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

16 files changed, 1069 insertions, 12 deletions

diff --git a/Firestore/CMakeLists.txt b/Firestore/CMakeLists.txt
index 25f27fa..28ac08f 100644
--- a/Firestore/CMakeLists.txt
+++ b/Firestore/CMakeLists.txt
@@ -68,3 +68,4 @@ include_directories(${FIREBASE_SOURCE_DIR})
 include_directories(${FIREBASE_SOURCE_DIR}/Firestore/Protos/nanopb)
 
 add_subdirectory(core)
+add_subdirectory(Protos)
diff --git a/Firestore/Protos/CMakeLists.txt b/Firestore/Protos/CMakeLists.txt
new file mode 100644
index 0000000..f20f702
--- /dev/null
+++ b/Firestore/Protos/CMakeLists.txt
@@ -0,0 +1,45 @@
+cc_library(
+  firebase_firestore_protos_nanopb
+  SOURCES
+    nanopb/firestore/local/maybe_document.pb.c
+    nanopb/firestore/local/maybe_document.pb.h
+    nanopb/firestore/local/mutation.pb.c
+    nanopb/firestore/local/mutation.pb.h
+    nanopb/firestore/local/target.pb.c
+    nanopb/firestore/local/target.pb.h
+    nanopb/google/api/annotations.pb.c
+    nanopb/google/api/annotations.pb.h
+    nanopb/google/api/http.pb.c
+    nanopb/google/api/http.pb.h
+    nanopb/google/firestore/v1beta1/common.pb.c
+    nanopb/google/firestore/v1beta1/common.pb.h
+    nanopb/google/firestore/v1beta1/document.pb.c
+    nanopb/google/firestore/v1beta1/document.pb.h
+    nanopb/google/firestore/v1beta1/firestore.pb.c
+    nanopb/google/firestore/v1beta1/firestore.pb.h
+    nanopb/google/firestore/v1beta1/query.pb.c
+    nanopb/google/firestore/v1beta1/query.pb.h
+    nanopb/google/firestore/v1beta1/write.pb.c
+    nanopb/google/firestore/v1beta1/write.pb.h
+    nanopb/google/protobuf/any.pb.c
+    nanopb/google/protobuf/any.pb.h
+    nanopb/google/protobuf/empty.pb.c
+    nanopb/google/protobuf/empty.pb.h
+    nanopb/google/protobuf/struct.pb.c
+    nanopb/google/protobuf/struct.pb.h
+    nanopb/google/protobuf/timestamp.pb.c
+    nanopb/google/protobuf/timestamp.pb.h
+    nanopb/google/protobuf/wrappers.pb.c
+    nanopb/google/protobuf/wrappers.pb.h
+    nanopb/google/rpc/status.pb.c
+    nanopb/google/rpc/status.pb.h
+    nanopb/google/type/latlng.pb.c
+    nanopb/google/type/latlng.pb.h
+  DEPENDS
+    nanopb
+)
+
+target_compile_definitions(
+  firebase_firestore_protos_nanopb PUBLIC
+    -DPB_FIELD_16BIT
+)
diff --git a/Firestore/Protos/nanopb/google/protobuf/any.pb.c b/Firestore/Protos/nanopb/google/protobuf/any.pb.c
new file mode 100644
index 0000000..b28d0ba
--- /dev/null
+++ b/Firestore/Protos/nanopb/google/protobuf/any.pb.c
@@ -0,0 +1,36 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* Automatically generated nanopb constant definitions */
+/* Generated by nanopb-0.3.8 at Mon Feb 12 11:03:06 2018. */
+
+#include "any.pb.h"
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+
+
+const pb_field_t google_protobuf_Any_fields[3] = {
+    PB_FIELD(  1, STRING  , SINGULAR, CALLBACK, FIRST, google_protobuf_Any, type_url, type_url, 0),
+    PB_FIELD(  2, BYTES   , SINGULAR, CALLBACK, OTHER, google_protobuf_Any, value, type_url, 0),
+    PB_LAST_FIELD
+};
+
+
+/* @@protoc_insertion_point(eof) */
diff --git a/Firestore/Protos/nanopb/google/protobuf/any.pb.h b/Firestore/Protos/nanopb/google/protobuf/any.pb.h
new file mode 100644
index 0000000..10a722e
--- /dev/null
+++ b/Firestore/Protos/nanopb/google/protobuf/any.pb.h
@@ -0,0 +1,69 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* Automatically generated nanopb header */
+/* Generated by nanopb-0.3.8 at Mon Feb 12 11:03:06 2018. */
+
+#ifndef PB_GOOGLE_PROTOBUF_ANY_PB_H_INCLUDED
+#define PB_GOOGLE_PROTOBUF_ANY_PB_H_INCLUDED
+#include <pb.h>
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Struct definitions */
+typedef struct _google_protobuf_Any {
+    pb_callback_t type_url;
+    pb_callback_t value;
+/* @@protoc_insertion_point(struct:google_protobuf_Any) */
+} google_protobuf_Any;
+
+/* Default values for struct fields */
