os: add Executable() (string, error)

// Executable returns the path name for the executable that started
// the current process. There is no guarantee that the path is still
// pointing to the correct executable. If a symlink was used to start
// the process, depending on the operating system, the result might
// be the symlink or the path it pointed to. If a stable result is
// needed, path/filepath.EvalSymlinks might help.
//
// Executable returns an absolute path unless an error occurred.
//
// The main use case is finding resources located relative to an
// executable.
//
// Executable is not supported on nacl or OpenBSD (unless procfs is
// mounted.)
func Executable() (string, error) {
	return executable()
}

Fixes golang#12773.

Change-Id: I469738d905b12f0b633ea4d88954f8859227a88c
Reviewed-on: https://go-review.googlesource.com/16551
Run-TryBot: Minux Ma <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

src/os/executable.go

@@ -0,0 +1,23 @@
+// Copyright 2016 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 os
+
+// Executable returns the path name for the executable that started
+// the current process. There is no guarantee that the path is still
+// pointing to the correct executable. If a symlink was used to start
+// the process, depending on the operating system, the result might
+// be the symlink or the path it pointed to. If a stable result is
+// needed, path/filepath.EvalSymlinks might help.
+//
+// Executable returns an absolute path unless an error occurred.
+//
+// The main use case is finding resources located relative to an
+// executable.
+//
+// Executable is not supported on nacl or OpenBSD (unless procfs is
+// mounted.)
+func Executable() (string, error) {
+	return executable()
+}

src/os/executable_darwin.go

@@ -0,0 +1,24 @@
+// Copyright 2016 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 os
+
+var executablePath string // set by ../runtime/os_darwin.go
+
+var initCwd, initCwdErr = Getwd()
+
+func executable() (string, error) {
+	ep := executablePath
+	if ep[0] != '/' {
+		if initCwdErr != nil {
+			return ep, initCwdErr
+		}
+		if len(ep) > 2 && ep[0:2] == "./" {
+			// skip "./"
+			ep = ep[2:]
+		}
+		ep = initCwd + "/" + ep
+	}
+	return ep, nil
+}

src/os/executable_freebsd.go

@@ -0,0 +1,33 @@
+// Copyright 2016 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 os
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func executable() (string, error) {
+	mib := [4]int32{1 /* CTL_KERN */, 14 /* KERN_PROC */, 12 /* KERN_PROC_PATHNAME */, -1}
+
+	n := uintptr(0)
+	// get length
+	_, _, err := syscall.Syscall6(syscall.SYS___SYSCTL, uintptr(unsafe.Pointer(&mib[0])), 4, 0, uintptr(unsafe.Pointer(&n)), 0, 0)
+	if err != 0 {
+		return "", err
+	}
+	if n == 0 { // shouldn't happen
+		return "", nil
+	}
+	buf := make([]byte, n)
+	_, _, err = syscall.Syscall6(syscall.SYS___SYSCTL, uintptr(unsafe.Pointer(&mib[0])), 4, uintptr(unsafe.Pointer(&buf[0])), uintptr(unsafe.Pointer(&n)), 0, 0)
+	if err != 0 {
+		return "", err
+	}
+	if n == 0 { // shouldn't happen
+		return "", nil
+	}
+	return string(buf[:n-1]), nil
+}

src/os/executable_plan9.go

@@ -0,0 +1,19 @@
+// Copyright 2016 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 plan9
+
+package os
+
+import "syscall"
+
+func executable() (string, error) {
+	fn := "/proc/" + itoa(Getpid()) + "/text"
+	f, err := Open(fn)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+	return syscall.Fd2path(int(f.Fd()))
+}

src/os/executable_procfs.go

@@ -0,0 +1,36 @@
+// Copyright 2016 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 linux netbsd openbsd dragonfly nacl
+
+package os
+
+import (
+	"errors"
+	"runtime"
+)
+
+// We query the executable path at init time to avoid the problem of
+// readlink returns a path appended with " (deleted)" when the original
+// binary gets deleted.
+var executablePath, executablePathErr = func () (string, error) {
+	var procfn string
+	switch runtime.GOOS {
+	default:
+		return "", errors.New("Executable not implemented for " + runtime.GOOS)
+	case "linux":
+		procfn = "/proc/self/exe"
+	case "netbsd":
+		procfn = "/proc/curproc/exe"
+	case "openbsd":
+		procfn = "/proc/curproc/file"
+	case "dragonfly":
+		procfn = "/proc/curproc/file"
+	}
+	return Readlink(procfn)
+}()
+
+func executable() (string, error) {
+	return executablePath, executablePathErr
+}

