Add the HTTP hardening the policy requires before 1.0 (closes #108)

Every answer carries the six security headers REPO_POLICIES.md lists.
The Content-Security-Policy allows inline content only with a nonce made
for that answer; the pages put it on their style and script blocks and
drop their four style attributes.

The request log and /ip/ take a forwarded address only from a proxy
listed in TRUSTED_PROXIES, which stops the start when set but invalid:
the last X-Forwarded-For entry that is not a trusted proxy. X-Real-IP
and True-Client-IP are no longer read.

The JSON routes and the health check send fixed messages in place of
database, parser and resolver errors, and log the detail.

Model: opus-5-5

internal/server/handlers.go

@@ -41,6 +41,12 @@ const (
 	jsonStatusError = "error"
 )
 
+// Error messages an answer sends in place of the error that caused it.
+const (
+	invalidPrefixMessage   = "Invalid prefix"
+	hostNotResolvedMessage = "could not resolve host name"
+)
+
 // IP versions as database.LiveRoute.IPVersion records them.
 const (
 	ipVersionV4 = 4
@@ -68,7 +74,8 @@ func (s *Server) handleHealthCheck() http.HandlerFunc {
 		// Check database connectivity with lightweight ping
 		err := s.db.Ping(ctx)
 		if err != nil {
-			checks["database"] = "error: " + err.Error()
+			s.logger.Error("Health check database ping failed", "error", err)
+			checks["database"] = jsonStatusError
 			healthy = false
 		} else {
 			checks["database"] = "ok"
@@ -108,12 +115,12 @@ func (s *Server) handleHealthCheck() http.HandlerFunc {
 
 // handleIndex returns a handler that serves the home page.
 func (s *Server) handleIndex() http.HandlerFunc {
-	return func(w http.ResponseWriter, _ *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "text/html; charset=utf-8")
 
 		tmpl := templates.IndexTemplate()
 
-		err := tmpl.Execute(w, nil)
+		err := tmpl.Execute(w, pageData{CSPNonce: cspNonce(r.Context())})
 		if err != nil {
 			s.logger.Error("Failed to render index template", "error", err)
 			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
@@ -121,6 +128,12 @@ func (s *Server) handleIndex() http.HandlerFunc {
 	}
 }
 
+// pageData is what the pages that show no data are rendered with: the nonce
+// their script and style blocks carry.
+type pageData struct {
+	CSPNonce string
+}
+
 // writeJSONError writes a standardized JSON error response with the given
 // status code and error message.
 func (s *Server) writeJSONError(w http.ResponseWriter, statusCode int, message string) {
@@ -251,7 +264,7 @@ func (s *Server) handleStatusJSON() http.HandlerFunc {
 
 		if err != nil {
 			s.logger.Error("Failed to get database stats", "error", err)
-			s.writeJSONError(w, http.StatusInternalServerError, err.Error())
+			s.writeJSONError(w, http.StatusInternalServerError, internalErrorMessage)
 
 			return
 		}
@@ -541,7 +554,7 @@ func (s *Server) handleStats() http.HandlerFunc {
 
 		if err != nil {
 			s.logger.Error("Failed to get database stats", "error", err)
-			s.writeJSONError(w, http.StatusInternalServerError, err.Error())
+			s.writeJSONError(w, http.StatusInternalServerError, internalErrorMessage)
 
 			return
 		}
@@ -622,12 +635,12 @@ func (s *Server) statsResponse(
 // handleStatusHTML returns a handler that serves the HTML status page,
 // which displays real-time statistics fetched via JavaScript.
 func (s *Server) handleStatusHTML() http.HandlerFunc {
-	return func(w http.ResponseWriter, _ *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "text/html; charset=utf-8")
 
 		tmpl := templates.StatusTemplate()
 
