Add the iCloud Private Relay list to the IP lookup, with is_relay (closes #237)

`icloud_private_relay` is Apple's list of Private Relay networks, downloaded once a day. Every result gains `flags.is_relay`.

`parseProtonVPN` becomes `parseLinesNotEmpty`, shared with the new parser, which reads only each line's first column.

Judgement call: a line with no comma fails the parse, so a plain list of networks at Apple's URL cannot replace a good copy.

Model: opus-5-5

README.md

@@ -287,6 +287,7 @@ address. Every entry has the same fields:
     - `is_tor`: true when the address is on the `tor_exits` list
     - `is_vpn`: true when the address is on any list of VPN servers (see IP
       lists)
+    - `is_relay`: true when the address is on the `icloud_private_relay` list
     - `is_bogon`: true when the address is reserved, so that no network should
       announce it on the internet
 - `vpn_providers`: the names of the lists of VPN servers the address is on, or
@@ -421,6 +422,9 @@ The lists:
   last 30 days. From
   [FireHOL](https://iplists.firehol.org/?ipset=firehol_level3), downloaded every
   3 hours.
+- `icloud_private_relay`: the networks where iCloud Private Relay traffic
+  leaves. From [Apple](https://mask-api.icloud.com/egress-ip-ranges.csv),
+  downloaded once a day.
 - `ivpn`: VPN servers run by IVPN. From
   [IVPN](https://api.ivpn.net/v5/servers.json), downloaded once a day.
 - `mullvad`: VPN servers run by Mullvad. From
@@ -606,6 +610,13 @@ The ceilings add up to 3.7 GiB:
   limit caps the SQLite library.
 - About 0.2 GiB for everything else in the runtime.
 
+The `icloud_private_relay` list has about 285,000 networks. Neighbouring
+networks merge, which leaves about 6,900 address ranges. Loaded, the list adds
+about 0.3 MiB to the Go heap and under 6 MiB to the process's resident memory.
+Parsing the file allocates about 94 MiB in about 0.2 seconds. The next garbage
+collection frees all of it but the 0.3 MiB above. Parsing happens at startup and
+whenever a download brings a new version.
+
 The SQLite library gets its memory from glibc, the C library. glibc keeps freed
 memory in pools called arenas, and hands it back to the kernel slowly. It
 creates up to eight arenas per processor core. So on a host with many cores the

TODO.md

@@ -53,6 +53,9 @@ problem the run finds.
 
 # Completed Steps
 
+- 2026-11-10: the IP lookup checks the `icloud_private_relay` list of Apple's
+  iCloud Private Relay networks, downloaded once a day. Each result has
+  `flags.is_relay` (closes https://git.eeqj.de/sneak/routewatch/issues/237).
 - 2026-11-10: the IP lookup checks the `protonvpn` list of ProtonVPN's /24
   networks and the `protonvpn_entry` list of its servers' IPv4 and IPv6
   addresses, from a public mirror of Proton's server list (closes

internal/iplist/download.go

@@ -21,7 +21,7 @@ const (
 	downloadTimeout = time.Minute
 
 	// maxDownloadSize is the size of the largest list file accepted, in
-	// bytes. The largest list, FireHOL abusers, is about 2.5 MiB.
+	// bytes. The largest list, iCloud Private Relay, is about 12 MiB.
 	maxDownloadSize = 200 << 20
 )
 

internal/iplist/iplist.go

@@ -56,6 +56,11 @@ const (
 	// that start with #. Unlike FormatLines, a file with no addresses or
 	// networks fails.
 	FormatProtonVPN
+
+	// FormatICloudPrivateRelayCSV is Apple's CSV file of iCloud Private Relay
+	// networks. Each line starts with a network, followed by its country,
+	// region and city.
+	FormatICloudPrivateRelayCSV
 )
 
 // List is one public IP list.

