os: add js/wasm architecture

This commit adds the js/wasm architecture to the os package.

Access to the actual file system is supported through Node.js.

Updates #18892

Change-Id: I6fa642fb294ca020b2c545649d4324d981aa0408
Reviewed-on: https://go-review.googlesource.com/109977Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/wasm/wasm_exec.js

@@ -143,6 +143,11 @@
 						mem().setInt32(sp + 16, (msec % 1000) * 1000000, true);
 					},
 
+					// func getRandomData(r []byte)
+					"runtime.getRandomData": (sp) => {
+						crypto.getRandomValues(loadSlice(sp + 8));
+					},
+
 					// func boolVal(value bool) Value
 					"syscall/js.boolVal": (sp) => {
 						storeValue(sp + 16, mem().getUint8(sp + 8) !== 0);

src/internal/poll/fd_poll_nacljs.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build nacl
+// +build nacl js,wasm
 
 package poll
 
@@ -42,6 +42,9 @@ func (pd *pollDesc) wait(mode int, isFile bool) error {
 	if pd.closing {
 		return errClosing(isFile)
 	}
+	if isFile { // TODO(neelance): wasm: Use callbacks from JS to block until the read/write finished.
+		return nil
+	}
 	return ErrTimeout
 }
 

src/internal/poll/fd_posix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris windows
 
 package poll
 

src/internal/poll/fd_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package poll
 

src/internal/poll/sys_cloexec.go

@@ -5,7 +5,7 @@
 // This file implements sysSocket and accept for platforms that do not
 // provide a fast path for setting SetNonblock and CloseOnExec.
 
-// +build darwin nacl solaris
+// +build darwin js,wasm nacl solaris
 
 package poll
 

src/internal/syscall/unix/nonblocking_js.go

+// 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.
+
+package unix
+
+func IsNonblock(fd int) (nonblocking bool, err error) {
+	return false, nil
+}

src/os/dir_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package os
 

src/os/error_posix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris windows
 
 package os
 

src/os/error_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package os
 

src/os/error_unix_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package os_test
 

src/os/exec/lp_js.go

+// 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.
+
+// +build js,wasm
+
+package exec
+
+import (
+	"errors"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = errors.New("executable file not found in $PATH")
+
+// LookPath searches for an executable named file in the
+// directories named by the PATH environment variable.
+// If file contains a slash, it is tried directly and the PATH is not consulted.
+// The result may be an absolute path or a path relative to the current directory.
+func LookPath(file string) (string, error) {
+	// Wasm can not execute processes, so act as if there are no executables at all.
+	return "", &Error{file, ErrNotFound}
+}

src/os/exec_posix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris windows
 
 package os
 

src/os/exec_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package os
 

src/os/executable_procfs.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux netbsd dragonfly nacl
+// +build linux netbsd dragonfly nacl js,wasm
 
 package os
 

src/os/file_posix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris windows
 
 package os
 

src/os/file_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package os
 

src/os/os_test.go

@@ -1390,7 +1390,7 @@ func TestSeek(t *testing.T) {
 
 func TestSeekError(t *testing.T) {
 	switch runtime.GOOS {
-	case "plan9", "nacl":
+	case "js", "nacl", "plan9":
 		t.Skipf("skipping test on %v", runtime.GOOS)
 	}
 
@@ -2252,6 +2252,8 @@ func TestPipeThreads(t *testing.T) {
 		t.Skip("skipping on Windows; issue 19098")
 	case "plan9":
 		t.Skip("skipping on Plan 9; does not support runtime poller")
+	case "js":
+		t.Skip("skipping on js; no support for os.Pipe")
 	}
 
 	threads := 100

src/os/path_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package os
 

src/os/pipe_bsd.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly nacl solaris
+// +build darwin dragonfly js,wasm nacl solaris
 
 package os
 

src/os/pipe_test.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // Test broken pipes on Unix systems.
-// +build !windows,!plan9,!nacl
+// +build !windows,!plan9,!nacl,!js
 
 package os_test
 

src/os/signal/signal_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris windows
 
 package signal
 

src/os/stat_nacl.go → src/os/stat_nacljs.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build js,wasm nacl
+
 package os
 
 import (

src/os/stat_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package os
 

src/os/sys_bsd.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd nacl netbsd openbsd
+// +build darwin dragonfly freebsd js,wasm nacl netbsd openbsd
 
 package os
 

src/os/sys_js.go

+// 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.
+
+// +build js,wasm
+
+package os
+
+// supportsCloseOnExec reports whether the platform supports the
+// O_CLOEXEC flag.
+const supportsCloseOnExec = false

src/os/timeout_test.go

@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build !nacl
+// +build !js
 // +build !plan9
 // +build !windows
 

src/os/user/lookup_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd !android,linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm !android,linux nacl netbsd openbsd solaris
 // +build !cgo osusergo
 
