Memoize AscIfDefault sorting function

ifaddrs.go

@@ -104,34 +104,29 @@ func AscIfAddress(p1Ptr, p2Ptr *IfAddr) int {
 // AscIfDefault is a sorting function to sort IfAddrs by whether or not they
 // have a default route or not.  Non-equal types are deferred in the sort.
 //
-// FIXME: This is a particularly expensive sorting operation because of the
-// non-memoized calls to NewRouteInfo().  In an ideal world the routeInfo data
-// once at the start of the sort and pass it along as a context or by wrapping
-// the IfAddr type with this information (this would also solve the inability to
-// return errors and the possibility of failing silently).  Fortunately,
-// N*log(N) where N = 3 is only ~6.2 invocations.  Not ideal, but not worth
-// optimizing today.  The common case is this gets called once or twice.
-// Patches welcome.
-func AscIfDefault(p1Ptr, p2Ptr *IfAddr) int {
+// Returns a sorting function containing a memoized default interface name.
+func AscIfDefault() func(p1Ptr, p2Ptr *IfAddr) int {
 	ri, err := NewRouteInfo()
 	if err != nil {
-		return sortDeferDecision
+		return func(p1Ptr, p2Ptr *IfAddr) int { return sortDeferDecision }
 	}
 
 	defaultIfName, err := ri.GetDefaultInterfaceName()
 	if err != nil {
-		return sortDeferDecision
+		return func(p1Ptr, p2Ptr *IfAddr) int { return sortDeferDecision }
 	}
 
-	switch {
-	case p1Ptr.Interface.Name == defaultIfName && p2Ptr.Interface.Name == defaultIfName:
-		return sortDeferDecision
-	case p1Ptr.Interface.Name == defaultIfName:
-		return sortReceiverBeforeArg
-	case p2Ptr.Interface.Name == defaultIfName:
-		return sortArgBeforeReceiver
-	default:
-		return sortDeferDecision
+	return func(p1Ptr, p2Ptr *IfAddr) int {
+		switch {
+		case p1Ptr.Interface.Name == defaultIfName && p2Ptr.Interface.Name == defaultIfName:
+			return sortDeferDecision
+		case p1Ptr.Interface.Name == defaultIfName:
+			return sortReceiverBeforeArg
+		case p2Ptr.Interface.Name == defaultIfName:
+			return sortArgBeforeReceiver
+		default:
+			return sortDeferDecision
+		}
 	}
 }
 
@@ -172,8 +167,11 @@ func DescIfAddress(p1Ptr, p2Ptr *IfAddr) int {
 }
 
 // DescIfDefault is identical to AscIfDefault but reverse ordered.
-func DescIfDefault(p1Ptr, p2Ptr *IfAddr) int {
-	return -1 * AscIfDefault(p1Ptr, p2Ptr)
+func DescIfDefault() func(p1Ptr, p2Ptr *IfAddr) int {
+	ascIfDefault := AscIfDefault()
+	return func(p1Ptr, p2Ptr *IfAddr) int {
+		return -1 * ascIfDefault(p1Ptr, p2Ptr)
+	}
 }
 
 // DescIfName is identical to AscIfName but reverse ordered.
@@ -330,7 +328,7 @@ func GetPrivateInterfaces() (IfAddrs, error) {
 		return IfAddrs{}, nil
 	}
 
-	OrderedIfAddrBy(AscIfDefault, AscIfType, AscIfNetworkSize).Sort(privateIfs)
+	OrderedIfAddrBy(AscIfDefault(), AscIfType, AscIfNetworkSize).Sort(privateIfs)
 
 	privateIfs, _, err = IfByRFC("6890", privateIfs)
 	if err != nil {
@@ -378,7 +376,7 @@ func GetPublicInterfaces() (IfAddrs, error) {
 		return IfAddrs{}, nil
 	}
 
-	OrderedIfAddrBy(AscIfDefault, AscIfType, AscIfNetworkSize).Sort(publicIfs)
+	OrderedIfAddrBy(AscIfDefault(), AscIfType, AscIfNetworkSize).Sort(publicIfs)
 
 	_, publicIfs, err = IfByRFC("6890", publicIfs)
 	if err != nil {
@@ -1045,9 +1043,9 @@ func SortIfBy(selectorParam string, inputIfAddrs IfAddrs) (IfAddrs, error) {
 		case "-address":
 			sortFuncs[i] = DescIfAddress
 		case "+default", "default":
-			sortFuncs[i] = AscIfDefault
+			sortFuncs[i] = AscIfDefault()
 		case "-default":
-			sortFuncs[i] = DescIfDefault
+			sortFuncs[i] = DescIfDefault()
 		case "+name", "name":
 			// The "name" selector returns an array of IfAddrs
 			// ordered by the interface name.