Add best-effort geolocation to the IP lookup from geojs and DB-IP City Lite (closes #239)

Every IP lookup result gains `geo`. One request to geojs carries all uncached addresses of a lookup, within 1 second. On a timeout, an error or an answer with no location, the lookup reads DB-IP City Lite, downloaded monthly into the state directory. Geojs answers stay in memory, at most 250,000, and in `cache.db` for 7 days. The home page footer credits DB-IP.

Judgement call: a reserved address goes to neither source, and its `geo` is null.
Judgement call: `updated` for a DB-IP answer is when the copy was downloaded.
Deviation: the cache is SQLite, by sneak's words, not the JSON file the standing rule asks for.

Model: opus-5-5

internal/server/handlers.go

@@ -17,6 +17,7 @@ import (
 
 	"git.eeqj.de/sneak/routewatch/internal/bogon"
 	"git.eeqj.de/sneak/routewatch/internal/database"
+	"git.eeqj.de/sneak/routewatch/internal/geo"
 	"git.eeqj.de/sneak/routewatch/internal/iplist"
 	"git.eeqj.de/sneak/routewatch/internal/metrics"
 	"git.eeqj.de/sneak/routewatch/internal/ristypes"
@@ -764,9 +765,9 @@ type IPLookupResponse struct {
 }
 
 // IPLookupResult is the answer for one address: its PTR names, its flags, its
-// live route and that route's AS, and the IP lists that contain it. Every
-// result has every field. The fields of IPInfo are null when the address has
-// no live route.
+// live route and that route's AS, the IP lists that contain it, and where it
+// is. Every result has every field. The fields of IPInfo are null when the
+// address has no live route.
 //
 //nolint:tagliatelle // snake_case keys, as the Go style guide asks
 type IPLookupResult struct {
@@ -784,6 +785,9 @@ type IPLookupResult struct {
 
 	// IPLists has one entry for each IP list the address is on.
 	IPLists []iplist.Listing `json:"ip_lists"`
+
+	// Geo is where the address is. It is nil when no source answers.
+	Geo *geo.Location `json:"geo"`
 }
 
 // IPLookupFlags are the yes-or-no facts about an address. Every result has
@@ -842,6 +846,8 @@ func (s *Server) handleIPInfo() http.HandlerFunc {
 			return
 		}
 
+		locations := s.geoLocations(ctx, ipsToLookup)
+
 		// Track ASNs that need WHOIS refresh
 		refreshASNs := make(map[int]bool)
 
@@ -877,7 +883,9 @@ func (s *Server) handleIPInfo() http.HandlerFunc {
 				return
 			}
 
-			response.Results = append(response.Results, s.ipLookupResult(ip, ptrs, ipInfo))
+			result := s.ipLookupResult(ip, ptrs, ipInfo)
+			result.Geo = locations[ip]
+			response.Results = append(response.Results, result)
 
 			if ipInfo.NeedsWHOISRefresh {
 				refreshASNs[*ipInfo.ASN] = true
@@ -1035,6 +1043,45 @@ func ipLookupFlags(ip string, listings []iplist.Listing) IPLookupFlags {
 	}
 }
 
+// geoLocations returns where ips are, by address. An address that does not
+// parse has no entry. Nor has a reserved one, which is sent to no outside
+// source and has no location.
+func (s *Server) geoLocations(
+	ctx context.Context, ips []string,
+) map[string]*geo.Location {
+	if s.geoLocator == nil {
+		return nil
+	}
+
+	var (
+		kept  []string
+		addrs []netip.Addr
+	)
+
+	for _, ip := range ips {
+		addr, err := netip.ParseAddr(ip)
+		if err != nil || isBogon(ip) {
+			continue
+		}
+
+		kept = append(kept, ip)
+		addrs = append(addrs, addr)
+	}
+
+	if len(addrs) == 0 {
+		return nil
+	}
+
+	answers := s.geoLocator.Lookup(ctx, addrs)
+	locations := make(map[string]*geo.Location, len(kept))
+
+	for i, ip := range kept {
+		locations[ip] = answers[i]
+	}
+
+	return locations
+}
+
 // isBogon says whether the address ip is reserved, as package bogon tells.
 func isBogon(ip string) bool {
 	addr, err := netip.ParseAddr(ip)