Do group lookup in listeners package

This used to be handled by go-connections, but now it only takes a group
ID (int).

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

pkg/listeners/group_unix.go

@@ -0,0 +1,32 @@
+// +build !windows
+
+package listeners
+
+import (
+	"fmt"
+	"strconv"
+
+	"github.com/opencontainers/runc/libcontainer/user"
+	"github.com/pkg/errors"
+)
+
+func lookupGID(name string) (int, error) {
+	groupFile, err := user.GetGroupPath()
+	if err != nil {
+		return -1, errors.Wrap(err, "error looking up groups")
+	}
+	groups, err := user.ParseGroupFileFilter(groupFile, func(g user.Group) bool {
+		return g.Name == name || strconv.Itoa(g.Gid) == name
+	})
+	if err != nil {
+		return -1, errors.Wrapf(err, "error parsing groups for %s", name)
+	}
+	if groups != nil && len(groups) > 0 {
+		return groups[0].Gid, nil
+	}
+	gid, err := strconv.Atoi(name)
+	if err == nil {
+		return gid, nil
+	}
+	return -1, fmt.Errorf("group %s not found", name)
+}

pkg/listeners/listeners_solaris.go

@@ -18,7 +18,11 @@ func Init(proto, addr, socketGroup string, tlsConfig *tls.Config) (ls []net.List
 		}
 		ls = append(ls, l)
 	case "unix":
-		l, err := sockets.NewUnixSocket(addr, socketGroup)
+		gid, err := lookupGID(socketGroup)
+		if err != nil {
+			return nil, err
+		}
+		l, err := sockets.NewUnixSocket(addr, gid)
 		if err != nil {
 			return nil, fmt.Errorf("can't create unix socket %s: %v", addr, err)
 		}

pkg/listeners/listeners_unix.go

@@ -31,10 +31,9 @@ func Init(proto, addr, socketGroup string, tlsConfig *tls.Config) ([]net.Listene
 		}
 		ls = append(ls, l)
 	case "unix":
-
-		gid, err := strconv.Atoi(socketGroup)
+		gid, err := lookupGID(socketGroup)
 		if err != nil {
-			return nil, fmt.Errorf("failed to parse socket group id: should be a number: %v", socketGroup)
+			return nil, err
 		}
 		l, err := sockets.NewUnixSocket(addr, gid)
 		if err != nil {