src/os/executable_solaris.go

@@ -0,0 +1,27 @@
+// Copyright 2016 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 os
+
+import "syscall"
+
+var initCwd, initCwdErr = Getwd()
+
+func executable() (string, error) {
+	path, err := syscall.Getexecname()
+	if err != nil {
+		return path, err
+	}
+	if len(path) > 0 && path[0] != '/' {
+		if initCwdErr != nil {
+			return path, initCwdErr
+		}
+		if len(path) > 2 && path[0:2] == "./" {
+			// skip "./"
+			path = path[2:]
+		}
+		return initCwd + "/" + path, nil
+	}
+	return path, nil
+}

src/os/executable_test.go

@@ -0,0 +1,87 @@
+// Copyright 2016 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 os_test
+
+import (
+	"fmt"
+	"internal/testenv"
+	"os"
+	osexec "os/exec"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+const executable_EnvVar = "OSTEST_OUTPUT_EXECPATH"
+
+func TestExecutable(t *testing.T) {
+	testenv.MustHaveExec(t) // will also execlude nacl, which doesn't support Executable anyway
+	ep, err := os.Executable()
+	if err != nil {
+		switch goos := runtime.GOOS; goos {
+		case "openbsd": // procfs is not mounted by default
+			t.Skipf("Executable failed on %s: %v, expected", goos, err)
+		}
+		t.Fatalf("Executable failed: %v", err)
+	}
+	// we want fn to be of the form "dir/prog"
+	dir := filepath.Dir(filepath.Dir(ep))
+	fn, err := filepath.Rel(dir, ep)
+	if err != nil {
+		t.Fatalf("filepath.Rel: %v", err)
+	}
+	cmd := &osexec.Cmd{}
+	// make child start with a relative program path
+	cmd.Dir = dir
+	cmd.Path = fn
+	// forge argv[0] for child, so that we can verify we could correctly
+	// get real path of the executable without influenced by argv[0].
+	cmd.Args = []string{"-", "-test.run=XXXX"}
+	cmd.Env = append(os.Environ(), fmt.Sprintf("%s=1", executable_EnvVar))
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("exec(self) failed: %v", err)
+	}
+	outs := string(out)
+	if !filepath.IsAbs(outs) {
+		t.Fatalf("Child returned %q, want an absolute path", out)
+	}
+	if !sameFile(outs, ep) {
+		t.Fatalf("Child returned %q, not the same file as %q", out, ep)
+	}
+}
+
+func sameFile(fn1, fn2 string) bool {
+	fi1, err := os.Stat(fn1)
+	if err != nil {
+		return false
+	}
+	fi2, err := os.Stat(fn2)
+	if err != nil {
+		return false
+	}
+	return os.SameFile(fi1, fi2)
+}
+
+func init() {
+	if e := os.Getenv(executable_EnvVar); e != "" {
+		// first chdir to another path
+		dir := "/"
+		if runtime.GOOS == "windows" {
+			cwd, err := os.Getwd()
+			if err != nil {
+				panic(err)
+			}
+			dir = filepath.VolumeName(cwd)
+		}
+		os.Chdir(dir)
+		if ep, err := os.Executable(); err != nil {
+			fmt.Fprint(os.Stderr, "ERROR: ", err)
+		} else {
+			fmt.Fprint(os.Stderr, ep)
+		}
+		os.Exit(0)
+	}
+}

src/os/executable_windows.go

@@ -0,0 +1,32 @@
+// Copyright 2016 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 os
+
+import (
+	"internal/syscall/windows"
+	"syscall"
+)
+
+func getModuleFileName(handle syscall.Handle) (string, error) {
+	n := uint32(1024)
+	var buf []uint16
+	for {
+		buf = make([]uint16, n)
+		r, err := windows.GetModuleFileName(handle, &buf[0], n)
+		if err != nil {
+			return "", err
+		}
+		if r < n {
+			break
+		}
+		// r == n means n not big enough
+		n += 1024
+	}
+	return syscall.UTF16ToString(buf), nil
+}
+
+func executable() (string, error) {
+	return getModuleFileName(0)
+}