feat(routing): add Network matcher for per-protocol node selection

Add Network() matcher to the routing DSL so nodes can be selected based on
connection network type (tcp/udp). Uses prefix matching so Network("tcp")
matches tcp, tcp4, tcp6 and Network("udp") matches udp, udp4, udp6.

- core/routing: add Network field to Request struct (core v0.4.3)
- x/routing/matcher: add network() matcher registered as "Network"
- x/hop: pass options.Network to routing.Request in Select()

Fixes go-gost/gost#703

routing/matcher.go

@@ -144,6 +144,7 @@ func (m *matchersTree) addRule(rule *rules.Tree, funcs matcherFuncs) error {
 
 var httpFuncs = map[string]func(*matchersTree, ...string) error{
 	"ClientIP":     expectNParameters(clientIP, 1),
+	"Network":      expectNParameters(network, 1),
 	"Proto":        expectNParameters(proto, 1),
 	"Host":         expectNParameters(host, 1),
 	"HostRegexp":   expectNParameters(hostRegexp, 1),
@@ -206,6 +207,18 @@ func proto(tree *matchersTree, protos ...string) error {
 	return nil
 }
 
+func network(tree *matchersTree, networks ...string) error {
+	network := strings.ToLower(networks[0])
+
+	tree.matcher = func(req *routing.Request) bool {
+		// Use prefix match so Network("tcp") matches "tcp", "tcp4", "tcp6"
+		// and Network("udp") matches "udp", "udp4", "udp6".
+		return strings.HasPrefix(req.Network, network)
+	}
+
+	return nil
+}
+
 func method(tree *matchersTree, methods ...string) error {
 	method := strings.ToUpper(methods[0])