 package user

src/os/wait_unimp.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly nacl netbsd openbsd solaris
+// +build darwin dragonfly js,wasm nacl netbsd openbsd solaris
 
 package os
 

src/path/filepath/path_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package filepath
 

src/runtime/debug/heapdump_test.go

@@ -13,8 +13,8 @@ import (
 )
 
 func TestWriteHeapDumpNonempty(t *testing.T) {
-	if runtime.GOOS == "nacl" {
-		t.Skip("WriteHeapDump is not available on NaCl.")
+	if runtime.GOOS == "nacl" || runtime.GOOS == "js" {
+		t.Skipf("WriteHeapDump is not available on %s.", runtime.GOOS)
 	}
 	f, err := ioutil.TempFile("", "heapdumptest")
 	if err != nil {
@@ -42,8 +42,8 @@ func objfin(x *Obj) {
 }
 
 func TestWriteHeapDumpFinalizers(t *testing.T) {
-	if runtime.GOOS == "nacl" {
-		t.Skip("WriteHeapDump is not available on NaCl.")
+	if runtime.GOOS == "nacl" || runtime.GOOS == "js" {
+		t.Skipf("WriteHeapDump is not available on %s.", runtime.GOOS)
 	}
 	f, err := ioutil.TempFile("", "heapdumptest")
 	if err != nil {

src/runtime/os_js.go

+// 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.
+
+// +build js,wasm
+
+package runtime
+
+import (
+	"unsafe"
+)
+
+func exit(code int32)
+
+func write(fd uintptr, p unsafe.Pointer, n int32) int32 {
+	if fd > 2 {
+		throw("runtime.write to fd > 2 is unsupported")
+	}
+	wasmWrite(fd, p, n)
+	return n
+}
+
+// Stubs so tests can link correctly. These should never be called.
+func open(name *byte, mode, perm int32) int32        { panic("not implemented") }
+func closefd(fd int32) int32                         { panic("not implemented") }
+func read(fd int32, p unsafe.Pointer, n int32) int32 { panic("not implemented") }
+
+//go:noescape
+func wasmWrite(fd uintptr, p unsafe.Pointer, n int32)
+
+func usleep(usec uint32)
+
+func exitThread(wait *uint32)
+
+type mOS struct{}
+
+func osyield()
+
+const _SIGSEGV = 0xb
+
+func sigpanic() {
+	g := getg()
+	if !canpanic(g) {
+		throw("unexpected signal during runtime execution")
+	}
+
+	// js only invokes the exception handler for memory faults.
+	g.sig = _SIGSEGV
+	panicmem()
+}
+
+type sigset struct{}
+
+// Called to initialize a new m (including the bootstrap m).
+// Called on the parent thread (main thread in case of bootstrap), can allocate memory.
+func mpreinit(mp *m) {
+	mp.gsignal = malg(32 * 1024)
+	mp.gsignal.m = mp
+}
+
+//go:nosplit
+func msigsave(mp *m) {
+}
+
+//go:nosplit
+func msigrestore(sigmask sigset) {
+}
+
+//go:nosplit
+//go:nowritebarrierrec
+func clearSignalHandlers() {
+}
+
+//go:nosplit
+func sigblock() {
+}
+
+// Called to initialize a new m (including the bootstrap m).
+// Called on the new thread, cannot allocate memory.
+func minit() {
+}
+
+// Called from dropm to undo the effect of an minit.
+func unminit() {
+}
+
+func osinit() {
+	ncpu = 1
+	getg().m.procid = 2
+	physPageSize = 64 * 1024
+}
+
+// wasm has no signals
+const _NSIG = 0
+
+func signame(sig uint32) string {
+	return ""
+}
+
+func crash() {
+	*(*int32)(nil) = 0
+}
+
+func getRandomData(r []byte)
+
+func goenvs() {
+	goenvs_unix()
+}
+
+func initsig(preinit bool) {
+}
+
+// May run with m.p==nil, so write barriers are not allowed.
+//go:nowritebarrier
+func newosproc(mp *m) {
+	panic("newosproc: not implemented")
+}
+
+func setProcessCPUProfiler(hz int32) {}
+func setThreadCPUProfiler(hz int32)  {}
+func sigdisable(uint32)              {}
+func sigenable(uint32)               {}
+func sigignore(uint32)               {}
+
+//go:linkname os_sigpipe os.sigpipe
+func os_sigpipe() {
+	throw("too many writes on closed pipe")
+}
+
+//go:nosplit
+func cputicks() int64 {
+	// Currently cputicks() is used in blocking profiler and to seed runtime·fastrand().
+	// runtime·nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
+	// TODO: need more entropy to better seed fastrand.
+	return nanotime()
+}
+
+//go:linkname syscall_now syscall.now
+func syscall_now() (sec int64, nsec int32) {
+	sec, nsec, _ = time_now()
+	return
+}
+
+// gsignalStack is unused on js.
+type gsignalStack struct{}

