flatbuffers-bigfoot/grpc

GRPC implementation and test

NOTE: files in src/ are shared with the GRPC project, and maintained there (any changes should be submitted to GRPC instead). These files are copied from GRPC, and work with both the Protobuf and FlatBuffers code generator.

tests/ contains a GRPC specific test, you need to have built and installed the GRPC libraries for this to compile. This test will build using the FLATBUFFERS_BUILD_GRPCTEST option to the main FlatBuffers CMake project.

Building Flatbuffers with gRPC

Linux

1. Download, build and install gRPC. See instructions.
   • Lets say your gRPC clone is at /your/path/to/grpc_repo.
   • Install gRPC in a custom directory by running make install prefix=/your/path/to/grpc_repo/install.
2. export GRPC_INSTALL_PATH=/your/path/to/grpc_repo/install
3. export PROTOBUF_DOWNLOAD_PATH=/your/path/to/grpc_repo/third_party/protobuf
4. mkdir build ; cd build
5. cmake -DFLATBUFFERS_BUILD_GRPCTEST=ON -DGRPC_INSTALL_PATH=${GRPC_INSTALL_PATH} -DPROTOBUF_DOWNLOAD_PATH=${PROTOBUF_DOWNLOAD_PATH} ..
6. make

For Bazel users:

$bazel test src/compiler/...

Running FlatBuffer gRPC tests

Linux

1. export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:${GRPC_INSTALL_PATH}/lib
2. make test ARGS=-V

For Bazel users:

$bazel test tests/...

C++ Callback API Generation

FlatBuffers gRPC C++ code generation now optionally supports the modern gRPC Callback API.

To enable generation of a CallbackService skeleton alongside the existing Service and async mixins, invoke flatc with both --grpc and --grpc-callback-api:

flatc --cpp --grpc --grpc-callback-api your_service.fbs

This adds (guarded by #if defined(GRPC_CALLBACK_API_NONEXPERIMENTAL)) a class:

class YourService::CallbackService : public ::grpc::Service { /* reactor virtuals */ };

Each RPC shape maps to the appropriate reactor return type:

• Unary -> ::grpc::ServerUnaryReactor* Method(...)
• Client streaming -> ::grpc::ServerReadReactor<Request>*
• Server streaming -> ::grpc::ServerWriteReactor<Response>*
• Bidi streaming -> ::grpc::ServerBidiReactor<Request, Response>*

Default generated implementations return nullptr; override in your derived class and return a reactor instance you manage (see gRPC docs for lifecycle patterns).

If your gRPC library predates the stable callback API macro, the code inside the guard will be skipped (no breaking changes). Ensure you build against a recent gRPC (1.38+; verify current minimum in grpc repo) to use this feature.

Client Callback Stubs

When --grpc-callback-api is supplied, the generated C++ client stub gains native callback / reactor based async methods in addition to the existing synchronous / generic async flavors, guarded by the same macro. For each RPC named Foo:

Unary:

void async_Foo(::grpc::ClientContext*, const Request&, Response*, std::function<void(::grpc::Status)>);
void async_Foo(::grpc::ClientContext*, const Request&, Response*, ::grpc::ClientUnaryReactor*);

Client streaming:

::grpc::ClientWriteReactor<Request>* async_Foo(::grpc::ClientContext*, Response*, ::grpc::ClientWriteReactor<Request>*);

Server streaming:

::grpc::ClientReadReactor<Response>* async_Foo(::grpc::ClientContext*, const Request&, ::grpc::ClientReadReactor<Response>*);

Bidirectional streaming:

::grpc::ClientBidiReactor<Request, Response>* async_Foo(::grpc::ClientContext*, ::grpc::ClientBidiReactor<Request, Response>*);

These map directly onto the native gRPC callback API factories (e.g. CallbackUnaryCall, ClientCallbackWriterFactory::Create, etc.) and do not spawn threads. Override the appropriate reactor callbacks per gRPC's documentation to drive I/O.

If your build uses an older gRPC lacking the non-experimental macro, these symbols will not be emitted, preserving backwards compatibility.