os/user: Current support on Plan 9

Current for Plan 9 is implemented with /dev/user for
Uid/Gid/Username/Name, and $home environment variable for
HomeDir.

Implementing Lookup/LookupId is not done, which would
require parsing /adm/users. It is unclear of how much benefit
this would be.

R=golang-dev
CC=bradfitz, golang-dev, r
https://golang.org/cl/13203043

src/pkg/os/user/lookup_plan9.go

+// Copyright 2013 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 user
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+)
+
+// Partial os/user support on Plan 9.
+// Supports Current(), but not Lookup()/LookupId().
+// The latter two would require parsing /adm/users.
+const (
+	userFile = "/dev/user"
+)
+
+func current() (*User, error) {
+	ubytes, err := ioutil.ReadFile(userFile)
+	if err != nil {
+		return nil, fmt.Errorf("user: %s", err)
+	}
+
+	uname := string(ubytes)
+
+	u := &User{
+		Uid:      uname,
+		Gid:      uname,
+		Username: uname,
+		Name:     uname,
+		HomeDir:  os.Getenv("home"),
+	}
+
+	return u, nil
+}
+
+func lookup(username string) (*User, error) {
+	return nil, syscall.EPLAN9
+}
+
+func lookupId(uid string) (*User, error) {
+	return nil, syscall.EPLAN9
+}

src/pkg/os/user/lookup_stubs.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 !cgo,!windows
+// +build !cgo,!windows,!plan9
 
 package user
 

src/pkg/os/user/user.go

@@ -16,6 +16,8 @@ var implemented = true // set to false by lookup_stubs.go's init
 // On posix systems Uid and Gid contain a decimal number
 // representing uid and gid. On windows Uid and Gid
 // contain security identifier (SID) in a string format.
+// On Plan 9, Uid, Gid, Username, and Name will be the
+// contents of /dev/user.
 type User struct {
 	Uid      string // user id
 	Gid      string // primary group id

src/pkg/os/user/user_test.go

@@ -14,7 +14,7 @@ func check(t *testing.T) {
 		t.Skip("user: not implemented; skipping tests")
 	}
 	switch runtime.GOOS {
-	case "linux", "freebsd", "darwin", "windows":
+	case "linux", "freebsd", "darwin", "windows", "plan9":
 		// test supported
 	default:
 		t.Skipf("user: Lookup not implemented on %q; skipping test", runtime.GOOS)
@@ -61,6 +61,10 @@ func compare(t *testing.T, want, got *User) {
 func TestLookup(t *testing.T) {
 	check(t)
 
+	if runtime.GOOS == "plan9" {
+		t.Skipf("Lookup not implemented on %q", runtime.GOOS)
+	}
+
 	want, err := Current()
 	if err != nil {
 		t.Fatalf("Current: %v", err)
@@ -75,6 +79,10 @@ func TestLookup(t *testing.T) {
 func TestLookupId(t *testing.T) {
 	check(t)
 
+	if runtime.GOOS == "plan9" {
+		t.Skipf("LookupId not implemented on %q", runtime.GOOS)
+	}
+
 	want, err := Current()
 	if err != nil {
 		t.Fatalf("Current: %v", err)