WIP

peer/hosts_test.go

@@ -28,8 +28,7 @@ func readManagedSection(t *testing.T, path, localDomain string) (inside, outside
 	if err != nil {
 		t.Fatal(err)
 	}
-	begin := hostsBegin + localDomain
-	end := hostsEnd + localDomain
+	begin, end := hostMarkers(localDomain)
 
 	inSection := false
 	for _, line := range strings.Split(string(raw), "\n") {
@@ -157,6 +156,45 @@ func TestUpdateHosts_Idempotent(t *testing.T) {
 	}
 }
 
+// TestUpdateHosts_PrefixDomainsCoexist guards finding 4.4: two domains where
+// one label is a prefix of the other ("net" vs "net2") must each manage their
+// own section without clobbering the other's, even sharing one hosts file.
+func TestUpdateHosts_PrefixDomainsCoexist(t *testing.T) {
+	path := writeTempHosts(t, "127.0.0.1 localhost\n")
+
+	if err := updateHosts(path, "net2.local", map[netip.Addr]*Peer{
+		netip.MustParseAddr("10.0.2.1"): peer("a"),
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if err := updateHosts(path, "net.local", map[netip.Addr]*Peer{
+		netip.MustParseAddr("10.0.1.1"): peer("b"),
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	// Both sections coexist after writing the prefix domain.
+	if in, _ := readManagedSection(t, path, "net2.local"); len(in) != 1 || in[0] != "10.0.2.1 a.net2.local" {
+		t.Errorf("net2 section clobbered: %v", in)
+	}
+	if in, _ := readManagedSection(t, path, "net.local"); len(in) != 1 || in[0] != "10.0.1.1 b.net.local" {
+		t.Errorf("net section wrong: %v", in)
+	}
+
+	// Re-updating net2 must not disturb the net section.
+	if err := updateHosts(path, "net2.local", map[netip.Addr]*Peer{
+		netip.MustParseAddr("10.0.2.2"): peer("c"),
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if in, _ := readManagedSection(t, path, "net.local"); len(in) != 1 || in[0] != "10.0.1.1 b.net.local" {
+		t.Errorf("net section disturbed by net2 update: %v", in)
+	}
+	if in, _ := readManagedSection(t, path, "net2.local"); len(in) != 1 || in[0] != "10.0.2.2 c.net2.local" {
+		t.Errorf("net2 section not updated: %v", in)
+	}
+}
+
 func contains(ss []string, s string) bool {
 	for _, x := range ss {
 		if x == s {