src/runtime/sys_wasm.s

@@ -193,3 +193,7 @@ TEXT ·nanotime(SB), NOSPLIT, $0
 TEXT ·walltime(SB), NOSPLIT, $0
 	CallImport
 	RET
+
+TEXT ·getRandomData(SB), NOSPLIT, $0
+	CallImport
+	RET

src/runtime/trace/trace_test.go

@@ -180,6 +180,9 @@ func testBrokenTimestamps(t *testing.T, data []byte) {
 }
 
 func TestTraceStress(t *testing.T) {
+	if runtime.GOOS == "js" {
+		t.Skip("no os.Pipe on js")
+	}
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}
@@ -322,6 +325,9 @@ func TestTraceStress(t *testing.T) {
 // Do a bunch of various stuff (timers, GC, network, etc) in a separate goroutine.
 // And concurrently with all that start/stop trace 3 times.
 func TestTraceStressStartStop(t *testing.T) {
+	if runtime.GOOS == "js" {
+		t.Skip("no os.Pipe on js")
+	}
 	if IsEnabled() {
 		t.Skip("skipping because -test.trace is set")
 	}

src/syscall/dirent.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package syscall
 

src/syscall/endian_little.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 //
-// +build 386 amd64 amd64p32 arm arm64 ppc64le mips64le mipsle
+// +build 386 amd64 amd64p32 arm arm64 ppc64le mips64le mipsle wasm
 
 package syscall
 

src/syscall/env_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 // Unix environment variables.
 