+
+/* Initializer values for message structs */
+#define google_protobuf_Any_init_default         {{{NULL}, NULL}, {{NULL}, NULL}}
+#define google_protobuf_Any_init_zero            {{{NULL}, NULL}, {{NULL}, NULL}}
+
+/* Field tags (for use in manual encoding/decoding) */
+#define google_protobuf_Any_type_url_tag         1
+#define google_protobuf_Any_value_tag            2
+
+/* Struct field encoding specification for nanopb */
+extern const pb_field_t google_protobuf_Any_fields[3];
+
+/* Maximum encoded size of messages (where known) */
+/* google_protobuf_Any_size depends on runtime parameters */
+
+/* Message IDs (where set with "msgid" option) */
+#ifdef PB_MSGID
+
+#define ANY_MESSAGES \
+
+
+#endif
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+/* @@protoc_insertion_point(eof) */
+
+#endif
diff --git a/Firestore/Protos/nanopb/google/protobuf/empty.pb.c b/Firestore/Protos/nanopb/google/protobuf/empty.pb.c
new file mode 100644
index 0000000..050af9c
--- /dev/null
+++ b/Firestore/Protos/nanopb/google/protobuf/empty.pb.c
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* Automatically generated nanopb constant definitions */
+/* Generated by nanopb-0.3.8 at Mon Feb 12 11:03:06 2018. */
+
+#include "empty.pb.h"
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+
+
+const pb_field_t google_protobuf_Empty_fields[1] = {
+    PB_LAST_FIELD
+};
+
+
+/* @@protoc_insertion_point(eof) */
diff --git a/Firestore/Protos/nanopb/google/protobuf/empty.pb.h b/Firestore/Protos/nanopb/google/protobuf/empty.pb.h
new file mode 100644
index 0000000..466e1fd
--- /dev/null
+++ b/Firestore/Protos/nanopb/google/protobuf/empty.pb.h
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* Automatically generated nanopb header */
+/* Generated by nanopb-0.3.8 at Mon Feb 12 11:03:06 2018. */
+
+#ifndef PB_GOOGLE_PROTOBUF_EMPTY_PB_H_INCLUDED
+#define PB_GOOGLE_PROTOBUF_EMPTY_PB_H_INCLUDED
+#include <pb.h>
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Struct definitions */
+typedef struct _google_protobuf_Empty {
+    char dummy_field;
+/* @@protoc_insertion_point(struct:google_protobuf_Empty) */
+} google_protobuf_Empty;
+
+/* Default values for struct fields */
+
+/* Initializer values for message structs */
+#define google_protobuf_Empty_init_default       {0}
+#define google_protobuf_Empty_init_zero          {0}
+
+/* Field tags (for use in manual encoding/decoding) */
+
+/* Struct field encoding specification for nanopb */
+extern const pb_field_t google_protobuf_Empty_fields[1];
+
+/* Maximum encoded size of messages (where known) */
+#define google_protobuf_Empty_size               0
+
+/* Message IDs (where set with "msgid" option) */
+#ifdef PB_MSGID
+
+#define EMPTY_MESSAGES \
+
+
+#endif
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+/* @@protoc_insertion_point(eof) */
+
+#endif
diff --git a/Firestore/Protos/nanopb/google/protobuf/wrappers.pb.c b/Firestore/Protos/nanopb/google/protobuf/wrappers.pb.c
new file mode 100644
index 0000000..41ab3c6
--- /dev/null
+++ b/Firestore/Protos/nanopb/google/protobuf/wrappers.pb.c
@@ -0,0 +1,81 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* Automatically generated nanopb constant definitions */
+/* Generated by nanopb-0.3.8 at Mon Feb 12 11:03:06 2018. */
+
+#include "wrappers.pb.h"
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+
+
+const pb_field_t google_protobuf_DoubleValue_fields[2] = {
+    PB_FIELD(  1, DOUBLE  , SINGULAR, STATIC  , FIRST, google_protobuf_DoubleValue, value, value, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t google_protobuf_FloatValue_fields[2] = {
+    PB_FIELD(  1, FLOAT   , SINGULAR, STATIC  , FIRST, google_protobuf_FloatValue, value, value, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t google_protobuf_Int64Value_fields[2] = {