internal/iplist/iplist_internal_test.go

@@ -83,6 +83,18 @@ const protonVPNEntryBody = "#\n# protonvpn_entry_ips.txt\n" +
 	"# Entry IPs clients connect to, resolved from ProtonVPN hostnames.\n#\n" +
 	"192.0.2.80\n2001:db8::80\n"
 
+// iCloudPrivateRelayAddr is an address on iCloudPrivateRelayBody.
+const iCloudPrivateRelayAddr = "2001:db8:1::5"
+
+// iCloudPrivateRelayBody is a small file in the format of Apple's iCloud
+// Private Relay file.
+const iCloudPrivateRelayBody = "192.0.2.0/31,GB,GB-EN,London,\n" +
+	"198.51.100.32/27,US,US-CA,Los Angeles,\n" +
+	"2001:db8:1::/64,US,US-AK,Anchorage,\n"
+
+// emptyFileCase names the case of a wrong document that is an empty file.
+const emptyFileCase = "an empty file"
+
 // errorPage is a file that is no list, as a publisher's error page is.
 const errorPage = "<!DOCTYPE html>\n<html></html>\n"
 
@@ -243,6 +255,15 @@ func TestLookupFindsListedAddresses(t *testing.T) {
 			},
 			unlisted: []string{"192.0.2.12", "2001:db8::2"},
 		},
+		{
+			name:   "iCloud Private Relay networks",
+			format: FormatICloudPrivateRelayCSV,
+			body:   iCloudPrivateRelayBody,
+			listed: []string{
+				"192.0.2.1", "198.51.100.63", iCloudPrivateRelayAddr,
+			},
+			unlisted: []string{"192.0.2.2", "198.51.100.64", "2001:db8:2::1"},
+		},
 	})
 }
 
@@ -490,7 +511,7 @@ func TestWrongVPNDocumentFailsToParse(t *testing.T) {
 			"no addresses": f.empty,
 			"bad address":  f.badAddress,
 			"cut off":      f.good[:len(f.good)/2],
-			"an empty file": "",
+			emptyFileCase:  "",
 		}
 
 		for name, body := range bodies {
@@ -516,7 +537,7 @@ func TestWrongProtonVPNDocumentFailsToParse(t *testing.T) {
 		"JSON":          `{"status":"ok"}`,
 		"comments only": "#\n# protonvpn_ip_ranges.txt\n#\n",
 		"bad network":   "192.0.2.0/24\nexample\n",
-		"an empty file": "",
+		emptyFileCase:   "",
 	}
 
 	for name, body := range bodies {
@@ -531,6 +552,34 @@ func TestWrongProtonVPNDocumentFailsToParse(t *testing.T) {
 	}
 }
 
+// TestWrongICloudPrivateRelayDocumentFailsToParse parses documents that are
+// not Apple's iCloud Private Relay file. Each fails, so none can replace a
+// good copy.
+func TestWrongICloudPrivateRelayDocumentFailsToParse(t *testing.T) {
+	t.Parallel()
+
+	bodies := map[string]string{
+		"error page":     errorPage,
+		"JSON":           `{"status":"ok","count":1}`,
+		"no other field": "192.0.2.0/24\n",
+		"bad network":    "192.0.2.0/24,GB,GB-EN,London,\nexample,GB,GB-EN,London,\n",
+		"an address":     "192.0.2.1,GB,GB-EN,London,\n",
+		emptyFileCase:    "",
+	}
+
+	for name, body := range bodies {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			addresses, err := parse(strings.NewReader(body),
+				FormatICloudPrivateRelayCSV)
+			if err == nil {
+				t.Errorf("parse returned %v and no error", addresses.Ranges())
+			}
+		})
+	}
+}
+
 // TestLookupMarksVPNLists looks up an address on a VPN list and on another
 // list. Only the VPN list's listing says it is one.
 func TestLookupMarksVPNLists(t *testing.T) {
@@ -885,15 +934,33 @@ func TestStopCancelsADownloadInProgress(t *testing.T) {
 func TestTorExitsListHoldsIPv6Exits(t *testing.T) {
 	t.Parallel()
 
