Develop (#250)

lib/renderer/bridge.go

@@ -0,0 +1,254 @@
+package renderer
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+	"sync"
+
+	"github.com/dchest/htmlmin"
+	"github.com/gorilla/websocket"
+	"github.com/leaanthony/mewn"
+	"github.com/wailsapp/wails/lib/interfaces"
+	"github.com/wailsapp/wails/lib/logger"
+	"github.com/wailsapp/wails/lib/messages"
+)
+
+type messageType int
+
+const (
+	jsMessage messageType = iota
+	cssMessage
+	htmlMessage
+	notifyMessage
+	bindingMessage
+	callbackMessage
+	wailsRuntimeMessage
+)
+
+func (m messageType) toString() string {
+	return [...]string{"j", "s", "h", "n", "b", "c", "w"}[m]
+}
+
+// Bridge is a backend that opens a local web server
+// and renders the files over a websocket
+type Bridge struct {
+	// Common
+	log          *logger.CustomLogger
+	ipcManager   interfaces.IPCManager
+	appConfig    interfaces.AppConfig
+	eventManager interfaces.EventManager
+	bindingCache []string
+
+	// Bridge specific
+	initialisationJS []string
+	server           *http.Server
+	theConnection    *websocket.Conn
+
+	// Mutex for writing to the socket
+	lock sync.Mutex
+}
+
+// Initialise the Bridge Renderer
+func (h *Bridge) Initialise(appConfig interfaces.AppConfig, ipcManager interfaces.IPCManager, eventManager interfaces.EventManager) error {
+	h.ipcManager = ipcManager
+	h.appConfig = appConfig
+	h.eventManager = eventManager
+	ipcManager.BindRenderer(h)
+	h.log = logger.NewCustomLogger("Bridge")
+	return nil
+}
+
+func (h *Bridge) evalJS(js string, mtype messageType) error {
+
+	message := mtype.toString() + js
+
+	if h.theConnection == nil {
+		h.initialisationJS = append(h.initialisationJS, message)
+	} else {
+		// Prepend message type to message
+		h.sendMessage(h.theConnection, message)
+	}
+
+	return nil
+}
+
+func (h *Bridge) injectCSS(css string) {
+	// Minify css to overcome issues in the browser with carriage returns
+	minified, err := htmlmin.Minify([]byte(css), &htmlmin.Options{
+		MinifyStyles: true,
+	})
+	if err != nil {
+		h.log.Fatal("Unable to minify CSS: " + css)
+	}
+	minifiedCSS := string(minified)
+	minifiedCSS = strings.Replace(minifiedCSS, "\\", "\\\\", -1)
+	minifiedCSS = strings.Replace(minifiedCSS, "'", "\\'", -1)
+	minifiedCSS = strings.Replace(minifiedCSS, "\n", " ", -1)
+	inject := fmt.Sprintf("wails._.InjectCSS('%s')", minifiedCSS)
+	h.evalJS(inject, cssMessage)
+}
+
+func (h *Bridge) wsBridgeHandler(w http.ResponseWriter, r *http.Request) {
+	conn, err := websocket.Upgrade(w, r, w.Header(), 1024, 1024)
+	if err != nil {
+		http.Error(w, "Could not open websocket connection", http.StatusBadRequest)
+	}
+	h.theConnection = conn
+	h.log.Infof("Connection from frontend accepted [%p].", h.theConnection)
+	conn.SetCloseHandler(func(int, string) error {
+		h.log.Infof("Connection dropped [%p].", h.theConnection)
+		h.theConnection = nil
+		return nil
+	})
+	go h.start(conn)
+}
+
+func (h *Bridge) sendMessage(conn *websocket.Conn, msg string) {
+
+	h.lock.Lock()
+	defer h.lock.Unlock()
+
+	if err := conn.WriteMessage(websocket.TextMessage, []byte(msg)); err != nil {
+		h.log.Error(err.Error())
+	}
+}
+
+func (h *Bridge) start(conn *websocket.Conn) {
+
+	// set external.invoke
+	h.log.Infof("Connected to frontend.")
