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gRPC-Lua

The Lua gRPC binding.

Dependencies

gRPC-Lua depends on

• grpc_cb_core
• lua-intf
• lua

See doc/conan-graph.html

All these libraries can be installed by conan C/C++ package manager.

Build

Quick Build

1. Install conan.
2. Add conan repositories
   • conan remote add remote_bintray_conan-community https://api.bintray.com/conan/conan-community/conan
   • conan remote add remote_bintray_bincrafters https://api.bintray.com/conan/bincrafters/public-conan
   • conan remote add remote_bintray_inexorgame https://api.bintray.com/conan/inexorgame/inexor-conan
   • conan remote add remote_bintray_conan https://api.bintray.com/conan/conan/conan-transit
   • conan remote add remote_bintray_jinq0123 https://api.bintray.com/conan/jinq0123/test
3. conan create . user/channel --build missing
   • The result grpc_lua.dll/grpc_lua.so is in ~/.conan/data/grpc-lua/0.1/user/channel/package/...

VS solution

See premake/README.md to use premake5 to generate VS solution.

Tutorial

Tutorial shows some codes in the route_guide example.

Define the service

See examples/route_guide/route_guide.proto.

// Interface exported by the server.
service RouteGuide {
  // A simple RPC.
  rpc GetFeature(Point) returns (Feature) {}

  // A server-to-client streaming RPC.
  rpc ListFeatures(Rectangle) returns (stream Feature) {}

  // A client-to-server streaming RPC.
  rpc RecordRoute(stream Point) returns (RouteSummary) {}

  // A Bidirectional streaming RPC.
  rpc RouteChat(stream RouteNote) returns (stream RouteNote) {}
}
...

Import proto file

For both client and server codes:

local grpc = require("grpc_lua.grpc_lua")
grpc.import_proto_file("route_guide.proto")

No need to generate codes.

Client

See examples/route_guide/route_guide_client.lua.

Create a stub

    local c_channel = grpc.channel("localhost:50051")
    local stub = grcp.service_stub(c_channel, "routeguide.RouteGuide")

Call service method

• Sync call

  • Simple RPC: sync_get_feature()

     local feature = stub.sync_request("GetFeature", point(409146138, -746188906))

  • Server-side streaming RPC: sync_list_features()

     local sync_reader = stub:sync_request_read("ListFeatures", rect)
     while true do
     	local feature = sync_reader.read_one()
     	if not feature then break end
     	print("Found feature: "..inspect(feature))
     end  -- while

  • Client-side streaming RPC: sync_record_route()

     local sync_writer = stub.sync_request_write("RecordRoute")
     for i = 1, 10 do
     	local feature = db.get_rand_feature()
     	local loc = assert(feature.location)
     	if not sync_writer.write(loc) then
     		break
     	end  -- if
     end  -- for
     
     -- Recv status and reponse.
     local summary, error_str, status_code = sync_writer.close()
     if summary then
     	print_route_sumary(summary)
     end

  • Bidirectional streaming RPC: sync_route_chat()

     local sync_rdwr = stub.sync_request_rdwr("RouteChat")
     
     for _, note in ipairs(notes) do
     	sync_rdwr.write(note)
     end
     sync_rdwr.close_writing()
     
     -- read remaining
     while true do
     	local server_note = sync_rdwr.read_one()
     	if not server_note then break end
     	print("Got message: "..inspect(server_note))
     end  -- while

• Async call

  • Simple RPC: get_feature_async()

     stub.async_request("GetFeature", point(409146138, -746188906),
     	function(resp)
     		print("Get feature: "..inspect(resp))
     		stub.shutdown()  -- to return
     	end)
     stub.run()  -- run async requests until stub.shutdown()

    • Ignore response

       stub.async_request("GetFeature", point())  -- ignore response

    • Set error callback

      stub.set_error_cb(function(error_str, status_code) ... end) before async_request()

  • Run the stub

    • Async calls need run()

       stub.run()  -- run async requests until stub.shutdown()

    • stub.shutdown() ends stub.run().

  • Server-side streaming RPC: list_features_async()

     stub.async_request_read("ListFeatures", rect,
     	function(f)
     		assert("table" == type(f))
     		print(string.format("Got feature %s at %f,%f", f.name,
     			f.location.latitude/kCoordFactor, f.location.longitude/kCoordFactor))
     	end,
     	function(error_str, status_code)
     		assert("number" == type(status_code))
     		stub.shutdown()  -- To break Run().
     	end)
     stub.run()  -- until stub.shutdown()

  • Client-side streaming RPC: record_route_async()

     local async_writer = stub.async_request_write("RecordRoute")
     for i = 1, 10 do
     	local f = db.get_rand_feature()
     	local loc = f.location
     	if not async_writer:write(loc) do break end  -- Broken stream.
     end  -- for
     
