Keep a trailing AS set out of the origin and the peerings (closes #75)

A path that ends in an AS set of several members, such as
[64496, 64497, [64498, 64499]], now has no origin: its route is stored
with origin 0 (none), and no member of the set is in a peering. A set of
one member counts as that AS. An announcement with an empty path is
still not stored.

ASPath keeps such a set apart from the sequence and gives the origin.
The prefix and AS handlers take the origin from it; the peering handler
uses the sequence only. The stored AS path still lists the set's members
at the end.

The prefix and prefix length pages show origin 0 as no known origin, the
IP lookup asks no WHOIS lookup for it, and the README says what it means.

Model: opus-5-5

README.md

@@ -54,6 +54,11 @@ DEBUG=routewatch ./routewatch
 - `GET /api/v1/as/{asn}` - Get prefixes announced by an AS
 - `GET /api/v1/prefix/{prefix}` - Get routes for a specific prefix
 
+An origin AS of 0 (`origin_asn` in a route, `asn` in an IP lookup, the key `0`
+in a prefix's `origins`) means the route has no known origin: its AS path ends
+in an AS set of several members, any of which may have originated it. The pages
+show such a route as having no known origin.
+
 ## Code Structure
 
 ```

internal/database/database.go

@@ -2141,11 +2141,12 @@ func (d *Database) GetIPInfoContext(
 		info.FirstSeen = prefixFirstSeen.Time
 	}
 
-	// Check if WHOIS data needs refresh (never fetched or older than 30 days)
+	// Check if WHOIS data needs refresh (never fetched or older than 30 days).
+	// A route with origin 0 has no known origin, so no AS to look up.
 	const staleThreshold = 30 * 24 * time.Hour
 
-	info.NeedsWHOISRefresh = !whoisUpdatedAt.Valid ||
-		time.Since(whoisUpdatedAt.Time) > staleThreshold
+	info.NeedsWHOISRefresh = info.ASN != 0 && (!whoisUpdatedAt.Valid ||
+		time.Since(whoisUpdatedAt.Time) > staleThreshold)
 
 	return info, nil
 }

internal/database/database_internal_test.go

@@ -213,6 +213,33 @@ func TestGetIPInfoIgnoresShortRoutes(t *testing.T) {
 	lookup("2001:db8::1", "2001:db8::/32", 64502)
 }
 
+// TestGetIPInfoNeedsNoWHOISRefreshForOriginZero checks that the IP lookup asks
+// for no WHOIS lookup when the address's route has origin 0, no known origin,
+// and still asks for one when its origin AS has no WHOIS data.
+func TestGetIPInfoNeedsNoWHOISRefreshForOriginZero(t *testing.T) {
+	t.Parallel()
+
+	db, err := New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("failed to create database: %v", err)
+	}
+	defer func() { _ = db.Close() }()
+
+	writeOriginRoutes(t, db, map[string]int{"10.0.0.0/8": 0, "11.0.0.0/8": 64500})
+
+	for ip, want := range map[string]bool{"10.0.0.1": false, "11.0.0.1": true} {
+		info, err := db.GetIPInfo(ip)
+		if err != nil {
+			t.Fatalf("GetIPInfo(%s): %v", ip, err)
+		}
+
+		if info.NeedsWHOISRefresh != want {
+			t.Errorf("GetIPInfo(%s) asks for a WHOIS lookup of AS%d: %t, want %t",
+				ip, info.ASN, info.NeedsWHOISRefresh, want)
+		}
+	}
+}
+
 // TestLiveRouteTablesHoldOneRoutePerPrefixAndPeer checks that each live route
 // table refuses a second route from a peer for a prefix, even with another
 // origin AS. An upsert updates the peer's route before it would insert one, so

internal/ristypes/ris.go

@@ -23,26 +23,43 @@ const (
 	StateDown = "down"
 )
 
-// ASPath represents a BGP AS path as a slice of AS numbers.
-// It handles JSON unmarshaling of both simple arrays and nested AS sets,
-// flattening any nested structures into a single sequence of AS numbers.
