lorca

README

Lorca

A very small library to build modern HTML5 desktop apps in Go. It uses Chrome browser as a UI layer. Unlike Electron it doesn't bundle Chrome into the app package, but rather reuses the one that is already installed. Lorca establishes a connection to the browser window and allows calling Go code from the UI and manipulating UI from Go in a seamless manner.

Features

• Pure Go library (no cgo) with a very simple API
• Small application size (normally 5-10MB)
• Best from the two worlds - the whole power of HTML/CSS to make your UI look good, combined with Go performance and ease of development
• Expose Go functions/methods and call them from JavaScript
• Call arbitrary JavaScript code from Go
• Asynchronous flow between UI and main app for both languages (async/await and Goroutines)
• Supports loading web UI from the local web server or via data URL
• Supports embedding all assets into a single binary
• Supports testing your app with the UI in the headless mode
• Supports multiple app windows
• Supports packaging and branding (e.g. custom app icons). Packaging for all three OS can be done on a single machine using GOOS and GOARCH variables.

Also, limitations by design:

• Requires Chrome/Chromium >= 70 to be installed.
• No control over the Chrome window yet (e.g. you can't remove border, make it transparent, control position or size).
• No window menu (tray menus and native OS dialogs are still possible via 3rd-party libraries)

If you want to have more control of the browser window - consider using webview library with a similar API, so migration would be smooth.

Example

ui, _ := lorca.New("", "", 480, 320)
defer ui.Close()

// Bind Go function to be available in JS. Go function may be long-running and
// blocking - in JS it's represented with a Promise.
ui.Bind("add", func(a, b int) int { return a + b })

// Call JS function from Go. Functions may be asynchronous, i.e. return promises
n := ui.Eval(`Math.random()`).Float()
fmt.Println(n)

// Call JS that calls Go and so on and so on...
m := ui.Eval(`add(2, 3)`).Int()
fmt.Println(m)

// Wait for the browser window to be closed
<-ui.Done()

Also, see examples for more details about binding functions, embedding assets and packaging binaries.

What's in a name?

There is kind of a legend, that before his execution Garcia Lorca have seen a sunrise over the heads of the soldiers and he said "And yet, the sun rises...". Probably it was the beginning of a poem. (J. Brodsky)

Lorca is an anagram of Carlo, a project with a similar goal for Node.js.

License

Code is distributed under MIT license, feel free to use it in your proprietary projects as well.

Documentation

Index

• Variables
• func Embed(file string, dirs ...string) error
• func LocateChrome() string
• func PromptDownload()
• type Bounds
• type UI
  • func New(url string, dir string, width, height int, customArgs ...string) (UI, error)
• type Value
• type WindowState

Variables

var ChromeExecutable = LocateChrome

ChromeExecutable returns a string which points to the preferred Chrome executable file.

Functions

func Embed

func Embed(file string, dirs ...string) error

Embed is a helper function that embeds assets from the given directories into a Go source file. It is designed to be called from some generator script, see example project to find out how it can be used.

func LocateChrome

func LocateChrome() string

LocateChrome returns a path to the Chrome binary, or an empty string if Chrome installation is not found.

func PromptDownload

func PromptDownload()

PromptDownload asks user if he wants to download and install Chrome, and opens a download web page if the user agrees.

Types

type Bounds

type Bounds struct {
	Left        int         `json:"left"`
	Top         int         `json:"top"`
	Width       int         `json:"width"`
	Height      int         `json:"height"`
	WindowState WindowState `json:"windowState"`
}

Bounds defines settable window properties.

type UI

type UI interface {
	Load(url string) error
	Bounds() (Bounds, error)
	SetBounds(Bounds) error
	Bind(name string, f interface{}) error
	Eval(js string) Value
	Done() <-chan struct{}
	Close() error
}

UI interface allows talking to the HTML5 UI from Go.

func New

func New(url string, dir string, width, height int, customArgs ...string) (UI, error)

New returns a new HTML5 UI for the given URL, user profile directory, window size and other options passed to the browser engine. If URL is an empty string - a blank page is displayed. If user profile directory is an empty string - a temporary directory is created and it will be removed on ui.Close(). You might want to use "--headless" custom CLI argument to test your UI code.

type Value

type Value interface {
	Err() error
	To(interface{}) error
	Float() float32
	Int() int
	String() string
	Bool() bool
	Object() map[string]Value
	Array() []Value
}

Value is a generic type of a JSON value (primitive, object, array) and optionally an error value.

type WindowState

type WindowState string

WindowState defines the state of the Chrome window, possible values are "normal", "maximized", "minimized" and "fullscreen".

const (
	// WindowStateNormal defines a normal state of the browser window
	WindowStateNormal WindowState = "normal"
	// WindowStateMaximized defines a maximized state of the browser window
	WindowStateMaximized WindowState = "maximized"
	// WindowStateMinimized defines a minimized state of the browser window
	WindowStateMinimized WindowState = "minimized"
	// WindowStateFullscreen defines a fullscreen state of the browser window
	WindowStateFullscreen WindowState = "fullscreen"
)