+	checkPublicListHolds(t, TorExitsList, onionooBody, onionooIPv6ExitAddr)
+}
+
+// TestICloudPrivateRelayListHoldsItsNetworks downloads a file in Apple's
+// format as the public iCloud Private Relay list, which is what an address's
+// is_relay answer comes from.
+func TestICloudPrivateRelayListHoldsItsNetworks(t *testing.T) {
+	t.Parallel()
+
+	checkPublicListHolds(t, ICloudPrivateRelayList, iCloudPrivateRelayBody,
+		iCloudPrivateRelayAddr)
+}
+
+// checkPublicListHolds downloads body as the public list called name and
+// checks that addr has one listing, which names that list.
+func checkPublicListHolds(t *testing.T, name, body, addr string) {
+	t.Helper()
+
 	index := slices.IndexFunc(Lists(), func(list List) bool {
-		return list.Name == TorExitsList
+		return list.Name == name
 	})
 	if index < 0 {
-		t.Fatalf("no list named %s", TorExitsList)
+		t.Fatalf("no list named %s", name)
 	}
 
 	list := Lists()[index]
-	_, list.URL = newPublisher(t, onionooBody)
+	_, list.URL = newPublisher(t, body)
 	b := newTestIPLists(t.TempDir(), list)
 
 	err := b.download(t.Context(), list)
@@ -901,9 +968,9 @@ func TestTorExitsListHoldsIPv6Exits(t *testing.T) {
 		t.Fatalf("download: %v", err)
 	}
 
-	listings := lookup(t, b, onionooIPv6ExitAddr)
+	listings := lookup(t, b, addr)
-	if len(listings) != 1 || listings[0].Name != TorExitsList {
+	if len(listings) != 1 || listings[0].Name != name {
-		t.Errorf("listings %+v, want one for %s", listings, TorExitsList)
+		t.Errorf("listings %+v, want one for %s", listings, name)
 	}
 }
 

internal/iplist/lists.go

@@ -8,6 +8,10 @@ import (
 // TorExitsList is the name of the list of Tor exit nodes.
 const TorExitsList = "tor_exits"
 
+// ICloudPrivateRelayList is the name of the list of iCloud Private Relay's
+// networks.
+const ICloudPrivateRelayList = "icloud_private_relay"
+
 // protonVPNIPsURL is where the ProtonVPN-IPs mirror publishes its files.
 const protonVPNIPsURL = "https://raw.githubusercontent.com/tn3w/ProtonVPN-IPs/master/"
 
@@ -30,6 +34,9 @@ const (
 	fireHOLAbusersInterval = 5 * time.Hour
 	fireHOLLevel3Interval  = 3 * time.Hour
 
+	// Apple's iCloud Private Relay file is 12 MB, so once a day.
+	iCloudPrivateRelayInterval = 24 * time.Hour
+
 	// Spamhaus asks that DROP be downloaded at most once a day:
 	// https://www.spamhaus.org/blocklists/do-not-route-or-peer/
 	spamhausDROPInterval = 24 * time.Hour
@@ -84,6 +91,13 @@ func nonVPNLists() []List {
 			Interval: fireHOLLevel3Interval,
 			Format:   FormatLines,
 		},
+		{
+			Name:        ICloudPrivateRelayList,
+			Description: "In a network where iCloud Private Relay traffic leaves",
+			URL:         "https://mask-api.icloud.com/egress-ip-ranges.csv",
+			Interval:    iCloudPrivateRelayInterval,
+			Format:      FormatICloudPrivateRelayCSV,
+		},
 		{
 			Name: "spamhaus_drop",
 			Description: "In an IPv4 network that Spamhaus says spammers " +

internal/iplist/parse.go

@@ -25,6 +25,10 @@ const (
 	// dshieldFieldSeparator separates the fields of a DShield line.
 	dshieldFieldSeparator = "\t"
 
