Support to init a ReadableStream from a io.Reader (#3740)

* Support to init a ReadableStream from a io.Reader

* streams.NewReadableStreamForReader test

* Fix linter complains

* Apply suggestions from code review

* Replace goja => sobek

js/modules/k6/experimental/streams/module.go

@@ -2,6 +2,9 @@
 package streams
 
 import (
+	"errors"
+	"io"
+
 	"github.com/grafana/sobek"
 	"go.k6.io/k6/js/common"
 	"go.k6.io/k6/js/modules"
@@ -46,21 +49,25 @@ func (mi *ModuleInstance) Exports() modules.Exports {
 
 // NewReadableStream is the constructor for the ReadableStream object.
 func (mi *ModuleInstance) NewReadableStream(call sobek.ConstructorCall) *sobek.Object {
-	rt := mi.vu.Runtime()
-	var err error
-
-	// 1. If underlyingSource is missing, set it to null.
-	var underlyingSource *sobek.Object
+	return newReadableStream(mi.vu, call)
+}
 
+func newReadableStream(vu modules.VU, call sobek.ConstructorCall) *sobek.Object {
 	var (
+		// 1. If underlyingSource is missing, set it to null.
+		underlyingSource *sobek.Object
+
+		rt = vu.Runtime()
+
+		err                  error
 		strategy             *sobek.Object
 		underlyingSourceDict UnderlyingSource
 	)
 
 	// We look for the queuing strategy first, and validate it before
 	// the underlying source, in order to pass the Web Platform Tests
 	// constructor tests.
-	strategy = mi.initializeStrategy(call)
+	strategy = initializeStrategy(rt, call)
 
 	// 2. Let underlyingSourceDict be underlyingSource, converted to an IDL value of type UnderlyingSource.
 	if len(call.Arguments) > 0 && !sobek.IsUndefined(call.Arguments[0]) {
@@ -79,8 +86,8 @@ func (mi *ModuleInstance) NewReadableStream(call sobek.ConstructorCall) *sobek.O
 
 	// 3. Perform ! InitializeReadableStream(this).
 	stream := &ReadableStream{
-		runtime: mi.vu.Runtime(),
-		vu:      mi.vu,
+		runtime: rt,
+		vu:      vu,
 	}
 	stream.initialize()
 
@@ -129,27 +136,25 @@ func (mi *ModuleInstance) NewReadableStream(call sobek.ConstructorCall) *sobek.O
 }
 func defaultSizeFunc(_ sobek.Value) (float64, error) { return 1.0, nil }
 
-func (mi *ModuleInstance) initializeStrategy(call sobek.ConstructorCall) *sobek.Object {
-	runtime := mi.vu.Runtime()
-
+func initializeStrategy(rt *sobek.Runtime, call sobek.ConstructorCall) *sobek.Object {
 	// Either if the strategy is not provided or if it doesn't have a 'highWaterMark',
 	// we need to set its default value (highWaterMark=1).
 	// https://streams.spec.whatwg.org/#rs-prototype
-	strArg := runtime.NewObject()
+	strArg := rt.NewObject()
 	if len(call.Arguments) > 1 && !common.IsNullish(call.Arguments[1]) {
-		strArg = call.Arguments[1].ToObject(runtime)
+		strArg = call.Arguments[1].ToObject(rt)
 	}
 	if common.IsNullish(strArg.Get("highWaterMark")) {
-		if err := strArg.Set("highWaterMark", runtime.ToValue(1)); err != nil {
-			common.Throw(runtime, newError(RuntimeError, err.Error()))
+		if err := strArg.Set("highWaterMark", rt.ToValue(1)); err != nil {
+			common.Throw(rt, newError(RuntimeError, err.Error()))
 		}
 	}
 
 	// If the stream type is 'bytes', we don't want the size function.
 	// Except, when it is manually specified.
-	size := runtime.ToValue(defaultSizeFunc)
+	size := rt.ToValue(defaultSizeFunc)
 	if len(call.Arguments) > 0 && !common.IsNullish(call.Arguments[0]) {
-		srcArg := call.Arguments[0].ToObject(runtime)
+		srcArg := call.Arguments[0].ToObject(rt)
 		srcTypeArg := srcArg.Get("type")
 		if !common.IsNullish(srcTypeArg) && srcTypeArg.String() == ReadableStreamTypeBytes {
 			size = nil
@@ -160,7 +165,7 @@ func (mi *ModuleInstance) initializeStrategy(call sobek.ConstructorCall) *sobek.
 	}
 
 	strCall := sobek.ConstructorCall{Arguments: []sobek.Value{strArg}}
-	return mi.newCountQueuingStrategy(runtime, strCall, size)
+	return newCountQueuingStrategy(rt, strCall, size)
 }
 
