syscall/js: add TypedArrayOf

The new function js.TypedArrayOf returns a JavaScript typed array for
a given slice.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays

This change also changes js.ValueOf to not accept a []byte any more.

Fixes #25532.

Change-Id: I8c7bc98ca4e21c3514d19eee7a1f92388d74ab2a
Reviewed-on: https://go-review.googlesource.com/121215
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/crypto/rand/rand_js.go

@@ -20,6 +20,8 @@ var jsCrypto = js.Global().Get("crypto")
 type reader struct{}
 
 func (r *reader) Read(b []byte) (int, error) {
-	jsCrypto.Call("getRandomValues", b)
+	a := js.TypedArrayOf(b)
+	jsCrypto.Call("getRandomValues", a)
+	a.Release()
 	return len(b), nil
 }

src/net/http/roundtrip_js.go

@@ -166,7 +166,9 @@ func (r *streamReader) Read(p []byte) (n int, err error) {
 				return
 			}
 			value := make([]byte, result.Get("value").Get("byteLength").Int())
-			js.ValueOf(value).Call("set", result.Get("value"))
+			a := js.TypedArrayOf(value)
+			a.Call("set", result.Get("value"))
+			a.Release()
 			bCh <- value
 		})
 		defer success.Close()
@@ -227,7 +229,9 @@ func (r *arrayReader) Read(p []byte) (n int, err error) {
 			// Wrap the input ArrayBuffer with a Uint8Array
 			uint8arrayWrapper := js.Global().Get("Uint8Array").New(args[0])
 			value := make([]byte, uint8arrayWrapper.Get("byteLength").Int())
-			js.ValueOf(value).Call("set", uint8arrayWrapper)
+			a := js.TypedArrayOf(value)
+			a.Call("set", uint8arrayWrapper)
+			a.Release()
 			bCh <- value
 		})
 		defer success.Close()

src/syscall/fs_js.go

@@ -374,7 +374,9 @@ func Read(fd int, b []byte) (int, error) {
 		return n, err
 	}
 
-	n, err := fsCall("readSync", fd, b, 0, len(b))
+	a := js.TypedArrayOf(b)
+	n, err := fsCall("readSync", fd, a, 0, len(b))
+	a.Release()
 	if err != nil {
 		return 0, err
 	}
@@ -395,7 +397,9 @@ func Write(fd int, b []byte) (int, error) {
 		return n, err
 	}
 
-	n, err := fsCall("writeSync", fd, b, 0, len(b))
+	a := js.TypedArrayOf(b)
+	n, err := fsCall("writeSync", fd, a, 0, len(b))
+	a.Release()
 	if err != nil {
 		return 0, err
 	}
@@ -405,7 +409,9 @@ func Write(fd int, b []byte) (int, error) {
 }
 
 func Pread(fd int, b []byte, offset int64) (int, error) {
-	n, err := fsCall("readSync", fd, b, 0, len(b), offset)
+	a := js.TypedArrayOf(b)
+	n, err := fsCall("readSync", fd, a, 0, len(b), offset)
+	a.Release()
 	if err != nil {
 		return 0, err
 	}
@@ -413,7 +419,9 @@ func Pread(fd int, b []byte, offset int64) (int, error) {
 }
 
 func Pwrite(fd int, b []byte, offset int64) (int, error) {
-	n, err := fsCall("writeSync", fd, b, 0, len(b), offset)
+	a := js.TypedArrayOf(b)
+	n, err := fsCall("writeSync", fd, a, 0, len(b), offset)
+	a.Release()
 	if err != nil {
 		return 0, err
 	}

src/syscall/js/js.go

@@ -81,13 +81,23 @@ func Global() Value {
 	return valueGlobal
 }
 
-var uint8Array = valueGlobal.Get("Uint8Array")
-
-// ValueOf returns x as a JavaScript value.
+// ValueOf returns x as a JavaScript value:
+//
+//  | Go                    | JavaScript            |
+//  | --------------------- | --------------------- |
+//  | js.Value              | [its value]           |
+//  | js.TypedArray         | [typed array]         |
+//  | js.Callback           | function              |
+//  | nil                   | null                  |
+//  | bool                  | boolean               |
+//  | integers and floats   | number                |
+//  | string                | string                |
 func ValueOf(x interface{}) Value {
 	switch x := x.(type) {
 	case Value:
 		return x
+	case TypedArray:
+		return x.Value
 	case Callback:
 		return x.enqueueFn
 	case nil:
@@ -128,13 +138,8 @@ func ValueOf(x interface{}) Value {
 		return floatValue(x)
 	case string:
 		return makeValue(stringVal(x))
-	case []byte:
-		if len(x) == 0 {
-			return uint8Array.New(memory.Get("buffer"), 0, 0)
-		}
-		return uint8Array.New(memory.Get("buffer"), unsafe.Pointer(&x[0]), len(x))
 	default:
-		panic("invalid value")
+		panic("ValueOf: invalid value")
 	}
 }
 