+
+	wailsRuntime := mewn.String("../../runtime/assets/wails.js")
+	h.evalJS(wailsRuntime, wailsRuntimeMessage)
+
+	// Inject bindings
+	for _, binding := range h.bindingCache {
+		h.evalJS(binding, bindingMessage)
+	}
+
+	// Emit that everything is loaded and ready
+	h.eventManager.Emit("wails:ready")
+
+	for {
+		messageType, buffer, err := conn.ReadMessage()
+		if messageType == -1 {
+			return
+		}
+		if err != nil {
+			h.log.Errorf("Error reading message: ", err)
+			continue
+		}
+
+		h.log.Debugf("Got message: %#v\n", string(buffer))
+
+		h.ipcManager.Dispatch(string(buffer))
+	}
+}
+
+// Run the app in Bridge mode!
+func (h *Bridge) Run() error {
+	h.server = &http.Server{Addr: ":34115"}
+	http.HandleFunc("/bridge", h.wsBridgeHandler)
+
+	h.log.Info("Bridge mode started.")
+	h.log.Info("The frontend will connect automatically.")
+
+	err := h.server.ListenAndServe()
+	if err != nil {
+		h.log.Fatal(err.Error())
+	}
+	return err
+}
+
+// NewBinding creates a new binding with the frontend
+func (h *Bridge) NewBinding(methodName string) error {
+	h.bindingCache = append(h.bindingCache, methodName)
+	return nil
+}
+
+// SelectFile is unsupported for Bridge but required
+// for the Renderer interface
+func (h *Bridge) SelectFile() string {
+	h.log.Warn("SelectFile() unsupported in bridge mode")
+	return ""
+}
+
+// SelectDirectory is unsupported for Bridge but required
+// for the Renderer interface
+func (h *Bridge) SelectDirectory() string {
+	h.log.Warn("SelectDirectory() unsupported in bridge mode")
+	return ""
+}
+
+// SelectSaveFile is unsupported for Bridge but required
+// for the Renderer interface
+func (h *Bridge) SelectSaveFile() string {
+	h.log.Warn("SelectSaveFile() unsupported in bridge mode")
+	return ""
+}
+
+// Callback sends a callback to the frontend
+func (h *Bridge) Callback(data string) error {
+	return h.evalJS(data, callbackMessage)
+}
+
+// NotifyEvent notifies the frontend of an event
+func (h *Bridge) NotifyEvent(event *messages.EventData) error {
+
+	// Look out! Nils about!
+	var err error
+	if event == nil {
+		err = fmt.Errorf("Sent nil event to renderer.webViewRenderer")
+		h.log.Error(err.Error())
+		return err
+	}
+
+	// Default data is a blank array
+	data := []byte("[]")
+
+	// Process event data
+	if event.Data != nil {
+		// Marshall the data
+		data, err = json.Marshal(event.Data)
+		if err != nil {
+			h.log.Errorf("Cannot unmarshall JSON data in event: %s ", err.Error())
+			return err
+		}
+	}
+
+	message := fmt.Sprintf("window.wails._.Notify('%s','%s')", event.Name, data)
+	return h.evalJS(message, notifyMessage)
+}
+
+// SetColour is unsupported for Bridge but required
+// for the Renderer interface
+func (h *Bridge) SetColour(colour string) error {
+	h.log.WarnFields("SetColour ignored for Bridge more", logger.Fields{"col": colour})
+	return nil
+}
+
+// Fullscreen is unsupported for Bridge but required
+// for the Renderer interface
+func (h *Bridge) Fullscreen() {
+	h.log.Warn("Fullscreen() unsupported in bridge mode")
+}
+
+// UnFullscreen is unsupported for Bridge but required
+// for the Renderer interface
+func (h *Bridge) UnFullscreen() {
+	h.log.Warn("UnFullscreen() unsupported in bridge mode")
+}
+
+// SetTitle is currently unsupported for Bridge but required
+// for the Renderer interface
+func (h *Bridge) SetTitle(title string) {