+    PB_FIELD(  1, INT64   , SINGULAR, STATIC  , FIRST, google_protobuf_Int64Value, value, value, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t google_protobuf_UInt64Value_fields[2] = {
+    PB_FIELD(  1, UINT64  , SINGULAR, STATIC  , FIRST, google_protobuf_UInt64Value, value, value, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t google_protobuf_Int32Value_fields[2] = {
+    PB_FIELD(  1, INT32   , SINGULAR, STATIC  , FIRST, google_protobuf_Int32Value, value, value, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t google_protobuf_UInt32Value_fields[2] = {
+    PB_FIELD(  1, UINT32  , SINGULAR, STATIC  , FIRST, google_protobuf_UInt32Value, value, value, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t google_protobuf_BoolValue_fields[2] = {
+    PB_FIELD(  1, BOOL    , SINGULAR, STATIC  , FIRST, google_protobuf_BoolValue, value, value, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t google_protobuf_StringValue_fields[2] = {
+    PB_FIELD(  1, STRING  , SINGULAR, CALLBACK, FIRST, google_protobuf_StringValue, value, value, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t google_protobuf_BytesValue_fields[2] = {
+    PB_FIELD(  1, BYTES   , SINGULAR, CALLBACK, FIRST, google_protobuf_BytesValue, value, value, 0),
+    PB_LAST_FIELD
+};
+
+
+/* On some platforms (such as AVR), double is really float.
+ * These are not directly supported by nanopb, but see example_avr_double.
+ * To get rid of this error, remove any double fields from your .proto.
+ */
+PB_STATIC_ASSERT(sizeof(double) == 8, DOUBLE_MUST_BE_8_BYTES)
+
+/* @@protoc_insertion_point(eof) */
diff --git a/Firestore/Protos/nanopb/google/protobuf/wrappers.pb.h b/Firestore/Protos/nanopb/google/protobuf/wrappers.pb.h
new file mode 100644
index 0000000..0e98785
--- /dev/null
+++ b/Firestore/Protos/nanopb/google/protobuf/wrappers.pb.h
@@ -0,0 +1,147 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* Automatically generated nanopb header */
+/* Generated by nanopb-0.3.8 at Mon Feb 12 11:03:06 2018. */
+
+#ifndef PB_GOOGLE_PROTOBUF_WRAPPERS_PB_H_INCLUDED
+#define PB_GOOGLE_PROTOBUF_WRAPPERS_PB_H_INCLUDED
+#include <pb.h>
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Struct definitions */
+typedef struct _google_protobuf_BytesValue {
+    pb_callback_t value;
+/* @@protoc_insertion_point(struct:google_protobuf_BytesValue) */
+} google_protobuf_BytesValue;
+
+typedef struct _google_protobuf_StringValue {
+    pb_callback_t value;
+/* @@protoc_insertion_point(struct:google_protobuf_StringValue) */
+} google_protobuf_StringValue;
+
+typedef struct _google_protobuf_BoolValue {
+    bool value;
+/* @@protoc_insertion_point(struct:google_protobuf_BoolValue) */
+} google_protobuf_BoolValue;
+
+typedef struct _google_protobuf_DoubleValue {
+    double value;
+/* @@protoc_insertion_point(struct:google_protobuf_DoubleValue) */
+} google_protobuf_DoubleValue;
+
+typedef struct _google_protobuf_FloatValue {
+    float value;
+/* @@protoc_insertion_point(struct:google_protobuf_FloatValue) */
+} google_protobuf_FloatValue;
+
+typedef struct _google_protobuf_Int32Value {
+    int32_t value;
+/* @@protoc_insertion_point(struct:google_protobuf_Int32Value) */
+} google_protobuf_Int32Value;
+
+typedef struct _google_protobuf_Int64Value {
+    int64_t value;
+/* @@protoc_insertion_point(struct:google_protobuf_Int64Value) */
+} google_protobuf_Int64Value;
+
+typedef struct _google_protobuf_UInt32Value {
+    uint32_t value;
+/* @@protoc_insertion_point(struct:google_protobuf_UInt32Value) */
+} google_protobuf_UInt32Value;
+
+typedef struct _google_protobuf_UInt64Value {
+    uint64_t value;
+/* @@protoc_insertion_point(struct:google_protobuf_UInt64Value) */
+} google_protobuf_UInt64Value;
+
+/* Default values for struct fields */
+
+/* Initializer values for message structs */
+#define google_protobuf_DoubleValue_init_default {0}
+#define google_protobuf_FloatValue_init_default  {0}
+#define google_protobuf_Int64Value_init_default  {0}