-type ASPath []int
+// ASPath is a BGP AS path as the feed writes it: an array of AS numbers in
+// which an AS set is an array of its members, such as [1, 2, [3, 4]].
+type ASPath struct {
+	// Sequence is the path's AS numbers in order. A set of one member that
+	// ends the path counts as that AS and is its last element. The members of
+	// a set anywhere else are flattened into it.
+	Sequence []int
+
+	// Set holds the members of a set of several members that ends the path.
+	// Any of them may be the origin, and they are not neighbours of each
+	// other or of the AS before them.
+	Set []int
+}
+
+// Origin returns the AS that originated the route: the last AS of the
+// sequence, or 0 (none) when the path ends in a set of several members or is
+// empty.
+func (p *ASPath) Origin() int {
+	if len(p.Set) > 0 || len(p.Sequence) == 0 {
+		return 0
+	}
+
+	return p.Sequence[len(p.Sequence)-1]
+}
 
 // UnmarshalJSON implements the json.Unmarshaler interface for ASPath.
-// It handles both simple integer arrays [1, 2, 3] and nested AS sets
-// like [1, [2, 3], 4], flattening them into a single slice of integers.
 func (p *ASPath) UnmarshalJSON(data []byte) error {
-	// First try to unmarshal as a simple array of integers
-	var simple []int
+	// Most paths have no AS set and decode as a plain array of integers.
+	var sequence []int
 
-	err := json.Unmarshal(data, &simple)
+	err := json.Unmarshal(data, &sequence)
 	if err == nil {
-		*p = ASPath(simple)
+		*p = ASPath{Sequence: sequence}
 
 		return nil
 	}
 
-	// If that fails, unmarshal as array of interfaces and flatten
 	var raw []any
 
 	err = json.Unmarshal(data, &raw)
@@ -50,24 +67,30 @@ func (p *ASPath) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
-	// Flatten the array
-	result := make([]int, 0)
+	path := ASPath{Sequence: make([]int, 0, len(raw))}
 
-	for _, item := range raw {
+	for i, item := range raw {
 		switch v := item.(type) {
 		case float64:
-			result = append(result, int(v))
+			path.Sequence = append(path.Sequence, int(v))
 		case []any:
-			// Nested array - flatten it
-			for _, nested := range v {
-				if num, ok := nested.(float64); ok {
-					result = append(result, int(num))
+			set := make([]int, 0, len(v))
+
+			for _, member := range v {
+				if num, ok := member.(float64); ok {
+					set = append(set, int(num))
 				}
 			}
+
+			if i == len(raw)-1 && len(set) > 1 {
+				path.Set = set
+			} else {
+				path.Sequence = append(path.Sequence, set...)
+			}
 		}
 	}
 
-	*p = ASPath(result)
+	*p = path
 
 	return nil
 }
@@ -97,7 +120,7 @@ type RISMessage struct {
 	RRC             string    `json:"rrc,omitempty"`
 	MrtTime         float64   `json:"mrt_time,omitempty"`
 	SocketTime      float64   `json:"socket_time,omitempty"`
-	Path            ASPath    `json:"path,omitempty"`
+	Path            ASPath    `json:"path,omitzero"`
 	// Community and Raw are present in the feed but read by no handler.
 	// They are the largest fields on a message that lives in up to four
 	// handler queues, so json:"-" keeps them out of the decoded message

internal/ristypes/ris_test.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"encoding/json"
 	"os"
+	"slices"
 	"testing"
 
 	"git.eeqj.de/sneak/routewatch/internal/ristypes"
@@ -58,7 +59,7 @@ func TestDecodeDropsCommunityAndRaw(t *testing.T) {
 			t.Errorf("message %d: Raw decoded, want empty", messages)
 		}
 
-		if len(msg.Path) > 0 {
+		if len(msg.Path.Sequence) > 0 {
 			withPath++
 		}
 
@@ -82,3 +83,65 @@ func TestDecodeDropsCommunityAndRaw(t *testing.T) {
 			withPath, withAnnouncements)
 	}
 }
+
+// TestASPathKeepsATrailingSetApart decodes AS paths as the feed writes them, an
+// AS set as an array inside the path. A set of several members that ends the
+// path is kept apart from the sequence, and the path has no origin, since any
+// member may be it. A set of one member counts as that AS, and a set anywhere
+// else is flattened into the sequence.
