Develop Android app using Golang

HelloAndroid.goSeongJae Park <sj38.park@gmail.com>

This work by SeongJae Park is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License. To

view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/.

This slides were presented during3rd GDG Korea Android Conference

(http://event.android.gdg.kr/3rd-GKAC/)

The talk video is available at: https://www.youtube.com/watch?v=vMZFjDipaK8&index=2&list=PL_WJkTbDHdBl5QXy6N_bMMBYlKLna5RER

Nice To Meet You

SeongJae Park

sj38.park@gmail.com

golang newbie programmer

Warning

● This speech could be useless for you○ This is just for fun

http://m.c.lnkd.licdn.com/mpr/mpr/p/4/005/095/091/210ae8c.jpg

Warning

● This speech could be useless for you○ This is just for fun

● Don’t try this at office○ The code is not stable yet

http://m.c.lnkd.licdn.com/mpr/mpr/p/4/005/095/091/210ae8c.jpg

golang: Programming Language

● For simple, reliable, and efficient software.

http://blog.golang.org/5years/gophers5th.jpg

golang: Programming Language

● For simple, reliable, and efficient software.● Could it be used for simple, reliable, and

efficient Android application?

http://blog.golang.org/5years/gophers5th.jpg

Golang and Android

● Golang supports Android from v1.4○ Though it’s still unstable

Golang and Android

● Golang supports Android from v1.4○ Though it’s still unstable

● https://github.com/golang/mobile○ Packages and build tools for using Go on Android

Goal of This Speak

● Showing how we can use golang on Android○ By exploring example code

Goal of This Speak

● Showing how we can use golang on Android○ By exploring example code

● Just for fun, rather than profit

Pre-requisites

● Basic development environment(vim, git, gcc, java, …)

http://www.theprospect.net/wp-content/uploads/2014/02/one-does-not-simply-skip-a-step.jpg

Pre-requisites

● Basic development environment(vim, git, gcc, java, …)

● Android SDK & NDK

http://www.theprospect.net/wp-content/uploads/2014/02/one-does-not-simply-skip-a-step.jpg

Pre-requisites

● Basic development environment(vim, git, gcc, java, …)

● Android SDK & NDK● Golang 1.4 or higher cross-compiled for

GOOS=android

http://www.theprospect.net/wp-content/uploads/2014/02/one-does-not-simply-skip-a-step.jpg

Pure Golang Android AppNO JAVA!

Main Idea: Use NDK

● c / c++ only apk is availableusing NativeActivity○ Golang be compiled to native binary, too. Why not?

http://www.android.pk/images/android-ndk.jpg

Main Idea: Use NDK

● c / c++ only apk is availableusing NativeActivity○ Golang be compiled to native binary, too. Why not?

Plan is...● Build golang program as .so file

○ ELF shared object● Implement every callbacks using OpenGL

http://www.android.pk/images/android-ndk.jpg

Main Idea: Use NDK

● c / c++ only apk is availableusing NativeActivity○ Golang be compiled to native binary, too. Why not?

Plan is...● Build golang program as .so file

○ ELF shared object● Implement every callbacks using OpenGL● Build NativeActivity apk using NDK / SDK

http://www.android.pk/images/android-ndk.jpg

Example Code

https://github.com/golang/mobile/tree/master/example/basic

Example Code

https://github.com/golang/mobile/tree/master/example/basic

$ tree.├── all.bash├── all.bat├── AndroidManifest.xml├── build.xml├── jni│ └── Android.mk├── main.go├── make.bash└── make.bat

1 directory, 8 files

main.go: Register Callbacks

Register callbacks from golang entrypoint

func main() {

app.Run(app.Callbacks{

Start: start,

Stop: stop,

Draw: draw,

Touch: touch,

})

}

(mobile/example/basic/main.go)

main.go: Use OpenGL

func draw() {gl.ClearColor(1, 0, 0, 1)...green += 0.01if green > 1 {

green = 0}gl.Uniform4f(color, 0, green, 0, 1)...debug.DrawFPS()

}

(mobile/example/basic/main.go)

NativeActivity

NativeActivity only application doesn’t need JAVA

<application android:label="Basic" android:hasCode="false"><activity android:name="android.app.NativeActivity"

android:label="Basic"android:configChanges="orientation|keyboardHidden"><meta-data android:name="android.app.lib_name" android:value="basic" /><intent-filter>

