fix: storing an empty Buffer

src/entity.ts

@@ -629,7 +629,10 @@ export namespace entity {
     }
 
     if (value instanceof Buffer) {
-      valueProto.blobValue = value;
+      // Convert the buffer to a base 64 string to workaround a bug of
+      // protobufs encoding empty buffer.
+      // See https://github.com/googleapis/nodejs-datastore/issues/755
+      valueProto.blobValue = value.toString('base64');
       return valueProto;
     }
 

system-test/datastore.ts

@@ -326,6 +326,20 @@ describe('Datastore', () => {
       await datastore.delete(datastore.key(['Post', assignedId as string]));
     });
 
+    it('should save/get/delete an empty buffer', async () => {
+      const postKey = datastore.key(['Post']);
+      const data = {
+        buf: Buffer.from([]),
+      };
+      await datastore.save({key: postKey, data});
+      const assignedId = postKey.id;
+      assert(assignedId);
+      const [entity] = await datastore.get(postKey);
+      delete entity[datastore.KEY];
+      assert.deepStrictEqual(entity, data);
+      await datastore.delete(datastore.key(['Post', assignedId as string]));
+    });
+
     it('should save/get/delete with a generated key id', async () => {
       const postKey = datastore.key('Post');
       await datastore.save({key: postKey, data: post});

test/entity.ts

@@ -849,7 +849,7 @@ describe('entity', () => {
       const value = Buffer.from('Hi');
 
       const expectedValueProto = {
-        blobValue: value,
+        blobValue: value.toString('base64'),
       };
 
       assert.deepStrictEqual(entity.encodeValue(value), expectedValueProto);