+func TestASPathKeepsATrailingSetApart(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		path         string
+		wantSequence []int
+		wantSet      []int
+		wantOrigin   int
+	}{
+		{
+			path:         "[64496, 64497]",
+			wantSequence: []int{64496, 64497},
+			wantOrigin:   64497,
+		},
+		{
+			path:         "[64496, 64497, [64498, 64499]]",
+			wantSequence: []int{64496, 64497},
+			wantSet:      []int{64498, 64499},
+		},
+		{
+			path:         "[64496, 64497, [64498]]",
+			wantSequence: []int{64496, 64497, 64498},
+			wantOrigin:   64498,
+		},
+		{
+			path:         "[64496, [64497, 64498], 64499]",
+			wantSequence: []int{64496, 64497, 64498, 64499},
+			wantOrigin:   64499,
+		},
+		{path: "[]"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.path, func(t *testing.T) {
+			t.Parallel()
+
+			var got ristypes.ASPath
+
+			err := json.Unmarshal([]byte(tt.path), &got)
+			if err != nil {
+				t.Fatalf("unmarshal %s: %v", tt.path, err)
+			}
+
+			if !slices.Equal(got.Sequence, tt.wantSequence) ||
+				!slices.Equal(got.Set, tt.wantSet) {
+				t.Errorf("%s decoded to sequence %v and set %v, want %v and %v",
+					tt.path, got.Sequence, got.Set, tt.wantSequence, tt.wantSet)
+			}
+
+			origin := got.Origin()
+			if origin != tt.wantOrigin {
+				t.Errorf("origin of %s = %d, want %d", tt.path, origin, tt.wantOrigin)
+			}
+		})
+	}
+}

internal/routewatch/ashandler.go

@@ -1,6 +1,7 @@
 package routewatch
 
 import (
+	"slices"
 	"sync"
 	"time"
 
@@ -98,18 +99,14 @@ func (h *ASHandler) QueueCapacity() int {
 
 // HandleMessage processes a RIS Live BGP message by extracting all ASNs from
 // the AS path and queuing them for batch insertion into the database. The
-// origin ASN (last element in the path) and all transit ASNs are recorded
-// with their associated timestamps. When the batch reaches the configured size
-// threshold, the flush goroutine is woken to write it.
+// origin ASN and all transit ASNs are recorded with their associated
+// timestamps. When the batch reaches the configured size threshold, the flush
+// goroutine is woken to write it.
 func (h *ASHandler) HandleMessage(msg *ristypes.RISMessage) {
 	// Use the pre-parsed timestamp
 	timestamp := msg.ParsedTimestamp
 
-	// Get origin ASN from path (last element)
-	var originASN int
-	if len(msg.Path) > 0 {
-		originASN = msg.Path[len(msg.Path)-1]
-	}
+	originASN := msg.Path.Origin()
 
 	h.mu.Lock()
 	defer h.mu.Unlock()
@@ -129,8 +126,8 @@ func (h *ASHandler) HandleMessage(msg *ristypes.RISMessage) {
 		})
 	}
 
-	// Also track all ASNs in the path
-	for _, asn := range msg.Path {
+	// Also track all ASNs in the path, the members of an AS set included
+	for _, asn := range slices.Concat(msg.Path.Sequence, msg.Path.Set) {
