Give every IP lookup result the same fields (closes #200)

Every result of /ip/, /ip/{addr} and /api/v1/ip/{ip} now has every
field. A field without a value is null instead of left out, so an
address with no live route has all its route and AS fields set to null.
ptr is an empty list when there are no PTR names.

Two new fields, num_origins and origin_asns, give how many origin ASes
peers carry the netblock with, and which. The routing table's prefix
summary now lists them. asn still names the origin that most peers
carry.

first_seen is null, no longer the zero time, when the database has not
stored the netblock yet.

Model: opus-5-5

README.md

@@ -235,10 +235,15 @@ so each answer's policy names a random nonce made for that answer, and the
 browser applies or runs only the blocks that carry it. The pages therefore use
 no `style` attributes, which a nonce cannot cover.
 
-An origin AS of 0 (`origin_asn` in a route, `asn` and `origin_asns` in an IP
+An origin AS of 0 means the route has no known origin. Its AS path ends in an AS
-lookup, the key `0` in a prefix's `origins`) means the route has no known
+set of several members, any of which may have originated it. The 0 appears in
-origin: its AS path ends in an AS set of several members, any of which may have
+these fields:
-originated it. The pages show such a route as having no known origin.
+
+- `origin_asn` in a route
+- `asn` and `origin_asns` in an IP lookup
+- the key `0` in a prefix's `origins`
+
+The pages show such a route as having no known origin.
 
 ## Blocklists
 

internal/server/handlers_internal_test.go

@@ -1316,6 +1316,9 @@ func TestIPLookupReportsBlocklists(t *testing.T) {
 // jsonNull is how JSON writes a field without a value.
 const jsonNull = "null"
 
+// jsonEmptyList is how JSON writes an empty list.
+const jsonEmptyList = "[]"
+
 // resultFields decodes an IP lookup answer and returns each of its results as
 // its JSON fields.
 func resultFields(t *testing.T, answer []byte) []map[string]json.RawMessage {
@@ -1451,6 +1454,37 @@ func TestIPLookupResultsHaveTheSameFields(t *testing.T) {
 	}
 }
 
+// TestIPLookupOfAnAddressWithoutPTRNamesOrStoredNetblock looks up a routed
+// address that has no PTR names, and whose netblock the database has not
+// stored. Its ptr is an empty list and its first_seen is null. Before the fix
+// ptr was left out, and first_seen was 0001-01-01T00:00:00Z
+// (https://git.eeqj.de/sneak/routewatch/issues/200).
+func TestIPLookupOfAnAddressWithoutPTRNamesOrStoredNetblock(t *testing.T) {
+	t.Parallel()
+
+	s := newServerWithTestRoutes(t)
+	s.resolver = &fakeResolver{}
+
+	path := "/api/v1/ip/" + addrInTestPrefixV4
+
+	results := resultFields(t, get(t, s, path).Body.Bytes())
+	if len(results) != 1 {
+		t.Fatalf("%s: %d results, want 1", path, len(results))
+	}
+
+	want := map[string]string{
+		"ptr":        jsonEmptyList,
+		"first_seen": jsonNull,
+	}
+
+	for name, value := range want {
+		got := string(results[0][name])
+		if got != value {
+			t.Errorf("%s: %s is %s, want %s", path, name, got, value)
+		}
+	}
+}
+
 // TestIPLookupAnswersMayBeCached checks the Cache-Control header of the IP
 // lookup answers. Caches may keep them for the blocklists' shortest interval,
 // and only the caller's own browser may keep the answer about the caller's