feat: support uid only form in NormalizeUidGid (#553)

This makes it valid to supply just the uid for operations setting file
ownership, like mkdir and push.

internals/osutil/export_test.go

@@ -39,6 +39,12 @@ func FakeUserLookup(f func(name string) (*user.User, error)) func() {
 	return func() { userLookup = oldUserLookup }
 }
 
+func FakeUserLookupId(f func(name string) (*user.User, error)) func() {
+	oldUserLookupId := userLookupId
+	userLookupId = f
+	return func() { userLookupId = oldUserLookupId }
+}
+
 func FakeUserLookupGroup(f func(name string) (*user.Group, error)) func() {
 	oldUserLookupGroup := userLookupGroup
 	userLookupGroup = f

internals/osutil/user.go

@@ -28,6 +28,7 @@ import (
 var (
 	userCurrent     = user.Current
 	userLookup      = user.Lookup
+	userLookupId    = user.LookupId
 	userLookupGroup = user.LookupGroup
 
 	enoentMessage = syscall.ENOENT.Error()
@@ -112,11 +113,6 @@ func NormalizeUidGid(uid, gid *int, username, group string) (*int, *int, error)
 				username, n, *uid)
 		}
 		uid = &n
-		if gid == nil && group == "" {
-			// Group not specified; use user's primary group ID
-			gidVal, _ := strconv.Atoi(u.Gid)
-			gid = &gidVal
-		}
 	}
 	if group != "" {
 		g, err := userLookupGroup(group)
@@ -134,12 +130,23 @@ func NormalizeUidGid(uid, gid *int, username, group string) (*int, *int, error)
 		}
 		gid = &n
 	}
+	if gid == nil {
+		// Neither gid nor group was specified
+		// Either uid or user must have been specified; use user's primary group ID
+		uidInfo, err := userLookupId(strconv.Itoa(*uid))
+		if err != nil {
+			if strings.Contains(err.Error(), enoentMessage) {
+				// Better error message to work around https://github.com/golang/go/issues/67912
+				return nil, nil, user.UnknownUserIdError(*uid)
+			}
+			return nil, nil, err
+		}
+		gidVal, _ := strconv.Atoi(uidInfo.Gid)
+		gid = &gidVal
+	}
 	if uid == nil && gid != nil {
 		return nil, nil, fmt.Errorf("must specify user, not just group")
 	}
-	if uid != nil && gid == nil {
-		return nil, nil, fmt.Errorf("must specify group, not just UID")
-	}
 	return uid, gid, nil
 }
 

internals/osutil/user_test.go

@@ -117,6 +117,13 @@ func (s *userSuite) TestNormalizeUidGid(c *check.C) {
 	})
 	defer restoreUser()
 
+	var userIdErr error
+	restoreUserId := osutil.FakeUserLookupId(func(uid string) (*user.User, error) {
+		c.Check(uid, check.Equals, "10")
+		return &user.User{Uid: "10", Gid: "20"}, userIdErr
+	})
+	defer restoreUserId()
+
 	var groupErr error
 	restoreGroup := osutil.FakeUserLookupGroup(func(name string) (*user.Group, error) {
 		c.Check(name, check.Equals, "GROUP")
@@ -127,14 +134,14 @@ func (s *userSuite) TestNormalizeUidGid(c *check.C) {
 	test(nil, nil, "", "", nil, nil, "")
 	test(nil, nil, "", "GROUP", nil, nil, "must specify user, not just group")
 	test(nil, nil, "USER", "", ptr(10), ptr(20), "")
+	test(ptr(10), nil, "", "", ptr(10), ptr(20), "")
 	test(nil, nil, "USER", "GROUP", ptr(10), ptr(30), "")
 
 	test(nil, ptr(2), "", "", nil, nil, "must specify user, not just group")
 	test(nil, ptr(2), "", "GROUP", nil, nil, `group "GROUP" GID \(30\) does not match group-id \(2\)`)
 	test(nil, ptr(2), "USER", "", ptr(10), ptr(2), "")
 	test(nil, ptr(2), "USER", "GROUP", nil, nil, `group "GROUP" GID \(30\) does not match group-id \(2\)`)
 
-	test(ptr(1), nil, "", "", nil, nil, "must specify group, not just UID")
 	test(ptr(1), nil, "", "GROUP", ptr(1), ptr(30), "")
 	test(ptr(1), nil, "USER", "", nil, nil, `user "USER" UID \(10\) does not match user-id \(1\)`)
 	test(ptr(1), nil, "USER", "GROUP", nil, nil, `user "USER" UID \(10\) does not match user-id \(1\)`)