pkg/lookup: Return ID-only pointers on ErrNo*Entries

Callers that only care about the IDs should try to convert the
identifier to an integer before calling the Get* functions, so they
can save the cost of hitting the filesystem and maybe or maybe not
finding the other fields (User.Name, etc.).  But callers that *want*
the other fields but only actually need the ID can, with this commit,
just call the Get* function and ignore ErrNo*Entries responses:

  user, err := lookup.GetUser(mount, userIDorName)
  if err != nil && err != ErrNoPasswdEntries {
    return err
  }

Previously, they'd have to perform their own integer-conversion
attempt in Get* error handling, with logic like:

  user, err := lookup.GetUser(mount, userIDorName)
  if err == ErrNoPasswdEntries {
    uuid, err := strconv.ParseUint(userIDorName, 10, 32)
    if err == nil {
      user.Uid = int(uuid)
    }
  } else if err != nil {
    return err
  }

Signed-off-by: W. Trevor King <wking@tremily.us>

1 files changed, 14 insertions, 4 deletions

diff --git a/pkg/lookup/lookup.go b/pkg/lookup/lookup.go
index a9d975b4b..70b97144f 100644
--- a/pkg/lookup/lookup.go
+++ b/pkg/lookup/lookup.go
@@ -99,9 +99,11 @@ func GetContainerGroups(groups []string, containerMount string, override *Overri
 	return uintgids, nil
 }
 
-// GetUser takes a containermount path and user name or id and returns
+// GetUser takes a containermount path and user name or ID and returns
 // a matching User structure from /etc/passwd.  If it cannot locate a user
 // with the provided information, an ErrNoPasswdEntries is returned.
+// When the provided user name was an ID, a User structure with Uid
+// set is returned along with ErrNoPasswdEntries.
 func GetUser(containerMount, userIDorName string) (*user.User, error) {
 	var inputIsName bool
 	uid, err := strconv.Atoi(userIDorName)
@@ -124,12 +126,17 @@ func GetUser(containerMount, userIDorName string) (*user.User, error) {
 	if len(users) > 0 {
 		return &users[0], nil
 	}
+	if !inputIsName {
+		return &user.User{Uid: uid}, user.ErrNoPasswdEntries
+	}
 	return nil, user.ErrNoPasswdEntries
 }
 
-// GetGroup takes ac ontainermount path and a group name or id and returns
-// a match Group struct from /etc/group.  if it cannot locate a group,
-// an ErrNoGroupEntries error is returned.
+// GetGroup takes a containermount path and a group name or ID and returns
+// a match Group struct from /etc/group.  If it cannot locate a group,
+// an ErrNoGroupEntries error is returned.  When the provided group name
+// was an ID, a Group structure with Gid set is returned along with
+// ErrNoGroupEntries.
 func GetGroup(containerMount, groupIDorName string) (*user.Group, error) {
 	var inputIsName bool
 	gid, err := strconv.Atoi(groupIDorName)
@@ -154,5 +161,8 @@ func GetGroup(containerMount, groupIDorName string) (*user.Group, error) {
 	if len(groups) > 0 {
 		return &groups[0], nil
 	}
+	if !inputIsName {
+		return &user.Group{Gid: gid}, user.ErrNoGroupEntries
+	}
 	return nil, user.ErrNoGroupEntries
 }