add throttling to image download

config.go

@@ -48,6 +48,10 @@ const (
 	Useragent string = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) " +
 		"AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36"
 	DefaultAdNameTemplate string = "{{.Slug}}"
+
+	// for image download throttling
+	MinThrottle int = 2
+	MaxThrottle int = 20
 )
 
 const Usage string = `This is kleingebaeck, the kleinanzeigen.de backup tool.

main.go

@@ -22,8 +22,10 @@ import (
 	"fmt"
 	"io"
 	"log/slog"
+	"math/rand"
 	"os"
 	"runtime/debug"
+	"time"
 
 	"github.com/lmittmann/tint"
 	"github.com/tlinden/yadu"
@@ -113,6 +115,9 @@ func Main(w io.Writer) int {
 	// used for all HTTP requests
 	fetch := NewFetcher(conf)
 
+	// randomization needed here and there
+	rand.Seed(time.Now().UnixNano())
+
 	if len(conf.Adlinks) >= 1 {
 		// directly backup ad listing[s]
 		for _, uri := range conf.Adlinks {

scrape.go

@@ -24,6 +24,7 @@ import (
 	"log/slog"
 	"path/filepath"
 	"strings"
+	"time"
 
 	"astuart.co/goq"
 	"golang.org/x/sync/errgroup"
@@ -150,6 +151,11 @@ func ScrapeImages(fetch *Fetcher, ad *Ad, addir string) error {
 		imguri := imguri
 		file := filepath.Join(adpath, fmt.Sprintf("%d.jpg", img))
 		g.Go(func() error {
+			// wait a little
+
+			t := GetThrottleTime()
+			time.Sleep(t)
+
 			body, err := fetch.Getimage(imguri)
 			if err != nil {
 				return err
@@ -163,7 +169,7 @@ func ScrapeImages(fetch *Fetcher, ad *Ad, addir string) error {
 
 			buf2 := buf.Bytes() // needed for image writing
 
-			image := NewImage(buf, "", imguri)
+			image := NewImage(buf, file, imguri)
 			err = image.CalcHash()
 			if err != nil {
 				return err
@@ -181,7 +187,7 @@ func ScrapeImages(fetch *Fetcher, ad *Ad, addir string) error {
 				return err
 			}
 
-			slog.Debug("wrote image", "image", image, "size", len(buf2))
+			slog.Debug("wrote image", "image", image, "size", len(buf2), "throttle", t)
 			return nil
 		})
 		img++

util.go

@@ -20,9 +20,11 @@ package main
 import (
 	"bytes"
 	"errors"
+	"math/rand"
 	"os"
 	"os/exec"
 	"runtime"
+	"time"
 
 	"github.com/mattn/go-isatty"
 )
@@ -66,3 +68,7 @@ func IsNoTty() bool {
 	// it is a tty
 	return false
 }
+
+func GetThrottleTime() time.Duration {
+	return time.Duration(rand.Intn(MaxThrottle-MinThrottle+1)+MinThrottle) * time.Millisecond
+}