route: support v4-mapped IPv6 nexthops on V6 routes - #1198

route_linux.go (1)

993-1001: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Duplicated v4-mapped conform logic between single-Gw and multipath nh.Gw paths.

The exact same conform condition/comment is repeated for route.Gw (Lines 993-1001) and nh.Gw (Lines 1036-1044). Extracting a small helper would keep the two paths from silently diverging if this logic is tweaked later.

♻️ Proposed refactor

+// conformV4MappedGatewayFamily conforms a v4-mapped IPv6 gateway
+// (::ffff:a.b.c.d, 16 bytes) to FAMILY_V6 when the caller explicitly
+// requested a V6 route via route.Family. This is opt-in rather than
+// silently reinterpreting an ambiguous address; a 4-byte IPv4 gateway
+// is left to error downstream.
+func conformV4MappedGatewayFamily(routeFamily int, gw net.IP, gwFamily int) int {
+	if routeFamily == FAMILY_V6 && gwFamily == FAMILY_V4 && len(gw) == net.IPv6len {
+		return FAMILY_V6
+	}
+	return gwFamily
+}
+
 	if route.Gw != nil {
 		gwFamily := nl.GetIPFamily(route.Gw)
-		if route.Family == FAMILY_V6 && gwFamily == FAMILY_V4 && len(route.Gw) == net.IPv6len {
-			gwFamily = FAMILY_V6
-		}
+		gwFamily = conformV4MappedGatewayFamily(route.Family, route.Gw, gwFamily)
 ...
 			if nh.Gw != nil {
 				gwFamily := nl.GetIPFamily(nh.Gw)
-				if route.Family == FAMILY_V6 && gwFamily == FAMILY_V4 && len(nh.Gw) == net.IPv6len {
-					gwFamily = FAMILY_V6
-				}
+				gwFamily = conformV4MappedGatewayFamily(route.Family, nh.Gw, gwFamily)

Also applies to: 1036-1044

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@route_linux.go` around lines 993 - 1001, The v4-mapped IPv6 gateway
conforming logic is duplicated in both the single-gateway and multipath nexthop
paths, which risks the two branches drifting apart. Extract the shared
FAMILY_V6/FAMILY_V4 + net.IPv6len check into a small helper and call it from
both the route.Gw handling and the nh.Gw handling so the behavior stays
identical in both places.

route_test.go (1)

2842-2890: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

No test exercises the multipath (nh.Gw) conform path.

All four new tests cover only route.Gw. The PR/AI summary states the v4-mapped conform is applied to route.MultiPath nexthops as well (route_linux.go Lines 1036-1044), but that duplicated logic is currently untested — a regression there (e.g. someone updates one conform block but not the other) would go unnoticed.

Consider adding a case using Route{Family: FAMILY_V6, MultiPath: []*NexthopInfo{{Gw: gw, LinkIndex: ...}}} and asserting the nested RTA_MULTIPATH attribute's child RTA_GATEWAY is 16 bytes.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@route_test.go` around lines 2842 - 2890, The current tests only cover the
direct Route.Gw path, so the multipath nexthop branch in prepareRouteReq remains
untested. Add a test in TestPrepareRouteReqV4MappedV6Gateway (or a sibling test)
that builds a Route with Family set to FAMILY_V6 and MultiPath containing a
NexthopInfo with Gw set to the v4-mapped IP, then verify the nested
RTA_MULTIPATH child RTA_GATEWAY is encoded as 16 bytes. Use the existing
prepareRouteReq, Route, and NexthopInfo symbols to locate the multipath conform
logic and ensure it matches the direct gateway behavior.