misc: update messages

public/v1/components/responses.yaml

@@ -197,7 +197,7 @@ components:
               value:
                 error:
                   type: too_many_requests
-                  message: Too Many Requests.
+                  message: Too many requests. Please retry in 4 seconds.
     probes200:
       description: |
         A successful request returns status `200 OK` and a body containing a list of all probes currently online and their metadata.

public/v1/spec.yaml

@@ -100,6 +100,9 @@ paths:
           1. Request the measurement to retrieve its status.
           2. If the status is `in-progress`, wait 500 milliseconds and start again at step 1. Note that it's important to wait 500 ms *after* receiving the response rather than using an "every 500ms" interval as for large measurements, the request itself may take a few hundred milliseconds to complete.
           3. If the status is anything **other** than `in-progress`, stop. The measurement is no longer running, and its results are final.
+
+        > **Important**: Do not query the results of a single measurement more often than every 500 milliseconds. Sending more than two
+        requests per second may trigger a rate limit and prevent you from accessing the results for a few seconds.
       responses:
         '200':
           $ref: 'components/responses.yaml#/components/responses/measurement200'

src/lib/rate-limiter/rate-limiter-get.ts

@@ -29,8 +29,11 @@ export const getMeasurementRateLimit = async (ctx: ExtendedContext, next: Next)
 		await rateLimiter.consume(id);
 	} catch (error) {
 		if (error instanceof RateLimiterRes) {
+			const retryAfter = Math.ceil(error.msBeforeNext / 1000);
+			const units = retryAfter === 1 ? 'second' : 'seconds';
+
 			setRateLimitHeaders(ctx, error);
-			throw createHttpError(429, 'Too Many Requests.', { type: 'too_many_requests' });
+			throw createHttpError(429, `Too many requests. Please retry in ${retryAfter} ${units}.`, { type: 'too_many_requests' });
 		}
 
 		throw createHttpError(500);
@@ -40,5 +43,5 @@ export const getMeasurementRateLimit = async (ctx: ExtendedContext, next: Next)
 };
 
 const setRateLimitHeaders = (ctx: ExtendedContext, error: RateLimiterRes) => {
-	ctx.set('Retry-After', `${Math.round(error.msBeforeNext / 1000)}`);
+	ctx.set('Retry-After', `${Math.ceil(error.msBeforeNext / 1000)}`);
 };