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 #12773.

Change-Id: I469738d905b12f0b633ea4d88954f8859227a88c
Reviewed-on: https://go-review.googlesource.com/16551
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/src/os/executable_procfs.go b/src/os/executable_procfs.go
new file mode 100644
index 0000000000..597ab7dd54
--- /dev/null
+++ b/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
+}