 // NewCountQueuingStrategy is the constructor for the [CountQueuingStrategy] object.
@@ -170,14 +175,14 @@ func (mi *ModuleInstance) NewCountQueuingStrategy(call sobek.ConstructorCall) *s
 	rt := mi.vu.Runtime()
 	// By default, the CountQueuingStrategy has a pre-defined 'size' property.
 	// It cannot be overwritten by the user.
-	return mi.newCountQueuingStrategy(rt, call, rt.ToValue(defaultSizeFunc))
+	return newCountQueuingStrategy(rt, call, rt.ToValue(defaultSizeFunc))
 }
 
 // newCountQueuingStrategy is the underlying constructor for the [CountQueuingStrategy] object.
 //
 // It allows to create a CountQueuingStrategy with or without the 'size' property,
 // depending on how the containing ReadableStream is initialized.
-func (mi *ModuleInstance) newCountQueuingStrategy(
+func newCountQueuingStrategy(
 	rt *sobek.Runtime,
 	call sobek.ConstructorCall,
 	size sobek.Value,
@@ -285,3 +290,49 @@ func (mi *ModuleInstance) NewReadableStreamDefaultReader(call sobek.ConstructorC
 
 	return object
 }
+
+// NewReadableStreamFromReader is the equivalent of [NewReadableStreamDefaultReader] but to initialize
+// a new [ReadableStream] from a given [io.Reader] in Go code.
+// It is useful for those situations when a [io.Reader] needs to be surfaced up to the JS runtime.
+func NewReadableStreamFromReader(vu modules.VU, reader io.Reader) *sobek.Object {
+	rt := vu.Runtime()
+	return newReadableStream(vu, sobek.ConstructorCall{
+		Arguments: []sobek.Value{rt.ToValue(underlyingSourceForReader(vu, reader))},
+		This:      rt.NewObject(),
+	})
+}
+
+func underlyingSourceForReader(vu modules.VU, reader io.Reader) *sobek.Object {
+	rt := vu.Runtime()
+
+	underlyingSource := vu.Runtime().NewObject()
+	if err := underlyingSource.Set("pull", rt.ToValue(func(controller *sobek.Object) *sobek.Promise {
+		// Prepare methods
+		cClose, _ := sobek.AssertFunction(controller.Get("close"))
+		cEnqueue, _ := sobek.AssertFunction(controller.Get("enqueue"))
+
+		buf := make([]byte, 1024)
+		n, err := reader.Read(buf)
+		if err != nil && !errors.Is(err, io.EOF) {
+			panic(err)
+		}
+
+		_, enqueueErr := cEnqueue(nil, rt.ToValue(string(buf[:n])))
+		if enqueueErr != nil {
+			panic(enqueueErr)
+		}
+
+		if err == io.EOF {
+			_, closeErr := cClose(nil)
+			if closeErr != nil {
+				panic(closeErr)
+			}
+		}
+
+		return newResolvedPromise(vu, sobek.Undefined())
+	})); err != nil {
+		throw(rt, err)
+	}
+
+	return underlyingSource
+}

js/modules/k6/experimental/streams/module_test.go

@@ -0,0 +1,41 @@
+package streams
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/grafana/sobek"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.k6.io/k6/js/modulestest"
+)
+
+func TestNewReadableStreamForReader(t *testing.T) {
+	t.Parallel()
+
+	// The value to be streamed.
+	exp := "Hello, World!"
+
+	// We initialize the runtime, with the ReadableStream(rs) accessible in JS.
+	r := modulestest.NewRuntime(t)
+	rs := NewReadableStreamFromReader(r.VU, bytes.NewReader([]byte(exp)))
+	require.NoError(t, r.VU.Runtime().Set("rs", rs))
+
+	// Then, we run some JS code that reads from the ReadableStream(rs).
+	var ret sobek.Value
+	err := r.EventLoop.Start(func() (err error) {
+		ret, err = r.VU.Runtime().RunString(`(async () => {
+  const reader = rs.getReader();
+  const {value} = await reader.read();
+  return value;
+})()`)
+		return err
+	})
+	assert.NoError(t, err)
+
+	// Finally, we expect the returned promise to resolve
+	// to the expected value (the one we streamed).
+	p, ok := ret.Export().(*sobek.Promise)
+	require.True(t, ok)
+	assert.Equal(t, exp, p.Result().String())
+}