2 files changed, 99 insertions, 0 deletions
diff --git a/modules/ratelimit/ratelimit.go b/modules/ratelimit/ratelimit.go
new file mode 100644
index 0000000..b02f5d5
--- /dev/null
+++ b/modules/ratelimit/ratelimit.go
@@ -0,0 +1,54 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package ratelimit
+
+import (
+	"time"
+
+	"github.com/philippta/flyscrape"
+)
+
+func init() {
+	flyscrape.RegisterModule(new(Module))
+}
+
+type Module struct {
+	Rate float64 `json:"rate"`
+
+	ticker    *time.Ticker
+	semaphore chan struct{}
+}
+
+func (m *Module) ID() string {
+	return "ratelimit"
+}
+
+func (m *Module) OnLoad(v flyscrape.Visitor) {
+	rate := time.Duration(float64(time.Second) / m.Rate)
+
+	m.ticker = time.NewTicker(rate)
+	m.semaphore = make(chan struct{}, 1)
+
+	go func() {
+		for range m.ticker.C {
+			m.semaphore <- struct{}{}
+		}
+	}()
+}
+
+func (m *Module) OnRequest(_ *flyscrape.Request) {
+	<-m.semaphore
+}
+
+func (m *Module) OnComplete() {
+	m.ticker.Stop()
+}
+
+var (
+	_ flyscrape.Module     = (*Module)(nil)
+	_ flyscrape.OnRequest  = (*Module)(nil)
+	_ flyscrape.OnLoad     = (*Module)(nil)
+	_ flyscrape.OnComplete = (*Module)(nil)
+)
diff --git a/modules/ratelimit/ratelimit_test.go b/modules/ratelimit/ratelimit_test.go
new file mode 100644
index 0000000..c166371
--- /dev/null
+++ b/modules/ratelimit/ratelimit_test.go
@@ -0,0 +1,45 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package ratelimit_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/philippta/flyscrape"
+	"github.com/philippta/flyscrape/modules/followlinks"
+	"github.com/philippta/flyscrape/modules/ratelimit"
+	"github.com/philippta/flyscrape/modules/starturl"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRatelimit(t *testing.T) {
+	scraper := flyscrape.NewScraper()
+	scraper.LoadModule(&starturl.Module{URL: "http://www.example.com/"})
+	scraper.LoadModule(&followlinks.Module{})
+	scraper.LoadModule(&ratelimit.Module{
+		Rate: 100,
+	})
+
+	scraper.SetTransport(flyscrape.MockTransport(200, `<a href="foo">foo</a>`))
+
+	var times []time.Time
+	scraper.OnRequest(func(req *flyscrape.Request) {
+		times = append(times, time.Now())
+	})
+
+	start := time.Now()
+
+	scraper.Run()
+
+	first := times[0].Add(-10 * time.Millisecond)
+	second := times[1].Add(-20 * time.Millisecond)
+
+	require.Less(t, first.Sub(start), 2*time.Millisecond)
+	require.Less(t, second.Sub(start), 2*time.Millisecond)
+
+	require.Less(t, start.Sub(first), 2*time.Millisecond)
+	require.Less(t, start.Sub(second), 2*time.Millisecond)
+}