0-length byte arrays not properly externalized? (Empty HTTP body causes errors with xhr2 polyfill.)

[flimzy]

I'm trying to get an XHR polyfill to work for testing in node.js, and discovered that with the xhr2 library, an empty body on a PUT request generates an error. To reproduce:

main.go:

package main

import (
	"fmt"
	"net/http"
)

func main() {
	req, _ := http.NewRequest("PUT", "http://bogusurl.com/", nil)
	client := &http.Client{}
	_, err := client.Do(req)
	if err != nil {
		fmt.Printf("Error: %s\n", err)
	}
}

main.inc.js:

try {
    global.XMLHttpRequest = require('xhr2');
} catch(e) {}

Then run these commands:

npm install xhr2
gopherjs run main.go main.inc.js

And observe the following output:

/home/jonhall/go/src/github.com/flimzy/jstest/node_modules/xhr2/lib/xhr2.js:844                                                                                                                                                  
throw new Error("Unsupported send() data " + data);                                                                                                                                                                      
^                                                                                                                                                                                                                  
Error: Unsupported send() data                                                                                                                                                                                                   
at XMLHttpRequestUpload._setData (/home/jonhall/go/src/github.com/flimzy/jstest/node_modules/xhr2/lib/xhr2.js:844:15)                                                                                                        
at XMLHttpRequest._sendHttp (/home/jonhall/go/src/github.com/flimzy/jstest/node_modules/xhr2/lib/xhr2.js:375:19)                                                                                                             
at XMLHttpRequest.send (/home/jonhall/go/src/github.com/flimzy/jstest/node_modules/xhr2/lib/xhr2.js:203:16)
at $packages.net/http.XHRTransport.ptr.RoundTrip (/home/jonhall/go/src/github.com/flimzy/jstest/http.go:99:3)
at send (/net/http/client.go:249:3)
at $packages.net/http.Client.ptr.send (/net/http/client.go:173:3)
at $packages.net/http.Client.ptr.Do (/net/http/client.go:595:7)
at main (/github.com/flimzy/jstest/main.go:11:3)
at $init (/home/jonhall/go/src/github.com/flimzy/jstest/main.go.863915836:99004:9)
at $goroutine (/home/jonhall/go/src/github.com/flimzy/jstest/main.go.863915836:1474:19)
at $runScheduled (/home/jonhall/go/src/github.com/flimzy/jstest/main.go.863915836:1514:7)
at $schedule (/home/jonhall/go/src/github.com/flimzy/jstest/main.go.863915836:1530:5)
at $go (/home/jonhall/go/src/github.com/flimzy/jstest/main.go.863915836:1506:3)
at Object.<anonymous> (/home/jonhall/go/src/github.com/flimzy/jstest/main.go.863915836:99015:1)
at Object.<anonymous> (/home/jonhall/go/src/github.com/flimzy/jstest/main.go.863915836:99018:4)
at Module._compile (module.js:570:32)
at Object.Module._extensions..js (module.js:579:10)
at Module.load (module.js:487:32)
at tryModuleLoad (module.js:446:12)
at Function.Module._load (module.js:438:3)
at Module.runMain (module.js:604:10)
at run (bootstrap_node.js:394:7)
at startup (bootstrap_node.js:149:9)
at bootstrap_node.js:509:3

If I make a minor change to the GopherJS's (*XHRTransport).RoundTrip implementation, the problem goes away:

@@ -96,7 +96,7 @@ func (t *XHRTransport) RoundTrip(req *Request) (*Response, error) {
                }
                req.Body.Close()
        }
-       xhr.Call("send", body)
+       xhr.Call("send", string(body))
 
        select {
        case resp := <-respCh:

I don't know if this is an appropriate fix, or if it's just working around/obscuring a larger problem. I also haven't tested that this doesn't break other functionality (it probably does).

[flimzy]

This is probably a much more appropriate change. I'll probably turn this into a PR:

@@ -86,17 +86,17 @@ func (t *XHRTransport) RoundTrip(req *Request) (*Response, error) {
                        xhr.Call("setRequestHeader", key, value)
                }
        }
-       var body []byte
-       if req.Body != nil {
-               var err error
-               body, err = ioutil.ReadAll(req.Body)
+       if req.Body == nil {
+               xhr.Call("send")
+       } else {
+               body, err := ioutil.ReadAll(req.Body)
                if err != nil {
                        req.Body.Close() // RoundTrip must always close the body, including on errors.
                        return nil, err
                }
                req.Body.Close()
+               xhr.Call("send", body)
        }
-       xhr.Call("send", body)
 
        select {
        case resp := <-respCh:

[flimzy]

Regardless of any change to XHRTransport, perhaps the underlying problem is demonstrated in this program:

package main

import "honnef.co/go/js/console"

func main() {
	x := []byte{}
	var y []byte
	z := []byte{0x01}
	console.Log(x)
	console.Log(y)
	console.Log(z)
}

Output:

[]
[]
Uint8Array [ 1 ]

Based on the type conversion table, I would have expected all three values to be converted to Uint8Arrays.