+	h.log.WarnFields("SetTitle() unsupported in bridge mode", logger.Fields{"title": title})
+}
+
+// Close is unsupported for Bridge but required
+// for the Renderer interface
+func (h *Bridge) Close() {
+	h.log.Warn("Close() unsupported in bridge mode")
+}

lib/renderer/webview.go

@@ -0,0 +1,357 @@
+package renderer
+
+import (
+	"encoding/json"
+	"fmt"
+	"math/rand"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/go-playground/colors"
+	"github.com/leaanthony/mewn"
+	"github.com/wailsapp/wails/lib/interfaces"
+	"github.com/wailsapp/wails/lib/logger"
+	"github.com/wailsapp/wails/lib/messages"
+	wv "github.com/wailsapp/wails/lib/renderer/webview"
+)
+
+// WebView defines the main webview application window
+// Default values in []
+type WebView struct {
+	window       wv.WebView // The webview object
+	ipc          interfaces.IPCManager
+	log          *logger.CustomLogger
+	config       interfaces.AppConfig
+	eventManager interfaces.EventManager
+	bindingCache []string
+}
+
+// NewWebView returns a new WebView struct
+func NewWebView() *WebView {
+	return &WebView{}
+}
+
+// Initialise sets up the WebView
+func (w *WebView) Initialise(config interfaces.AppConfig, ipc interfaces.IPCManager, eventManager interfaces.EventManager) error {
+
+	// Store reference to eventManager
+	w.eventManager = eventManager
+
+	// Set up logger
+	w.log = logger.NewCustomLogger("WebView")
+
+	// Set up the dispatcher function
+	w.ipc = ipc
+	ipc.BindRenderer(w)
+
+	// Save the config
+	w.config = config
+
+	// Create the WebView instance
+	w.window = wv.NewWebview(wv.Settings{
+		Width:     config.GetWidth(),
+		Height:    config.GetHeight(),
+		Title:     config.GetTitle(),
+		Resizable: config.GetResizable(),
+		URL:       config.GetDefaultHTML(),
+		Debug:     !config.GetDisableInspector(),
+		ExternalInvokeCallback: func(_ wv.WebView, message string) {
+			w.ipc.Dispatch(message)
+		},
+	})
+
+	// SignalManager.OnExit(w.Exit)
+
+	// Set colour
+	err := w.SetColour(config.GetColour())
+	if err != nil {
+		return err
+	}
+
+	w.log.Info("Initialised")
+	return nil
+}
+
+// SetColour sets the window colour
+func (w *WebView) SetColour(colour string) error {
+	color, err := colors.Parse(colour)
+	if err != nil {
+		return err
+	}
+	rgba := color.ToRGBA()
+	alpha := uint8(255 * rgba.A)
+	w.window.Dispatch(func() {
+		w.window.SetColor(rgba.R, rgba.G, rgba.B, alpha)
+	})
+
+	return nil
+}
+
+// evalJS evaluates the given js in the WebView
+// I should rename this to evilJS lol
+func (w *WebView) evalJS(js string) error {
+	outputJS := fmt.Sprintf("%.45s", js)
+	if len(js) > 45 {
+		outputJS += "..."
+	}
+	w.log.DebugFields("Eval", logger.Fields{"js": outputJS})
+	//
+	w.window.Dispatch(func() {
+		w.window.Eval(js)
+	})
+	return nil
+}
+
+// Escape the Javascripts!
+func escapeJS(js string) (string, error) {
+	result := strings.Replace(js, "\\", "\\\\", -1)
+	result = strings.Replace(result, "'", "\\'", -1)
+	result = strings.Replace(result, "\n", "\\n", -1)
+	return result, nil
+}
+
+// evalJSSync evaluates the given js in the WebView synchronously
+// Do not call this from the main thread or you'll nuke your app because
+// you won't get the callback.
+func (w *WebView) evalJSSync(js string) error {
+
+	minified, err := escapeJS(js)
+
+	if err != nil {
+		return err
+	}
+
+	outputJS := fmt.Sprintf("%.45s", js)
+	if len(js) > 45 {
+		outputJS += "..."
