| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you 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. |
| #pragma once |
| |
| #include <cstddef> |
| #include <memory> |
| #include <vector> |
| |
| #include <boost/container/small_vector.hpp> |
| #include <google/protobuf/repeated_field.h> // IWYU pragma: keep |
| #include <google/protobuf/stubs/port.h> |
| |
| #include "kudu/rpc/transfer.h" |
| #include "kudu/util/slice.h" |
| |
| namespace kudu { |
| |
| class Status; |
| class faststring; |
| |
| namespace rpc { |
| |
| typedef boost::container::small_vector<Slice, 2> SidecarSliceVector; |
| |
| // An RpcSidecar is a mechanism which allows replies to RPCs to reference blocks of data |
| // without extra copies. In other words, whenever a protobuf would have a large field |
| // where additional copies become expensive, one may opt instead to use an RpcSidecar. |
| // |
| // The RpcSidecar saves on an additional copy to/from the protobuf on both the server and |
| // client side. Both Inbound- and OutboundCall classes accept sidecars to be sent to the |
| // client and server respectively. They are ignorant of the sidecar's format, requiring |
| // only that it can be represented as a series of Slices. Data is concatenated from the |
| // Slices produced by AppendSlices() to the socket that is responding to the original |
| // RPC. The slices should remain valid for as long as the call it is attached to takes to |
| // complete. |
| // |
| // In order to distinguish between separate sidecars, whenever a sidecar is added to the |
| // RPC response on the server side, an index for that sidecar is returned. This index must |
| // then in some way (i.e., via protobuf) be communicated to the recipient. |
| // |
| // After reconstructing the array of sidecars, servers and clients may retrieve the |
| // sidecar data through the RpcContext or RpcController interfaces respectively. |
| class RpcSidecar { |
| public: |
| static std::unique_ptr<RpcSidecar> FromFaststring(faststring data); |
| static std::unique_ptr<RpcSidecar> FromFaststrings(std::vector<faststring> data); |
| static std::unique_ptr<RpcSidecar> FromSlice(Slice slice); |
| |
| // Utility method to parse a series of sidecar slices into 'sidecars' from 'buffer' and |
| // a set of offsets. |
| static Status ParseSidecars( |
| const ::google::protobuf::RepeatedField<::google::protobuf::uint32>& offsets, |
| Slice buffer, |
| SidecarSliceVector* sidecars); |
| |
| // Append Slice representation of the sidecar's data to the given payload. |
| // |
| // Note that, even if a sidecar appends multiple slices here, the receiver will |
| // see a single concatenated slice on the other end of this call or response. |
| virtual void AppendSlices(TransferPayload* payload) const = 0; |
| |
| // Return the total size of the slices to be appended. |
| virtual size_t TotalSize() const = 0; |
| virtual ~RpcSidecar() { } |
| |
| }; |
| |
| } // namespace rpc |
| } // namespace kudu |