src/syscall/fs_js.go

+// 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.
+
+// +build js,wasm
+
+package syscall
+
+import (
+	"io"
+	"sync"
+	"syscall/js"
+)
+
+// Provided by package runtime.
+func now() (sec int64, nsec int32)
+
+var jsProcess = js.Global.Get("process")
+var jsFS = js.Global.Get("fs")
+var constants = jsFS.Get("constants")
+
+var (
+	nodeWRONLY   = constants.Get("O_WRONLY").Int()
+	nodeRDWR     = constants.Get("O_RDWR").Int()
+	nodeCREATE   = constants.Get("O_CREAT").Int()
+	nodeTRUNC    = constants.Get("O_TRUNC").Int()
+	nodeAPPEND   = constants.Get("O_APPEND").Int()
+	nodeEXCL     = constants.Get("O_EXCL").Int()
+	nodeNONBLOCK = constants.Get("O_NONBLOCK").Int()
+	nodeSYNC     = constants.Get("O_SYNC").Int()
+)
+
+type jsFile struct {
+	path    string
+	entries []string
+	pos     int64
+	seeked  bool
+}
+
+var filesMu sync.Mutex
+var files = map[int]*jsFile{
+	0: &jsFile{},
+	1: &jsFile{},
+	2: &jsFile{},
+}
+
+func fdToFile(fd int) (*jsFile, error) {
+	filesMu.Lock()
+	f, ok := files[fd]
+	filesMu.Unlock()
+	if !ok {
+		return nil, EBADF
+	}
+	return f, nil
+}
+
+func Open(path string, openmode int, perm uint32) (int, error) {
+	if err := checkPath(path); err != nil {
+		return 0, err
+	}
+
+	flags := 0
+	if openmode&O_WRONLY != 0 {
+		flags |= nodeWRONLY
+	}
+	if openmode&O_RDWR != 0 {
+		flags |= nodeRDWR
+	}
+	if openmode&O_CREATE != 0 {
+		flags |= nodeCREATE
+	}
+	if openmode&O_TRUNC != 0 {
+		flags |= nodeTRUNC
+	}
+	if openmode&O_APPEND != 0 {
+		flags |= nodeAPPEND
+	}
+	if openmode&O_EXCL != 0 {
+		flags |= nodeEXCL
+	}
+	if openmode&O_NONBLOCK != 0 {
+		flags |= nodeNONBLOCK
+	}
+	if openmode&O_SYNC != 0 {
+		flags |= nodeSYNC
+	}
+
+	jsFD, err := fsCall("openSync", path, flags, perm)
+	if err != nil {
+		return 0, err
+	}
+	fd := jsFD.Int()
+
+	var entries []string
+	if stat, err := fsCall("fstatSync", fd); err == nil && stat.Call("isDirectory").Bool() {
+		dir, err := fsCall("readdirSync", path)
+		if err != nil {
+			return 0, err
+		}
+		entries = make([]string, dir.Length())
+		for i := range entries {
+			entries[i] = dir.Index(i).String()
+		}
+	}
+
+	f := &jsFile{
+		path:    path,
+		entries: entries,
+	}
+	filesMu.Lock()
+	files[fd] = f
+	filesMu.Unlock()
+	return fd, nil
+}
+
+func Close(fd int) error {
+	filesMu.Lock()
+	delete(files, fd)
+	filesMu.Unlock()
+	_, err := fsCall("closeSync", fd)
+	return err
+}
+
+func CloseOnExec(fd int) {
+	// nothing to do - no exec
+}
+
+func Mkdir(path string, perm uint32) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	_, err := fsCall("mkdirSync", path, perm)
+	return err
+}
+
+func ReadDirent(fd int, buf []byte) (int, error) {
+	f, err := fdToFile(fd)
+	if err != nil {
+		return 0, err
+	}
+	if f.entries == nil {
+		return 0, EINVAL
+	}
+
+	n := 0
+	for len(f.entries) > 0 {
+		entry := f.entries[0]
+		l := 2 + len(entry)
+		if l > len(buf) {
+			break
+		}
+		buf[0] = byte(l)
+		buf[1] = byte(l >> 8)
+		copy(buf[2:], entry)
+		buf = buf[l:]
+		n += l
+		f.entries = f.entries[1:]
+	}
+
+	return n, nil
+}
+
+func setStat(st *Stat_t, jsSt js.Value) {
+	st.Dev = int64(jsSt.Get("dev").Int())
+	st.Ino = uint64(jsSt.Get("ino").Int())
+	st.Mode = uint32(jsSt.Get("mode").Int())
+	st.Nlink = uint32(jsSt.Get("nlink").Int())
+	st.Uid = uint32(jsSt.Get("uid").Int())
+	st.Gid = uint32(jsSt.Get("gid").Int())
+	st.Rdev = int64(jsSt.Get("rdev").Int())
+	st.Size = int64(jsSt.Get("size").Int())
+	st.Blksize = int32(jsSt.Get("blksize").Int())
+	st.Blocks = int32(jsSt.Get("blocks").Int())
+	atime := int64(jsSt.Get("atimeMs").Int())
+	st.Atime = atime / 1000
+	st.AtimeNsec = (atime % 1000) * 1000000
+	mtime := int64(jsSt.Get("mtimeMs").Int())
+	st.Mtime = mtime / 1000
+	st.MtimeNsec = (mtime % 1000) * 1000000
+	ctime := int64(jsSt.Get("ctimeMs").Int())
+	st.Ctime = ctime / 1000
+	st.CtimeNsec = (ctime % 1000) * 1000000
+}
+
+func Stat(path string, st *Stat_t) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	jsSt, err := fsCall("statSync", path)
+	if err != nil {
+		return err
+	}
+	setStat(st, jsSt)
+	return nil
+}
+
+func Lstat(path string, st *Stat_t) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	jsSt, err := fsCall("lstatSync", path)
+	if err != nil {
+		return err
+	}
+	setStat(st, jsSt)
+	return nil
+}
+
+func Fstat(fd int, st *Stat_t) error {
+	jsSt, err := fsCall("fstatSync", fd)
+	if err != nil {
+		return err
+	}
+	setStat(st, jsSt)
+	return nil
+}
+
+func Unlink(path string) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	_, err := fsCall("unlinkSync", path)
+	return err
+}
+
+func Rmdir(path string) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	_, err := fsCall("rmdirSync", path)
+	return err
+}
+
+func Chmod(path string, mode uint32) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	_, err := fsCall("chmodSync", path, mode)