<action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" />

</intent-filter></activity></application>

(mobile/example/basic/AndroidManifest.xml)

NativeActivity

NativeActivity only application doesn’t need JAVA

<application android:label="Basic" android:hasCode="false"><activity android:name="android.app.NativeActivity"

android:label="Basic"android:configChanges="orientation|keyboardHidden"><meta-data android:name="android.app.lib_name" android:value="basic" /><intent-filter>

<action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" />

</intent-filter></activity></application>

(mobile/example/basic/AndroidManifest.xml)

NativeActivity

NativeActivity only application doesn’t need JAVA

<application android:label="Basic" android:hasCode="false"><activity android:name="android.app.NativeActivity"

android:label="Basic"android:configChanges="orientation|keyboardHidden"><meta-data android:name="android.app.lib_name" android:value="basic" /><intent-filter>

<action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" />

</intent-filter></activity></application>

(mobile/example/basic/AndroidManifest.xml)

Build Process

Build golang code into ELF shared object for ARM

mkdir -p jni/armeabiCGO_ENABLED=1 GOOS=android GOARCH=arm GOARM=7 \

go build -ldflags="-shared" -o jni/armeabi/libbasic.so .ndk-build NDK_DEBUG=1ant debug

(mobile/example/basic/make.bash)

Build Process

Build golang code into ELF shared object for ARMNDK to add the so file

mkdir -p jni/armeabiCGO_ENABLED=1 GOOS=android GOARCH=arm GOARM=7 \

go build -ldflags="-shared" -o jni/armeabi/libbasic.so .ndk-build NDK_DEBUG=1ant debug

(mobile/example/basic/make.bash)

Build Process

Build golang code into ELF shared object for ARMNDK to add the so fileSDK to build apk file

mkdir -p jni/armeabiCGO_ENABLED=1 GOOS=android GOARCH=arm GOARM=7 \

go build -ldflags="-shared" -o jni/armeabi/libbasic.so .ndk-build NDK_DEBUG=1ant debug

(mobile/example/basic/make.bash)

Pure Golang Android App

Pros: No more JAVA! Yay!!!

Cons: Should I learn OpenGL to show a cat?

Golang as a LibraryCooperate Java and Golang

Java and C language connected via JNI

Main Idea: Use JNI-like way

Java CPPJNI

Main Idea: Use JNI-like way

Java and C language connected via JNIC language and Golang connected via cgo

Java CPP GOJNI CGO

Main Idea: Use JNI-like way

Java and C language connected via JNIC language and Golang connected via cgo

...But, JNI and then cgo looks tedious

Java CPP GOJNI CGO

Main Idea: Use JNI-like way

Java and C language connected via JNIC language and Golang connected via cgo

...But, JNI and then cgo looks tedious

Golang supports Java-Golang bind

Java CPP GOJNI CGO

bind/seq

Example Code

https://github.com/golang/mobile/tree/master/example/libhello

Example Code

https://github.com/golang/mobile/tree/master/example/libhello

$ tree.├── all.bash├── all.bat├── AndroidManifest.xml├── build.xml├── hi│ ├── go_hi│ │ └── go_hi.go│ └── hi.go├── main.go├── make.bash├── make.bat├── README└── src ├── com │ └── example │ └── hello │ └── MainActivity.java └── go └── hi └── Hi.java

8 directories, 12 files

Callee in Go

Golang code is implementing Hello() function

func Hello(name string) {fmt.Printf("Hello, %s!\n", name)

}

(mobile/example/libhello/hi/hi.go)

Caller in JAVA

Java code is calling Golang function, Hello()

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Go.init(getApplicationContext()); Hi.Hello("world"); }

(mobile/example/libhello/src/com/example/hello/MainActivity.java)

gobind

generate language bindings that make it possible to call Go code and pass objects from Java

go install golang.org/x/mobile/cmd/gobindgobind -lang=go github.com/libhello/hi > hi/go_hi/go_hi.gogobind -lang=java github.com/libhello/hi > src/go/hi/Hi.java

gobind: Generated .java

Provides wrapper function for golang calling code

public static void Hello(String name) { go.Seq _in = new go.Seq(); go.Seq _out = new go.Seq(); _in.writeUTF16(name); Seq.send(DESCRIPTOR, CALL_Hello, _in, _out); }

private static final int CALL_Hello = 1; private static final String DESCRIPTOR = "hi";