 		if asn > 0 {
 			h.batch = append(h.batch, asnOp{
 				number:    asn,

internal/routewatch/batchwrite_internal_test.go

@@ -222,7 +222,7 @@ func handleAtMaxBatchSize(
 func prefixAnnouncement(prefixes []string) *ristypes.RISMessage {
 	return &ristypes.RISMessage{
 		Peer: testPeerIP,
-		Path: ristypes.ASPath{testASNA},
+		Path: ristypes.ASPath{Sequence: []int{testASNA}},
 		Announcements: []ristypes.RISAnnouncement{
 			{NextHop: testPeerIP, Prefixes: prefixes},
 		},
@@ -255,10 +255,10 @@ func TestASHandlerHandlesMessagesWhileAWriteIsBlocked(t *testing.T) {
 
 	store := newBlockingStore()
 	h := NewASHandler(store, logger.New())
-	fill := slices.Repeat(ristypes.ASPath{testASNA}, asnBatchSize)
+	fill := ristypes.ASPath{Sequence: slices.Repeat([]int{testASNA}, asnBatchSize)}
 	handleWhileAWriteIsBlocked(t, store, h,
 		[]*ristypes.RISMessage{{Path: fill}},
-		&ristypes.RISMessage{Path: ristypes.ASPath{testASNB}})
+		&ristypes.RISMessage{Path: ristypes.ASPath{Sequence: []int{testASNB}}})
 
 	store.mu.Lock()
 	defer store.mu.Unlock()
@@ -317,12 +317,12 @@ func TestASHandlerWaitsAtTheMaximumBatchSize(t *testing.T) {
 
 	store := newBlockingStore()
 	h := NewASHandler(store, logger.New())
-	fill := slices.Repeat(ristypes.ASPath{testASNA}, asnBatchSize)
-	toMax := slices.Repeat(ristypes.ASPath{testASNA}, asnBatchMaxSize)
+	fill := ristypes.ASPath{Sequence: slices.Repeat([]int{testASNA}, asnBatchSize)}
+	toMax := ristypes.ASPath{Sequence: slices.Repeat([]int{testASNA}, asnBatchMaxSize)}
 	handleAtMaxBatchSize(t, store, h,
 		[]*ristypes.RISMessage{{Path: fill}},
 		[]*ristypes.RISMessage{{Path: toMax}},
-		&ristypes.RISMessage{Path: ristypes.ASPath{testASNB}})
+		&ristypes.RISMessage{Path: ristypes.ASPath{Sequence: []int{testASNB}}})
 
 	store.mu.Lock()
 	defer store.mu.Unlock()
@@ -386,7 +386,7 @@ func TestHandlersWakeTheFlushGoroutineWhenTheBatchIsFull(t *testing.T) {
 				h := &ASHandler{batchFullCh: make(chan struct{}, 1)}
 				// The origin AS and each AS in the path are one update each.
 				h.HandleMessage(&ristypes.RISMessage{
-					Path: slices.Repeat(ristypes.ASPath{testASNA}, n-1),
+					Path: ristypes.ASPath{Sequence: slices.Repeat([]int{testASNA}, n-1)},
 				})
 
 				return h.batchFullCh

internal/routewatch/peeringhandler.go

@@ -87,15 +87,20 @@ func (h *PeeringHandler) QueueCapacity() int {
 // than minPathLengthForPeering are ignored as they cannot contain valid
 // peering information.
 func (h *PeeringHandler) HandleMessage(msg *ristypes.RISMessage) {
+	// Peerings are between neighbours in the path's sequence only: the
+	// members of an AS set that ends the path are not neighbours of each
+	// other or of the AS before them.
