From 0d6494d164cc490d62473eae0fbd79d5573bb380 Mon Sep 17 00:00:00 2001
From: Philipp Tanlak <philipp.tanlak@gmail.com>
Date: Wed, 7 Feb 2024 23:20:55 +0100
Subject: Add retry module and change rate to requests per minute (#37)

---
 modules/ratelimit/ratelimit.go      | 62 +++++++++++++++++++++++--------------
 modules/ratelimit/ratelimit_test.go | 48 +++++++++++++++++++++++-----
 2 files changed, 80 insertions(+), 30 deletions(-)

(limited to 'modules/ratelimit')

diff --git a/modules/ratelimit/ratelimit.go b/modules/ratelimit/ratelimit.go
index b23cd7a..152c6fd 100644
--- a/modules/ratelimit/ratelimit.go
+++ b/modules/ratelimit/ratelimit.go
@@ -5,6 +5,7 @@
 package ratelimit
 
 import (
+	"math"
 	"net/http"
 	"time"
 
@@ -16,10 +17,12 @@ func init() {
 }
 
 type Module struct {
-	Rate float64 `json:"rate"`
+	Rate        int `json:"rate"`
+	Concurrency int `json:"concurrency"`
 
-	ticker    *time.Ticker
-	semaphore chan struct{}
+	ticker      *time.Ticker
+	ratelimit   chan struct{}
+	concurrency chan struct{}
 }
 
 func (Module) ModuleInfo() flyscrape.ModuleInfo {
@@ -30,41 +33,54 @@ func (Module) ModuleInfo() flyscrape.ModuleInfo {
 }
 
 func (m *Module) Provision(v flyscrape.Context) {
-	if m.disabled() {
-		return
-	}
-
-	rate := time.Duration(float64(time.Second) / m.Rate)
+	if m.rateLimitEnabled() {
+		rate := time.Duration(float64(time.Minute) / float64(m.Rate))
+		m.ticker = time.NewTicker(rate)
+		m.ratelimit = make(chan struct{}, int(math.Max(float64(m.Rate)/10, 1)))
 
-	m.ticker = time.NewTicker(rate)
-	m.semaphore = make(chan struct{}, 1)
+		go func() {
+			m.ratelimit <- struct{}{}
+			for range m.ticker.C {
+				m.ratelimit <- struct{}{}
+			}
+		}()
+	}
 
-	go func() {
-		for range m.ticker.C {
-			m.semaphore <- struct{}{}
+	if m.concurrencyEnabled() {
+		m.concurrency = make(chan struct{}, m.Concurrency)
+		for i := 0; i < m.Concurrency; i++ {
+			m.concurrency <- struct{}{}
 		}
-	}()
+	}
 }
 
 func (m *Module) AdaptTransport(t http.RoundTripper) http.RoundTripper {
-	if m.disabled() {
-		return t
-	}
 	return flyscrape.RoundTripFunc(func(r *http.Request) (*http.Response, error) {
-		<-m.semaphore
+		if m.rateLimitEnabled() {
+			<-m.ratelimit
+		}
+
+		if m.concurrencyEnabled() {
+			<-m.concurrency
+			defer func() { m.concurrency <- struct{}{} }()
+		}
+
 		return t.RoundTrip(r)
 	})
 }
 
 func (m *Module) Finalize() {
-	if m.disabled() {
-		return
+	if m.rateLimitEnabled() {
+		m.ticker.Stop()
 	}
-	m.ticker.Stop()
 }
 
-func (m *Module) disabled() bool {
-	return m.Rate == 0
+func (m *Module) rateLimitEnabled() bool {
+	return m.Rate != 0
+}
+
+func (m *Module) concurrencyEnabled() bool {
+	return m.Concurrency > 0
 }
 
 var (
diff --git a/modules/ratelimit/ratelimit_test.go b/modules/ratelimit/ratelimit_test.go
index 7be29a1..23cc8c8 100644
--- a/modules/ratelimit/ratelimit_test.go
+++ b/modules/ratelimit/ratelimit_test.go
@@ -32,7 +32,7 @@ func TestRatelimit(t *testing.T) {
 			},
 		},
 		&ratelimit.Module{
-			Rate: 100,
+			Rate: 240,
 		},
 	}
 
@@ -41,12 +41,46 @@ func TestRatelimit(t *testing.T) {
 	scraper.Modules = mods
 	scraper.Run()
 
-	first := times[0].Add(-10 * time.Millisecond)
-	second := times[1].Add(-20 * time.Millisecond)
+	first := times[0].Add(-250 * time.Millisecond)
+	second := times[1].Add(-500 * time.Millisecond)
 
-	require.Less(t, first.Sub(start), 2*time.Millisecond)
-	require.Less(t, second.Sub(start), 2*time.Millisecond)
+	require.Less(t, first.Sub(start), 250*time.Millisecond)
+	require.Less(t, second.Sub(start), 250*time.Millisecond)
 
-	require.Less(t, start.Sub(first), 2*time.Millisecond)
-	require.Less(t, start.Sub(second), 2*time.Millisecond)
+	require.Less(t, start.Sub(first), 250*time.Millisecond)
+	require.Less(t, start.Sub(second), 250*time.Millisecond)
+}
+
+func TestRatelimitConcurrency(t *testing.T) {
+	var times []time.Time
+
+	mods := []flyscrape.Module{
+		&starturl.Module{URL: "http://www.example.com"},
+		&followlinks.Module{},
+		hook.Module{
+			AdaptTransportFn: func(rt http.RoundTripper) http.RoundTripper {
+				return flyscrape.RoundTripFunc(func(r *http.Request) (*http.Response, error) {
+					times = append(times, time.Now())
+					time.Sleep(10 * time.Millisecond)
+					return flyscrape.MockResponse(200, `
+						<a href="foo"></a>
+						<a href="bar"></a>
+						<a href="baz"></a>
+						<a href="qux"></a>
+					`)
+				})
+			},
+		},
+		&ratelimit.Module{
+			Concurrency: 2,
+		},
+	}
+
+	scraper := flyscrape.NewScraper()
+	scraper.Modules = mods
+	scraper.Run()
+
+	require.Len(t, times, 5)
+	require.Less(t, times[2].Sub(times[1]), time.Millisecond)
+	require.Less(t, times[4].Sub(times[3]), time.Millisecond)
 }
-- 
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