Develop Android app using Golang

HelloAndroid.goSeongJae Park <[email protected]>

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/.

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

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

https://www.youtube.com/watch?v=vMZFjDipaK8&index=2&list=PL_WJkTbDHdBl5QXy6N_bMMBYlKLna5RER

https://www.youtube.com/watch?v=vMZFjDipaK8&index=2&list=PL_WJkTbDHdBl5QXy6N_bMMBYlKLna5RER

Nice To Meet You

SeongJae Park

[email protected]

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




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

https://github.com/golang/mobile

https://github.com/golang/mobile

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


● Android SDK & NDK




Pre-requisites


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

GOOS=android




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


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

○ ELF shared object● Implement every callbacks using OpenGL




Main Idea: Use NDK


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

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




Example Code

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




Example Code


$ 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







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




Build Process

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




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


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

Java CPP GOJNI CGO



...But, JNI and then cgo looks tedious

Java CPP GOJNI 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


$ 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...




Go supports ARM & Linux Officiallywith static-linking




Go supports ARM & Linux Officiallywith static-linking

Remember the philosophy of Unix

Example Code

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

https://github.com/sjp38/goOnAndroid


https://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/)





http://devfair2014.gdg.kr/



https://developers.google.com/events/5381849181323264/




Golang Process on Android: Plan

1. Cross compile Go program as ARM / Linux


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


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


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


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


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

https://github.com/camlistore/camlistore


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

Cons: Hacky, a little

https://github.com/camlistore/camlistore

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/.




Technology

Develop Android app using Golang