beater/api/intake: fix rate limiting (#5518)

* beater/api/intake: fix rate limiting

Copy the batch processor in the closure before
copying, to avoid wrapping it multiple times.

* systemtest: fix rate limiting test

The test was wrong, and only passed because of
the bug that has been fixed. We should be using
up the per-IP event limits on the first two
requests, but weren't taking into account the
burst multiplier (limit x 3).

beater/api/intake/handler.go

@@ -81,6 +81,8 @@ func Handler(handler StreamHandler, requestMetadataFunc RequestMetadataFunc, bat
 			return
 		}
 
+		// copy batchProcessor to avoid updating closure below
+		batchProcessor := batchProcessor
 		if limiter, ok := ratelimit.FromContext(c.Request.Context()); ok {
 			// Apply rate limiting after reading but before processing any events.
 			batchProcessor = modelprocessor.Chained{

beater/api/intake/handler_test.go

@@ -217,6 +217,32 @@ func TestRateLimiting(t *testing.T) {
 	}
 }
 
+func TestRateLimitingRequests(t *testing.T) {
+	// Check that rate limiting across multiple requests is handled correctly.
+	//
+	// ratelimit.ndjson contains 19 events, and we rate limit in batches of 10
+	// events. The burst of 41 should be enough for 2 iterations with one left.
+	limiter := rate.NewLimiter(1, 41)
+	processor := stream.BackendProcessor(config.DefaultConfig())
+	handler := Handler(processor, emptyRequestMetadata, modelprocessor.Nop{})
+
+	data, err := ioutil.ReadFile("../../../testdata/intake-v2/ratelimit.ndjson")
+	require.NoError(t, err)
+	for i := 0; i < 2; i++ {
+		r := httptest.NewRequest("POST", "/", bytes.NewBuffer(data))
+		r = r.WithContext(ratelimit.ContextWithLimiter(r.Context(), limiter))
+		r.Header.Add("Content-Type", "application/x-ndjson")
+
+		w := httptest.NewRecorder()
+		c := request.NewContext()
+		c.Reset(w, r)
+		handler(c)
+		assert.Equal(t, http.StatusAccepted, w.Code)
+	}
+	assert.True(t, limiter.Allow())
+	assert.False(t, limiter.Allow())
+}
+
 type testcaseIntakeHandler struct {
 	c              *request.Context
 	w              *httptest.ResponseRecorder

systemtest/rum_test.go

@@ -184,13 +184,11 @@ func TestRUMRateLimit(t *testing.T) {
 	// Just check that rate limiting is wired up. More specific rate limiting scenarios are unit tested.
 
 	var g errgroup.Group
-	g.Go(func() error { return sendEvents("10.11.12.13", srv.Config.RUM.RateLimit.EventLimit) })
-	g.Go(func() error { return sendEvents("10.11.12.14", srv.Config.RUM.RateLimit.EventLimit) })
+	g.Go(func() error { return sendEvents("10.11.12.13", srv.Config.RUM.RateLimit.EventLimit*3) })
+	g.Go(func() error { return sendEvents("10.11.12.14", srv.Config.RUM.RateLimit.EventLimit*3) })
 	assert.NoError(t, g.Wait())
 
 	g = errgroup.Group{}
-	g.Go(func() error { return sendEvents("10.11.12.13", srv.Config.RUM.RateLimit.EventLimit) })
-	g.Go(func() error { return sendEvents("10.11.12.14", srv.Config.RUM.RateLimit.EventLimit) })
 	g.Go(func() error { return sendEvents("10.11.12.15", srv.Config.RUM.RateLimit.EventLimit) })
 	err = g.Wait()
 	require.Error(t, err)