初版功能完成

internal/platform/windows/netinfo/prefixes.go

@@ -0,0 +1,55 @@
+// Package netinfo inspects local IPv4 networks without mutating Windows state.
+package netinfo
+
+import (
+	"fmt"
+	"net"
+	"net/netip"
+)
+
+// DirectIPv4Prefixes returns assigned non-loopback IPv4 interface prefixes,
+// excluding the named RemLink adapter.
+func DirectIPv4Prefixes(excludedInterface string) ([]netip.Prefix, error) {
+	interfaces, err := net.Interfaces()
+	if err != nil {
+		return nil, fmt.Errorf("list network interfaces: %w", err)
+	}
+	var prefixes []netip.Prefix
+	for _, networkInterface := range interfaces {
+		if networkInterface.Name == excludedInterface || networkInterface.Flags&net.FlagLoopback != 0 || networkInterface.Flags&net.FlagUp == 0 {
+			continue
+		}
+		addresses, err := networkInterface.Addrs()
+		if err != nil {
+			return nil, fmt.Errorf("list addresses for %s: %w", networkInterface.Name, err)
+		}
+		for _, address := range addresses {
+			prefix, err := netip.ParsePrefix(address.String())
+			if err != nil || !prefix.Addr().Is4() {
+				continue
+			}
+			prefixes = append(prefixes, prefix.Masked())
+		}
+	}
+	return prefixes, nil
+}
+
+// PrefixesOverlap performs true containment-based IPv4 prefix overlap.
+func PrefixesOverlap(left, right netip.Prefix) bool {
+	if !left.Addr().Is4() || !right.Addr().Is4() {
+		return false
+	}
+	left = left.Masked()
+	right = right.Masked()
+	return left.Contains(right.Addr()) || right.Contains(left.Addr())
+}
+
+// FindConflict returns the first local network overlapping desired.
+func FindConflict(desired netip.Prefix, existing []netip.Prefix) (netip.Prefix, bool) {
+	for _, candidate := range existing {
+		if PrefixesOverlap(desired, candidate) {
+			return candidate, true
+		}
+	}
+	return netip.Prefix{}, false
+}

internal/platform/windows/netinfo/prefixes_test.go

@@ -0,0 +1,23 @@
+package netinfo
+
+import (
+	"net/netip"
+	"testing"
+)
+
+func TestPrefixesOverlap(t *testing.T) {
+	for _, test := range []struct {
+		left, right string
+		want        bool
+	}{
+		{"192.168.0.0/16", "192.168.13.0/24", true},
+		{"192.168.13.0/24", "192.168.13.10/32", true},
+		{"10.88.0.0/16", "10.89.0.0/16", false},
+		{"0.0.0.0/0", "10.88.0.0/16", true},
+	} {
+		got := PrefixesOverlap(netip.MustParsePrefix(test.left), netip.MustParsePrefix(test.right))
+		if got != test.want {
+			t.Errorf("PrefixesOverlap(%s, %s) = %v, want %v", test.left, test.right, got, test.want)
+		}
+	}
+}