+	sequence := msg.Path.Sequence
+
 	// Skip if no AS path or only one AS
-	if len(msg.Path) < minPathLengthForPeering {
+	if len(sequence) < minPathLengthForPeering {
 		return
 	}
 
 	timestamp := msg.ParsedTimestamp
 
 	// Encode AS path as JSON for use as map key
-	pathJSON, err := json.Marshal(msg.Path)
+	pathJSON, err := json.Marshal(sequence)
 	if err != nil {
 		h.logger.Error("Failed to encode AS path", "error", err)
 

internal/routewatch/peeringhandler_internal_test.go

@@ -2,6 +2,9 @@ package routewatch
 
 import (
 	"encoding/json"
+	"fmt"
+	"maps"
+	"slices"
 	"strconv"
 	"sync"
 	"testing"
@@ -16,6 +19,7 @@ const (
 	testASNA = 64500
 	testASNB = 64501
 	testASNC = 64502
+	testASND = 64503
 )
 
 // recordingStore wraps mockStore to count every RecordPeering call, so a
@@ -64,7 +68,7 @@ func snapshot(h *PeeringHandler) (int, int) {
 func pathKey(t *testing.T, asns ...int) string {
 	t.Helper()
 
-	b, err := json.Marshal(ristypes.ASPath(asns))
+	b, err := json.Marshal(asns)
 	if err != nil {
 		t.Fatalf("failed to marshal path: %v", err)
 	}
@@ -74,11 +78,80 @@ func pathKey(t *testing.T, asns ...int) string {
 
 func handle(h *PeeringHandler, ts time.Time, asns ...int) {
 	h.HandleMessage(&ristypes.RISMessage{
-		Path:            ristypes.ASPath(asns),
+		Path:            ristypes.ASPath{Sequence: asns},
 		ParsedTimestamp: ts,
 	})
 }
 
+// decodePath decodes an AS path from the JSON the feed writes for it, in which
+// an AS set is an array inside the path: decodePath(t, 1, 2, []int{3, 4})
+// decodes [1, 2, [3, 4]].
+func decodePath(t *testing.T, elements ...any) ristypes.ASPath {
+	t.Helper()
+
+	data, err := json.Marshal(elements)
+	if err != nil {
+		t.Fatalf("failed to marshal path: %v", err)
+	}
+
+	var path ristypes.ASPath
+
+	err = json.Unmarshal(data, &path)
+	if err != nil {
+		t.Fatalf("failed to decode path %s: %v", data, err)
+	}
+
+	return path
+}
+
+// TestPeeringHandlerLeavesATrailingASSetOutOfThePeerings handles AS paths that
+// end in an AS set. The members of a set are not neighbours of each other or of
+// the AS before the set, so a set of several members is in no peering; a set of
+// one member counts as that AS.
+func TestPeeringHandlerLeavesATrailingASSetOutOfThePeerings(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		path []any
+		// The peerings recorded, keyed as the mock store keys them.
+		wantPeerings []string
+	}{
+		{
+			name:         "a set of several members",
+			path:         []any{testASNA, testASNB, []int{testASNC, testASND}},
+			wantPeerings: []string{fmt.Sprintf("%d_%d", testASNA, testASNB)},
+		},
+		{
+			name: "a set of one member",
+			path: []any{testASNA, testASNB, []int{testASNC}},
+			wantPeerings: []string{
+				fmt.Sprintf("%d_%d", testASNA, testASNB),
+				fmt.Sprintf("%d_%d", testASNB, testASNC),
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			store := newMockStore()
+			h := newTestHandler(store)
+			h.HandleMessage(&ristypes.RISMessage{
+				Path:            decodePath(t, tt.path...),
+				ParsedTimestamp: time.Now().UTC(),
+			})
+			h.ProcessPeeringsNow()
+
+			got := slices.Sorted(maps.Keys(store.Peerings))
+			if !slices.Equal(got, tt.wantPeerings) {
+				t.Errorf("peerings recorded = %v, want %v", got, tt.wantPeerings)
+			}
+		})
+	}
+}
+
 // TestPeeringHandlerProcessesEachRunAndEmpties verifies that a processing run
 // empties the path map (the swap) and that a path seen again after a run is
 // recorded in the next run too.

internal/routewatch/prefixhandler.go

@@ -73,6 +73,9 @@ type prefixUpdate struct {
 	messageType string
 	timestamp   time.Time
 	path        []int
+	// endsInSet says the path ends in an AS set of several members, so it
+	// gives no origin.
+	endsInSet bool
 }
 
 // NewPrefixHandler creates a new batched prefix tracking handler
@@ -127,11 +130,11 @@ func (h *PrefixHandler) HandleMessage(msg *ristypes.RISMessage) {
 	// Use the pre-parsed timestamp
 	timestamp := msg.ParsedTimestamp
 
-	// Get origin ASN from path (last element)
-	var originASN int
-	if len(msg.Path) > 0 {
-		originASN = msg.Path[len(msg.Path)-1]
-	}
+	originASN := msg.Path.Origin()
+
+	// The stored and shown AS path lists the members of an AS set that ends
+	// the path after the rest of it.
