Add JSON validation middleware to ensure valid API responses

- Created JSONValidationMiddleware that validates all JSON responses
- Ensures that even on timeout or internal errors, a valid JSON error response is returned
- Applied to all API endpoints including /status.json
- Prevents client-side JSON parse errors when server encounters issues

internal/database/database.go

@@ -1482,6 +1482,7 @@ func (d *Database) GetASPeersContext(ctx context.Context, asn int) ([]ASPeer, er
 		err := rows.Scan(&peer.ASN, &peer.Handle, &peer.Description, &peer.FirstSeen, &peer.LastSeen)
 		if err != nil {
 			d.logger.Error("Failed to scan peer row", "error", err, "asn", asn)
+
 			continue
 		}
 		peers = append(peers, peer)

internal/server/middleware.go

@@ -217,3 +217,68 @@ func TimeoutMiddleware(timeout time.Duration) func(http.Handler) http.Handler {
 		})
 	}
 }
+
+// JSONValidationMiddleware ensures all JSON API responses are valid JSON
+func JSONValidationMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Create a custom response writer to capture the response
+		rw := &responseWriter{
+			ResponseWriter: w,
+			body:           &bytes.Buffer{},
+			statusCode:     http.StatusOK,
+		}
+
+		// Serve the request
+		next.ServeHTTP(rw, r)
+
+		// Check if it's meant to be a JSON response
+		contentType := rw.Header().Get("Content-Type")
+		isJSON := contentType == "application/json" || contentType == ""
+
+		// If it's not JSON or has content, pass through
+		if !isJSON && rw.body.Len() > 0 {
+			w.WriteHeader(rw.statusCode)
+			_, _ = w.Write(rw.body.Bytes())
+
+			return
+		}
+
+		// For JSON responses, validate the JSON
+		if rw.body.Len() > 0 {
+			var testParse interface{}
+			if err := json.Unmarshal(rw.body.Bytes(), &testParse); err == nil {
+				// Valid JSON, write it out
+				w.Header().Set("Content-Type", "application/json")
+				w.WriteHeader(rw.statusCode)
+				_, _ = w.Write(rw.body.Bytes())
+
+				return
+			}
+		}
+
+		// If we get here, either there's no body or invalid JSON
+		// Write a proper error response
+		w.Header().Set("Content-Type", "application/json")
+
+		// Determine appropriate status code
+		statusCode := rw.statusCode
+		if statusCode == http.StatusOK {
+			statusCode = http.StatusInternalServerError
+		}
+		w.WriteHeader(statusCode)
+
+		errorMsg := "Internal server error"
+		if statusCode == http.StatusRequestTimeout {
+			errorMsg = "Request timeout"
+		}
+
+		response := map[string]interface{}{
+			"status": "error",
+			"error": map[string]interface{}{
+				"msg":  errorMsg,
+				"code": statusCode,
+			},
+		}
+		_ = json.NewEncoder(w).Encode(response)
+	})
+}

internal/server/routes.go

@@ -23,7 +23,7 @@ func (s *Server) setupRoutes() {
 	// Routes
 	r.Get("/", s.handleRoot())
 	r.Get("/status", s.handleStatusHTML())
-	r.Get("/status.json", s.handleStatusJSON())
+	r.Get("/status.json", JSONValidationMiddleware(s.handleStatusJSON()).ServeHTTP)
 
 	// AS and prefix detail pages
 	r.Get("/as/{asn}", s.handleASDetail())
@@ -33,6 +33,7 @@ func (s *Server) setupRoutes() {
 
 	// API routes
 	r.Route("/api/v1", func(r chi.Router) {
+		r.Use(JSONValidationMiddleware)
 		r.Get("/stats", s.handleStats())
 		r.Get("/ip/{ip}", s.handleIPLookup())
 		r.Get("/as/{asn}", s.handleASDetailJSON())