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syscall/js: panic: property readSync is not a function #27773

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AchalaSB opened this issue Sep 20, 2018 · 4 comments
Closed

syscall/js: panic: property readSync is not a function #27773

AchalaSB opened this issue Sep 20, 2018 · 4 comments
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arch-wasm WebAssembly issues FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@AchalaSB
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AchalaSB commented Sep 20, 2018

Please answer these questions before submitting your issue. Thanks!

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

go version go1.11 linux/amd64

Does this issue reproduce with the latest release?

yes

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/achala/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/achala/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build813004705=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Running Go code on server . main.go code is working on terminal but not in server.
here's my code

package main

import "fmt"

func main() {
	fmt.Println("Enter First String: ") //Print function is used to display output in same line
	var first string
	fmt.Scanln(&first) // Take input from user
	fmt.Println("Enter Second String: ")
	var second string
	fmt.Scanln(&second)
	fmt.Println(first + second) // Addition of two string
}
<!doctype html>
<!--
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.
-->
<html>

<head>
	<meta charset="utf-8">
	<title>Go wasm</title>
</head>

<body>

	<script src="wasm_exec.js"></script>

	<script>
		if (!WebAssembly.instantiateStreaming) { // polyfill
			WebAssembly.instantiateStreaming = async (resp, importObject) => {
				const source = await (await resp).arrayBuffer();
				return await WebAssembly.instantiate(source, importObject);
			};
		}

		const go = new Go();
		
		let mod, inst;

		WebAssembly.instantiateStreaming(fetch("lib.wasm"), go.importObject).then((result) => {
			mod = result.module;
			inst = result.instance;
			document.getElementById("runButton").disabled = false;
		});

		async function run() {
			await go.run(inst);
			inst = await WebAssembly.instantiate(mod, go.importObject); // reset instance
		}

	</script>

	<button onClick="run();" id="runButton" disabled>Run</button>
</body>
</html>

server.go

package main

import (
	"flag"
	"log"
	"net/http"
)

var (
	listen = flag.String("listen", ":8080", "listen address")
	dir    = flag.String("dir", ".", "directory to serve")
)

func main() {
	flag.Parse()
	log.Printf("listening on %q...", *listen)
	log.Fatal(http.ListenAndServe(*listen, http.FileServer(http.Dir(*dir))))
}

What did you see ?