+	path := slices.Concat(msg.Path.Sequence, msg.Path.Set)
 
 	h.mu.Lock()
 	defer h.mu.Unlock()
@@ -169,7 +172,8 @@ func (h *PrefixHandler) HandleMessage(msg *ristypes.RISMessage) {
 				peer:        msg.Peer,
 				messageType: "announcement",
 				timestamp:   timestamp,
-				path:        msg.Path,
+				path:        path,
+				endsInSet:   len(msg.Path.Set) > 0,
 			})
 			// Record announcement in metrics
 			if h.metrics != nil {
@@ -297,7 +301,11 @@ func (h *PrefixHandler) flushBatch() {
 			prefixesToUpdate[update.prefix] = update.timestamp
 		}
 
-		if update.messageType == "announcement" && update.originASN > 0 {
+		// An announcement is stored when its path gives an origin, or when it
+		// ends in an AS set of several members: that route is stored with
+		// origin 0 (none). An announcement with an empty path is not stored.
+		if update.messageType == "announcement" &&
+			(update.originASN > 0 || update.endsInSet) {
 			// Create live route for batch upsert
 			route := h.createLiveRoute(update)
 			if route != nil {

internal/routewatch/prefixhandler_internal_test.go

@@ -40,7 +40,7 @@ func TestPrefixHandlerStoresPrefixesTheIPLookupFinds(t *testing.T) {
 	ts := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
 	h.HandleMessage(&ristypes.RISMessage{
 		Peer:            testPeerIP,
-		Path:            ristypes.ASPath{testASNA, testASNB},
+		Path:            ristypes.ASPath{Sequence: []int{testASNA, testASNB}},
 		ParsedTimestamp: ts,
 		Announcements: []ristypes.RISAnnouncement{{
 			NextHop:  testPeerIP,
@@ -99,7 +99,7 @@ func TestPrefixHandlerAppliesEachPeersLastUpdateInABatch(t *testing.T) {
 	announce := func(peer string) *ristypes.RISMessage {
 		return &ristypes.RISMessage{
 			Peer:            peer,
-			Path:            ristypes.ASPath{testASNA, testASNB},
+			Path:            ristypes.ASPath{Sequence: []int{testASNA, testASNB}},
 			ParsedTimestamp: ts,
 			Announcements: []ristypes.RISAnnouncement{
 				{NextHop: peer, Prefixes: []string{prefix}},
@@ -216,7 +216,7 @@ func TestPrefixHandlerKeepsOneRoutePerPrefixAndPeer(t *testing.T) {
 		// One message that announces otherPrefix with origin AS testASNB and
 		// withdraws prefix.
 		announceOtherAndWithdraw := announce(
-			ristypes.ASPath{testASNA, testASNB}, otherPrefix)
+			ristypes.ASPath{Sequence: []int{testASNA, testASNB}}, otherPrefix)
 		announceOtherAndWithdraw.Withdrawals = []string{prefix}
 
 		tests := []struct {
@@ -230,8 +230,8 @@ func TestPrefixHandlerKeepsOneRoutePerPrefixAndPeer(t *testing.T) {
 			{
 				name: "the peer announces the prefix with a new origin AS",
 				batches: [][]*ristypes.RISMessage{
-					{announce(ristypes.ASPath{testASNA}, prefix)},
-					{announce(ristypes.ASPath{testASNA, testASNB}, prefix)},
+					{announce(ristypes.ASPath{Sequence: []int{testASNA}}, prefix)},
+					{announce(ristypes.ASPath{Sequence: []int{testASNA, testASNB}}, prefix)},
 				},
 				wantOrigins: map[string]int{prefix: testASNB},
 			},
@@ -239,7 +239,7 @@ func TestPrefixHandlerKeepsOneRoutePerPrefixAndPeer(t *testing.T) {
 				name: "one message announces a prefix with another origin AS " +
 					"and withdraws the prefix",
 				batches: [][]*ristypes.RISMessage{
-					{announce(ristypes.ASPath{testASNA}, prefix)},
+					{announce(ristypes.ASPath{Sequence: []int{testASNA}}, prefix)},
 					{announceOtherAndWithdraw},
 				},
 				wantOrigins: map[string]int{otherPrefix: testASNB},
@@ -264,6 +264,70 @@ func TestPrefixHandlerKeepsOneRoutePerPrefixAndPeer(t *testing.T) {
 	}
 }
 
+// TestPrefixHandlerStoresNoOriginForAPathEndingInASet announces a prefix with
+// AS paths that end in an AS set through the prefix handler into a real
+// database. Any member of a set of several may be the origin, so the route is
+// stored with origin 0 (none); a set of one member counts as that AS. The
+// stored AS path lists the set's members after the rest of the path.
