Add asn= and prefix= tags from a routewatch instance (closes #204)

SWW_ROUTEWATCH_URL names the instance. The new heuristic routewatch_tags
asks it in the background about each client and tags the request. Answers
are kept in memory for an hour. A request without tags gives the reason in
routewatch_tags_missing, and it is never delayed or refused.

Model: opus-5-5

internal/config/config.go

@@ -466,6 +466,9 @@ var (
 	errNotLAPIURL = errors.New(
 		"is not an http or https URL without a user or a fragment, " +
 			"such as http://172.17.0.1:8080")
+	errNotRouteWatchURL = errors.New(
+		"is not an http or https URL without a user or a fragment, " +
+			"such as https://routewatch.example")
 	errNeedsLAPIKey  = errors.New("the engine answers no request without it")
 	errLAPIKeyUnused = errors.New("it is sent only to the engine at that URL")
 	errAnotherList   = errors.New(
@@ -531,7 +534,7 @@ func FromEnvironment(
 		TagLists:             env.tagLists("SWW_TAG_LISTS"),
 		TagDeny:              env.tags("SWW_TAG_DENY"),
 		TagLimitPercent:      env.tagPercents("SWW_TAG_LIMIT_PERCENT"),
-		RouteWatchURL:        env.listURL("SWW_ROUTEWATCH_URL"),
+		RouteWatchURL:        env.routeWatchURL("SWW_ROUTEWATCH_URL"),
 		ASNBytesPercent:      env.percents("SWW_ASN_BYTES_PERCENT", ParseASN),
 		CountryBytesPercent:  env.percents("SWW_COUNTRY_BYTES_PERCENT", parseCountry),
 		UnknownLimitPercent:  env.percent("SWW_UNKNOWN_LIMIT_PERCENT", "100"),
@@ -1027,6 +1030,22 @@ func (e *environment) crowdSecDecisionsURL(name string) string {
 	return lapi.JoinPath("v1", "decisions").String()
 }
 
+// routeWatchURL reads the setting that is the URL of a routewatch instance,
+// "" while it is unset or empty.
+func (e *environment) routeWatchURL(name string) string {
+	value := e.value(name, "")
+	if value == "" {
+		return ""
+	}
+
+	instance, err := url.Parse(value)
+	if err != nil || !isHTTPURL(instance) {
+		e.check(name, fmt.Errorf("%q %w", value, errNotRouteWatchURL))
+	}
+
+	return value
+}
+
 // lookupSource reads the setting that is where clients are looked up:
 // geojs, file, or off.
 func (e *environment) lookupSource(name, defaultValue string) string {

internal/config/config_test.go

@@ -1450,6 +1450,15 @@ func TestRouteWatchURLAndPrefixTags(t *testing.T) {
 			t.Errorf("%v gave the error %v, want one naming %s", stopped.env, err, stopped.name)
 		}
 	}
+
+	badURL := environment{routeWatchURL: "ftp://routewatch.example"}
+	_, err := config.FromEnvironment(badURL.lookupEnv)
+
+	want := routeWatchURL + `: "ftp://routewatch.example" is not an http or https URL ` +
+		"without a user or a fragment, such as https://routewatch.example"
+	if err == nil || err.Error() != want {
+		t.Errorf("error %v, want %s", err, want)
+	}
 }
 
 func TestTagThatNoRequestCanGetIsToldApartFromOneItCan(t *testing.T) {