+	}
+	w.log.DebugFields("EvalSync", logger.Fields{"js": outputJS})
+
+	ID := fmt.Sprintf("syncjs:%d:%d", time.Now().Unix(), rand.Intn(9999))
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	go func() {
+		exit := false
+		// We are done when we receive the Callback ID
+		w.log.Debug("SyncJS: sending with ID = " + ID)
+		w.eventManager.On(ID, func(...interface{}) {
+			w.log.Debug("SyncJS: Got callback ID = " + ID)
+			wg.Done()
+			exit = true
+		})
+		command := fmt.Sprintf("wails._.AddScript('%s', '%s')", minified, ID)
+		w.window.Dispatch(func() {
+			w.window.Eval(command)
+		})
+		for exit == false {
+			time.Sleep(time.Millisecond * 1)
+		}
+	}()
+
+	wg.Wait()
+
+	return nil
+}
+
+// injectCSS adds the given CSS to the WebView
+func (w *WebView) injectCSS(css string) {
+	w.window.Dispatch(func() {
+		w.window.InjectCSS(css)
+	})
+}
+
+// Exit closes the window
+func (w *WebView) Exit() {
+	w.window.Exit()
+}
+
+// Run the window main loop
+func (w *WebView) Run() error {
+
+	w.log.Info("Running...")
+
+	// Runtime assets
+	wailsRuntime := mewn.String("../../runtime/assets/wails.js")
+	w.evalJS(wailsRuntime)
+
+	// Ping the wait channel when the wails runtime is loaded
+	w.eventManager.On("wails:loaded", func(...interface{}) {
+
+		// Run this in a different go routine to free up the main process
+		go func() {
+
+			// Inject Bindings
+			for _, binding := range w.bindingCache {
+				w.evalJSSync(binding)
+			}
+
+			// Inject user CSS
+			if w.config.GetCSS() != "" {
+				outputCSS := fmt.Sprintf("%.45s", w.config.GetCSS())
+				if len(outputCSS) > 45 {
+					outputCSS += "..."
+				}
+				w.log.DebugFields("Inject User CSS", logger.Fields{"css": outputCSS})
+				w.injectCSS(w.config.GetCSS())
+			} else {
+				// Use default wails css
+				w.log.Debug("Injecting Default Wails CSS")
+				defaultCSS := mewn.String("../../runtime/assets/wails.css")
+
+				w.injectCSS(defaultCSS)
+			}
+
+			// Inject user JS
+			if w.config.GetJS() != "" {
+				outputJS := fmt.Sprintf("%.45s", w.config.GetJS())
+				if len(outputJS) > 45 {
+					outputJS += "..."
+				}
+				w.log.DebugFields("Inject User JS", logger.Fields{"js": outputJS})
+				w.evalJSSync(w.config.GetJS())
+			}
+
+			// Emit that everything is loaded and ready
+			w.eventManager.Emit("wails:ready")
+		}()
+	})
+
+	// Kick off main window loop
+	w.window.Run()
+
+	return nil
+}
+
+// NewBinding registers a new binding with the frontend
+func (w *WebView) NewBinding(methodName string) error {
+	objectCode := fmt.Sprintf("window.wails._.NewBinding('%s');", methodName)
+	w.bindingCache = append(w.bindingCache, objectCode)
+	return nil
+}
+
+// SelectFile opens a dialog that allows the user to select a file
+func (w *WebView) SelectFile() string {
+	var result string
+
+	// We need to run this on the main thread, however Dispatch is
+	// non-blocking so we launch this in a goroutine and wait for
+	// dispatch to finish before returning the result
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		w.window.Dispatch(func() {
+			result = w.window.Dialog(wv.DialogTypeOpen, 0, "Select File", "")
+			wg.Done()
+		})
+	}()
+	wg.Wait()
+	return result
+}
+
+// SelectDirectory opens a dialog that allows the user to select a directory
+func (w *WebView) SelectDirectory() string {
+	var result string
+	// We need to run this on the main thread, however Dispatch is
+	// non-blocking so we launch this in a goroutine and wait for
+	// dispatch to finish before returning the result
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		w.window.Dispatch(func() {
+			result = w.window.Dialog(wv.DialogTypeOpen, wv.DialogFlagDirectory, "Select Directory", "")
+			wg.Done()
+		})
+	}()
+	wg.Wait()
+	return result
+}
+
+// SelectSaveFile opens a dialog that allows the user to select a file to save
+func (w *WebView) SelectSaveFile() string {
+	var result string
+	// We need to run this on the main thread, however Dispatch is
+	// non-blocking so we launch this in a goroutine and wait for
+	// dispatch to finish before returning the result
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		w.window.Dispatch(func() {
+			result = w.window.Dialog(wv.DialogTypeSave, 0, "Save file", "")
+			wg.Done()
+		})
+	}()
+	wg.Wait()
+	return result
+}
+
+// Callback sends a callback to the frontend
+func (w *WebView) Callback(data string) error {
+	callbackCMD := fmt.Sprintf("window.wails._.Callback('%s');", data)
+	return w.evalJS(callbackCMD)
+}
+
+// NotifyEvent notifies the frontend about a backend runtime event
+func (w *WebView) NotifyEvent(event *messages.EventData) error {
+
+	// Look out! Nils about!