+	return err
+}
+
+func Fchmod(fd int, mode uint32) error {
+	_, err := fsCall("fchmodSync", fd, mode)
+	return err
+}
+
+func Chown(path string, uid, gid int) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	return ENOSYS
+}
+
+func Fchown(fd int, uid, gid int) error {
+	return ENOSYS
+}
+
+func Lchown(path string, uid, gid int) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	return ENOSYS
+}
+
+func UtimesNano(path string, ts []Timespec) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	if len(ts) != 2 {
+		return EINVAL
+	}
+	atime := ts[0].Sec
+	mtime := ts[1].Sec
+	_, err := fsCall("utimesSync", path, atime, mtime)
+	return err
+}
+
+func Rename(from, to string) error {
+	if err := checkPath(from); err != nil {
+		return err
+	}
+	if err := checkPath(to); err != nil {
+		return err
+	}
+	_, err := fsCall("renameSync", from, to)
+	return err
+}
+
+func Truncate(path string, length int64) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	_, err := fsCall("truncateSync", path, length)
+	return err
+}
+
+func Ftruncate(fd int, length int64) error {
+	_, err := fsCall("ftruncateSync", fd, length)
+	return err
+}
+
+func Getcwd(buf []byte) (n int, err error) {
+	defer recoverErr(&err)
+	cwd := jsProcess.Call("cwd").String()
+	n = copy(buf, cwd)
+	return n, nil
+}
+
+func Chdir(path string) (err error) {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	defer recoverErr(&err)
+	jsProcess.Call("chdir", path)
+	return
+}
+
+func Fchdir(fd int) error {
+	f, err := fdToFile(fd)
+	if err != nil {
+		return err
+	}
+	return Chdir(f.path)
+}
+
+func Readlink(path string, buf []byte) (n int, err error) {
+	if err := checkPath(path); err != nil {
+		return 0, err
+	}
+	dst, err := fsCall("readlinkSync", path)
+	if err != nil {
+		return 0, err
+	}
+	n = copy(buf, dst.String())
+	return n, nil
+}
+
+func Link(path, link string) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	if err := checkPath(link); err != nil {
+		return err
+	}
+	_, err := fsCall("linkSync", path, link)
+	return err
+}
+
+func Symlink(path, link string) error {
+	if err := checkPath(path); err != nil {
+		return err
+	}
+	if err := checkPath(link); err != nil {
+		return err
+	}
+	_, err := fsCall("symlinkSync", path, link)
+	return err
+}
+
+func Fsync(fd int) error {
+	_, err := fsCall("fsyncSync", fd)
+	return err
+}
+
+func Read(fd int, b []byte) (int, error) {
+	f, err := fdToFile(fd)
+	if err != nil {
+		return 0, err
+	}
+
+	if f.seeked {
+		n, err := Pread(fd, b, f.pos)
+		f.pos += int64(n)
+		return n, err
+	}
+
+	n, err := fsCall("readSync", fd, b, 0, len(b))
+	if err != nil {
+		return 0, err
+	}
+	n2 := n.Int()
+	f.pos += int64(n2)
+	return n2, err
+}
+
+func Write(fd int, b []byte) (int, error) {
+	f, err := fdToFile(fd)
+	if err != nil {
+		return 0, err
+	}
+
+	if f.seeked {
+		n, err := Pwrite(fd, b, f.pos)
+		f.pos += int64(n)
+		return n, err
+	}
+
+	n, err := fsCall("writeSync", fd, b, 0, len(b))
+	if err != nil {
+		return 0, err
+	}
+	n2 := n.Int()
+	f.pos += int64(n2)
+	return n2, err
+}
+
+func Pread(fd int, b []byte, offset int64) (int, error) {
+	n, err := fsCall("readSync", fd, b, 0, len(b), offset)
+	if err != nil {
+		return 0, err
+	}
+	return n.Int(), nil
+}
+
+func Pwrite(fd int, b []byte, offset int64) (int, error) {
+	n, err := fsCall("writeSync", fd, b, 0, len(b), offset)
+	if err != nil {
+		return 0, err
+	}
+	return n.Int(), nil
+}
+
+func Seek(fd int, offset int64, whence int) (int64, error) {
+	f, err := fdToFile(fd)
+	if err != nil {
+		return 0, err
+	}
+
+	var newPos int64
+	switch whence {
+	case io.SeekStart:
+		newPos = offset
+	case io.SeekCurrent:
+		newPos = f.pos + offset
+	case io.SeekEnd:
+		var st Stat_t
+		if err := Fstat(fd, &st); err != nil {
+			return 0, err
+		}
+		newPos = st.Size + offset
+	default:
+		return 0, errnoErr(EINVAL)
+	}
+
+	if newPos < 0 {
+		return 0, errnoErr(EINVAL)
+	}
+
+	f.seeked = true
+	f.pos = newPos
+	return newPos, nil
+}
+
+func Dup(fd int) (int, error) {
+	return 0, ENOSYS
+}
+
+func Dup2(fd, newfd int) error {
+	return ENOSYS
+}
+
+func Pipe(fd []int) error {
+	return ENOSYS
+}
+
+func fsCall(name string, args ...interface{}) (res js.Value, err error) {
+	defer recoverErr(&err)
+	res = jsFS.Call(name, args...)
+	return
+}
+
+// checkPath checks that the path is not empty and that it contains no null characters.
+func checkPath(path string) error {
+	if path == "" {
+		return EINVAL
+	}
+	for i := 0; i < len(path); i++ {
+		if path[i] == '\x00' {
+			return EINVAL
+		}
+	}
+	return nil
+}
+
+func recoverErr(errPtr *error) {
+	if err := recover(); err != nil {
+		jsErr, ok := err.(js.Error)
+		if !ok {
+			panic(err)
+		}
+		errno, ok := errnoByCode[jsErr.Get("code").String()]
+		if !ok {
+			panic(err)
+		}
+		*errPtr = errnoErr(Errno(errno))
+	}
+}

