gRPC for Objective-C

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.

Install protoc with the gRPC plugin

On Mac OS X, install homebrew. On Linux, install linuxbrew.

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. After the command completes, you're ready to proceed.

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:

Pod::Spec.new do |s|
  s.name     = '<Podspec file name>'
  s.version  = '0.0.1'
  s.license  = '...'

  s.ios.deployment_target = '6.0'
  s.osx.deployment_target = '10.8'

  # 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.
  s.prepare_command = "protoc --objc_out=. --objcgrpc_out=. *.proto"

  # 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 = "*.pbobjc.{h,m}"
    ms.header_mappings_dir = "."
    ms.requires_arc = false
    ms.dependency "Protobuf", "~> 3.0.0-alpha-3"
  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 = "*.pbrpc.{h,m}"
    ss.header_mappings_dir = "."
    ss.requires_arc = true
    ss.dependency "gRPC", "~> 0.5"
    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 = "protoc --objc_out=. --objcgrpc_out=. *.proto **/*.proto"
  ...
    ms.source_files = "*.pbobjc.{h,m}", "**/*.pbobjc.{h,m}"
  ...
    ss.source_files = "*.pbrpc.{h,m}", "**/*.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 this sample app for examples of how to use a generated gRPC library.

Use gRPC without Protobuf

The sample app has an example of how to use the generic gRPC Objective-C client without generated files.

Alternative installation methods

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 plugins

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 .pbpbjc.* files (the enums and messages) without ARC support, and the generated .pbrpc.* files (the services) with ARC support. The generated code depends on v0.5+ of the Objective-C gRPC runtime library and v3.0.0-alpha-3+ 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.