resetting attempts after 1 hour

beedb-gateway/src/main/java/com/memcache/gateway/api/KvController.java

@@ -69,8 +69,11 @@ private ResponseEntity<String> rateLimited(HttpServletRequest request) {
             return null;
         }
         LOGGER.warn("rate limit hit by {} ({} writes/hour)", client, rateLimiter.maxWritesPerHour());
+        // Retry-After is when this client's window really ends, not a flat hour: a visitor who
+        // hit the limit 50 minutes into their window only has 10 minutes to wait.
+        long retryAfter = Math.max(1, rateLimiter.resetInSeconds(client));
         return ResponseEntity.status(HttpStatus.TOO_MANY_REQUESTS)
-                .header("Retry-After", "3600")
+                .header("Retry-After", String.valueOf(retryAfter))
                 .body("write limit reached: " + rateLimiter.maxWritesPerHour()
                       + " writes per hour. This is a shared demo.");
     }

beedb-gateway/src/main/java/com/memcache/gateway/api/QuotaController.java

@@ -10,10 +10,6 @@
 
 import com.memcache.gateway.kv.WriteRateLimiter;
 
-/**
- * How many writes this client has left this hour, so the page shows the server's real count
- * instead of guessing
- */
 @RestController
 @RequestMapping("/api")
 public class QuotaController {
@@ -25,9 +21,10 @@ public QuotaController(WriteRateLimiter rateLimiter) {
     }
 
     @GetMapping("/quota")
-    public Map<String, Integer> quota(HttpServletRequest request) {
+    public Map<String, Long> quota(HttpServletRequest request) {
         String client = request.getRemoteAddr();
-        return Map.of("remaining", rateLimiter.remaining(client),
-                      "limit", rateLimiter.maxWritesPerHour());
+        return Map.of("remaining", (long) rateLimiter.remaining(client),
+                      "limit", (long) rateLimiter.maxWritesPerHour(),
+                      "resetInSeconds", rateLimiter.resetInSeconds(client));
     }
 }

beedb-gateway/src/main/java/com/memcache/gateway/kv/WriteRateLimiter.java

@@ -83,6 +83,14 @@ public int remaining(String clientId) {
         return Math.max(0, maxWritesPerHour - used);
     }
 
+    public long resetInSeconds(String clientId) {
+        return writesPerClient.policy().expireAfterWrite()
+                .flatMap(window -> window.ageOf(clientId)
+                        .map(age -> window.getExpiresAfter().minus(age)))
+                .map(left -> Math.max(0L, (left.toMillis() + 999) / 1000))
+                .orElse(0L);
+    }
+
     public int maxWritesPerHour() {
         return maxWritesPerHour;
     }