+func TestPrefixHandlerStoresNoOriginForAPathEndingInASet(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name       string
+		path       []any
+		wantOrigin int
+		wantPath   []int
+	}{
+		{
+			name:     "a set of several members",
+			path:     []any{testASNA, testASNB, []int{testASNC, testASND}},
+			wantPath: []int{testASNA, testASNB, testASNC, testASND},
+		},
+		{
+			name:       "a set of one member",
+			path:       []any{testASNA, testASNB, []int{testASNC}},
+			wantOrigin: testASNC,
+			wantPath:   []int{testASNA, testASNB, testASNC},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			msg := peerAnnouncement(testPeerIP, testV4Prefix)
+			msg.Path = decodePath(t, tt.path...)
+			db := handleBatches(t, [][]*ristypes.RISMessage{{msg}})
+
+			routes, _, err := db.GetPrefixDetailsContext(
+				context.Background(), testV4Prefix)
+			if err != nil {
+				t.Fatalf("GetPrefixDetailsContext(%s): %v", testV4Prefix, err)
+			}
+
+			if len(routes) != 1 || routes[0].OriginASN != tt.wantOrigin ||
+				!slices.Equal(routes[0].ASPath, tt.wantPath) {
+				t.Errorf("live routes for %s = %+v, "+
+					"want one with origin AS%d and AS path %v",
+					testV4Prefix, routes, tt.wantOrigin, tt.wantPath)
+			}
+		})
+	}
+}
+
+// TestPrefixHandlerDoesNotStoreAnAnnouncementWithAnEmptyPath announces a
+// prefix with an empty AS path, which gives no origin and does not end in an
+// AS set, so no live route is stored.
+func TestPrefixHandlerDoesNotStoreAnAnnouncementWithAnEmptyPath(t *testing.T) {
+	t.Parallel()
+
+	msg := peerAnnouncement(testPeerIP, testV4Prefix)
+	msg.Path = ristypes.ASPath{}
+	db := handleBatches(t, [][]*ristypes.RISMessage{{msg}})
+
+	assertPeers(t, db, map[string][]string{testV4Prefix: nil})
+}
+
 // TestStateMessagesGoToThePrefixHandlerNotThePeerHandler checks that STATE
 // messages go to the prefix handler, which acts on a down, and not to the peer
 // handler, which would record a peer whose session never comes up as active.
@@ -540,7 +604,7 @@ func peerAnnouncement(peer string, prefixes ...string) *ristypes.RISMessage {
 	return &ristypes.RISMessage{
 		Type:            ristypes.MessageTypeUpdate,
 		Peer:            peer,
-		Path:            ristypes.ASPath{testASNA, testASNB},
+		Path:            ristypes.ASPath{Sequence: []int{testASNA, testASNB}},
 		ParsedTimestamp: time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC),
 		Announcements: []ristypes.RISAnnouncement{
 			{NextHop: peer, Prefixes: prefixes},

internal/server/handlers_internal_test.go

@@ -331,6 +331,63 @@ func TestPrefixDetailShowsOriginNames(t *testing.T) {
 	}
 }
 
+// TestPagesSayOriginZeroIsNoKnownOrigin stores a route with origin 0, as the
+// prefix handler stores a route whose AS path ends in an AS set of several
+// members, and checks that the prefix page and the prefix length page say it
+// has no known origin, without a link to AS0 or the description of the
+// reserved AS 0 (https://git.eeqj.de/sneak/routewatch/issues/75).