     -- Recv reponse and status.
     async_writer.close(
     	function(resp, error_str, status_code)
     		if resp then
     			print_route_summary(resp)
     		end  -- if
     		stub.shutdown()  -- to break run()
     	end)
     stub.run()  -- until stutdown()

  • Bidirectional streaming RPC: route_chat_async()

     local rdwr = stub.async_request_rdwr("RouteChat",
     	function(error_str, status_code)
     		stub.shutdown()  -- to break run()
     	end)
    
     for _, note in ipairs(notes) do
     	rdwr.write(note)
     end
     rdwr.close_writing()  -- Optional.
     rdwr.read_each(function(server_note)
     	assert("table" == type(server_note))
     	print("Got message: "..inspect(server_note))
     end)
    
     stub.run()  -- until shutdown()

Server

See examples/route_guide/route_guide_server.lua.

Start server

    local svr = grpc.server()
    svr:add_listening_port("0.0.0.0:50051")
    -- Service implementation is a table.
    local service = require("route_guide_service")
    svr:register_service("routeguide.RouteGuide", service)
    svr:run()

Implement service

Service is a table with the service functions defined in the proto file. The function name must be the same as in the proto file. The function parameters are different for different RPC method types.

1. Simple RPC: GetFeature()

   --- Simple RPC method.
   -- @tab request
   -- @tparam Replier replier
   function M.GetFeature(request, replier)
   	assert("table" == type(request))
   	assert("table" == type(replier))
   	local name = get_feature_name(request)
   	local response = { name = name, location = request }
   	replier:reply(response);
   end  -- GetFeature()

   replier can be copied and reply() later.

2. Server-side streaming RPC: ListFeatures()

   --- Server-to-client streaming method.
   -- @table rectangle
   -- @tparam Writer writer
   function M.ListFeatures(rectangle, writer)
   	assert("table" == type(rectangle))
   	assert("table" == type(writer))
   	...
   	for _, f in ipairs(db.features) do
   		local l = f.location
   		if l... then
   			if not writer.write(f) then
   				print("Failed to write.")
   				break
   			end  -- if not writer.write()
   		end  -- if l
   	end  -- for _, f
   	writer.close()
   end  -- ListFeatures()

3. Client-side streaming RPC: RecordRoute()

   • Should return a reader table:

      --- Client-to-server streaming method.
      -- @tab replier `Replier` object
      -- @treturn table server reader object
      function M.RecordRoute(replier)
      	assert("table" == type(replier))
      	return require("server_reader.RecordRouteReader"):new(replier, db)
      end  -- RecordRoute()

   • the reader table should optionally have these methods

     • function Reader:on_msg(msg)
     • function Reader:on_error(error_str, status_code)
     • function Reader:on_end()

4. Bidirectional streaming RPC: RouteChat()

   • Should return a reader table.

      --- Bi-directional streaming method.
      -- @table writer `Writer` object
      -- @treturn table server reader object
      function M.RouteChat(writer)
      	assert("table" == type(writer))
      	return require("server_reader.RouteChatReader"):new(writer, db)
      end  -- RouteChat()

   • The reader table should optionally have methods as client-side streaming reader.

Example codes

• greeter_client.lua
• greeter_server.lua
• route_guide_client.lua
• route_guide_server.lua

How to run examples

1. Install dependencies into ~/.conan/data using conan install

   1. Rename examples/conan_install.bat.example to conan_install.bat
   2. Run it.

2. Copy required exe and dll.

   1. Rename examples/copy_from_conan.bat.example to copy_from_conan.bat
   2. Change variables in copy_from_conan.bat
      • conandata, conan data dir, default ~/.conan/data
      • package names, conan package names for dependencies
        • lua_cpp_package
        • luapbintf_package
        • grpc_lua_package
   3. Run it, which will copy exe and dlls from ~/.conan/data
      • lua-cpp.exe
      • lua-cpp.dll
      • luapbintf.dll
      • grpc_lua.dll

3. Start lua script

   • helloworld
     • lua-cpp.exe greeter_server.lua
     • lua-cpp.exe greeter_client.lua
   • route_guide
     • lua-cpp.exe route_guide_server.lua
     • lua-cpp.exe route_guide_client.lua

API doc

See doc/ldoc/html/index.html

TODO: Integrate into Unity

Note: If you are using grpc only as client, grpc-tolua is another option.

I think it is easy to integrate grpc-lua into Unity, but I have no time to do this. Work is:

• Use C version of Lua
• Support Lua5.1 and LuaJIT
• Build for iOS and Android

Unity uses Lua library compiled as C. If use lua.exe and lua.lib compiled as C, C++ objects on stack must be destructed correctly on error. See LuaIntf error handling.

Building with Lua51 or LuaJIT library should succeed. LuaPbIntf, which is used to encode and decode protobuf messages, need to be recompiled with Lua51 or LuaJIT.