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//go:build js
// +build js
// Package wsjs implements typed access to the browser javascript WebSocket API.
//
// https://developer.mozilla.org/en-US/docs/Web/API/WebSocket
package wsjs
import (
"syscall/js"
)
func handleJSError(err *error, onErr func()) {
r := recover()
if jsErr, ok := r.(js.Error); ok {
*err = jsErr
if onErr != nil {
onErr()
}
return
}
if r != nil {
panic(r)
}
}
// New is a wrapper around the javascript WebSocket constructor.
func New(url string, protocols []string) (c WebSocket, err error) {
defer handleJSError(&err, func() {
c = WebSocket{}
})
jsProtocols := make([]interface{}, len(protocols))
for i, p := range protocols {
jsProtocols[i] = p
}
c = WebSocket{
v: js.Global().Get("WebSocket").New(url, jsProtocols),
}
c.setBinaryType("arraybuffer")
return c, nil
}
// WebSocket is a wrapper around a javascript WebSocket object.
type WebSocket struct {
v js.Value
}
func (c WebSocket) setBinaryType(typ string) {
c.v.Set("binaryType", string(typ))
}
func (c WebSocket) addEventListener(eventType string, fn func(e js.Value)) func() {
f := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
fn(args[0])
return nil
})
c.v.Call("addEventListener", eventType, f)
return func() {
c.v.Call("removeEventListener", eventType, f)
f.Release()
}
}
// CloseEvent is the type passed to a WebSocket close handler.
type CloseEvent struct {
Code uint16
Reason string
WasClean bool
}
// OnClose registers a function to be called when the WebSocket is closed.
func (c WebSocket) OnClose(fn func(CloseEvent)) (remove func()) {
return c.addEventListener("close", func(e js.Value) {
ce := CloseEvent{
Code: uint16(e.Get("code").Int()),
Reason: e.Get("reason").String(),
WasClean: e.Get("wasClean").Bool(),
}
fn(ce)
})
}
// OnError registers a function to be called when there is an error
// with the WebSocket.
func (c WebSocket) OnError(fn func(e js.Value)) (remove func()) {
return c.addEventListener("error", fn)
}
// MessageEvent is the type passed to a message handler.
type MessageEvent struct {
// string or []byte.
Data interface{}
// There are more fields to the interface but we don't use them.
// See https://developer.mozilla.org/en-US/docs/Web/API/MessageEvent
}
// OnMessage registers a function to be called when the WebSocket receives a message.
func (c WebSocket) OnMessage(fn func(m MessageEvent)) (remove func()) {
return c.addEventListener("message", func(e js.Value) {
var data interface{}
arrayBuffer := e.Get("data")
if arrayBuffer.Type() == js.TypeString {
data = arrayBuffer.String()
} else {
data = extractArrayBuffer(arrayBuffer)
}
me := MessageEvent{
Data: data,
}
fn(me)
})
}
// Subprotocol returns the WebSocket subprotocol in use.
func (c WebSocket) Subprotocol() string {
return c.v.Get("protocol").String()
}
// OnOpen registers a function to be called when the WebSocket is opened.
func (c WebSocket) OnOpen(fn func(e js.Value)) (remove func()) {
return c.addEventListener("open", fn)
}
// Close closes the WebSocket with the given code and reason.
func (c WebSocket) Close(code int, reason string) (err error) {
defer handleJSError(&err, nil)
c.v.Call("close", code, reason)
return err
}
// SendText sends the given string as a text message
// on the WebSocket.
func (c WebSocket) SendText(v string) (err error) {
defer handleJSError(&err, nil)
c.v.Call("send", v)
return err
}
// SendBytes sends the given message as a binary message
// on the WebSocket.
func (c WebSocket) SendBytes(v []byte) (err error) {
defer handleJSError(&err, nil)
c.v.Call("send", uint8Array(v))
return err
}
func extractArrayBuffer(arrayBuffer js.Value) []byte {
uint8Array := js.Global().Get("Uint8Array").New(arrayBuffer)
dst := make([]byte, uint8Array.Length())
js.CopyBytesToGo(dst, uint8Array)
return dst
}
func uint8Array(src []byte) js.Value {
uint8Array := js.Global().Get("Uint8Array").New(len(src))
js.CopyBytesToJS(uint8Array, src)
return uint8Array
}
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