+func TestPagesSayOriginZeroIsNoKnownOrigin(t *testing.T) {
+	t.Parallel()
+
+	db, err := database.New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("database.New: %v", err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	err = db.UpsertLiveRouteBatch([]*database.LiveRoute{{
+		ID: uuid.New(), Prefix: testPrefixV4, MaskLength: 24, IPVersion: 4,
+		OriginASN: 0, PeerIP: testPeerV4, ASPath: []int{64500, 64501, 64502},
+		NextHop: testPeerV4, LastUpdated: time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC),
+	}})
+	if err != nil {
+		t.Fatalf("UpsertLiveRouteBatch: %v", err)
+	}
+
+	reserved, ok := asinfo.Get(0)
+	if !ok {
+		t.Fatal("AS0 is not in the AS info data")
+	}
+
+	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	for _, path := range []string{"/prefix/" + testPrefixV4, "/prefixlength/24"} {
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, path, nil))
+
+		if rec.Code != http.StatusOK {
+			t.Fatalf("%s: status %d, want %d; body %s",
+				path, rec.Code, http.StatusOK, rec.Body)
+		}
+
+		page := rec.Body.String()
+
+		if !strings.Contains(page, "No known origin") {
+			t.Errorf("%s does not say the route has no known origin", path)
+		}
+
+		if strings.Contains(page, `href="/as/0"`) {
+			t.Errorf("%s links to AS0", path)
+		}
+
+		if strings.Contains(page, html.EscapeString(reserved.Description)) {
+			t.Errorf("%s shows AS0's description %q", path, reserved.Description)
+		}
+	}
+}
+
 // shortRequestDeadline is the deadline the tests below give a request. The
 // server's 30-second limit and the stats handlers' 4-second limit inherit it,
 // so the tests do not wait for either.

internal/templates/prefix_detail.html

@@ -281,9 +281,13 @@
             <div class="origin-list">
                 {{range .Origins}}
                 <div class="origin-item">
+                    {{if .ASN}}
                     <a href="/as/{{.ASN}}" class="as-link">AS{{.ASN}}</a>
                     {{if .Handle}} ({{.Handle}}){{end}}
                     {{if .Description}} {{.Description}}{{end}}
+                    {{else}}
+                    No known origin
+                    {{end}}
                     <span style="color: #7f8c8d; margin-left: 10px;">{{.PeerCount}} peer{{if ne .PeerCount 1}}s{{end}}</span>
                 </div>
                 {{end}}
@@ -312,7 +316,11 @@
                     {{range .Routes}}
                     <tr>
                         <td>
+                            {{if .OriginASN}}
                             <a href="/as/{{.OriginASN}}" class="as-link">AS{{.OriginASN}}</a>
+                            {{else}}
+                            No known origin
+                            {{end}}
                         </td>
                         <td class="peer-ip">{{.PeerIP}}</td>
                         <td class="as-path">{{range $i, $as := .ASPathWithHandle}}{{if $i}} → {{end}}<a href="/as/{{$as.ASN}}" class="as-link">{{if $as.Handle}}{{$as.Handle}}{{else}}AS{{$as.ASN}}{{end}}</a>{{end}}</td>

internal/templates/prefix_length.html

@@ -172,9 +172,13 @@
                 <td><a href="{{ .Prefix | prefixURL }}" class="prefix-link">{{ .Prefix }}</a></td>
                 <td class="age">{{ .Age }}</td>
                 <td>
+                    {{ if .OriginASN }}
                     <a href="/as/{{ .OriginASN }}" class="as-link">
                         AS{{ .OriginASN }}{{ if .OriginASDescription }} ({{ .OriginASDescription }}){{ end }}
                     </a>
+                    {{ else }}
+                    No known origin
+                    {{ end }}
                 </td>
             </tr>
             {{ end }}