(mobile/example/libhello/src/go/hi/Hi.java)

gobind: Generated .go

Provides proxy and registering for the exported function

func proxy_Hello(out, in *seq.Buffer) {param_name := in.ReadUTF16()hi.Hello(param_name)

}

func init() {seq.Register("hi", 1, proxy_Hello)

}

(mobile/example/libhello/hi/go_hi/go_hi.go)

Golang as a Library

Pros: JAVA for UI, Golang for background (Looks efficient enough)

Golang as a Library

Pros: JAVA for UI, Golang for background (Looks efficient enough)

Cons: bind/seq is not so efficient, yet

Inter-Process Communication

Philosophy of Unix

Main Idea: Android is a Linux

http://www.kitguru.net/wp-content/uploads/2012/03/linux-android.png

Android is a variant of Linux system with ARMx86 Androids exist, though...

Main Idea: Android is a Linux

http://www.kitguru.net/wp-content/uploads/2012/03/linux-android.png

Android is a variant of Linux system with ARMx86 Androids exist, though...

Go supports ARM & Linux Officiallywith static-linking

Main Idea: Android is a Linux

http://www.kitguru.net/wp-content/uploads/2012/03/linux-android.png

Android is a variant of Linux system with ARMx86 Androids exist, though...

Go supports ARM & Linux Officiallywith static-linking

Remember the philosophy of Unix

Example Code

https://github.com/sjp38/goOnAndroidhttps://github.com/sjp38/goOnAndroidFA

Example Code

https://github.com/sjp38/goOnAndroidhttps://github.com/sjp38/goOnAndroidFA

Were demonstrated by live-coding from GDG Korea DevFair 2014 (http://devfair2014.gdg.kr/) and GDG Golang Seoul Meetup 2015 (https://developers.google.com/events/5381849181323264/)

Golang Process on Android: Plan

1. Cross compile Go program as ARM / Linux

Golang Process on Android: Plan

1. Cross compile Go program as ARM / Linux2. Include the binary in assets/ of Android app

Golang Process on Android: Plan

1. Cross compile Go program as ARM / Linux2. Include the binary in assets/ of Android app3. Copy the binary in private space of the app

Golang Process on Android: Plan

1. Cross compile Go program as ARM / Linux2. Include the binary in assets/ of Android app3. Copy the binary in private space of the app4. Give execute permission to the binary

/data/data/com.example.goRunner/files # ls -al-rwxrwxrwx u0_a55 u0_a55 4512840 2014-11-28 17:45 gobin

Golang Process on Android: Plan

1. Cross compile Go program as ARM / Linux2. Include the binary in assets/ of Android app3. Copy the binary in private space of the app4. Give execute permission to the binary5. Execute it

/data/data/com.example.goRunner/files # ls -al-rwxrwxrwx u0_a55 u0_a55 4512840 2014-11-28 17:45 gobin

Go bin Loading

Load golang program from assets to private dir

private void copyGoBinary() { String dstFile = getBaseContext().getFilesDir().getAbsolutePath() + "/verChecker.bin"; try { InputStream is = getAssets().open("go.bin"); FileOutputStream fos = getBaseContext().openFileOutput( "verChecker.bin", MODE_PRIVATE); byte[] buf = new byte[8192]; int offset; while ((offset = is.read(buf)) > 0) { fos.write(buf, 0, offset); } Runtime.getRuntime().exec("chmod 0777 " + dstFile); } catch (IOException e) { } }

Execute Go process

Spawn new process for the program and communicates using stdio

ProcessBuilder pb = new ProcessBuilder(); pb.command(goBinPath()); pb.redirectErrorStream(false); goProcess = pb.start(); new CopyToAndroidLogThread("stderr",

goProcess.getErrorStream()) .start();

Inter Process Communication

Pros: Just normal unix way

Inter Process Communication

Pros: Just normal unix way Golang team is using this for Camlistore (https://github.com/camlistore/camlistore)

Inter Process Communication

Pros: Just normal unix way Golang team using this for Camlistore (https://github.com/camlistore/camlistore)

Cons: Hacky, a little

Summary

You can use Golang for Androidthough it’s not stable yetJust for fun

This work by SeongJae Park is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported

License. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/.