# Building mobile libraries

## Prerequisites

### Go language

- [Install](https://github.com/lightningnetwork/lnd/blob/master/docs/INSTALL.md#preliminaries-for-installing-from-source) `GO` language.
- Provide `$GOPATH` to `.zshrc` or `.bash_profile` files.

```shell
export GOPATH=$HOME/go
export PATH=$PATH:$GOPATH/bin
```

Or any path you want it to be in.

### Docker

- Install and run [Docker](https://www.docker.com/products/docker-desktop).

### Make

- Check that `make` is available by running the following command without errors:

```shell
⛰  make --version
```

### Go mobile

- Install [gomobile](https://github.com/golang/go/wiki/Mobile):

```shell
⛰  go install golang.org/x/mobile/cmd/gomobile@latest
```

- Install `gobind`

```shell
⛰  go install golang.org/x/mobile/cmd/gobind@latest
```

## Building the libraries

Note that `gomobile` only supports building projects from `GOPATH` at this point. So, before continuing, be sure to be in the `src` folder:

```shell
⛰  cd $GOPATH/src/github.com/lightningnetwork/lnd
```

To checkout the latest tagged release of lnd, run

```shell
⛰  git checkout $(git describe --tags --abbrev=0)
```

Or, the second option: just clone the project and checkout to any branch/tag (pay attention to the dot in the end).

```shell
⛰  git clone https://github.com/lightningnetwork/lnd .
```

#### For Android:

Move to the folder or create one:

```shell
⛰  cd $GOPATH/src/golang.org/x
```

After that clone the goland mobile repo

```shell
⛰  git clone https://github.com/golang/mobile
```

### Building `lnd` for iOS

```shell
⛰  make ios
```

### Building `lnd` for Android

Go to `$GOPATH/src/github.com/lightningnetwork/lnd` and run the command below (make sure that the Docker  engine is running):

```shell
⛰  make android
```

`make mobile` will build both iOS and Android libraries.

### Libraries

After the build has succeeded, the libraries will be found in
`mobile/build/ios/Lndmobile.xcframework` and
`mobile/build/android/Lndmobile.aar`. Reference your platforms' SDK
documentation for how to add the library to your project.

## Generating proto definitions

In order to call the methods in the generated library, the serialized proto for
the given RPC call must be provided. Similarly, the response will be a
serialized proto.

### iOS

In order to generate protobuf definitions for iOS, add `--swift_out=.` to the
first `protoc` invocation found in [ `gen_protos.sh` ](../lnrpc/gen_protos.sh).

Then, some changes to [Dockerfile](../lnrpc/Dockerfile) need to be done in
order to use the [Swift protobuf](https://github.com/apple/swift-protobuf)
plugin with protoc:

1. Replace the base image with `FROM swift:focal` so that Swift can be used.
2. `clang-format='1:7.0*'` is unavailable in Ubuntu Focal. Change that to
`clang-format='1:10.0*`.
3. On the next line, install Go and set the environment variables by adding the
following commands:

```
RUN apt-get install -y wget \
    && wget -c https://golang.org/dl/go1.17.3.linux-amd64.tar.gz -O - \
    | tar -xz -C /usr/local
ENV GOPATH=/go
ENV PATH=$PATH:/usr/local/go/bin:/go/bin
```

4. At the end of the file, just above `CMD`, add the following `RUN` command.
This will download and compile the latest tagged release of Swift protobuf.

```
RUN git clone https://github.com/apple/swift-protobuf.git \
&& cd swift-protobuf \ 
&& git checkout $(git describe --tags --abbrev=0) \
&& swift build -c release \
&& mv .build/release/protoc-gen-swift /bin
```

Finally, run `make rpc`.

Tip: The generated Swift files will be found in various folders. If you’d like
to move them to the same folder as the framework file, run

```shell
⛰  `find . -name "*.swift" -print0 | xargs -0 -I {} mv {} mobile/build/ios`.
```

`Lndmobile.xcframework` and all Swift files should now be added to your Xcode
project. You will also need to add [Swift Protobuf](https://github.com/apple/swift-protobuf)
to your project to support the generated code.  

### Android

#### First option:

In order to generate protobuf definitions for Android, add `--java_out=.`

to the first `protoc` invocation found in
[ `gen_protos.sh` ](../lnrpc/gen_protos.sh). Then, run `make rpc`.


#### Second option (preferable):

- You have to install the profobuf plugin to your Android application. 
Please, follow this link https://github.com/google/protobuf-gradle-plugin.
- Add this line to your `app build.gradle` file.
```shell
classpath "com.google.protobuf:protobuf-gradle-plugin:0.8.17"
```
- Create a `proto` folder under the `main` folder.

![proto_folder](docs/proto_folder.png)

- Add `aar` file to libs folder.

- After that add these lines to your `module's` `build.gradle` file:

```shell
plugins {
    id "com.google.protobuf"
}

android {
    sourceSets {
        main {
            proto {

            }
        }
    }
}

dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation "com.google.protobuf:protobuf-javalite:${rootProject.ext.javalite_version}"
}

protobuf {
    protoc {
        artifact = "com.google.protobuf:protoc:${rootProject.ext.protoc_version}"
    }
    generateProtoTasks {
        all().each { task ->
            task.builtins {
                java {
                    option "lite"
                }
            }
        }
    }
}
```
- Then, copy all the proto files from `lnd/lnrpc` to your `proto` folder, saving the structure.
- Build the project and wait until you see the generated Java proto files in the `build` folder.

#### Note:

If Android Studio tells you that the `aar` file cannot be included into the `app-bundle`, this is a workaround:

1. Create a separate gradle module
2. Remove everything from there and leave only `aar` and `build.gradle`.

![separate_gradle_module](docs/separate_gradle_module.png)

3. Gradle file should contain only these lines:

```shell
configurations.maybeCreate("default")
artifacts.add("default", file('Lndmobile.aar'))
```

4. In `dependencies` add this line instead of depending on `libs` folder:
```shell
implementation project(":lndmobile", { "default" })
```


## Options

Similar to lnd, subservers can be conditionally compiled with the build by setting the tags argument:

```shell
⛰  make ios
```

To support subservers that have APIs with name conflicts, pass the "prefix" flag. This will add the subserver name as a prefix to each method name:

```shell
⛰  make ios prefix=1
```

## API docs

[LND gRPC API Reference](https://api.lightning.community)

TODO(halseth)