+#define google_protobuf_UInt64Value_init_default {0}
+#define google_protobuf_Int32Value_init_default  {0}
+#define google_protobuf_UInt32Value_init_default {0}
+#define google_protobuf_BoolValue_init_default   {0}
+#define google_protobuf_StringValue_init_default {{{NULL}, NULL}}
+#define google_protobuf_BytesValue_init_default  {{{NULL}, NULL}}
+#define google_protobuf_DoubleValue_init_zero    {0}
+#define google_protobuf_FloatValue_init_zero     {0}
+#define google_protobuf_Int64Value_init_zero     {0}
+#define google_protobuf_UInt64Value_init_zero    {0}
+#define google_protobuf_Int32Value_init_zero     {0}
+#define google_protobuf_UInt32Value_init_zero    {0}
+#define google_protobuf_BoolValue_init_zero      {0}
+#define google_protobuf_StringValue_init_zero    {{{NULL}, NULL}}
+#define google_protobuf_BytesValue_init_zero     {{{NULL}, NULL}}
+
+/* Field tags (for use in manual encoding/decoding) */
+#define google_protobuf_BytesValue_value_tag     1
+#define google_protobuf_StringValue_value_tag    1
+#define google_protobuf_BoolValue_value_tag      1
+#define google_protobuf_DoubleValue_value_tag    1
+#define google_protobuf_FloatValue_value_tag     1
+#define google_protobuf_Int32Value_value_tag     1
+#define google_protobuf_Int64Value_value_tag     1
+#define google_protobuf_UInt32Value_value_tag    1
+#define google_protobuf_UInt64Value_value_tag    1
+
+/* Struct field encoding specification for nanopb */
+extern const pb_field_t google_protobuf_DoubleValue_fields[2];
+extern const pb_field_t google_protobuf_FloatValue_fields[2];
+extern const pb_field_t google_protobuf_Int64Value_fields[2];
+extern const pb_field_t google_protobuf_UInt64Value_fields[2];
+extern const pb_field_t google_protobuf_Int32Value_fields[2];
+extern const pb_field_t google_protobuf_UInt32Value_fields[2];
+extern const pb_field_t google_protobuf_BoolValue_fields[2];
+extern const pb_field_t google_protobuf_StringValue_fields[2];
+extern const pb_field_t google_protobuf_BytesValue_fields[2];
+
+/* Maximum encoded size of messages (where known) */
+#define google_protobuf_DoubleValue_size         9
+#define google_protobuf_FloatValue_size          5
+#define google_protobuf_Int64Value_size          11
+#define google_protobuf_UInt64Value_size         11
+#define google_protobuf_Int32Value_size          11
+#define google_protobuf_UInt32Value_size         6
+#define google_protobuf_BoolValue_size           2
+/* google_protobuf_StringValue_size depends on runtime parameters */
+/* google_protobuf_BytesValue_size depends on runtime parameters */
+
+/* Message IDs (where set with "msgid" option) */
+#ifdef PB_MSGID
+
+#define WRAPPERS_MESSAGES \
+
+
+#endif
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+/* @@protoc_insertion_point(eof) */
+
+#endif
diff --git a/Firestore/Protos/protos/google/protobuf/any.proto b/Firestore/Protos/protos/google/protobuf/any.proto
new file mode 100644
index 0000000..c748667
--- /dev/null
+++ b/Firestore/Protos/protos/google/protobuf/any.proto
@@ -0,0 +1,149 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+syntax = "proto3";
+
+package google.protobuf;
+
+option csharp_namespace = "Google.Protobuf.WellKnownTypes";
+option go_package = "github.com/golang/protobuf/ptypes/any";
+option java_package = "com.google.protobuf";
+option java_outer_classname = "AnyProto";
+option java_multiple_files = true;
+option objc_class_prefix = "GPB";
+
+// `Any` contains an arbitrary serialized protocol buffer message along with a
+// URL that describes the type of the serialized message.
+//
+// Protobuf library provides support to pack/unpack Any values in the form
+// of utility functions or additional generated methods of the Any type.
+//
+// Example 1: Pack and unpack a message in C++.
+//
+//     Foo foo = ...;
+//     Any any;
+//     any.PackFrom(foo);
+//     ...