Getting an error

panic: syscall/js: Value.Call: property readSync is not a function, got undefined [recovered] wasm_exec.js:45:6
	panic: syscall/js: Value.Call: property readSync is not a function, got undefined [recovered] wasm_exec.js:45:6
	panic: syscall/js: Value.Call: property readSync is not a function, got undefined wasm_exec.js:45:6
wasm_exec.js:45:6
goroutine 1 [running]: wasm_exec.js:45:6
fmt.errorHandler(0xc053e28) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:1031 +0x1a wasm_exec.js:45:6
panic(0x12e80, 0xc00e210) wasm_exec.js:45:6
	/usr/lib/go/src/runtime/panic.go:513 +0x1d wasm_exec.js:45:6
syscall.recoverErr(0xc0537d8) wasm_exec.js:45:6
	/usr/lib/go/src/syscall/fs_js.go:493 +0x2b wasm_exec.js:45:6
panic(0x12e80, 0xc00e210) wasm_exec.js:45:6
	/usr/lib/go/src/runtime/panic.go:513 +0x1d wasm_exec.js:45:6
syscall/js.Value.Call(0x7ff8000000000016, 0x2c96b, 0x8, 0xc053828, 0x4, 0x4, 0xc01e048) wasm_exec.js:45:6
	/usr/lib/go/src/syscall/js/js.go:282 +0x79 wasm_exec.js:45:6
syscall.fsCall(0x2c96b, 0x8, 0xc053828, 0x4, 0x4, 0x0, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/syscall/fs_js.go:472 +0x4 wasm_exec.js:45:6
syscall.Read(0x0, 0xc028260, 0x1, 0x4, 0x14450003, 0x7ff8000300000011, 0xc04c020) wasm_exec.js:45:6
	/usr/lib/go/src/syscall/fs_js.go:374 +0xb wasm_exec.js:45:6
internal/poll.(*FD).Read(0xc02e060, 0xc028260, 0x1, 0x4, 0x0, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/internal/poll/fd_unix.go:165 +0x18 wasm_exec.js:45:6
os.(*File).read(0xc00c018, 0xc028260, 0x1, 0x4, 0x0, 0x15, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/os/file_unix.go:249 +0x4 wasm_exec.js:45:6
os.(*File).Read(0xc00c018, 0xc028260, 0x1, 0x4, 0x0, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/os/file.go:108 +0x7 wasm_exec.js:45:6
io.ReadAtLeast(0x3ebe0, 0xc00c018, 0xc028260, 0x1, 0x4, 0x1, 0x0, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/io/io.go:310 +0x5 wasm_exec.js:45:6
io.ReadFull(0x3ebe0, 0xc00c018, 0xc028260, 0x1, 0x4, 0x0, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/io/io.go:329 +0x2 wasm_exec.js:45:6
fmt.(*readRune).readByte(0xc028240, 0x4035000000000000, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:321 +0x5 wasm_exec.js:45:6
fmt.(*readRune).ReadRune(0xc028240, 0x0, 0x20, 0xc04c040, 0x15f4d0) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:337 +0x1a wasm_exec.js:45:6
fmt.(*ss).ReadRune(0xc02e180, 0x3, 0x0, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:189 +0x7 wasm_exec.js:45:6
fmt.(*ss).getRune(0xc02e180, 0x12a00) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:211 +0x2 wasm_exec.js:45:6
fmt.(*ss).SkipSpace(0xc02e180) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:422 +0x3 wasm_exec.js:45:6
fmt.(*ss).convertString(0xc02e180, 0x76, 0xc00e1f0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:804 +0x4 wasm_exec.js:45:6
fmt.(*ss).scanOne(0xc02e180, 0x76, 0x10ac0, 0xc00e1f0) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:979 +0xcc wasm_exec.js:45:6
fmt.(*ss).doScan(0xc02e180, 0xc053f58, 0x1, 0x1, 0x0, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:1040 +0x8 wasm_exec.js:45:6
fmt.Fscanln(0x3ebe0, 0xc00c018, 0xc048f58, 0x1, 0x1, 0x12e80, 0x1, 0xc00e1f0) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:132 +0x3 wasm_exec.js:45:6
fmt.Scanln(0xc048f58, 0x1, 0x1, 0x15, 0x0, 0x0) wasm_exec.js:45:6
	/usr/lib/go/src/fmt/scan.go:70 +0x2 wasm_exec.js:45:6
main.main() wasm_exec.js:45:6
	/home/achala/gocode/tests/src/main.go:8 +0x4 wasm_exec.js:45:6
exit code: 2 wasm_exec.js:67:6
@theclapp
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Since you've posted HTML I assume you're running in a browser. That environment does not support reading from stdin. (I agree that the panic message could use a little work.)

@bcmills
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bcmills commented Sep 22, 2018

CC @neelance @cherrymui

@bcmills bcmills added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Sep 22, 2018
@bcmills bcmills added this to the Go1.12 milestone Sep 22, 2018
@bcmills bcmills changed the title panic: syscall/js: Value.Call: property readSync is not a function, got undefined [recovered] syscall/js: panic: property readSync is not a function Sep 22, 2018
@bcmills bcmills added the arch-wasm WebAssembly issues label Sep 22, 2018
@justinclift
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justinclift commented Sep 22, 2018

@AchalaSB As an idea, the Wasm intro talk by @johanbrandhorst on YouTube might help you get started:

    https://www.youtube.com/watch?v=iTrx0BbUXI4

Have you gone through that yet? 😄

There are also several other tutorials and examples of working Go Wasm code linked to from the wiki page:

    https://github.com/golang/go/wiki/WebAssembly#further-reference-examples

The https://github.com/stdiopt/gowasm-experiments examples should be good to cut-n-paste into your own repo, then modify as needed.

@gopherbot
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Change https://golang.org/cl/150617 mentions this issue: misc/wasm: add stub for fs.read on browsers

bradfitz pushed a commit that referenced this issue Nov 21, 2018
Using fmt.Scanln in a browser environment caused a panic, since there
was no stub for fs.read. This commit adds a stub that returns ENOSYS.

Fixes #27773.

Change-Id: I79b019039e4bc90da51d71a4edddf3bd7809ff45
Reviewed-on: https://go-review.googlesource.com/c/150617
Run-TryBot: Richard Musiol <neelance@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
@golang golang locked and limited conversation to collaborators Nov 20, 2019
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