Serialize and deserialize null (#783)

* Build (grpc's) nanopb with -DPB_FIELD_16BIT

We require (at least) 16 bit fields. (By default, nanopb uses 8 bit
fields, ie allowing up to 256 field tags.)

Also note that this patch adds this to grpc's nanopb, rather than to our
nanopb. We'll need to eventually either:
a) we instruct grpc to use our nanopb
b) we rely on grpc's nanopb instead of using our own.

(^ marked as a TODO for now.)

* Add some dependant protos

Imported from protobuf. Nanopb requires these to be present (though
anything using libprotobuf does not, as these are already built into
that.)

* Add generated nanopb protos based off of newly added proto definitions

* Build the nanopb protos

* Serialize and deserialize null

1 files changed, 70 insertions, 1 deletions

diff --git a/Firestore/core/test/firebase/firestore/remote/serializer_test.cc b/Firestore/core/test/firebase/firestore/remote/serializer_test.cc
index 1be5a87..35f417e 100644
--- a/Firestore/core/test/firebase/firestore/remote/serializer_test.cc
+++ b/Firestore/core/test/firebase/firestore/remote/serializer_test.cc
@@ -16,8 +16,15 @@
 
 #include "Firestore/core/src/firebase/firestore/remote/serializer.h"
 
-#include <gtest/gtest.h>
+#include <pb.h>
 #include <pb_encode.h>
+#include <vector>
+
+#include "Firestore/core/src/firebase/firestore/model/field_value.h"
+#include "gtest/gtest.h"
+
+using firebase::firestore::model::FieldValue;
+using firebase::firestore::remote::Serializer;
 
 TEST(Serializer, CanLinkToNanopb) {
   // This test doesn't actually do anything interesting as far as actually using
@@ -26,3 +33,65 @@ TEST(Serializer, CanLinkToNanopb) {
   // the test.
   pb_ostream_from_buffer(NULL, 0);
 }
+
+// Fixture for running serializer tests.
+class SerializerTest : public ::testing::Test {
+ public:
+  SerializerTest() : serializer(/*DatabaseId("p", "d")*/) {
+  }
+  Serializer serializer;
+
+  void ExpectRoundTrip(const FieldValue& model,
+                       const Serializer::TypedValue& proto,
+                       FieldValue::Type type) {
+    EXPECT_EQ(type, model.type());
+    EXPECT_EQ(type, proto.type);
+    Serializer::TypedValue actual_proto = serializer.EncodeFieldValue(model);
+    EXPECT_EQ(type, actual_proto.type);
+    EXPECT_EQ(proto, actual_proto);
+    EXPECT_EQ(model, serializer.DecodeFieldValue(proto));
+  }
+
+  void ExpectRoundTrip(const Serializer::TypedValue& proto,
+                       std::vector<uint8_t> bytes,
+                       FieldValue::Type type) {
+    EXPECT_EQ(type, proto.type);
+    std::vector<uint8_t> actual_bytes;
+    Serializer::EncodeTypedValue(proto, &actual_bytes);
+    EXPECT_EQ(bytes, actual_bytes);
+    Serializer::TypedValue actual_proto = Serializer::DecodeTypedValue(bytes);
+    EXPECT_EQ(type, actual_proto.type);
+    EXPECT_EQ(proto, actual_proto);
+  }
+};
+
+TEST_F(SerializerTest, EncodesNullModelToProto) {
+  FieldValue model = FieldValue::NullValue();
+  Serializer::TypedValue proto{FieldValue::Type::Null,
+                               google_firestore_v1beta1_Value_init_default};
+  // sanity check (the _init_default above should set this to _NULL_VALUE)
+  EXPECT_EQ(google_protobuf_NullValue_NULL_VALUE, proto.value.null_value);
+  ExpectRoundTrip(model, proto, FieldValue::Type::Null);
+}
+
+TEST_F(SerializerTest, EncodesNullProtoToBytes) {
+  Serializer::TypedValue proto{FieldValue::Type::Null,
+                               google_firestore_v1beta1_Value_init_default};
+  // sanity check (the _init_default above should set this to _NULL_VALUE)
+  EXPECT_EQ(google_protobuf_NullValue_NULL_VALUE, proto.value.null_value);
+
+  /* NB: proto bytes were created via:
+       echo 'null_value: NULL_VALUE' \
+         | ./build/external/protobuf/src/protobuf-build/src/protoc \
+             -I./Firestore/Protos/protos \
+             -I./build/external/protobuf/src/protobuf/src/ \
+             --encode=google.firestore.v1beta1.Value \
+             google/firestore/v1beta1/document.proto \
+             > output.bin
+   */
+  std::vector<uint8_t> bytes{0x58, 0x00};
+  ExpectRoundTrip(proto, bytes, FieldValue::Type::Null);
+}
+
+// TODO(rsgowman): Test [en|de]coding multiple protos into the same output
+// vector.