+//     if (any.UnpackTo(&foo)) {
+//       ...
+//     }
+//
+// Example 2: Pack and unpack a message in Java.
+//
+//     Foo foo = ...;
+//     Any any = Any.pack(foo);
+//     ...
+//     if (any.is(Foo.class)) {
+//       foo = any.unpack(Foo.class);
+//     }
+//
+//  Example 3: Pack and unpack a message in Python.
+//
+//     foo = Foo(...)
+//     any = Any()
+//     any.Pack(foo)
+//     ...
+//     if any.Is(Foo.DESCRIPTOR):
+//       any.Unpack(foo)
+//       ...
+//
+//  Example 4: Pack and unpack a message in Go
+//
+//      foo := &pb.Foo{...}
+//      any, err := ptypes.MarshalAny(foo)
+//      ...
+//      foo := &pb.Foo{}
+//      if err := ptypes.UnmarshalAny(any, foo); err != nil {
+//        ...
+//      }
+//
+// The pack methods provided by protobuf library will by default use
+// 'type.googleapis.com/full.type.name' as the type URL and the unpack
+// methods only use the fully qualified type name after the last '/'
+// in the type URL, for example "foo.bar.com/x/y.z" will yield type
+// name "y.z".
+//
+//
+// JSON
+// ====
+// The JSON representation of an `Any` value uses the regular
+// representation of the deserialized, embedded message, with an
+// additional field `@type` which contains the type URL. Example:
+//
+//     package google.profile;
+//     message Person {
+//       string first_name = 1;
+//       string last_name = 2;
+//     }
+//
+//     {
+//       "@type": "type.googleapis.com/google.profile.Person",
+//       "firstName": <string>,
+//       "lastName": <string>
+//     }
+//
+// If the embedded message type is well-known and has a custom JSON
+// representation, that representation will be embedded adding a field
+// `value` which holds the custom JSON in addition to the `@type`
+// field. Example (for message [google.protobuf.Duration][]):
+//
+//     {
+//       "@type": "type.googleapis.com/google.protobuf.Duration",
+//       "value": "1.212s"
+//     }
+//
+message Any {
+  // A URL/resource name whose content describes the type of the
+  // serialized protocol buffer message.
+  //
+  // For URLs which use the scheme `http`, `https`, or no scheme, the
+  // following restrictions and interpretations apply:
+  //
+  // * If no scheme is provided, `https` is assumed.
+  // * The last segment of the URL's path must represent the fully
+  //   qualified name of the type (as in `path/google.protobuf.Duration`).
+  //   The name should be in a canonical form (e.g., leading "." is
+  //   not accepted).
+  // * An HTTP GET on the URL must yield a [google.protobuf.Type][]
+  //   value in binary format, or produce an error.
+  // * Applications are allowed to cache lookup results based on the
+  //   URL, or have them precompiled into a binary to avoid any
+  //   lookup. Therefore, binary compatibility needs to be preserved
+  //   on changes to types. (Use versioned type names to manage
+  //   breaking changes.)
+  //
+  // Schemes other than `http`, `https` (or the empty scheme) might be
+  // used with implementation specific semantics.
+  //
+  string type_url = 1;
+
+  // Must be a valid serialized protocol buffer of the above specified type.
+  bytes value = 2;
+}
diff --git a/Firestore/Protos/protos/google/protobuf/empty.proto b/Firestore/Protos/protos/google/protobuf/empty.proto
new file mode 100644
index 0000000..03cacd2
--- /dev/null
+++ b/Firestore/Protos/protos/google/protobuf/empty.proto
@@ -0,0 +1,52 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+syntax = "proto3";
+
+package google.protobuf;
+
+option csharp_namespace = "Google.Protobuf.WellKnownTypes";
+option go_package = "github.com/golang/protobuf/ptypes/empty";
+option java_package = "com.google.protobuf";
+option java_outer_classname = "EmptyProto";
+option java_multiple_files = true;
+option objc_class_prefix = "GPB";
+option cc_enable_arenas = true;
+
+// A generic empty message that you can re-use to avoid defining duplicated
+// empty messages in your APIs. A typical example is to use it as the request
+// or the response type of an API method. For instance:
+//
+//     service Foo {
+//       rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty);
+//     }
+//
+// The JSON representation for `Empty` is empty JSON object `{}`.