src/syscall/syscall_js.go

+// 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.
+
+// +build js,wasm
+
+package syscall
+
+import (
+	"sync"
+	"unsafe"
+)
+
+const direntSize = 8 + 8 + 2 + 256
+
+type Dirent struct {
+	Reclen uint16
+	Name   [256]byte
+}
+
+func direntIno(buf []byte) (uint64, bool) {
+	return 1, true
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	reclen, ok := direntReclen(buf)
+	if !ok {
+		return 0, false
+	}
+	return reclen - uint64(unsafe.Offsetof(Dirent{}.Name)), true
+}
+
+const PathMax = 256
+
+// An Errno is an unsigned number describing an error condition.
+// It implements the error interface. The zero Errno is by convention
+// a non-error, so code to convert from Errno to error should use:
+//	err = nil
+//	if errno != 0 {
+//		err = errno
+//	}
+type Errno uintptr
+
+func (e Errno) Error() string {
+	if 0 <= int(e) && int(e) < len(errorstr) {
+		s := errorstr[e]
+		if s != "" {
+			return s
+		}
+	}
+	return "errno " + itoa(int(e))
+}
+
+func (e Errno) Temporary() bool {
+	return e == EINTR || e == EMFILE || e.Timeout()
+}
+
+func (e Errno) Timeout() bool {
+	return e == EAGAIN || e == EWOULDBLOCK || e == ETIMEDOUT
+}
+
+// A Signal is a number describing a process signal.
+// It implements the os.Signal interface.
+type Signal int
+
+const (
+	_ Signal = iota
+	SIGCHLD
+	SIGINT
+	SIGKILL
+	SIGTRAP
+	SIGQUIT
+)
+
+func (s Signal) Signal() {}
+
+func (s Signal) String() string {
+	if 0 <= s && int(s) < len(signals) {
+		str := signals[s]
+		if str != "" {
+			return str
+		}
+	}
+	return "signal " + itoa(int(s))
+}
+
+var signals = [...]string{}
+
+// File system
+
+const (
+	Stdin  = 0
+	Stdout = 1
+	Stderr = 2
+)
+
+const (
+	O_RDONLY = 0
+	O_WRONLY = 1
+	O_RDWR   = 2
+
+	O_CREAT    = 0100
+	O_CREATE   = O_CREAT
+	O_TRUNC    = 01000
+	O_APPEND   = 02000
+	O_EXCL     = 0200
+	O_NONBLOCK = 04000
+	O_SYNC     = 010000
+
+	O_CLOEXEC = 0
+)
+
+const (
+	F_DUPFD   = 0
+	F_GETFD   = 1
+	F_SETFD   = 2
+	F_GETFL   = 3
+	F_SETFL   = 4
+	F_GETOWN  = 5
+	F_SETOWN  = 6
+	F_GETLK   = 7
+	F_SETLK   = 8
+	F_SETLKW  = 9
+	F_RGETLK  = 10
+	F_RSETLK  = 11
+	F_CNVT    = 12
+	F_RSETLKW = 13
+
+	F_RDLCK   = 1
+	F_WRLCK   = 2
+	F_UNLCK   = 3
+	F_UNLKSYS = 4
+)
+
+const (
+	S_IFMT        = 0000370000
+	S_IFSHM_SYSV  = 0000300000
+	S_IFSEMA      = 0000270000
+	S_IFCOND      = 0000260000
+	S_IFMUTEX     = 0000250000
+	S_IFSHM       = 0000240000
+	S_IFBOUNDSOCK = 0000230000
+	S_IFSOCKADDR  = 0000220000
+	S_IFDSOCK     = 0000210000
+
+	S_IFSOCK = 0000140000
+	S_IFLNK  = 0000120000
+	S_IFREG  = 0000100000
+	S_IFBLK  = 0000060000
+	S_IFDIR  = 0000040000
+	S_IFCHR  = 0000020000
+	S_IFIFO  = 0000010000
+
+	S_UNSUP = 0000370000
+
+	S_ISUID = 0004000
+	S_ISGID = 0002000
+	S_ISVTX = 0001000
+
+	S_IREAD  = 0400
+	S_IWRITE = 0200
+	S_IEXEC  = 0100
+
+	S_IRWXU = 0700
+	S_IRUSR = 0400
+	S_IWUSR = 0200
+	S_IXUSR = 0100
+
+	S_IRWXG = 070
+	S_IRGRP = 040
+	S_IWGRP = 020
+	S_IXGRP = 010
+
+	S_IRWXO = 07
+	S_IROTH = 04
+	S_IWOTH = 02
+	S_IXOTH = 01
+)
+