+	var err error
+	if event == nil {
+		err = fmt.Errorf("Sent nil event to renderer.WebView")
+		w.log.Error(err.Error())
+		return err
+	}
+
+	// Default data is a blank array
+	data := []byte("[]")
+
+	// Process event data
+	if event.Data != nil {
+		// Marshall the data
+		data, err = json.Marshal(event.Data)
+		if err != nil {
+			w.log.Errorf("Cannot unmarshall JSON data in event: %s ", err.Error())
+			return err
+		}
+	}
+
+	message := fmt.Sprintf("wails._.Notify('%s','%s')", event.Name, data)
+	return w.evalJS(message)
+}
+
+// Fullscreen makes the main window go fullscreen
+func (w *WebView) Fullscreen() {
+	if w.config.GetResizable() == false {
+		w.log.Warn("Cannot call Fullscreen() - App.Resizable = false")
+		return
+	}
+	w.window.Dispatch(func() {
+		w.window.SetFullscreen(true)
+	})
+}
+
+// UnFullscreen returns the window to the position prior to a fullscreen call
+func (w *WebView) UnFullscreen() {
+	if w.config.GetResizable() == false {
+		w.log.Warn("Cannot call UnFullscreen() - App.Resizable = false")
+		return
+	}
+	w.window.Dispatch(func() {
+		w.window.SetFullscreen(false)
+	})
+}
+
+// SetTitle sets the window title
+func (w *WebView) SetTitle(title string) {
+	w.window.Dispatch(func() {
+		w.window.SetTitle(title)
+	})
+}
+
+// Close closes the window
+func (w *WebView) Close() {
+	w.window.Dispatch(func() {
+		w.window.Terminate()
+	})
+}

lib/renderer/webview/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 Serge Zaitsev
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

lib/renderer/webview/webview.go

@@ -0,0 +1,372 @@
+// Package wails implements Go bindings to https://github.com/zserge/webview C library.
+// It is a modified version of webview.go from that repository
+
+// Bindings closely repeat the C APIs and include both, a simplified
+// single-function API to just open a full-screen webview window, and a more
+// advanced and featureful set of APIs, including Go-to-JavaScript bindings.
+//
+// The library uses gtk-webkit, Cocoa/Webkit and MSHTML (IE8..11) as a browser
+// engine and supports Linux, MacOS and Windows 7..10 respectively.