+message Empty {}
diff --git a/Firestore/Protos/protos/google/protobuf/wrappers.proto b/Firestore/Protos/protos/google/protobuf/wrappers.proto
new file mode 100644
index 0000000..0194763
--- /dev/null
+++ b/Firestore/Protos/protos/google/protobuf/wrappers.proto
@@ -0,0 +1,118 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Wrappers for primitive (non-message) types. These types are useful
+// for embedding primitives in the `google.protobuf.Any` type and for places
+// where we need to distinguish between the absence of a primitive
+// typed field and its default value.
+
+syntax = "proto3";
+
+package google.protobuf;
+
+option csharp_namespace = "Google.Protobuf.WellKnownTypes";
+option cc_enable_arenas = true;
+option go_package = "github.com/golang/protobuf/ptypes/wrappers";
+option java_package = "com.google.protobuf";
+option java_outer_classname = "WrappersProto";
+option java_multiple_files = true;
+option objc_class_prefix = "GPB";
+
+// Wrapper message for `double`.
+//
+// The JSON representation for `DoubleValue` is JSON number.
+message DoubleValue {
+  // The double value.
+  double value = 1;
+}
+
+// Wrapper message for `float`.
+//
+// The JSON representation for `FloatValue` is JSON number.
+message FloatValue {
+  // The float value.
+  float value = 1;
+}
+
+// Wrapper message for `int64`.
+//
+// The JSON representation for `Int64Value` is JSON string.
+message Int64Value {
+  // The int64 value.
+  int64 value = 1;
+}
+
+// Wrapper message for `uint64`.
+//
+// The JSON representation for `UInt64Value` is JSON string.
+message UInt64Value {
+  // The uint64 value.
+  uint64 value = 1;
+}
+
+// Wrapper message for `int32`.
+//
+// The JSON representation for `Int32Value` is JSON number.
+message Int32Value {
+  // The int32 value.
+  int32 value = 1;
+}
+
+// Wrapper message for `uint32`.
+//
+// The JSON representation for `UInt32Value` is JSON number.
+message UInt32Value {
+  // The uint32 value.
+  uint32 value = 1;
+}
+
+// Wrapper message for `bool`.
+//
+// The JSON representation for `BoolValue` is JSON `true` and `false`.
+message BoolValue {
+  // The bool value.
+  bool value = 1;
+}
+
+// Wrapper message for `string`.
+//
+// The JSON representation for `StringValue` is JSON string.
+message StringValue {
+  // The string value.
+  string value = 1;
+}
+
+// Wrapper message for `bytes`.
+//
+// The JSON representation for `BytesValue` is JSON string.
+message BytesValue {
+  // The bytes value.
+  bytes value = 1;
+}
diff --git a/Firestore/core/src/firebase/firestore/remote/CMakeLists.txt b/Firestore/core/src/firebase/firestore/remote/CMakeLists.txt
index a218e3b..7f528fb 100644
--- a/Firestore/core/src/firebase/firestore/remote/CMakeLists.txt
+++ b/Firestore/core/src/firebase/firestore/remote/CMakeLists.txt
@@ -20,6 +20,8 @@ cc_library(
     serializer.h
     serializer.cc
   DEPENDS
+    firebase_firestore_model
+    firebase_firestore_protos_nanopb
     grpc::grpc
     nanopb
 )
diff --git a/Firestore/core/src/firebase/firestore/remote/serializer.cc b/Firestore/core/src/firebase/firestore/remote/serializer.cc
index d3cdd3f..e503d09 100644
--- a/Firestore/core/src/firebase/firestore/remote/serializer.cc
+++ b/Firestore/core/src/firebase/firestore/remote/serializer.cc
@@ -16,16 +16,94 @@
 
 #include "Firestore/core/src/firebase/firestore/remote/serializer.h"
 
-// TODO(rsgowman): These are (currently!) unnecessary includes. Adding for now
-// to ensure we can find nanopb's generated header files.
-#include "Firestore/Protos/nanopb/google/firestore/v1beta1/document.pb.h"
-#include "Firestore/Protos/nanopb/google/protobuf/timestamp.pb.h"
+#include <pb_decode.h>
+#include <pb_encode.h>
 
 namespace firebase {
 namespace firestore {
 namespace remote {
 
-Serializer::Serializer() {
+using firebase::firestore::model::FieldValue;
+
+Serializer::TypedValue Serializer::EncodeFieldValue(
+    const FieldValue& field_value) {
+  Serializer::TypedValue proto_value{
+      field_value.type(), google_firestore_v1beta1_Value_init_default};
+  switch (field_value.type()) {
+    case FieldValue::Type::Null:
+      proto_value.value.null_value = google_protobuf_NullValue_NULL_VALUE;
+      break;
+    default:
+      // TODO(rsgowman): implement the other types
+      abort();
+  }
+  return proto_value;
+}
+
+void Serializer::EncodeTypedValue(const TypedValue& value,
+                                  std::vector<uint8_t>* out_bytes) {
+  bool status;
+  // TODO(rsgowman): how large should the output buffer be? Do some
+  // investigation to see if we can get nanopb to tell us how much space it's
+  // going to need.