+type Stat_t struct {
+	Dev       int64
+	Ino       uint64
+	Mode      uint32
+	Nlink     uint32
+	Uid       uint32
+	Gid       uint32
+	Rdev      int64
+	Size      int64
+	Blksize   int32
+	Blocks    int32
+	Atime     int64
+	AtimeNsec int64
+	Mtime     int64
+	MtimeNsec int64
+	Ctime     int64
+	CtimeNsec int64
+}
+
+// Processes
+// Not supported - just enough for package os.
+
+var ForkLock sync.RWMutex
+
+type WaitStatus uint32
+
+func (w WaitStatus) Exited() bool       { return false }
+func (w WaitStatus) ExitStatus() int    { return 0 }
+func (w WaitStatus) Signaled() bool     { return false }
+func (w WaitStatus) Signal() Signal     { return 0 }
+func (w WaitStatus) CoreDump() bool     { return false }
+func (w WaitStatus) Stopped() bool      { return false }
+func (w WaitStatus) Continued() bool    { return false }
+func (w WaitStatus) StopSignal() Signal { return 0 }
+func (w WaitStatus) TrapCause() int     { return 0 }
+
+// XXX made up
+type Rusage struct {
+	Utime Timeval
+	Stime Timeval
+}
+
+// XXX made up
+type ProcAttr struct {
+	Dir   string
+	Env   []string
+	Files []uintptr
+	Sys   *SysProcAttr
+}
+
+type SysProcAttr struct {
+}
+
+func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno) {
+	return 0, 0, ENOSYS
+}
+
+func Syscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno) {
+	return 0, 0, ENOSYS
+}
+
+func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno) {
+	return 0, 0, ENOSYS
+}
+
+func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno) {
+	return 0, 0, ENOSYS
+}
+
+func Sysctl(key string) (string, error) {
+	if key == "kern.hostname" {
+		return "js", nil
+	}
+	return "", ENOSYS
+}
+
+const ImplementsGetwd = true
+
+func Getwd() (wd string, err error) {
+	var buf [PathMax]byte
+	n, err := Getcwd(buf[0:])
+	if err != nil {
+		return "", err
+	}
+	return string(buf[:n]), nil
+}
+
+func Getegid() int                      { return 1 }
+func Geteuid() int                      { return 1 }
+func Getgid() int                       { return 1 }
+func Getgroups() ([]int, error)         { return []int{1}, nil }
+func Getppid() int                      { return 2 }
+func Getpid() int                       { return 3 }
+func Gettimeofday(tv *Timeval) error    { return ENOSYS }
+func Getuid() int                       { return 1 }
+func Kill(pid int, signum Signal) error { return ENOSYS }
+func Sendfile(outfd int, infd int, offset *int64, count int) (written int, err error) {
+	return 0, ENOSYS
+}
+func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle uintptr, err error) {
+	return 0, 0, ENOSYS
+}
+func Wait4(pid int, wstatus *WaitStatus, options int, rusage *Rusage) (wpid int, err error) {
+	return 0, ENOSYS
+}
+
+type Iovec struct{} // dummy
+
+type Timespec struct {
+	Sec  int64
+	Nsec int64
+}
+
+type Timeval struct {
+	Sec  int64
+	Usec int64
+}
+
+func setTimespec(sec, nsec int64) Timespec {
+	return Timespec{Sec: sec, Nsec: nsec}
+}
+
+func setTimeval(sec, usec int64) Timeval {
+	return Timeval{Sec: sec, Usec: usec}
+}