+	// iCloudPrivateRelayFieldSeparator separates the fields of a line of
+	// Apple's iCloud Private Relay file.
+	iCloudPrivateRelayFieldSeparator = ","
+
 	// spamhausMetadataType is the type of the line that ends a Spamhaus
 	// file. That line holds the file's metadata and no network.
 	spamhausMetadataType = "metadata"
@@ -59,7 +63,9 @@ func parse(r io.Reader, format Format) (*netipx.IPSet, error) {
 	case FormatIVPNJSON:
 		return parseIVPN(r)
 	case FormatProtonVPN:
-		return parseProtonVPN(r)
+		return parseLinesNotEmpty(r, addAddressOrNetwork)
+	case FormatICloudPrivateRelayCSV:
+		return parseLinesNotEmpty(r, addICloudPrivateRelayNetwork)
 	default:
 		return nil, errUnknownFormat
 	}
@@ -331,11 +337,12 @@ func parseIVPN(r io.Reader) (*netipx.IPSet, error) {
 	return addressSet(texts)
 }
 
-// parseProtonVPN returns the addresses or networks in a ProtonVPN-IPs list. A
+// parseLinesNotEmpty is parseLines for a list that always holds addresses, so
-// file with no addresses or networks fails, because the service always has
+// a file with none fails.
-// servers.
+func parseLinesNotEmpty(
-func parseProtonVPN(r io.Reader) (*netipx.IPSet, error) {
+	r io.Reader, addLine func(*netipx.IPSetBuilder, string) error,
-	addresses, err := parseLines(r, addAddressOrNetwork)
+) (*netipx.IPSet, error) {
+	addresses, err := parseLines(r, addLine)
 	if err != nil {
 		return nil, err
 	}
@@ -347,6 +354,24 @@ func parseProtonVPN(r io.Reader) (*netipx.IPSet, error) {
 	return addresses, nil
 }
 
+// addICloudPrivateRelayNetwork adds the network at the start of a line of
+// Apple's iCloud Private Relay file to builder.
+func addICloudPrivateRelayNetwork(builder *netipx.IPSetBuilder, line string) error {
+	field, _, found := strings.Cut(line, iCloudPrivateRelayFieldSeparator)
+	if !found {
+		return errNoNetwork
+	}
+
+	network, err := netip.ParsePrefix(field)
+	if err != nil {
+		return err
+	}
+
+	builder.AddPrefix(network)
+
+	return nil
+}
+
 // readJSON reads r to its end and decodes it, as one JSON document, into v.
 func readJSON(r io.Reader, v any) error {
 	data, err := io.ReadAll(r)

internal/server/handlers.go

@@ -797,6 +797,9 @@ type IPLookupFlags struct {
 	// IsVPN says that the address is on a list of VPN servers.
 	IsVPN bool `json:"is_vpn"`
 
+	// IsRelay says that the address is on the iCloud Private Relay list.
+	IsRelay bool `json:"is_relay"`
+
 	// IsBogon says that the address is reserved, as package bogon tells.
 	IsBogon bool `json:"is_bogon"`
 }
@@ -1025,6 +1028,9 @@ func ipLookupFlags(ip string, listings []iplist.Listing) IPLookupFlags {
 		IsVPN: slices.ContainsFunc(listings, func(l iplist.Listing) bool {
 			return l.VPN
 		}),
+		IsRelay: slices.ContainsFunc(listings, func(l iplist.Listing) bool {
+			return l.Name == iplist.ICloudPrivateRelayList
+		}),
 		IsBogon: isBogon(ip),
 	}
 }

internal/server/handlers_internal_test.go

@@ -1504,6 +1504,10 @@ const listedUnroutedAddr = "203.0.113.1"
 // torExitAddr is the address that fakeIPLists lists on the Tor exit list.
 const torExitAddr = "203.0.113.2"
 