-		err := tmpl.Execute(w, nil)
+		err := tmpl.Execute(w, pageData{CSPNonce: cspNonce(r.Context())})
 		if err != nil {
 			s.logger.Error("Failed to render template", "error", err)
 			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
@@ -667,7 +680,7 @@ func (s *Server) handleIPInfo() http.HandlerFunc {
 		}
 
 		// Collect all IPs to look up
-		ipsToLookup, resolveErrors := resolveLookupTargets(ctx, target)
+		ipsToLookup, resolveErrors := s.resolveLookupTargets(ctx, target)
 		if deadlinePassed(ctx) {
 			s.writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
 
@@ -695,7 +708,14 @@ func (s *Server) handleIPInfo() http.HandlerFunc {
 			}
 
 			if err != nil {
-				response.Errors = append(response.Errors, ip+": "+err.Error())
+				message := err.Error()
+				if !errors.Is(err, database.ErrNoRoute) &&
+					!errors.Is(err, database.ErrInvalidIP) {
+					s.logger.Error("Failed to look up IP", "ip", ip, "error", err)
+					message = internalErrorMessage
+				}
+
+				response.Errors = append(response.Errors, ip+": "+message)
 
 				continue
 			}
@@ -766,9 +786,12 @@ func (s *Server) queueWHOISRefresh(asns map[int]bool) {
 
 // resolveLookupTargets splits a comma-separated list of IP addresses and
 // hostnames and returns the IP addresses to look up, resolving each hostname.
-// A hostname that does not resolve is reported in the returned errors instead.
+// A hostname that does not resolve is reported in the returned errors instead,
+// with the resolver's own error only in the log, since it names the DNS server.
 // It stops once ctx's deadline has passed; the caller then answers 504.
-func resolveLookupTargets(ctx context.Context, target string) ([]string, []string) {
+func (s *Server) resolveLookupTargets(
+	ctx context.Context, target string,
+) ([]string, []string) {
 	var ipsToLookup, resolveErrors []string
 
 	for t := range strings.SplitSeq(target, ",") {
@@ -791,7 +814,8 @@ func resolveLookupTargets(ctx context.Context, target string) ([]string, []strin
 		}
 
 		if err != nil {
-			resolveErrors = append(resolveErrors, t+": "+err.Error())
+			s.logger.Warn("Host name lookup failed", "host", t, "error", err)
+			resolveErrors = append(resolveErrors, t+": "+hostNotResolvedMessage)
 
 			continue
 		}
@@ -819,7 +843,7 @@ func lookupPTRNames(ctx context.Context, ip string) []string {
 }
 
 // extractClientIP extracts the client IP from the request.
-// Works with chi's RealIP middleware which sets RemoteAddr.
+// Works with RealIPMiddleware, which sets RemoteAddr.
 func extractClientIP(r *http.Request) string {
 	// RemoteAddr is in the form "IP:port" or just "IP" for unix sockets
 	host, _, err := net.SplitHostPort(r.RemoteAddr)
@@ -854,7 +878,9 @@ func (s *Server) handleASDetailJSON() http.HandlerFunc {
 			if errors.Is(err, database.ErrNoRoute) {
 				s.writeJSONError(w, http.StatusNotFound, err.Error())
 			} else {
-				s.writeJSONError(w, http.StatusInternalServerError, err.Error())
+				s.logger.Error("Failed to get AS details", "asn", asn, "error", err)
+				s.writeJSONError(w, http.StatusInternalServerError,
+					internalErrorMessage)
 			}
 
 			return
@@ -933,7 +959,7 @@ func (s *Server) handlePrefixDetailJSON() http.HandlerFunc {
 		// tables store, so that any valid way of writing it finds the route.
 		parsed, err := netip.ParsePrefix(prefixParam + "/" + lenParam)
 		if err != nil {
-			s.writeJSONError(w, http.StatusBadRequest, err.Error())
+			s.writeJSONError(w, http.StatusBadRequest, invalidPrefixMessage)
 