+  uint8_t buf[1024];
+  pb_ostream_t stream = pb_ostream_from_buffer(buf, sizeof(buf));
+  switch (value.type) {
+    case FieldValue::Type::Null:
+      status = pb_encode_tag(&stream, PB_WT_VARINT,
+                             google_firestore_v1beta1_Value_null_value_tag);
+      if (!status) {
+        // TODO(rsgowman): figure out error handling
+        abort();
+      }
+
+      status = pb_encode_varint(&stream, value.value.null_value);
+      if (!status) {
+        // TODO(rsgowman): figure out error handling
+        abort();
+      }
+
+      out_bytes->insert(out_bytes->end(), buf, buf + stream.bytes_written);
+
+      break;
+
+    default:
+      // TODO(rsgowman): implement the other types
+      abort();
+  }
+}
+
+FieldValue Serializer::DecodeFieldValue(
+    const Serializer::TypedValue& value_proto) {
+  switch (value_proto.type) {
+    case FieldValue::Type::Null:
+      return FieldValue::NullValue();
+    default:
+      // TODO(rsgowman): implement the other types
+      abort();
+  }
+}
+
+Serializer::TypedValue Serializer::DecodeTypedValue(const uint8_t* bytes,
+                                                    size_t length) {
+  pb_istream_t stream = pb_istream_from_buffer(bytes, length);
+  pb_wire_type_t wire_type;
+  uint32_t tag;
+  bool eof;
+  bool status = pb_decode_tag(&stream, &wire_type, &tag, &eof);
+  if (!status || wire_type != PB_WT_VARINT) {
+    // TODO(rsgowman): figure out error handling
+    abort();
+  }
+
+  switch (tag) {
+    case google_firestore_v1beta1_Value_null_value_tag:
+      return Serializer::TypedValue{
+          FieldValue::Type::Null, google_firestore_v1beta1_Value_init_default};
+    default:
+      // TODO(rsgowman): figure out error handling
+      abort();
+  }
 }
 
 }  // namespace remote
diff --git a/Firestore/core/src/firebase/firestore/remote/serializer.h b/Firestore/core/src/firebase/firestore/remote/serializer.h
index 4dc6b9e..518cff4 100644
--- a/Firestore/core/src/firebase/firestore/remote/serializer.h
+++ b/Firestore/core/src/firebase/firestore/remote/serializer.h
@@ -17,16 +17,26 @@
 #ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_REMOTE_SERIALIZER_H_
 #define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_REMOTE_SERIALIZER_H_
 
+#include <stdint.h>
+#include <stdlib.h>
+#include <vector>
+
+#include "Firestore/Protos/nanopb/google/firestore/v1beta1/document.pb.h"
+#include "Firestore/core/src/firebase/firestore/model/field_value.h"
+#include "Firestore/core/src/firebase/firestore/util/firebase_assert.h"
+
 namespace firebase {
 namespace firestore {
 namespace remote {
 
 /**
  * @brief Converts internal model objects to their equivalent protocol buffer
- * form.
+ * form, and protocol buffer objects to their equivalent bytes.
  *
- * Methods starting with "Encode" convert to a protocol buffer and methods
- * starting with "Decode" convert from a protocol buffer.
+ * Methods starting with "Encode" either convert from a model object to a
+ * protocol buffer or from a protocol buffer to bytes, and methods starting with
+ * "Decode" either convert from a protocol buffer to a model object or from
+ * bytes to a protocol buffer.
  *
  */
 // TODO(rsgowman): Original docs also has this: "Throws an exception if a
@@ -34,10 +44,102 @@ namespace remote {
 // interpret." Adjust for C++.
 class Serializer {
  public:
-  // TODO(rsgowman): Adjust ctor to accept a DatabaseID... once that exists.
-  Serializer(/*DatabaseID databaseId*/);
+  /**
+   * @brief Wraps (nanopb) google_firestore_v1beta1_Value with type information.
