# gRPC for Objective-C

- [Install protoc with the gRPC plugin](#install)
- [Write your API declaration in proto format](#write-protos)
- [Integrate a proto library in your project](#cocoapods)
- [Use the generated library in your code](#use)
- [Use gRPC without Protobuf](#no-proto)
- [Alternative installation methods](#alternatives)
    - [Install protoc and the gRPC plugin without using Homebrew](#no-homebrew)
    - [Integrate the generated gRPC library without using Cocoapods](#no-cocoapods)

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.

<a name="install"></a>
## 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:
```sh
$ 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.

<a name="write-protos"></a>
## Write your API declaration in proto format

For this you can consult the [Protocol Buffers][]' official documentation, or learn from a quick
example [here](https://github.com/grpc/grpc-common#defining-a-service).

<a name="cocoapods"></a>
## Integrate a proto library in your project

Install [Cocoapods](https://cocoapods.org/#install).

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:

```ruby
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:

```ruby
  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:

```sh
pod init
```

Next add a line to your Podfile to refer to your library's Podspec. Use `:path` as described
[here](https://guides.cocoapods.org/using/the-podfile.html#using-the-files-from-a-folder-local-to-the-machine):

```ruby
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:

```sh
pod install
```

<a name="use"></a>
## Use the generated library in your code

Please check this [sample app][] for examples of how to use a generated gRPC library.

<a name="no-proto"></a>
## Use gRPC without Protobuf

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

<a name="alternatives"></a>
## Alternative installation methods

<a name="no-homebrew"></a>
### Install protoc and the gRPC plugin without using Homebrew

First install v3 of the Protocol Buffers compiler (_protoc_), by cloning
[its Git repository](https://github.com/google/protobuf) and following these
[installation instructions](https://github.com/google/protobuf#c-installation---unix)
(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_:
```sh
make plugins
```

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

<a name="no-cocoapods"></a>
### 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](https://github.com/grpc/grpc/blob/master/gRPC.podspec) for the Objective-C gRPC runtime
library. This can be tedious to configure manually.
* [Podspec](https://github.com/google/protobuf/blob/master/Protobuf.podspec) for the
Objective-C Protobuf runtime library.

[Protocol Buffers]:https://developers.google.com/protocol-buffers/
[homebrew]:http://brew.sh
[linuxbrew]:https://github.com/Homebrew/linuxbrew
[gRPC install script]:https://raw.githubusercontent.com/grpc/homebrew-grpc/master/scripts/install
[example Podfile]:https://github.com/grpc/grpc/blob/master/src/objective-c/examples/Sample/Podfile
[sample app]: https://github.com/grpc/grpc/tree/master/src/objective-c/examples/Sample