gRPC/Protocol Buffers

Protocol Buffers is an open-source cross-platform data format used to serialize structured data. gRPC uses Protocol Buffers as Interface Definition Language to create service contracts, detailing all of its remote functions and message formats. The `Protocol Buffers to Ballerina` tooling makes it easy for users to develop a service documented in a Protocol Buffers by generating Ballerina service/client stub files and skeletons.

Usage of the tool

The code generation tool can produce service/client stub files and service/client skeletons in the Ballerina Language.

In Ballerina, Protocol Buffers serialization is supported only in the gRPC module. Therefore, you can only use this tool to generate Ballerina source code for gRPC service definitions.

Protocol Buffers to Ballerina

You can generate Ballerina source code using the following command.

$ bal grpc --input <proto-file-path> 
         [--output <path>] 
         [--mode client|service]
         [--proto-path <proto-directory>]

CLI command options

--input - Path to a '.proto' file or a directory containing multiple '.proto' files. This is a mandatory field. You need to provide the path of the definition file or the directory that contains multiple ‘.proto’ files.

--output - Location of the generated Ballerina source files. This is an optional field. If the output path is not specified, the output is written to a directory corresponding to the package in the Protocol Buffers definition. If the package is not specified, the output is written to a directory named 'temp' in the current location.

--mode - Set the mode as client or service to generate code samples. If not specified, only the stub file is generated.

-- proto-path - Path to a directory in which to look for '.proto' files when resolving import directives. If omitted, the current directory is used. The '.proto' file specified in the 'input' must reside in the 'proto-path' so that the compiler can determine its canonical name.

Sample

The example below shows how you can generate Ballerina source code from the following Protocol Buffers definition (in the helloworld.proto file).

Note: The sample service definition is taken from the quick start guide on the gRPC official site.

Execute the sample

  • Execute the below command to generate the client/service stub and service template files.
$ bal grpc --input helloworld.proto --mode service --output service

Once you execute the command, the stub file (helloworld_pb.bal) and the service template file (greeter_service.bal) are generated inside the service directory.

Note: If you have multiple services in a Protocol Buffers definition, this command will generate a stub file with common message types and a service template file for each service definition. This is to avoid duplicating message types in all the service files.

  • Execute the following command to generate the client/service stub and client template files.
$ bal grpc --input helloworld.proto --mode client --output client

Once you execute the command, the stub file (helloworld_pb.bal) and the client template file (greeter_client.bal) are generated inside the client directory.

  • Execute the following command to generate only the client/service stub file.
$ bal grpc --input helloworld.proto --output stubs

Once you execute the command, only the stub file (helloworld_pb.bal) is generated inside the stubs directory.