Add missing readtime (#10972)

* Add missing readtime as resume type

* Add unit test

* feedback

Author: wu-hui

Firestore/core/src/remote/serializer.cc

@@ -42,13 +42,15 @@
 #include "Firestore/core/src/model/resource_path.h"
 #include "Firestore/core/src/model/server_timestamp_util.h"
 #include "Firestore/core/src/model/set_mutation.h"
+#include "Firestore/core/src/model/snapshot_version.h"
 #include "Firestore/core/src/model/value_util.h"
 #include "Firestore/core/src/model/verify_mutation.h"
 #include "Firestore/core/src/nanopb/byte_string.h"
 #include "Firestore/core/src/nanopb/nanopb_util.h"
 #include "Firestore/core/src/nanopb/reader.h"
 #include "Firestore/core/src/nanopb/writer.h"
 #include "Firestore/core/src/timestamp_internal.h"
+#include "Firestore/core/src/util/comparison.h"
 #include "Firestore/core/src/util/hard_assert.h"
 #include "Firestore/core/src/util/status.h"
 #include "Firestore/core/src/util/statusor.h"
@@ -111,6 +113,7 @@ using nanopb::SetRepeatedField;
 using nanopb::SharedMessage;
 using nanopb::Writer;
 using remote::WatchChange;
+using util::ComparisonResult;
 using util::ReadContext;
 using util::Status;
 using util::StatusOr;
@@ -635,6 +638,11 @@ google_firestore_v1_Target Serializer::EncodeTarget(
     result.which_resume_type = google_firestore_v1_Target_resume_token_tag;
     result.resume_type.resume_token =
         nanopb::CopyBytesArray(target_data.resume_token().get());
+  } else if (target_data.snapshot_version().CompareTo(
+                 SnapshotVersion::None()) == ComparisonResult::Descending) {
+    result.which_resume_type = google_firestore_v1_Target_read_time_tag;
+    result.resume_type.read_time =
+        EncodeVersion(target_data.snapshot_version());
   }
 
   return result;

Firestore/core/test/unit/remote/serializer_test.cc

@@ -1124,6 +1124,42 @@ TEST_F(SerializerTest, EncodesFirstLevelKeyQueries) {
   ExpectRoundTrip(model, proto);
 }
 
+TEST_F(SerializerTest, EncodesTargetDataWithExpectedResumeType) {
+  TargetData target = CreateTargetData("docs/1");
+
+  {
+    SCOPED_TRACE("EncodesTargetDataWithoutResumeType");
+    v1::Target proto;
+    proto.mutable_documents()->add_documents(ResourceName("docs/1"));
+    proto.set_target_id(1);
+    ExpectRoundTrip(target, proto);
+  }
+
+  {
+    SCOPED_TRACE("EncodesTargetDataWithResumeToken");
+    v1::Target proto;
+    proto.mutable_documents()->add_documents(ResourceName("docs/1"));
+    proto.set_target_id(1);
+    proto.set_resume_token("resume_token");
+    ExpectRoundTrip(target.WithResumeToken(nanopb::ByteString{"resume_token"},
+                                           model::SnapshotVersion::None()),
+                    proto);
+  }
+
+  {
+    SCOPED_TRACE("EncodesTargetDataWithResumeByReadTime");
+    v1::Target proto;
+    proto.mutable_documents()->add_documents(ResourceName("docs/1"));
+    proto.set_target_id(1);
+    proto.mutable_read_time()->set_seconds(1000);
+    proto.mutable_read_time()->set_nanos(42);
+    ExpectRoundTrip(
+        target.WithResumeToken(nanopb::ByteString{""},
+                               model::SnapshotVersion(Timestamp(1000, 42))),
+        proto);
+  }
+}
+
 TEST_F(SerializerTest, EncodesFirstLevelAncestorQueries) {
   TargetData model = CreateTargetData("messages");