Make the home page's AS name search work (closes #151)

The AS Name Search card on the home page said the search was coming
soon. It now asks the new GET /api/v1/search/as?q=<text>, which
searches the AS list built into asinfo, and lists the matches as links
to their AS pages. An empty q answers 400. asinfo.Search now ignores
case and returns its matches in AS number order.

A match can be an AS that the database does not hold yet. Its AS page
and /api/v1/as/{asn} now answer with its handle and description from
asinfo and no prefixes, instead of 404. Empty prefix lists in that JSON
answer are [] rather than null.

Model: opus-5-5

internal/server/handlers.go

@@ -56,10 +56,18 @@ const (
 // Error messages an answer sends, in place of the error behind it where there
 // is one.
 const (
-	invalidPrefixMessage   = "Invalid prefix"
-	hostNotResolvedMessage = "could not resolve host name"
-	hostNotPublicMessage   = "host name has no public address"
-	tooManyTargetsMessage  = "Too many addresses or host names"
+	invalidPrefixMessage      = "Invalid prefix"
+	hostNotResolvedMessage    = "could not resolve host name"
+	hostNotPublicMessage      = "host name has no public address"
+	tooManyTargetsMessage     = "Too many addresses or host names"
+	searchQueryMissingMessage = "Missing search query"
+)
+
+// The AS name search reads the text it looks for from the URL query parameter
+// asSearchQueryParam, and answers with at most maxASSearchResults matches.
+const (
+	asSearchQueryParam = "q"
+	maxASSearchResults = 50
 )
 
 // IP versions as database.LiveRoute.IPVersion records them.
@@ -1001,11 +1009,12 @@ func (s *Server) handleASDetailJSON() http.HandlerFunc {
 	}
 }
 
-// splitRoutesByIPVersion groups routes into the IPv4 and the IPv6 ones.
+// splitRoutesByIPVersion groups routes into the IPv4 and the IPv6 ones. Neither
+// group is nil, so that a JSON answer holds [] for an empty one and not null.
 func splitRoutesByIPVersion(
 	routes []database.LiveRoute,
 ) ([]database.LiveRoute, []database.LiveRoute) {
-	var ipv4Routes, ipv6Routes []database.LiveRoute
+	ipv4Routes, ipv6Routes := []database.LiveRoute{}, []database.LiveRoute{}
 
 	for _, route := range routes {
 		if route.IPVersion == ipVersionV4 {
@@ -1105,6 +1114,46 @@ func (s *Server) handlePrefixDetailJSON() http.HandlerFunc {
 	}
 }
 
+// ASSearchResponse is the answer to an AS name search: the text searched for,
+// the number of ASes that match it, and the first maxASSearchResults of them in
+// AS number order.
+type ASSearchResponse struct {
+	Query   string        `json:"query"`
+	Total   int           `json:"total"`
+	Results []asinfo.Info `json:"results"`
+}
+
+// handleASSearch returns a handler that searches the AS list built into
+// asinfo for the text in the q parameter, without its leading and trailing
+// spaces. It answers 400 when no text is left.
+func (s *Server) handleASSearch() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		query := strings.TrimSpace(r.URL.Query().Get(asSearchQueryParam))
+		if query == "" {
+			s.writeJSONError(w, http.StatusBadRequest, searchQueryMissingMessage)
+
+			return
+		}
+
+		matches := asinfo.Search(query)
+
+		// results is an empty list rather than nil when nothing matches, so
+		// that the answer holds [] and not null.
+		shown := min(len(matches), maxASSearchResults)
+		results := make([]asinfo.Info, 0, shown)
+		results = append(results, matches[:shown]...)
+
+		err := writeJSONSuccess(w, ASSearchResponse{
+			Query:   query,
+			Total:   len(matches),
+			Results: results,
+		})
+		if err != nil {
+			s.logger.Error("Failed to encode AS search results", "error", err)
+		}
+	}
+}
+
 // handleASDetail returns a handler that serves the AS detail HTML page
 func (s *Server) handleASDetail() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {