grpc-swift/Sources/GRPCCore/Documentation.docc/Articles/Generating-stubs.md

Generating stubs

Learn how to generate stubs for gRPC Swift from a service defined using the Protocol Buffers IDL.

Using protoc

If you've used Protocol Buffers before then generating gRPC Swift stubs should be simple. If you're unfamiliar with Protocol Buffers then you should get comfortable with the concepts before continuing; the Protocol Buffers website is a great place to start.

The grpc-swift-protobuf package provides protoc-gen-grpc-swift, a program which is a plugin for the Protocol Buffers compiler, protoc.

protoc-gen-grpc-swift only generates gRPC stubs, it doesn't generate messages. You must use protoc-gen-swift to generate messages in addition to gRPC Stubs.

To generate gRPC stubs for your .proto files you must run the protoc command with the --grpc-swift_out=<DIRECTORY> option:

protoc --grpc-swift_out=. my-service.proto

The presence of --grpc-swift_out tells protoc to use the protoc-gen-grpc-swift plugin. By default it'll look for the plugin in your PATH. You can also specify the path to the plugin explicitly:

protoc --plugin=/path/to/protoc-gen-grpc-swift --grpc-swift_out=. my-service.proto

You can also specify various option the protoc-gen-grpc-swift via protoc using the --grpc-swift_opt argument:

protoc --grpc-swift_opt=<OPTION_NAME>=<OPTION_VALUE> --grpc-swift_out=.

You can specify multiple options by passing the --grpc-swift_opt argument multiple times:

protoc \
  --grpc-swift_opt=<OPTION_NAME1>=<OPTION_VALUE1> \
  --grpc-swift_opt=<OPTION_NAME2>=<OPTION_VALUE2> \
  --grpc-swift_out=.

Generator options

Name	Possible Values	Default	Description
Visibility	Public, Package, Internal	Internal	Access level for generated stubs
Server	True, False	True	Generate server stubs
Client	True, False	True	Generate client stubs
FileNaming	FullPath, PathToUnderscore, DropPath	FullPath	How generated source files should be named. (See below.)
ProtoPathModuleMappings			Path to module map .asciipb file. (See below.)
UseAccessLevelOnImports	True, False	False	Whether imports should have explicit access levels.

The FileNaming option has three possible values, for an input of foo/bar/baz.proto the following output file will be generated:

• FullPath: foo/bar/baz.grpc.swift.
• PathToUnderscore: foo_bar_baz.grpc.swift
• DropPath: baz.grpc.swift

The code generator assumes all inputs are generated into the same module, ProtoPathModuleMappings allows you to specify a mapping from .proto files to the Swift module they are generated in. This allows the code generator to add appropriate imports to your generated stubs. This is described in more detail in the SwiftProtobuf documentation.

Building the plugin

The version of protoc-gen-grpc-swift you use mustn't be newer than the version of the grpc-swift-protobuf you're using.

If your package depends on grpc-swift-protobuf then you can get a copy of protoc-gen-grpc-swift by building it directly:

swift build --product protoc-gen-grpc-swift

This command will build the plugin into .build/debug directory. You can get the full path using swift build --show-bin-path.