add LookupId, LookupGroupId

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

src/os/user/lookup_unix.go

@@ -10,11 +10,17 @@ package user
 import (
  "bufio"
  "os"
+ "strconv"
  "strings"
 )
 
+const (
+ userFile = "/etc/passwd"
+ groupFile = "/etc/group"
+)
+
 func lookupUser(username string) (*User, error) {
- f, err := os.Open("/etc/passwd")
+ f, err := os.Open(userFile)
  if err != nil {
  return nil, err
  }
@@ -43,3 +49,72 @@ func lookupUser(username string) (*User, error) {
 
  return nil, UnknownUserError(username)
 }
+
+func lookupUserId(uid string) (*User, error) {
+ f, err := os.Open(userFile)
+ 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[2] == uid {
+ return &User{
+ Uid: fragments[2],
+ Gid: fragments[3],
+ Username: fragments[0],
+ Name: fragments[4],
+ HomeDir: fragments[5],
+ }, nil
+ }
+ }
+
+ id, err := strconv.Atoi(uid)
+ if err != nil {
+ return nil, err
+ }
+
+ return nil, UnknownUserIdError(id)
+}
+
+func lookupGroupId(gid string) (*Group, error) {
+ f, err := os.Open(groupFile)
+ if err != nil {
+ return nil, err
+ }
+ defer f.Close()
+
+ // parse file format group_name:password:GID:user_list
+ // group_name: the name of the group.
+ // password: the (encrypted) group password. If this field is empty, no password is needed.
+ // GID: the numeric group ID.
+ // user_list: a list of the usernames that are members of this group, separated by commas.
+
+ lines := bufio.NewScanner(f)
+ for lines.Scan() {
+ line := lines.Text()
+ fragments := strings.Split(line, ":")
+
+ if len(fragments) < 4 {
+ continue
+ }
+
+ if fragments[2] == gid {
+ return &Group{
+ Gid: fragments[2],
+ Name: fragments[0],
+ }, nil
+ }
+ }
+
+ return nil, UnknownGroupIdError(gid)
+}

src/os/user/user.go

@@ -4,7 +4,10 @@
 
 package user
 
-import "errors"
+import (
+ "errors"
+ "strconv"
+)
 
 // User represents a user account.
 type User struct {
@@ -38,6 +41,29 @@ func (e UnknownUserError) Error() string {
  return "user: unknown user " + string(e)
 }
 
+// Group represents a grouping of users.
+//
+// On POSIX systems Gid contains a decimal number representing the group ID.
+type Group struct {
+ Gid string // group ID
+ Name string // group name
+}
+
+// UnknownGroupIdError is returned by [LookupGroupId] when
+// a group cannot be found.
+type UnknownGroupIdError string
+
+func (e UnknownGroupIdError) Error() string {
+ return "group: unknown groupid " + string(e)
+}
+
+// UnknownUserIdError is returned by [LookupId] when a user cannot be found.
+type UnknownUserIdError int
+
+func (e UnknownUserIdError) Error() string {
+ return "user: unknown userid " + strconv.Itoa(int(e))
+}
+
 // Current returns the current user.
 //
 // The first call will cache the current user information.
@@ -55,3 +81,18 @@ func Current() (*User, error) {
 func Lookup(username string) (*User, error) {
  return lookupUser(username)
 }
+
+// LookupId looks up a user by userid. If the user cannot be found, the
+// returned error is of type UnknownUserIdError.
+func LookupId(uid string) (*User, error) {
+ if u, err := Current(); err == nil && u.Uid == uid {
+ return u, err
+ }
+ return lookupUserId(uid)
+}
+
+// LookupGroupId looks up a group by groupid. If the group cannot be found, the
+// returned error is of type [UnknownGroupIdError].
+func LookupGroupId(gid string) (*Group, error) {
+ return lookupGroupId(gid)
+}

src/os/user_test.go

@@ -54,6 +54,16 @@ func TestUserLookup(t *testing.T) {
  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)
  }
+
+ userId, err := LookupId(tc.user.Uid)
+ if (err != nil && !tc.wantErr) || (err == nil && tc.wantErr) {
+ t.Fatalf("LookupId(%q) = %v; want %v, got error %v", tc.user.Username, userId, tc.user, err)
+ }
+
+ group, err := LookupGroupId(tc.user.Gid)
+ if (err != nil && !tc.wantErr) || (err == nil && tc.wantErr) {
+ t.Fatalf("LookupGroupId(%q) = %v; want %v, got error %v", tc.user.Gid, group, tc.user.Gid, err)
+ }
  })
  }
 }