+//
+package webview
+
+/*
+#cgo linux openbsd freebsd CFLAGS: -DWEBVIEW_GTK=1
+#cgo linux openbsd freebsd pkg-config: gtk+-3.0 webkit2gtk-4.0
+
+#cgo windows CFLAGS: -DWEBVIEW_WINAPI=1
+#cgo windows LDFLAGS: -lole32 -lcomctl32 -loleaut32 -luuid -lgdi32
+
+#cgo darwin CFLAGS: -DWEBVIEW_COCOA=1 -x objective-c
+#cgo darwin LDFLAGS: -framework Cocoa -framework WebKit
+
+#include <stdlib.h>
+#include <stdint.h>
+#define WEBVIEW_STATIC
+#define WEBVIEW_IMPLEMENTATION
+#include "webview.h"
+
+extern void _webviewExternalInvokeCallback(void *, void *);
+
+static inline void CgoWebViewFree(void *w) {
+	free((void *)((struct webview *)w)->title);
+	free((void *)((struct webview *)w)->url);
+	free(w);
+}
+
+static inline void *CgoWebViewCreate(int width, int height, char *title, char *url, int resizable, int debug) {
+	struct webview *w = (struct webview *) calloc(1, sizeof(*w));
+	w->width = width;
+	w->height = height;
+	w->title = title;
+	w->url = url;
+	w->resizable = resizable;
+	w->debug = debug;
+	w->external_invoke_cb = (webview_external_invoke_cb_t) _webviewExternalInvokeCallback;
+	if (webview_init(w) != 0) {
+		CgoWebViewFree(w);
+		return NULL;
+	}
+	return (void *)w;
+}
+
+static inline int CgoWebViewLoop(void *w, int blocking) {
+	return webview_loop((struct webview *)w, blocking);
+}
+
+static inline void CgoWebViewTerminate(void *w) {
+	webview_terminate((struct webview *)w);
+}
+
+static inline void CgoWebViewExit(void *w) {
+	webview_exit((struct webview *)w);
+}
+
+static inline void CgoWebViewSetTitle(void *w, char *title) {
+	webview_set_title((struct webview *)w, title);
+}
+
+static inline void CgoWebViewSetFullscreen(void *w, int fullscreen) {
+	webview_set_fullscreen((struct webview *)w, fullscreen);
+}
+
+static inline void CgoWebViewSetColor(void *w, uint8_t r, uint8_t g, uint8_t b, uint8_t a) {
+	webview_set_color((struct webview *)w, r, g, b, a);
+}
+
+static inline void CgoDialog(void *w, int dlgtype, int flags,
+		char *title, char *arg, char *res, size_t ressz) {
+	webview_dialog(w, dlgtype, flags,
+		(const char*)title, (const char*) arg, res, ressz);
+}
+
+static inline int CgoWebViewEval(void *w, char *js) {
+	return webview_eval((struct webview *)w, js);
+}
+
+static inline void CgoWebViewInjectCSS(void *w, char *css) {
+	webview_inject_css((struct webview *)w, css);
+}
+
+extern void _webviewDispatchGoCallback(void *);
+static inline void _webview_dispatch_cb(struct webview *w, void *arg) {
+	_webviewDispatchGoCallback(arg);
+}
+static inline void CgoWebViewDispatch(void *w, uintptr_t arg) {
+	webview_dispatch((struct webview *)w, _webview_dispatch_cb, (void *)arg);
+}
+*/
+import "C"
+import (
+	"errors"
+	"runtime"
+	"sync"
+	"unsafe"
+)
+
+func init() {
+	// Ensure that main.main is called from the main thread
+	runtime.LockOSThread()
+}
+
+// Open is a simplified API to open a single native window with a full-size webview in
+// it. It can be helpful if you want to communicate with the core app using XHR
+// or WebSockets (as opposed to using JavaScript bindings).
+//
+// Window appearance can be customized using title, width, height and resizable parameters.
+// URL must be provided and can user either a http or https protocol, or be a
+// local file:// URL. On some platforms "data:" URLs are also supported
+// (Linux/MacOS).
+func Open(title, url string, w, h int, resizable bool) error {
+	titleStr := C.CString(title)
+	defer C.free(unsafe.Pointer(titleStr))
+	urlStr := C.CString(url)
+	defer C.free(unsafe.Pointer(urlStr))
+	resize := C.int(0)
+	if resizable {
+		resize = C.int(1)
+	}
+
+	r := C.webview(titleStr, urlStr, C.int(w), C.int(h), resize)
+	if r != 0 {
+		return errors.New("failed to create webview")
+	}
+	return nil
+}
+
+// ExternalInvokeCallbackFunc is a function type that is called every time
+// "window.external.invoke()" is called from JavaScript. Data is the only
+// obligatory string parameter passed into the "invoke(data)" function from
+// JavaScript. To pass more complex data serialized JSON or base64 encoded
+// string can be used.
+type ExternalInvokeCallbackFunc func(w WebView, data string)
+
+// Settings is a set of parameters to customize the initial WebView appearance
+// and behavior. It is passed into the webview.New() constructor.
