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webview.go
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webview.go
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package webview
/*
#cgo linux openbsd freebsd CXXFLAGS: -DWEBVIEW_GTK -std=c++11
#cgo linux openbsd freebsd pkg-config: gtk+-3.0 webkit2gtk-4.0
#cgo darwin CXXFLAGS: -DWEBVIEW_COCOA -std=c++11
#cgo darwin LDFLAGS: -framework WebKit
#cgo windows CXXFLAGS: -std=c++11
#cgo windows,amd64 LDFLAGS: -L./dll/x64 -lwebview -lWebView2Loader
#cgo windows,386 LDFLAGS: -L./dll/x86 -lwebview -lWebView2Loader
#define WEBVIEW_HEADER
#include "webview.h"
#include <stdlib.h>
#include <stdint.h>
extern void _webviewDispatchGoCallback(void *);
static inline void _webview_dispatch_cb(webview_t w, void *arg) {
_webviewDispatchGoCallback(arg);
}
static inline void CgoWebViewDispatch(webview_t w, uintptr_t arg) {
webview_dispatch(w, _webview_dispatch_cb, (void *)arg);
}
struct binding_context {
webview_t w;
uintptr_t index;
};
extern void _webviewBindingGoCallback(webview_t, char *, char *, uintptr_t);
static inline void _webview_binding_cb(const char *id, const char *req, void *arg) {
struct binding_context *ctx = (struct binding_context *) arg;
_webviewBindingGoCallback(ctx->w, (char *)id, (char *)req, ctx->index);
}
static inline void CgoWebViewBind(webview_t w, const char *name, uintptr_t index) {
struct binding_context *ctx = calloc(1, sizeof(struct binding_context));
ctx->w = w;
ctx->index = index;
webview_bind(w, name, _webview_binding_cb, (void *)ctx);
}
*/
import "C"
import (
"encoding/json"
"errors"
"reflect"
"runtime"
"sync"
"unsafe"
)
func init() {
// Ensure that main.main is called from the main thread
runtime.LockOSThread()
}
// Hints are used to configure window sizing and resizing
type Hint int
const (
// Width and height are default size
HintNone = C.WEBVIEW_HINT_NONE
// Window size can not be changed by a user
HintFixed = C.WEBVIEW_HINT_FIXED
// Width and height are minimum bounds
HintMin = C.WEBVIEW_HINT_MIN
// Width and height are maximum bounds
HintMax = C.WEBVIEW_HINT_MAX
)
type WebView interface {
// Run runs the main loop until it's terminated. After this function exits -
// you must destroy the webview.
Run()
// Terminate stops the main loop. It is safe to call this function from
// a background thread.
Terminate()
// Dispatch posts a function to be executed on the main thread. You normally
// do not need to call this function, unless you want to tweak the native
// window.
Dispatch(f func())
// Destroy destroys a webview and closes the native window.
Destroy()
// Window returns a native window handle pointer. When using GTK backend the
// pointer is GtkWindow pointer, when using Cocoa backend the pointer is
// NSWindow pointer, when using Win32 backend the pointer is HWND pointer.
Window() unsafe.Pointer
// SetTitle updates the title of the native window. Must be called from the UI
// thread.
SetTitle(title string)
// SetSize updates native window size. See Hint constants.
SetSize(w int, h int, hint Hint)
// Navigate navigates webview to the given URL. URL may be a data URI, i.e.
// "data:text/text,<html>...</html>". It is often ok not to url-encode it
// properly, webview will re-encode it for you.
Navigate(url string)
// Init injects JavaScript code at the initialization of the new page. Every
// time the webview will open a the new page - this initialization code will
// be executed. It is guaranteed that code is executed before window.onload.
Init(js string)
// Eval evaluates arbitrary JavaScript code. Evaluation happens asynchronously,
// also the result of the expression is ignored. Use RPC bindings if you want
// to receive notifications about the results of the evaluation.
Eval(js string)
// Bind binds a callback function so that it will appear under the given name
// as a global JavaScript function. Internally it uses webview_init().
// Callback receives a request string and a user-provided argument pointer.
// Request string is a JSON array of all the arguments passed to the
// JavaScript function.
//
// f must be a function
// f must return either value and error or just error
Bind(name string, f interface{}) error
}
type webview struct {
w C.webview_t
}
var (
m sync.Mutex
index uintptr
dispatch = map[uintptr]func(){}
bindings = map[uintptr]func(id, req string) (interface{}, error){}
)
func boolToInt(b bool) C.int {
if b {
return 1
}
return 0
}
// New calls NewWindow to create a new window and a new webview instance. If debug
// is non-zero - developer tools will be enabled (if the platform supports them).
func New(debug bool) WebView { return NewWindow(debug, nil) }
// NewWindow creates a new webview instance. If debug is non-zero - developer
// tools will be enabled (if the platform supports them). Window parameter can be
// a pointer to the native window handle. If it's non-null - then child WebView is
// embedded into the given parent window. Otherwise a new window is created.
