysByteBuffer.lime → functional-tests/functional/input/lime/Blobs.lime

@@ -64,3 +64,8 @@ class ArraysByteBuffer {
         errorFlag: Boolean
     ): /* Output buffer */ Blob throws Explosive
 }
+
+class BlobNulls {
+    static fun getBreakingNull(): Blob
+    static fun getValidNull(): Blob?
+}

functional-tests/functional/input/src/cpp/ArraysByteBuffer.cpp → functional-tests/functional/input/src/cpp/Blobs.cpp

@@ -19,6 +19,7 @@
 // -------------------------------------------------------------------------------------------------
 
 #include "test/ArraysByteBuffer.h"
+#include "test/BlobNulls.h"
 #include "another/TypeCollectionWithEnums.h"
 
 namespace test
@@ -84,4 +85,14 @@ ArraysByteBuffer::method_that_explodes( const bool error_flag )
     }
 }
 
-}  // namespace test
+std::shared_ptr<std::vector<uint8_t>>
+BlobNulls::get_breaking_null() {
+    return {};
+}
+
+lorem_ipsum::test::optional<std::shared_ptr<std::vector<uint8_t>>>
+BlobNulls::get_valid_null() {
+    return {};
+}
+
+}

gluecodium/src/main/resources/templates/jni/utils/JniCppConversionUtilsImplementation.mustache

@@ -194,7 +194,7 @@ convert_to_jni( JNIEnv* env, const std::shared_ptr< std::vector< uint8_t > >& nv
 {
     if ( !nvalue )
     {
-        return {};
+        return make_local_ref(env, env->NewByteArray(0));
     }
 
     jsize size = static_cast< jsize >( nvalue->size( ) );