Zs/oplog export zero size attachment fix (#911)

* Unit test coverage for zero byte file handling in oplogs
* Unit test fixes for the zero length file case
* Fixes for zero length file attachments
* Additional fix for zero length file attachments

1 files changed, 96 insertions, 0 deletions

diff --git a/src/zenserver-test/projectstore-tests.cpp b/src/zenserver-test/projectstore-tests.cpp
index d72b897c8..cec453511 100644
--- a/src/zenserver-test/projectstore-tests.cpp
+++ b/src/zenserver-test/projectstore-tests.cpp
@@ -341,6 +341,102 @@ TEST_CASE("project.basic")
 			ZEN_INFO("+++++++");
 		}
 
+		SUBCASE("snapshot zero byte file")
+		{
+			// A zero-byte file referenced in an oplog entry must survive a
+			// snapshot: the file is read, compressed, stored in CidStore, and
+			// the oplog is rewritten with a BinaryAttachment reference. After
+			// the snapshot the chunk must be retrievable and decompress to an
+			// empty payload.
+
+			std::filesystem::path EmptyFileRelPath = std::filesystem::path("zerobyte_snapshot_test") / "empty.bin";
+			std::filesystem::path EmptyFileAbsPath = RootPath / EmptyFileRelPath;
+			CreateDirectories(MakeSafeAbsolutePath(EmptyFileAbsPath.parent_path()));
+			// Create a zero-byte file on disk.
+			WriteFile(MakeSafeAbsolutePath(EmptyFileAbsPath), IoBuffer{});
+			REQUIRE(IsFile(MakeSafeAbsolutePath(EmptyFileAbsPath)));
+
+			const std::string_view EmptyChunkId{
+				"00000000"
+				"00000000"
+				"00030000"};
+			auto EmptyFileOid = zen::Oid::FromHexString(EmptyChunkId);
+
+			zen::CbObjectWriter OpWriter;
+			OpWriter << "key"
+					 << "zero_byte_test";
+			OpWriter.BeginArray("files");
+			OpWriter.BeginObject();
+			OpWriter << "id" << EmptyFileOid;
+			OpWriter << "clientpath"
+					 << "/{engine}/empty_file";
+			OpWriter << "serverpath" << EmptyFileRelPath.c_str();
+			OpWriter.EndObject();
+			OpWriter.EndArray();
+
+			zen::CbObject  Op = OpWriter.Save();
+			zen::CbPackage OpPackage(Op);
+
+			zen::BinaryWriter MemOut;
+			legacy::SaveCbPackage(OpPackage, MemOut);
+
+			HttpClient Http{BaseUri};
+
+			{
+				auto Response = Http.Post("/new", IoBufferBuilder::MakeFromMemory(MemOut.GetView()));
+				REQUIRE(Response);
+				CHECK(Response.StatusCode == HttpResponseCode::Created);
+			}
+
+			// Read file data before snapshot - raw and uncompressed, 0 bytes.
+			// http.sys converts a 200 OK with empty body to 204 No Content, so
+			// accept either status code.
+			{
+				zen::StringBuilder<128> ChunkGetUri;
+				ChunkGetUri << "/" << EmptyChunkId;
+				auto Response = Http.Get(ChunkGetUri);
+
+				REQUIRE(Response);
+				CHECK((Response.StatusCode == HttpResponseCode::OK || Response.StatusCode == HttpResponseCode::NoContent));
+				CHECK(Response.ResponsePayload.GetSize() == 0);
+			}
+
+			// Trigger snapshot.
+			{
+				IoBuffer Payload  = MakeCbObjectPayload([&](CbObjectWriter& Writer) { Writer.AddString("method"sv, "snapshot"sv); });
+				auto	 Response = Http.Post("/rpc"sv, Payload);
+				REQUIRE(Response);
+				CHECK(Response.StatusCode == HttpResponseCode::OK);
+			}
+
+			// Read chunk after snapshot - compressed, decompresses to 0 bytes.
+			{
+				zen::StringBuilder<128> ChunkGetUri;
+				ChunkGetUri << "/" << EmptyChunkId;
+				auto Response = Http.Get(ChunkGetUri, {{"Accept-Type", "application/x-ue-comp"}});
+
+				REQUIRE(Response);
+				REQUIRE(Response.StatusCode == HttpResponseCode::OK);
+
+				IoBuffer		 Data = Response.ResponsePayload;
+				IoHash			 RawHash;
+				uint64_t		 RawSize;
+				CompressedBuffer Compressed = CompressedBuffer::FromCompressed(SharedBuffer(Data), RawHash, RawSize);
+				REQUIRE(Compressed);
+				CHECK(RawSize == 0);
+				IoBuffer DataDecompressed = Compressed.Decompress().AsIoBuffer();
+				CHECK(DataDecompressed.GetSize() == 0);
+			}
+
+			// Cleanup
+			{
+				std::error_code Ec;
+				DeleteDirectories(MakeSafeAbsolutePath(RootPath / "zerobyte_snapshot_test"), Ec);
+			}
+
+			ZEN_INFO("+++++++");
+		}
+
 		SUBCASE("test chunk not found error")
 		{
 			HttpClient Http{BaseUri};