gRPC for Objective-C

Write your API declaration in proto format
Integrate a proto library in your project
Use the generated library in your code
Use gRPC without Protobuf
Alternatives to the steps above

While gRPC doesn't require the use of an IDL to describe the API of services, using one simplifies usage and adds some interoperability guarantees. Here we use Protocol Buffers, and provide a plugin for the Protobuf Compiler (protoc) to generate client libraries to communicate with gRPC services.

Write your API declaration in proto format

For this you can consult the Protocol Buffers' official documentation, or learn from a quick example here.

Integrate a proto library in your project

Install Cocoapods.

You need to create a Podspec file for your proto library. You may simply copy the following example to the directory where your .proto files are located, updating the name, version and license as necessary. You also need to set the pods_root variable to the correct value, depending on where you place this podspec relative to your Podfile.

Pod::Spec.new do |s|
  s.name     = '<Podspec file name>'
  s.version  = '0.0.1'
  s.license  = '...'
  s.authors  = { '<your name>' => '<your email>' }
  s.homepage = '...'
  s.summary = '...'
  s.source = { :git => 'https://github.com/...' }

  s.ios.deployment_target = '7.1'
  s.osx.deployment_target = '10.9'

  # Base directory where the .proto files are.
  src = '.'

  # We'll use protoc with the gRPC plugin.
  s.dependency '!ProtoCompiler-gRPCPlugin', '~> 1.0.0-pre1.2'

  # Pods directory corresponding to this app's Podfile, relative to the location of this podspec.
  pods_root = '<path to your Podfile>/Pods'

  # Path where Cocoapods downloads protoc and the gRPC plugin.
  protoc_dir = "#{pods_root}/!ProtoCompiler"
  protoc = "#{protoc_dir}/protoc"
  plugin = "#{pods_root}/!ProtoCompiler-gRPCPlugin/grpc_objective_c_plugin"

  # Directory where you want the generated files to be placed. This is an example.
  dir = "#{pods_root}/#{s.name}"

  # Run protoc with the Objective-C and gRPC plugins to generate protocol messages and gRPC clients.
  # You can run this command manually if you later change your protos and need to regenerate.
  # Alternatively, you can advance the version of this podspec and run `pod update`.
  s.prepare_command = <<-CMD
    mkdir -p #{dir}
    #{protoc} \
        --plugin=protoc-gen-grpc=#{plugin} \
        --objc_out=#{dir} \
        --grpc_out=#{dir} \
        -I #{src} \
        -I #{protoc_dir} \
        #{src}/*.proto
  CMD

  # The --objc_out plugin generates a pair of .pbobjc.h/.pbobjc.m files for each .proto file.
  s.subspec 'Messages' do |ms|
    ms.source_files = "#{dir}/*.pbobjc.{h,m}"
    ms.header_mappings_dir = dir
    ms.requires_arc = false
    # The generated files depend on the protobuf runtime.
    ms.dependency 'Protobuf'
    # This is needed by all pods that depend on Protobuf:
    ms.pod_target_xcconfig = {
      'GCC_PREPROCESSOR_DEFINITIONS' => '$(inherited) GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1',
    }
  end

  # The --objcgrpc_out plugin generates a pair of .pbrpc.h/.pbrpc.m files for each .proto file with
  # a service defined.
  s.subspec 'Services' do |ss|
    ss.source_files = "#{dir}/*.pbrpc.{h,m}"
    ss.header_mappings_dir = dir
    ss.requires_arc = true
    # The generated files depend on the gRPC runtime, and on the files generated by `--objc_out`.
    ss.dependency 'gRPC-ProtoRPC'
    ss.dependency "#{s.name}/Messages"
  end
end

The file should be named <Podspec file name>.podspec.

Note: If your proto files are in a directory hierarchy, you might want to adjust the globs used in the sample Podspec above. For example, you could use:

  s.prepare_command = <<-CMD
    ...
        #{src}/*.proto #{src}/**/*.proto
  CMD
  ...
    ms.source_files = "#{dir}/*.pbobjc.{h,m}", "#{dir}/**/*.pbobjc.{h,m}"
  ...
    ss.source_files = "#{dir}/*.pbrpc.{h,m}", "#{dir}/**/*.pbrpc.{h,m}"

Once your library has a Podspec, Cocoapods can install it into any XCode project. For that, go into your project's directory and create a Podfile by running:

pod init

Next add a line to your Podfile to refer to your library's Podspec. Use :path as described here:

pod '<Podspec file name>', :path => 'path/to/the/directory/of/your/podspec'

You can look at this example Podfile.

Finally, in your project's directory, run:

pod install

Use the generated library in your code

Please check the example apps for examples of how to use a generated gRPC library.

Use gRPC without Protobuf

This tests file shows how to use the generic gRPC Objective-C client without generated protobuf files.

Alternatives to the steps above

Install protoc with the gRPC plugin

Although it's not recommended (because it can lead to hard-to-solve version conflicts), it is sometimes more convenient to install protoc and the gRPC plugin in your development machine, instead of letting Cocoapods download the appropriate versions for you. To do so, on Mac OS X or later, install homebrew.

The run the following command to install protoc and the gRPC protoc plugin:

$ curl -fsSL https://goo.gl/getgrpc | bash -

This will download and run the gRPC install script.

Install protoc and the gRPC plugin without using Homebrew

First install v3 of the Protocol Buffers compiler (protoc), by cloning its Git repository and following these installation instructions (the ones titled C++; don't miss the note for Mac users).

Then clone this repository and execute the following commands from the root directory where it was cloned.

Compile the gRPC plugins for protoc:

make grpc_objective_c_plugin

Create a symbolic link to the compiled plugin binary somewhere in your $PATH:

ln -s `pwd`/bins/opt/grpc_objective_c_plugin /usr/local/bin/protoc-gen-objcgrpc

(Notice that the name of the created link must begin with "protoc-gen-" for protoc to recognize it as a plugin).

If you don't want to create the symbolic link, you can alternatively copy the binary (with the appropriate name). Or you might prefer instead to specify the plugin's path as a flag when invoking protoc, in which case no system modification nor renaming is necessary.

Integrate the generated gRPC library without using Cocoapods

You need to compile the generated .pbobjc.* files (the enums and messages) without ARC support, and the generated .pbrpc.* files (the services) with ARC support. The generated code depends on v0.12+ of the Objective-C gRPC runtime library and v3.0.0-alpha-4+ of the Objective-C Protobuf runtime library.

These libraries need to be integrated into your project as described in their respective Podspec files:

Podspec for the Objective-C gRPC runtime library. This can be tedious to configure manually.
Podspec for the Objective-C Protobuf runtime library.