add support for responding with partial cache chunks (#11)

* add support for responding with partial cache chunks

1 files changed, 33 insertions, 3 deletions

diff --git a/src/zenstore/cache/cacherpc.cpp b/src/zenstore/cache/cacherpc.cpp
index e6ba6629d..27bc4b016 100644
--- a/src/zenstore/cache/cacherpc.cpp
+++ b/src/zenstore/cache/cacherpc.cpp
@@ -229,7 +229,7 @@ CacheRpcHandler::HandleRpcRequest(const CacheRequestContext& Context,
 	}
 	else if (Method == "GetCacheChunks"sv)
 	{
-		OutResultPackage = HandleRpcGetCacheChunks(Context, Object);
+		OutResultPackage = HandleRpcGetCacheChunks(Context, OutAcceptFlags, Object);
 	}
 	else
 	{
@@ -1102,7 +1102,7 @@ CacheRpcHandler::HandleRpcGetCacheValues(const CacheRequestContext& Context, CbO
 }
 
 CbPackage
-CacheRpcHandler::HandleRpcGetCacheChunks(const CacheRequestContext& Context, CbObjectView RpcRequest)
+CacheRpcHandler::HandleRpcGetCacheChunks(const CacheRequestContext& Context, RpcAcceptOptions AcceptOptions, CbObjectView RpcRequest)
 {
 	ZEN_TRACE_CPU("Z$::RpcGetCacheChunks");
 	using namespace cache::detail;
@@ -1133,7 +1133,7 @@ CacheRpcHandler::HandleRpcGetCacheChunks(const CacheRequestContext& Context, CbO
 	GetUpstreamCacheChunks(Context, Namespace, UpstreamChunks, RequestKeys, Requests);
 
 	// Send the payload and descriptive data about each chunk to the client
-	return WriteGetCacheChunksResponse(Context, Namespace, Requests);
+	return WriteGetCacheChunksResponse(Context, Namespace, AcceptOptions, Requests);
 }
 
 bool
@@ -1542,12 +1542,15 @@ CacheRpcHandler::GetUpstreamCacheChunks(const CacheRequestContext&				  Context,
 CbPackage
 CacheRpcHandler::WriteGetCacheChunksResponse([[maybe_unused]] const CacheRequestContext& Context,
 											 std::string_view							 Namespace,
+											 RpcAcceptOptions							 AcceptOptions,
 											 std::vector<cache::detail::ChunkRequest>&	 Requests)
 {
 	ZEN_TRACE_CPU("Z$::WriteGetCacheChunksResponse");
 
 	using namespace cache::detail;
 
+	const bool AcceptsPartialChunks = EnumHasAnyFlags(AcceptOptions, RpcAcceptOptions::kAllowPartialCacheChunks);
+
 	CbPackage	   RpcResponse;
 	CbObjectWriter Writer;
 
@@ -1563,6 +1566,33 @@ CacheRpcHandler::WriteGetCacheChunksResponse([[maybe_unused]] const CacheRequest
 				Writer.AddHash("RawHash"sv, Request.Key->ChunkId);
 				if (Request.Value && !EnumHasAllFlags(Request.DownstreamPolicy, CachePolicy::SkipData))
 				{
+					if (AcceptsPartialChunks && (Request.RequestedOffset != 0 || Request.RequestedSize < Request.RawSize))
+					{
+						uint64_t RawOffset = 0;
+						if (Request.RequestedOffset > 0)
+						{
+							OodleCompressor		  Compressor;
+							OodleCompressionLevel CompressionLevel;
+							uint64_t			  BlockSize = 0;
+							const bool			  bOk = Request.Value.TryGetCompressParameters(Compressor, CompressionLevel, BlockSize);
+							ZEN_ASSERT(bOk);
+							if (BlockSize > 0)
+							{
+								RawOffset = (Request.RequestedOffset / BlockSize) * BlockSize;
+							}
+							else
+							{
+								RawOffset = Request.RequestedOffset;
+							}
+						}
+						// Technically the receiver can figure this offset out based on the assumption that we reply with
+						// a set of blocks that encapsulates the requested range, but since the UE side was not initially
+						// written to handle this we need to indicate that we do indeed reply with a partial response.
+						// And as we already need to add a field, why not provide some useful information so the client
+						// don't need to calculate this for us...
+						Writer.AddInteger("RawOffset", RawOffset);
+						Request.Value = Request.Value.GetRange(Request.RequestedOffset, Request.RequestedSize);
+					}
 					RpcResponse.AddAttachment(CbAttachment(Request.Value, Request.Key->ChunkId));
 				}
 				else