net/http: roundtrip_js.go unusable in Node.js tests

[fabioberger]

What version of Go are you using (go version)?

$ go version
go version go1.12.3 darwin/amd64

Does this issue reproduce with the latest release? Yes.

What operating system and processor architecture are you using (go env)?

go env

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/fabioberger/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/fabioberger/Documents/projects/0x_project/go"
GOPROXY=""
GORACE=""
GOROOT="/Users/fabioberger/.go"
GOTMPDIR=""
GOTOOLDIR="/Users/fabioberger/.go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/91/m4w_p4fj06vc8vdzwqw7cqfc0000gn/T/go-build121993023=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I wrote a test that requires a network request to localhost using the net/http library, compiled it to WASM and attempted to run it using Node.js. In order to get it to work in a Node.js environment, I add a shim for fetch by requiring the isomorphic-fetch NPM package.

package main

import (
	"fmt"
	"net/http"
)

func TestRequest(t *testing.T) {

	client := &http.Client{}

	req, err := http.NewRequest("GET", "http://localhost:8545", nil)
	if err != nil {
		t.Fatal(err)
	}

	_, err = client.Do(req)
	if err != nil {
		t.Fatal(err)
	}

}

What did you expect to see?

I expected the request to complete without an error.

What did you see instead?

Post http://localhost:8545: dial tcp: Protocol not available

Digging into roundtrip_js.go, I found this check:

if useFakeNetwork() {
	return t.roundTrip(req)
}

Where useFakeNetwork is defined as:

// useFakeNetwork is used to determine whether the request is made
// by a test and should be made to use the fake in-memory network.
func useFakeNetwork() bool {
	return len(os.Args) > 0 && strings.HasSuffix(os.Args[0], ".test")
}

This logic means that any test making a network request that gets compiled to WASM is re-routed to a fake in-memory network. Non-WASM tests do not exhibit this behavior.

Is there any chance the core devs would consider making this behavior optional? Perhaps via an environment variable?

[agnivade]

In order to get it to work in a Node.js environment, I add a shim for fetch by requiring the isomorphic-fetch NPM package.

That is the catch here.

@johanbrandhorst @neelance

[johanbrandhorst]

In order to get it to work in a Node.js environment, I add a shim for fetch by requiring the isomorphic-fetch NPM package.

That is the catch here.

@johanbrandhorst @neelance

I could be wrong but my impression is that this was just an assertion, not a question. I think the request here is that we make it possible to use the fetch wrapper while running a test.

Unfortunately, before we can do that, we need #26051 finished, so we can reliably run the existing test under js/wasm. The short circuit is there to allow them to pass without relying on a custom runner type. I think we could consider this a dupe of #26358.

[fabioberger]

@johanbrandhorst is spot on, thanks for chiming in.