lnd/mobile/README.md

## Building mobile libraries

### Prerequisites
#### protoc
Install the dependencies for generating protobuf definitions as stated in
[lnrpc docs]( ../lnrpc/README.md#generate-protobuf-definitions)

#### gomobile
Follow [gomobile](https://github.com/golang/go/wiki/Mobile) in order to install
`gomobile` and dependencies.

Remember to run `gomobile init` (otherwise the `lnd` build might just hang).

Note that `gomobile` only supports building projects from `GOPATH` at this
point.

#### falafel
Install [`falafel`](https://github.com/lightninglabs/falafel):
```shell
⛰  go get -u -v github.com/lightninglabs/falafel
```

### Building `lnd` for iOS
```shell
⛰  make ios
```

### Building `lnd` for Android
```shell
⛰  make android
```

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

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

#### Generating proto definitions for your language.
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/go1.17.2.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`.

##### Android

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`.

### 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
TODO(halseth)