+   */
+  struct TypedValue {
+    firebase::firestore::model::FieldValue::Type type;
+    google_firestore_v1beta1_Value value;
+  };
+
+  Serializer() {
+  }
+  // TODO(rsgowman): We eventually need the DatabaseId, but can't add it just
+  // yet since it's not used yet (which travis complains about). So for now,
+  // we'll create a parameterless ctor (above) that likely won't exist in the
+  // final version of this class.
+  ///**
+  // * @param database_id Must remain valid for the lifetime of this Serializer
+  // * object.
+  // */
+  // explicit Serializer(const firebase::firestore::model::DatabaseId&
+  // database_id)
+  //    : database_id_(database_id) {
+  //}
+
+  /**
+   * Converts the FieldValue model passed into the Value proto equivalent.
+   *
+   * @param field_value the model to convert.
+   * @return the proto representation of the model.
+   */
+  static Serializer::TypedValue EncodeFieldValue(
+      const firebase::firestore::model::FieldValue& field_value);
+
+  /**
+   * @brief Converts the value proto passed into bytes.
+   *
+   * @param[out] out_bytes A buffer to place the output. The bytes will be
+   * appended to this vector.
+   */
+  // TODO(rsgowman): error handling, incl return code.
+  static void EncodeTypedValue(const TypedValue& value,
+                               std::vector<uint8_t>* out_bytes);
+
+  /**
+   * Converts from the proto Value format to the model FieldValue format
+   *
+   * @return The model equivalent of the proto data.
+   */
+  static firebase::firestore::model::FieldValue DecodeFieldValue(
+      const Serializer::TypedValue& value_proto);
+
+  /**
+   * @brief Converts from bytes to the nanopb proto.
+   *
+   * @param bytes The bytes to convert. It's assumed that exactly all of the
+   * bytes will be used by this conversion.
+   * @return The (nanopb) proto equivalent of the bytes.
+   */
+  // TODO(rsgowman): error handling.
+  static TypedValue DecodeTypedValue(const uint8_t* bytes, size_t length);
+
+  /**
+   * @brief Converts from bytes to the nanopb proto.
+   *
+   * @param bytes The bytes to convert. It's assumed that exactly all of the
+   * bytes will be used by this conversion.
+   * @return The (nanopb) proto equivalent of the bytes.
+   */
+  // TODO(rsgowman): error handling.
+  static TypedValue DecodeTypedValue(const std::vector<uint8_t>& bytes) {
+    return DecodeTypedValue(bytes.data(), bytes.size());
+  }
+
+ private:
+  // TODO(rsgowman): We don't need the database_id_ yet (but will eventually).
+  // const firebase::firestore::model::DatabaseId& database_id_;
 };
 
+inline bool operator==(const Serializer::TypedValue& lhs,
+                       const Serializer::TypedValue& rhs) {
+  if (lhs.type != rhs.type) {
+    return false;
+  }
+
+  switch (lhs.type) {
+    case firebase::firestore::model::FieldValue::Type::Null:
+      FIREBASE_DEV_ASSERT(lhs.value.null_value ==
+                          google_protobuf_NullValue_NULL_VALUE);
+      FIREBASE_DEV_ASSERT(rhs.value.null_value ==
+                          google_protobuf_NullValue_NULL_VALUE);
+      return true;
+    default:
+      // TODO(rsgowman): implement the other types
+      abort();
+  }
+}
+
 }  // namespace remote
 }  // namespace firestore
 }  // namespace firebase
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.
diff --git a/cmake/external/grpc.cmake b/cmake/external/grpc.cmake
index 0af6b31..d545087 100644
--- a/cmake/external/grpc.cmake
+++ b/cmake/external/grpc.cmake
@@ -68,7 +68,15 @@ else()
 
     PREFIX ${PROJECT_BINARY_DIR}/external/grpc
 
-    CMAKE_ARGS ${CMAKE_ARGS}
+    # TODO(rsgowman): We're currently building nanopb twice; once via grpc, and
+    # once via nanopb. The version from grpc is the one that actually ends up
+    # being used. We need to fix this such that either:
+    # a) we instruct grpc to use our nanopb
+    # b) we rely on grpc's nanopb instead of using our own.
+    # For now, we'll pass in the necessary nanopb cflags into grpc. (We require
+    # 16 bit fields. Without explicitly requesting this, nanopb uses 8 bit
+    # fields.)
+    CMAKE_ARGS ${CMAKE_ARGS};-DCMAKE_C_FLAGS=-DPB_FIELD_16BIT;DCMAKE_CXX_FLAGS=-DPB_FIELD_16BIT
 
     BUILD_COMMAND
       ${CMAKE_COMMAND} --build . --target grpc