src/syscall/tables_nacljs.go

@@ -2,10 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build nacl
+// +build nacl js,wasm
 
 package syscall
 
+import "runtime"
+
 // TODO: generate with runtime/mknacl.sh, allow override with IRT.
 const (
 	sys_null                 = 1
@@ -254,7 +256,7 @@ var errorstr = [...]string{
 	EMLINK:          "Too many links",
 	EPIPE:           "Broken pipe",
 	ENAMETOOLONG:    "File name too long",
-	ENOSYS:          "not implemented on Native Client",
+	ENOSYS:          "not implemented on " + runtime.GOOS,
 	EDQUOT:          "Quota exceeded",
 	EDOM:            "Math arg out of domain of func",
 	ERANGE:          "Math result not representable",
@@ -361,3 +363,128 @@ func errnoErr(e Errno) error {
 	}
 	return e
 }
+
+var errnoByCode = map[string]Errno{
+	"EPERM":           EPERM,
+	"ENOENT":          ENOENT,
+	"ESRCH":           ESRCH,
+	"EINTR":           EINTR,
+	"EIO":             EIO,
+	"ENXIO":           ENXIO,
+	"E2BIG":           E2BIG,
+	"ENOEXEC":         ENOEXEC,
+	"EBADF":           EBADF,
+	"ECHILD":          ECHILD,
+	"EAGAIN":          EAGAIN,
+	"ENOMEM":          ENOMEM,
+	"EACCES":          EACCES,
+	"EFAULT":          EFAULT,
+	"EBUSY":           EBUSY,
+	"EEXIST":          EEXIST,
+	"EXDEV":           EXDEV,
+	"ENODEV":          ENODEV,
+	"ENOTDIR":         ENOTDIR,
+	"EISDIR":          EISDIR,
+	"EINVAL":          EINVAL,
+	"ENFILE":          ENFILE,
+	"EMFILE":          EMFILE,
+	"ENOTTY":          ENOTTY,
+	"EFBIG":           EFBIG,
+	"ENOSPC":          ENOSPC,
+	"ESPIPE":          ESPIPE,
+	"EROFS":           EROFS,
+	"EMLINK":          EMLINK,
+	"EPIPE":           EPIPE,
+	"ENAMETOOLONG":    ENAMETOOLONG,
+	"ENOSYS":          ENOSYS,
+	"EDQUOT":          EDQUOT,
+	"EDOM":            EDOM,
+	"ERANGE":          ERANGE,
+	"EDEADLK":         EDEADLK,
+	"ENOLCK":          ENOLCK,
+	"ENOTEMPTY":       ENOTEMPTY,
+	"ELOOP":           ELOOP,
+	"ENOMSG":          ENOMSG,
+	"EIDRM":           EIDRM,
+	"ECHRNG":          ECHRNG,
+	"EL2NSYNC":        EL2NSYNC,
+	"EL3HLT":          EL3HLT,
+	"EL3RST":          EL3RST,
+	"ELNRNG":          ELNRNG,
+	"EUNATCH":         EUNATCH,
+	"ENOCSI":          ENOCSI,
+	"EL2HLT":          EL2HLT,
+	"EBADE":           EBADE,
+	"EBADR":           EBADR,
+	"EXFULL":          EXFULL,
+	"ENOANO":          ENOANO,
+	"EBADRQC":         EBADRQC,
+	"EBADSLT":         EBADSLT,
+	"EDEADLOCK":       EDEADLOCK,
+	"EBFONT":          EBFONT,
+	"ENOSTR":          ENOSTR,
+	"ENODATA":         ENODATA,
+	"ETIME":           ETIME,
+	"ENOSR":           ENOSR,
+	"ENONET":          ENONET,
+	"ENOPKG":          ENOPKG,
+	"EREMOTE":         EREMOTE,
+	"ENOLINK":         ENOLINK,
+	"EADV":            EADV,
+	"ESRMNT":          ESRMNT,
+	"ECOMM":           ECOMM,
+	"EPROTO":          EPROTO,
+	"EMULTIHOP":       EMULTIHOP,
+	"EDOTDOT":         EDOTDOT,
+	"EBADMSG":         EBADMSG,
+	"EOVERFLOW":       EOVERFLOW,
+	"ENOTUNIQ":        ENOTUNIQ,
+	"EBADFD":          EBADFD,
+	"EREMCHG":         EREMCHG,
+	"ELIBACC":         ELIBACC,
+	"ELIBBAD":         ELIBBAD,
+	"ELIBSCN":         ELIBSCN,
+	"ELIBMAX":         ELIBMAX,
+	"ELIBEXEC":        ELIBEXEC,
+	"EILSEQ":          EILSEQ,
+	"EUSERS":          EUSERS,
+	"ENOTSOCK":        ENOTSOCK,
+	"EDESTADDRREQ":    EDESTADDRREQ,
+	"EMSGSIZE":        EMSGSIZE,
+	"EPROTOTYPE":      EPROTOTYPE,
+	"ENOPROTOOPT":     ENOPROTOOPT,
+	"EPROTONOSUPPORT": EPROTONOSUPPORT,
+	"ESOCKTNOSUPPORT": ESOCKTNOSUPPORT,
+	"EOPNOTSUPP":      EOPNOTSUPP,
+	"EPFNOSUPPORT":    EPFNOSUPPORT,
+	"EAFNOSUPPORT":    EAFNOSUPPORT,
+	"EADDRINUSE":      EADDRINUSE,
+	"EADDRNOTAVAIL":   EADDRNOTAVAIL,
+	"ENETDOWN":        ENETDOWN,
+	"ENETUNREACH":     ENETUNREACH,
+	"ENETRESET":       ENETRESET,
+	"ECONNABORTED":    ECONNABORTED,
+	"ECONNRESET":      ECONNRESET,
+	"ENOBUFS":         ENOBUFS,
+	"EISCONN":         EISCONN,
+	"ENOTCONN":        ENOTCONN,
+	"ESHUTDOWN":       ESHUTDOWN,
+	"ETOOMANYREFS":    ETOOMANYREFS,
+	"ETIMEDOUT":       ETIMEDOUT,
+	"ECONNREFUSED":    ECONNREFUSED,
+	"EHOSTDOWN":       EHOSTDOWN,
+	"EHOSTUNREACH":    EHOSTUNREACH,
+	"EALREADY":        EALREADY,
+	"EINPROGRESS":     EINPROGRESS,
+	"ESTALE":          ESTALE,
+	"ENOTSUP":         ENOTSUP,
+	"ENOMEDIUM":       ENOMEDIUM,
+	"ECANCELED":       ECANCELED,
+	"ELBIN":           ELBIN,
+	"EFTYPE":          EFTYPE,
+	"ENMFILE":         ENMFILE,
+	"EPROCLIM":        EPROCLIM,
+	"ENOSHARE":        ENOSHARE,
+	"ECASECLASH":      ECASECLASH,
+	"EWOULDBLOCK":     EWOULDBLOCK,
+}