Multiplatform Support via Unified Go Codebase

at GDG Helsinki

7 May 2019

Ninchat client library

• Juggle WebSocket and long-poll connections
• Manage acknowledgements, retries, backoff etc.
• Hide complexity
• Messaging-style API: send actions, receive events via callbacks
• For building UIs, bots etc.

Multiple platforms

• JavaScript in the browser
• Node.js
• Android
• iOS
• Python
• Go

GopherJS

• Compiles a Go package to JavaScript
• Currently more or less in maintenance mode
• It just works
• Will support future Go releases
• Upgrade path to WebAssembly
• Original author is developing WebAssembly support for Go

github.com/gopherjs/gopherjs

NinchatClient.js

• Foundation of ninchat.com/app and embedded web UI
• Implemented in Go because older JavaScript wasn't helpful
• Supports IE8+
• Used with Node.js to implement bots
• Can be used with React Native
• See savo.la/talks/gopherjs for details

github.com/ninchat/ninchat-js

Go mobile

• Go compiler supports Android and Darwin targets
• Go mobile adds more Android and iOS platform support
• "Experimental" - not actively developed, but bugs get fixed
• Includes framework for standalone apps (OpenGL ES games)
• Includes binding generator
• See tanelikorri.com/presentation/2017/01/using-go-in-mobile-development

github.com/golang/go/wiki/Mobile

Go mobile binding generator

• Takes a Go package with an exported API
• Builds native libraries (C ABI)
• Generates Java wrapper code (JNI) for Android
• Generates Objective-C wrapper code for iOS
• Restrictions on Go types and function signatures

Mobile API binding restrictions

• Functions can return at most one value, with optional error value
• Maps and non-byte slices are not supported
• Simplified API layer: godoc.org/github.com/ninchat/ninchat-go/mobile
• Slices and maps are wrapped with custom objects
• Visitor pattern is used to iterate over mappings with variant value types
• Callback functions work out of the box

Example: String slice

type Strings struct{ a []string }

func NewStrings() *Strings { return new(Strings) }

func (ss *Strings) Append(val string) { ss.a = append(ss.a, val) }
func (ss *Strings) Get(i int) string  { return ss.a[i] }
func (ss *Strings) Length() int       { return len(ss.a) }

Generated Java:

public final class Strings implements Seq.Proxy {
    public Strings() {
        this.refnum = __NewStrings();
        Seq.trackGoRef(refnum, this);
    }

    public native void append(String val);
    public native String get(long i);
    public native long length();

    // ...
}

iOS bitcode issue

• Apple wants developers to enable LLVM bitcode for apps
• Easy for LLVM-based compilers, unrealistic for Go compiler
• Bitcode must be disabled unless all components support it
• Turns out that marker section is enough; actual bitcode not needed
• Workaround implemented in Go 1.13 (August 2019)

github.com/golang/go/issues/22395#issuecomment-472638175

Python module

• Go package is built into a native library (like in Go mobile case)
• go build -buildmode=c-archive
• Wrapped into a Python module with CFFI
• Nice asyncio API implemented manually on top of core
• Used for implementing bots
• Same approach could be used for other languages/platforms

github.com/ninchat/ninchat-python

Ninchat client library - future

• Now covers most important platforms
• Add more functionality to the shared codebase?
• Will Apple require bitcode for reals?
• Will GopherJS be deprecated in favor of WebAssembly?

Thank you