// Depending on the platform, a GtkWindow, NSWindow or HWND pointer can be passed
// here.
func NewWindow(debug bool, window unsafe.Pointer) WebView {
w := &webview{}
w.w = C.webview_create(boolToInt(debug), window)
return w
}
func (w *webview) Destroy() {
C.webview_destroy(w.w)
}
func (w *webview) Run() {
C.webview_run(w.w)
}
func (w *webview) Terminate() {
C.webview_terminate(w.w)
}
func (w *webview) Window() unsafe.Pointer {
return C.webview_get_window(w.w)
}
func (w *webview) Navigate(url string) {
s := C.CString(url)
defer C.free(unsafe.Pointer(s))
C.webview_navigate(w.w, s)
}
func (w *webview) SetTitle(title string) {
s := C.CString(title)
defer C.free(unsafe.Pointer(s))
C.webview_set_title(w.w, s)
}
func (w *webview) SetSize(width int, height int, hint Hint) {
C.webview_set_size(w.w, C.int(width), C.int(height), C.int(hint))
}
func (w *webview) Init(js string) {
s := C.CString(js)
defer C.free(unsafe.Pointer(s))
C.webview_init(w.w, s)
}
func (w *webview) Eval(js string) {
s := C.CString(js)
defer C.free(unsafe.Pointer(s))
C.webview_eval(w.w, s)
}
func (w *webview) Dispatch(f func()) {
m.Lock()
for ; dispatch[index] != nil; index++ {
}
dispatch[index] = f
m.Unlock()
C.CgoWebViewDispatch(w.w, C.uintptr_t(index))
}
//export _webviewDispatchGoCallback
func _webviewDispatchGoCallback(index unsafe.Pointer) {
m.Lock()
f := dispatch[uintptr(index)]
delete(dispatch, uintptr(index))
m.Unlock()
f()
}
//export _webviewBindingGoCallback
func _webviewBindingGoCallback(w C.webview_t, id *C.char, req *C.char, index uintptr) {
m.Lock()
f := bindings[uintptr(index)]
m.Unlock()
jsString := func(v interface{}) string { b, _ := json.Marshal(v); return string(b) }
status, result := 0, ""
if res, err := f(C.GoString(id), C.GoString(req)); err != nil {
status = -1
result = jsString(err.Error())
} else if b, err := json.Marshal(res); err != nil {
status = -1
result = jsString(err.Error())
} else {
status = 0
result = string(b)
}
s := C.CString(result)
defer C.free(unsafe.Pointer(s))
C.webview_return(w, id, C.int(status), s)
}
func (w *webview) Bind(name string, f interface{}) error {
v := reflect.ValueOf(f)
// f must be a function
if v.Kind() != reflect.Func {
return errors.New("only functions can be bound")
}
// f must return either value and error or just error
if n := v.Type().NumOut(); n > 2 {
return errors.New("function may only return a value or a value+error")
}
binding := func(id, req string) (interface{}, error) {
raw := []json.RawMessage{}
if err := json.Unmarshal([]byte(req), &raw); err != nil {
return nil, err
}
isVariadic := v.Type().IsVariadic()
numIn := v.Type().NumIn()
if (isVariadic && len(raw) < numIn-1) || (!isVariadic && len(raw) != numIn) {
return nil, errors.New("function arguments mismatch")
}
args := []reflect.Value{}
for i := range raw {
var arg reflect.Value
if isVariadic && i >= numIn-1 {
arg = reflect.New(v.Type().In(numIn - 1).Elem())
} else {
arg = reflect.New(v.Type().In(i))
}
if err := json.Unmarshal(raw[i], arg.Interface()); err != nil {
return nil, err
}
args = append(args, arg.Elem())
}
errorType := reflect.TypeOf((*error)(nil)).Elem()
res := v.Call(args)
switch len(res) {
case 0:
// No results from the function, just return nil
return nil, nil
case 1:
// One result may be a value, or an error
if res[0].Type().Implements(errorType) {
if res[0].Interface() != nil {
return nil, res[0].Interface().(error)
}
return nil, nil
}
return res[0].Interface(), nil
case 2:
// Two results: first one is value, second is error
if !res[1].Type().Implements(errorType) {
return nil, errors.New("second return value must be an error")
}
if res[1].Interface() == nil {
return res[0].Interface(), nil
}
return res[0].Interface(), res[1].Interface().(error)
default:
return nil, errors.New("unexpected number of return values")
}
}
m.Lock()
for ; bindings[index] != nil; index++ {
}
bindings[index] = binding
m.Unlock()
cname := C.CString(name)
defer C.free(unsafe.Pointer(cname))
C.CgoWebViewBind(w.w, cname, C.uintptr_t(index))
return nil
}