Carry over non-zero Content-Length to Response

internal/jshttp/response.go

@@ -32,12 +32,12 @@ func ToResponse(res js.Value) (*http.Response, error) {
 
 // ToJSResponse converts *http.Response to JavaScript sides Response class object.
 func ToJSResponse(res *http.Response) js.Value {
-	return newJSResponse(res.StatusCode, res.Header, res.Body, nil)
+	return newJSResponse(res.StatusCode, res.Header, res.ContentLength, res.Body, nil)
 }
 
 // newJSResponse creates JavaScript sides Response class object.
 //   - Response: https://developer.mozilla.org/docs/Web/API/Response
-func newJSResponse(statusCode int, headers http.Header, body io.ReadCloser, rawBody *js.Value) js.Value {
+func newJSResponse(statusCode int, headers http.Header, contentLength int64, body io.ReadCloser, rawBody *js.Value) js.Value {
 	status := statusCode
 	if status == 0 {
 		status = http.StatusOK
@@ -55,6 +55,8 @@ func newJSResponse(statusCode int, headers http.Header, body io.ReadCloser, rawB
 	var readableStream js.Value
 	if rawBody != nil {
 		readableStream = *rawBody
+	} else if contentLength > 0 {
+		readableStream = jsutil.ConvertReaderToFixedLengthStream(body, contentLength)
 	} else {
 		readableStream = jsutil.ConvertReaderToReadableStream(body)
 	}

internal/jshttp/responsewriter.go

@@ -3,6 +3,7 @@ package jshttp
 import (
 	"io"
 	"net/http"
+	"strconv"
 	"sync"
 	"syscall/js"
 
@@ -51,5 +52,6 @@ func (w *ResponseWriter) WriteRawJSBody(body js.Value) {
 // ToJSResponse converts *ResponseWriter to JavaScript sides Response.
 //   - Response: https://developer.mozilla.org/docs/Web/API/Response
 func (w *ResponseWriter) ToJSResponse() js.Value {
-	return newJSResponse(w.StatusCode, w.HeaderValue, w.Reader, w.RawJSBody)
+	contentLength, _ := strconv.ParseInt(w.HeaderValue.Get("Content-Length"), 10, 64)
+	return newJSResponse(w.StatusCode, w.HeaderValue, contentLength, w.Reader, w.RawJSBody)
 }

internal/jsutil/jsutil.go

@@ -7,19 +7,20 @@ import (
 )
 
 var (
-	RuntimeContext      = js.Global().Get("context")
-	Binding             = js.Global().Get("context").Get("binding")
-	ObjectClass         = js.Global().Get("Object")
-	PromiseClass        = js.Global().Get("Promise")
-	RequestClass        = js.Global().Get("Request")
-	ResponseClass       = js.Global().Get("Response")
-	HeadersClass        = js.Global().Get("Headers")
-	ArrayClass          = js.Global().Get("Array")
-	Uint8ArrayClass     = js.Global().Get("Uint8Array")
-	ErrorClass          = js.Global().Get("Error")
-	ReadableStreamClass = js.Global().Get("ReadableStream")
-	DateClass           = js.Global().Get("Date")
-	Null                = js.ValueOf(nil)
+	RuntimeContext         = js.Global().Get("context")
+	Binding                = js.Global().Get("context").Get("binding")
+	ObjectClass            = js.Global().Get("Object")
+	PromiseClass           = js.Global().Get("Promise")
+	RequestClass           = js.Global().Get("Request")
+	ResponseClass          = js.Global().Get("Response")
+	HeadersClass           = js.Global().Get("Headers")
+	ArrayClass             = js.Global().Get("Array")
+	Uint8ArrayClass        = js.Global().Get("Uint8Array")
+	ErrorClass             = js.Global().Get("Error")
+	ReadableStreamClass    = js.Global().Get("ReadableStream")
+	FixedLengthStreamClass = js.Global().Get("FixedLengthStream")
+	DateClass              = js.Global().Get("Date")
+	Null                   = js.ValueOf(nil)
 )
 
 func NewObject() js.Value {

internal/jsutil/stream.go

@@ -198,3 +198,26 @@ func ConvertReaderToReadableStream(reader io.ReadCloser) js.Value {
 	}))
 	return ReadableStreamClass.New(rsInit)
 }
+
+// ConvertReaderToFixedLengthStream converts io.ReadCloser to TransformStream.
+func ConvertReaderToFixedLengthStream(rc io.ReadCloser, size int64) js.Value {
+	stream := FixedLengthStreamClass.New(js.ValueOf(size))
+	go func(writer js.Value) {
+		defer rc.Close()
+
+		chunk := make([]byte, min(size, defaultChunkSize))
+		for {
+			n, err := rc.Read(chunk)
+			if n > 0 {
+				b := Uint8ArrayClass.New(n)
+				js.CopyBytesToJS(b, chunk[:n])
+				writer.Call("write", b)
+			}
+			if err != nil {
+				writer.Call("close")
+				return
+			}
+		}
+	}(stream.Get("writable").Call("getWriter"))
+	return stream.Get("readable")
+}