add os/user.Lookup

Signed-off-by: leongross <[email protected]>

src/os/user/lookup_unix.go

@@ -0,0 +1,45 @@
+// Copyright 2024 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.
+
+//go:build !baremetal && !js && !wasip1 && !windows
+// +build !baremetal,!js,!wasip1,!windows
+
+package user
+
+import (
+ "bufio"
+ "os"
+ "strings"
+)
+
+func lookupUser(username string) (*User, error) {
+ f, err := os.Open("/etc/passwd")
+ if err != nil {
+ return nil, err
+ }
+ defer f.Close()
+
+ // parse file format <username>:<password>:<uid>:<gid>:<gecos>:<home>:<shell>
+ lines := bufio.NewScanner(f)
+ for lines.Scan() {
+ line := lines.Text()
+ fragments := strings.Split(line, ":")
+
+ if len(fragments) < 7 {
+ continue
+ }
+
+ if fragments[0] == username {
+ return &User{
+ Uid: fragments[2],
+ Gid: fragments[3],
+ Username: fragments[0],
+ Name: fragments[4],
+ HomeDir: fragments[5],
+ }, nil
+ }
+ }
+
+ return nil, UnknownUserError(username)
+}

src/os/user/user.go

@@ -31,11 +31,27 @@ type User struct {
  HomeDir string
 }
 
+// UnknownUserError is returned by Lookup when a user cannot be found.
+type UnknownUserError string
+
+func (e UnknownUserError) Error() string {
+ return "user: unknown user " + string(e)
+}
+
 // Current returns the current user.
 //
 // The first call will cache the current user information.
 // Subsequent calls will return the cached value and will not reflect
 // changes to the current user.
+// TODO: implement syscall.Getuid() and syscall.Getgid() to get the current user.
 func Current() (*User, error) {
  return nil, errors.New("user: Current not implemented")
 }
+
+// Lookup looks up a user by username.
+//
+// If the user cannot be found, the returned error is of type UnknownUserError.
+// NOTE: This implementation does not support caching as the golang implementation does.
+func Lookup(username string) (*User, error) {
+ return lookupUser(username)
+}

src/os/user_test.go

@@ -0,0 +1,59 @@
+// Copyright 2024 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.
+
+//go:build !baremetal && !js && !wasip1 && !windows
+// +build !baremetal,!js,!wasip1,!windows
+
+package os_test
+
+import (
+ . "os/user"
+ "runtime"
+ "testing"
+)
+
+// NOTE: This test requires some users to be present in the CI environment.
+// If the test fails, it may be because the users are not present.
+// We can guarantee that the root user is present on all systems.
+// Currently we can also guarantee that the user with UID 1001 and GID 127 is present on all systems.
+func TestUserLookup(t *testing.T) {
+ if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+ t.Skip()
+ }
+
+ testCases := map[string]struct {
+ user User
+ wantErr bool
+ }{
+ "root": {
+ wantErr: false,
+ user: User{
+ Uid: "0",
+ Gid: "0",
+ Username: "root",
+ Name: "root",
+ HomeDir: "/root",
+ },
+ },
+ "error": {
+ wantErr: true,
+ user: User{
+ Uid: "1000000",
+ Gid: "1000000",
+ Username: "nonexistentuser",
+ Name: "nonexistentuser",
+ HomeDir: "/home/nonexistentuser",
+ },
+ },
+ }
+
+ for name, tc := range testCases {
+ t.Run(name, func(t *testing.T) {
+ user, err := Lookup(tc.user.Username)
+ if (err != nil && !tc.wantErr) || (err == nil && tc.wantErr) {
+ t.Fatalf("Lookup(%q) = %v; want %v, got error %v", tc.user.Username, user, tc.user, err)
+ }
+ })
+ }
+}