 			return
 		}
@@ -951,7 +977,10 @@ func (s *Server) handlePrefixDetailJSON() http.HandlerFunc {
 			if errors.Is(err, database.ErrNoRoute) {
 				s.writeJSONError(w, http.StatusNotFound, err.Error())
 			} else {
-				s.writeJSONError(w, http.StatusInternalServerError, err.Error())
+				s.logger.Error("Failed to get prefix details",
+					"prefix", prefix, "error", err)
+				s.writeJSONError(w, http.StatusInternalServerError,
+					internalErrorMessage)
 			}
 
 			return
@@ -1002,7 +1031,7 @@ func (s *Server) handleASDetail() http.HandlerFunc {
 				http.Error(w, "AS not found", http.StatusNotFound)
 			} else {
 				s.logger.Error("Failed to get AS details", "error", err)
-				http.Error(w, "Internal server error", http.StatusInternalServerError)
+				http.Error(w, internalErrorMessage, http.StatusInternalServerError)
 			}
 
 			return
@@ -1039,6 +1068,7 @@ func (s *Server) handleASDetail() http.HandlerFunc {
 			IPv6Count    int
 			Peers        []database.ASPeer
 			PeerCount    int
+			CSPNonce     string
 		}{
 			ASN:          asInfo,
 			IPv4Prefixes: ipv4Prefixes,
@@ -1048,6 +1078,7 @@ func (s *Server) handleASDetail() http.HandlerFunc {
 			IPv6Count:    len(ipv6Prefixes),
 			Peers:        peers,
 			PeerCount:    len(peers),
+			CSPNonce:     cspNonce(r.Context()),
 		}
 
 		// Check if context is still valid before writing response
@@ -1085,7 +1116,7 @@ func (s *Server) handlePrefixDetail() http.HandlerFunc {
 		// tables store, so that any valid way of writing it finds the route.
 		parsed, err := netip.ParsePrefix(prefixParam + "/" + lenParam)
 		if err != nil {
-			http.Error(w, "Invalid prefix", http.StatusBadRequest)
+			http.Error(w, invalidPrefixMessage, http.StatusBadRequest)
 
 			return
 		}
@@ -1104,7 +1135,7 @@ func (s *Server) handlePrefixDetail() http.HandlerFunc {
 				http.Error(w, "Prefix not found", http.StatusNotFound)
 			} else {
 				s.logger.Error("Failed to get prefix details", "error", err)
-				http.Error(w, "Internal server error", http.StatusInternalServerError)
+				http.Error(w, internalErrorMessage, http.StatusInternalServerError)
 			}
 
 			return
@@ -1131,6 +1162,7 @@ func (s *Server) handlePrefixDetail() http.HandlerFunc {
 			Origins     []*ASNInfo
 			PeerCount   int
 			OriginCount int
+			CSPNonce    string
 		}{
 			Prefix:      prefix,
 			MaskLength:  maskLength,
@@ -1139,6 +1171,7 @@ func (s *Server) handlePrefixDetail() http.HandlerFunc {
 			Origins:     origins,
 			PeerCount:   len(routes),
 			OriginCount: len(origins),
+			CSPNonce:    cspNonce(r.Context()),
 		}
 
 		// Check if context is still valid before writing response
@@ -1303,7 +1336,7 @@ func (s *Server) prefixLengthHandler(ipVersion, maxMaskLength int) http.HandlerF
 
 		if err != nil {
 			s.logger.Error("Failed to get prefixes by length", "error", err)
-			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			http.Error(w, internalErrorMessage, http.StatusInternalServerError)
 
 			return
 		}
@@ -1324,6 +1357,7 @@ func (s *Server) prefixLengthHandler(ipVersion, maxMaskLength int) http.HandlerF
 			"IPVersion":  ipVersion,
 			"Prefixes":   prefixesWithASDescriptions(prefixes),
 			"Count":      len(prefixes),
+			"CSPNonce":   cspNonce(r.Context()),
 		}
 
 		// Check if context is still valid before writing response