+type Settings struct {
+	// WebView main window title
+	Title string
+	// URL to open in a webview
+	URL string
+	// Window width in pixels
+	Width int
+	// Window height in pixels
+	Height int
+	// Allows/disallows window resizing
+	Resizable bool
+	// Enable debugging tools (Linux/BSD/MacOS, on Windows use Firebug)
+	Debug bool
+	// A callback that is executed when JavaScript calls "window.external.invoke()"
+	ExternalInvokeCallback ExternalInvokeCallbackFunc
+}
+
+// WebView is an interface that wraps the basic methods for controlling the UI
+// loop, handling multithreading and providing JavaScript bindings.
+type WebView interface {
+	// Run() starts the main UI loop until the user closes the webview window or
+	// Terminate() is called.
+	Run()
+	// Loop() runs a single iteration of the main UI.
+	Loop(blocking bool) bool
+	// SetTitle() changes window title. This method must be called from the main
+	// thread only. See Dispatch() for more details.
+	SetTitle(title string)
+	// SetFullscreen() controls window full-screen mode. This method must be
+	// called from the main thread only. See Dispatch() for more details.
+	SetFullscreen(fullscreen bool)
+	// SetColor() changes window background color. This method must be called from
+	// the main thread only. See Dispatch() for more details.
+	SetColor(r, g, b, a uint8)
+	// Eval() evaluates an arbitrary JS code inside the webview. This method must
+	// be called from the main thread only. See Dispatch() for more details.
+	Eval(js string) error
+	// InjectJS() injects an arbitrary block of CSS code using the JS API. This
+	// method must be called from the main thread only. See Dispatch() for more
+	// details.
+	InjectCSS(css string)
+	// Dialog() opens a system dialog of the given type and title. String
+	// argument can be provided for certain dialogs, such as alert boxes. For
+	// alert boxes argument is a message inside the dialog box.
+	Dialog(dlgType DialogType, flags int, title string, arg string) string
+	// Terminate() breaks the main UI loop. This method must be called from the main thread
+	// only. See Dispatch() for more details.
+	Terminate()
+	// Dispatch() schedules some arbitrary function to be executed on the main UI
+	// thread. This may be helpful if you want to run some JavaScript from
+	// background threads/goroutines, or to terminate the app.
+	Dispatch(func())
+	// Exit() closes the window and cleans up the resources. Use Terminate() to
+	// forcefully break out of the main UI loop.
+	Exit()
+}
+
+// DialogType is an enumeration of all supported system dialog types
+type DialogType int
+
+const (
+	// DialogTypeOpen is a system file open dialog
+	DialogTypeOpen DialogType = iota
+	// DialogTypeSave is a system file save dialog
+	DialogTypeSave
+	// DialogTypeAlert is a system alert dialog (message box)
+	DialogTypeAlert
+)
+
+const (
+	// DialogFlagFile is a normal file picker dialog
+	DialogFlagFile = C.WEBVIEW_DIALOG_FLAG_FILE
+	// DialogFlagDirectory is an open directory dialog
+	DialogFlagDirectory = C.WEBVIEW_DIALOG_FLAG_DIRECTORY
+	// DialogFlagInfo is an info alert dialog
+	DialogFlagInfo = C.WEBVIEW_DIALOG_FLAG_INFO
+	// DialogFlagWarning is a warning alert dialog
+	DialogFlagWarning = C.WEBVIEW_DIALOG_FLAG_WARNING
+	// DialogFlagError is an error dialog
+	DialogFlagError = C.WEBVIEW_DIALOG_FLAG_ERROR
+)
+
+var (
+	m     sync.Mutex
+	index uintptr
+	fns   = map[uintptr]func(){}
+	cbs   = map[WebView]ExternalInvokeCallbackFunc{}
+)
+
+type webview struct {
+	w unsafe.Pointer
+}
+
+var _ WebView = &webview{}
+
+func boolToInt(b bool) int {
+	if b {
+		return 1
+	}
+	return 0
+}
+
+// NewWebview creates and opens a new webview window using the given settings. The
+// returned object implements the WebView interface. This function returns nil
+// if a window can not be created.
+func NewWebview(settings Settings) WebView {
+	if settings.Width == 0 {
+		settings.Width = 640
+	}
+	if settings.Height == 0 {
+		settings.Height = 480
+	}
+	if settings.Title == "" {
+		settings.Title = "WebView"
+	}
+	w := &webview{}
+	w.w = C.CgoWebViewCreate(C.int(settings.Width), C.int(settings.Height),
+		C.CString(settings.Title), C.CString(settings.URL),
+		C.int(boolToInt(settings.Resizable)), C.int(boolToInt(settings.Debug)))
+	m.Lock()
+	if settings.ExternalInvokeCallback != nil {
+		cbs[w] = settings.ExternalInvokeCallback
+	} else {
+		cbs[w] = func(w WebView, data string) {}
+	}
+	m.Unlock()
+	return w
+}
+
+func (w *webview) Loop(blocking bool) bool {
+	block := C.int(0)
+	if blocking {
+		block = 1
+	}
+	return C.CgoWebViewLoop(w.w, block) == 0
+}
+
+func (w *webview) Run() {
+	for w.Loop(true) {
+	}
+}
+
+func (w *webview) Exit() {
+	C.CgoWebViewExit(w.w)
+}
+
+func (w *webview) Dispatch(f func()) {
+	m.Lock()
+	for ; fns[index] != nil; index++ {
+	}
+	fns[index] = f
+	m.Unlock()
+	C.CgoWebViewDispatch(w.w, C.uintptr_t(index))
+}
+
+func (w *webview) SetTitle(title string) {
+	p := C.CString(title)
+	defer C.free(unsafe.Pointer(p))
+	C.CgoWebViewSetTitle(w.w, p)
+}
+
+func (w *webview) SetColor(r, g, b, a uint8) {
+	C.CgoWebViewSetColor(w.w, C.uint8_t(r), C.uint8_t(g), C.uint8_t(b), C.uint8_t(a))
+}
+
+func (w *webview) SetFullscreen(fullscreen bool) {
+	C.CgoWebViewSetFullscreen(w.w, C.int(boolToInt(fullscreen)))
+}
+
+func (w *webview) Dialog(dlgType DialogType, flags int, title string, arg string) string {
+	const maxPath = 4096
+	titlePtr := C.CString(title)
+	defer C.free(unsafe.Pointer(titlePtr))
+	argPtr := C.CString(arg)
+	defer C.free(unsafe.Pointer(argPtr))
+	resultPtr := (*C.char)(C.calloc((C.size_t)(unsafe.Sizeof((*C.char)(nil))), (C.size_t)(maxPath)))
+	defer C.free(unsafe.Pointer(resultPtr))
+	C.CgoDialog(w.w, C.int(dlgType), C.int(flags), titlePtr,
+		argPtr, resultPtr, C.size_t(maxPath))
+	return C.GoString(resultPtr)
+}
+
+func (w *webview) Eval(js string) error {
+	p := C.CString(js)
+	defer C.free(unsafe.Pointer(p))
+	switch C.CgoWebViewEval(w.w, p) {
+	case -1:
+		return errors.New("evaluation failed")
+	}
+	return nil
+}
+
+func (w *webview) InjectCSS(css string) {
+	p := C.CString(css)
+	defer C.free(unsafe.Pointer(p))
+	C.CgoWebViewInjectCSS(w.w, p)
+}
+
+func (w *webview) Terminate() {
+	C.CgoWebViewTerminate(w.w)
+}
+
+//export _webviewDispatchGoCallback
+func _webviewDispatchGoCallback(index unsafe.Pointer) {
+	var f func()
+	m.Lock()
+	f = fns[uintptr(index)]
+	delete(fns, uintptr(index))
+	m.Unlock()
+	f()
+}
+
+//export _webviewExternalInvokeCallback
+func _webviewExternalInvokeCallback(w unsafe.Pointer, data unsafe.Pointer) {
+	m.Lock()
+	var (
+		cb ExternalInvokeCallbackFunc
+		wv WebView
+	)
+	for wv, cb = range cbs {
+		if wv.(*webview).w == w {
+			break
+		}
+	}
+	m.Unlock()
+	cb(wv, C.GoString((*C.char)(data)))
+}