src/objective-c/README.md

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# gRPC for Objective-C
gRPC Objective C library provides Objective C API for users to make gRPC calls on iOS or OS X
platforms. Currently, the minimum supported iOS version is 9.0 and OS X version is 10.10 (Yosemite).

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](#write-protos)
- [Integrate a proto library in your project](#cocoapods)
- [Use the generated library in your code](#use)
- [Use gRPC without Protobuf](#no-proto)
- [Alternatives to the steps above](#alternatives)
    - [Install protoc with the gRPC plugin](#install)
    - [Install protoc and the gRPC plugin without using Homebrew](#no-homebrew)
    - [Integrate the generated gRPC library without using Cocoapods](#no-cocoapods)

<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/tree/master/examples#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. You also need to set the `pods_root` variable to the correct value, depending on where
you place this podspec relative to your Podfile.

```ruby
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 = '9.0'
  s.osx.deployment_target = '10.10'

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

  # We'll use protoc with the gRPC plugin.
  s.dependency '!ProtoCompiler-gRPCPlugin', '~> 1.0'

  # 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'
  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

  s.pod_target_xcconfig = {
    # This is needed by all pods that depend on Protobuf:
    'GCC_PREPROCESSOR_DEFINITIONS' => '$(inherited) GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1',
    # This is needed by all pods that depend on gRPC-RxLibrary:
    'CLANG_ALLOW_NON_MODULAR_INCLUDES_IN_FRAMEWORK_MODULES' => 'YES',
  }
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 = <<-CMD
    ...
        `find . -name *.proto -print | xargs`
  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:

```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 the [example apps][] for examples of how to use a generated gRPC library.

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

This [tests file](https://github.com/grpc/grpc/tree/master/src/objective-c/tests/GRPCClientTests.m)
shows how to use the generic gRPC Objective-C client without generated protobuf files.

<a name="alternatives"></a>
## Alternatives to the steps above

<a name="install"></a>
### 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:
```sh
$ curl -fsSL https://goo.gl/getgrpc | bash -
```
This will download and run the [gRPC install script][].

<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 grpc_objective_c_plugin
```

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 `.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](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
[gRPC install script]:https://raw.githubusercontent.com/grpc/homebrew-grpc/master/scripts/install
[example Podfile]:https://github.com/grpc/grpc/blob/master/examples/objective-c/helloworld/Podfile
[example apps]: https://github.com/grpc/grpc/tree/master/examples/objective-c

## Use gRPC with OpenSSL
gRPC uses BoringSSL as its dependency, which is a fork of OpenSSL and export a number of symbols
that are the same as OpenSSL. gRPC avoids conflicts of these symbols by renaming BoringSSL symbols.

If you need gRPC to use OpenSSL instead of BoringSSL (e.g. for the benefit of reducing the binary
size of your product), you need to make a local `gRPC-Core` podspec and tweak it accordingly:
- Copy the version of `/gRPC-Core.podspec` you wish to use from Github into the repository of your
  app;
- In your `Podfile`, add the following line:
```
pod `gRPC-Core`, :podspec => "." # assuming gRPC-Core.podspec is in the same directory as your Podfile
```
- Remove [the
  macro](https://github.com/grpc/grpc/blob/b24b212ee585d376c618235905757b2445ac6461/gRPC-Core.podspec#L186)
  `GRPC_SHADOW_BORINGSSL_SYMBOLS` to disable symbol renaming;
- Substitude the `BoringSSL-GRPC`
  [dependency](https://github.com/grpc/grpc/blob/b24b212ee585d376c618235905757b2445ac6461/gRPC-Core.podspec#L184)
  to whatever pod of OpenSSL your other libraries use.

These steps should allow gRPC to use OpenSSL and drop BoringSSL dependency. If you see any issue,
file an issue to us.

## Upgrade issue with BoringSSL
If you were using an old version of gRPC (<= v1.14) which depended on pod `BoringSSL` rather than
`BoringSSL-GRPC` and meet issue with the library like:
```
ld: framework not found openssl
```
updating `-framework openssl` in Other Linker Flags to `-framework openssl_grpc` in your project
may resolve this issue (see [#16821](https://github.com/grpc/grpc/issues/16821)).