+// relayAddr is the address that fakeIPLists lists on the iCloud Private Relay
+// list.
+const relayAddr = "203.0.113.5"
+
 // The addresses that fakeIPLists lists on one and on two VPN lists, and the
 // names of those lists.
 const (
@@ -1513,10 +1517,11 @@ const (
 	otherTestVPN    = "other_test_vpn"
 )
 
-// fakeIPLists has four lists. The test list holds addrInTestPrefixV4,
+// fakeIPLists has five lists. The test list holds addrInTestPrefixV4,
 // listedUnroutedAddr and twoVPNListsAddr. The Tor exit list holds torExitAddr.
-// The test VPN list holds oneVPNListAddr and twoVPNListsAddr, and the other
+// The iCloud Private Relay list holds relayAddr. The test VPN list holds
-// test VPN list holds twoVPNListsAddr.
+// oneVPNListAddr and twoVPNListsAddr, and the other test VPN list holds
+// twoVPNListsAddr.
 type fakeIPLists struct{}
 
 func testListing() iplist.Listing {
@@ -1537,6 +1542,10 @@ func (fakeIPLists) Lookup(addr netip.Addr) []iplist.Listing {
 		return []iplist.Listing{{Name: iplist.TorExitsList}}
 	}
 
+	if addr == netip.MustParseAddr(relayAddr) {
+		return []iplist.Listing{{Name: iplist.ICloudPrivateRelayList}}
+	}
+
 	if addr == netip.MustParseAddr(oneVPNListAddr) {
 		return []iplist.Listing{{Name: testVPNList, VPN: true}}
 	}
@@ -1569,20 +1578,22 @@ func TestIPLookupFlags(t *testing.T) {
 		name  string
 		addr  string
 		tor   bool
+		relay bool
 		bogon bool
 	}{
-		{"on the Tor exit list", torExitAddr, true, true},
+		{"on the Tor exit list", torExitAddr, true, false, true},
-		{"on another list", listedUnroutedAddr, false, true},
+		{"on the iCloud Private Relay list", relayAddr, false, true, true},
-		{"routed IPv4", addrInTestPrefixV4, false, true},
+		{"on another list", listedUnroutedAddr, false, false, true},
-		{"routed IPv6", addrInTestPrefixV6, false, true},
+		{"routed IPv4", addrInTestPrefixV4, false, false, true},
-		{"private IPv4", "10.0.0.1", false, true},
+		{"routed IPv6", addrInTestPrefixV6, false, false, true},
-		{"loopback IPv4", "127.0.0.1", false, true},
+		{"private IPv4", "10.0.0.1", false, false, true},
-		{"public IPv4", "1.1.1.1", false, false},
+		{"loopback IPv4", "127.0.0.1", false, false, true},
-		{"private IPv6", "fd00::1", false, true},
+		{"public IPv4", "1.1.1.1", false, false, false},
-		{"loopback IPv6", "::1", false, true},
+		{"private IPv6", "fd00::1", false, false, true},
-		{"public IPv6", "2606:4700:4700::1111", false, false},
+		{"loopback IPv6", "::1", false, false, true},
-		{"public IPv4 in IPv6 form", "::ffff:1.1.1.1", false, false},
+		{"public IPv6", "2606:4700:4700::1111", false, false, false},
-		{"private IPv4 in IPv6 form", "::ffff:10.0.0.1", false, true},
+		{"public IPv4 in IPv6 form", "::ffff:1.1.1.1", false, false, false},
+		{"private IPv4 in IPv6 form", "::ffff:10.0.0.1", false, false, true},
 	}
 
 	for _, tt := range tests {
@@ -1604,7 +1615,8 @@ func TestIPLookupFlags(t *testing.T) {
 			}
 
 			want := map[string]bool{
-				"is_tor": tt.tor, "is_vpn": false, "is_bogon": tt.bogon,
+				"is_tor": tt.tor, "is_vpn": false, "is_relay": tt.relay,
+				"is_bogon": tt.bogon,
 			}
 			if !maps.Equal(got, want) {
 				t.Errorf("%s: flags %v, want %v", path, got, want)