src/syscall/js/js_test.go

@@ -109,6 +109,28 @@ func TestObject(t *testing.T) {
 	}
 }
 
+func TestTypedArrayOf(t *testing.T) {
+	testTypedArrayOf(t, "[]int8", []int8{0, -42, 0}, -42)
+	testTypedArrayOf(t, "[]int16", []int16{0, -42, 0}, -42)
+	testTypedArrayOf(t, "[]int32", []int32{0, -42, 0}, -42)
+	testTypedArrayOf(t, "[]uint8", []uint8{0, 42, 0}, 42)
+	testTypedArrayOf(t, "[]uint16", []uint16{0, 42, 0}, 42)
+	testTypedArrayOf(t, "[]uint32", []uint32{0, 42, 0}, 42)
+	testTypedArrayOf(t, "[]float32", []float32{0, -42.5, 0}, -42.5)
+	testTypedArrayOf(t, "[]float64", []float64{0, -42.5, 0}, -42.5)
+}
+
+func testTypedArrayOf(t *testing.T, name string, slice interface{}, want float64) {
+	t.Run(name, func(t *testing.T) {
+		a := js.TypedArrayOf(slice)
+		got := a.Index(1).Float()
+		a.Release()
+		if got != want {
+			t.Errorf("got %#v, want %#v", got, want)
+		}
+	})
+}
+
 func TestNaN(t *testing.T) {
 	want := js.ValueOf(math.NaN())
 	got := dummys.Get("NaN")

src/syscall/js/typedarray.go

+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build js,wasm
+
+package js
+
+import (
+	"sync"
+	"unsafe"
+)
+
+var (
+	int8Array    = Global().Get("Int8Array")
+	int16Array   = Global().Get("Int16Array")
+	int32Array   = Global().Get("Int32Array")
+	uint8Array   = Global().Get("Uint8Array")
+	uint16Array  = Global().Get("Uint16Array")
+	uint32Array  = Global().Get("Uint32Array")
+	float32Array = Global().Get("Float32Array")
+	float64Array = Global().Get("Float64Array")
+)
+
+// TypedArray represents a JavaScript typed array.
+type TypedArray struct {
+	Value
+}
+
+// Release frees up resources allocated for the typed array.
+// The typed array and its buffer must not be accessed after calling Release.
+func (a TypedArray) Release() {
+	openTypedArraysMutex.Lock()
+	delete(openTypedArrays, a)
+	openTypedArraysMutex.Unlock()
+}
+
+var (
+	openTypedArraysMutex sync.Mutex
+	openTypedArrays      = make(map[TypedArray]interface{})
+)
+
+// TypedArrayOf returns a JavaScript typed array backed by the slice's underlying array.
+// It can be passed to functions of this package that accept interface{}, for example Value.Set and Value.Call.
+//
+// The supported types are []int8, []int16, []int32, []uint8, []uint16, []uint32, []float32 and []float64.
+// Passing an unsupported value causes a panic.
+//
+// TypedArray.Release must be called to free up resources when the typed array will not be used any more.
+func TypedArrayOf(slice interface{}) TypedArray {
+	a := TypedArray{typedArrayOf(slice)}
+	openTypedArraysMutex.Lock()
+	openTypedArrays[a] = slice
+	openTypedArraysMutex.Unlock()
+	return a
+}
+
+func typedArrayOf(slice interface{}) Value {
+	switch slice := slice.(type) {
+	case []int8:
+		if len(slice) == 0 {
+			return int8Array.New(memory.Get("buffer"), 0, 0)
+		}
+		return int8Array.New(memory.Get("buffer"), unsafe.Pointer(&slice[0]), len(slice))
+	case []int16:
+		if len(slice) == 0 {
+			return int16Array.New(memory.Get("buffer"), 0, 0)
+		}
+		return int16Array.New(memory.Get("buffer"), unsafe.Pointer(&slice[0]), len(slice))
+	case []int32:
+		if len(slice) == 0 {
+			return int32Array.New(memory.Get("buffer"), 0, 0)
+		}
+		return int32Array.New(memory.Get("buffer"), unsafe.Pointer(&slice[0]), len(slice))
+	case []uint8:
+		if len(slice) == 0 {
+			return uint8Array.New(memory.Get("buffer"), 0, 0)
+		}
+		return uint8Array.New(memory.Get("buffer"), unsafe.Pointer(&slice[0]), len(slice))
+	case []uint16:
+		if len(slice) == 0 {
+			return uint16Array.New(memory.Get("buffer"), 0, 0)
+		}
+		return uint16Array.New(memory.Get("buffer"), unsafe.Pointer(&slice[0]), len(slice))
+	case []uint32:
+		if len(slice) == 0 {
+			return uint32Array.New(memory.Get("buffer"), 0, 0)
+		}
+		return uint32Array.New(memory.Get("buffer"), unsafe.Pointer(&slice[0]), len(slice))
+	case []float32:
+		if len(slice) == 0 {
+			return float32Array.New(memory.Get("buffer"), 0, 0)
+		}
+		return float32Array.New(memory.Get("buffer"), unsafe.Pointer(&slice[0]), len(slice))
+	case []float64:
+		if len(slice) == 0 {
+			return float64Array.New(memory.Get("buffer"), 0, 0)
+		}
+		return float64Array.New(memory.Get("buffer"), unsafe.Pointer(&slice[0]), len(slice))
+	default:
+		panic("TypedArrayOf: not a supported slice")
+	}
+}