rate limit asses.Cksum to 10MBps

go.mod

@@ -2,7 +2,10 @@ module show-rss
 
 go 1.23.3
 
-require modernc.org/sqlite v1.37.0
+require (
+	golang.org/x/time v0.11.0
+	modernc.org/sqlite v1.37.0
+)
 
 require (
 	github.com/PuerkitoBio/goquery v1.8.0 // indirect

go.sum

@@ -59,6 +59,8 @@ golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9sn
 golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.5.0 h1:OLmvp0KP+FVG99Ct/qFiL/Fhk4zp4QQnZ7b2U+5piUM=
 golang.org/x/text v0.5.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
+golang.org/x/time v0.11.0 h1:/bpjEDfN9tkoN/ryeYHnv5hcMlc8ncjMcM4XBk5NWV0=
+golang.org/x/time v0.11.0/go.mod h1:CDIdPxbZBQxdj6cxyCIdrNogrJKMJ7pr37NYpMcMDSg=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.31.0 h1:0EedkvKDbh+qistFTd0Bcwe/YLh4vHwWEkiI0toFIBU=
 golang.org/x/tools v0.31.0/go.mod h1:naFTU+Cev749tSJRXJlna0T3WxKvb1kWEx15xA4SdmQ=

src/asses/one.go

@@ -10,6 +10,7 @@ import (
 	"math/rand"
 	"os"
 	"path"
+	"show-rss/src/slow"
 	"time"
 )
 
@@ -31,7 +32,7 @@ func One(ctx context.Context, p string) error {
 
 	if err := func() error {
 		if len(last.Cksum) > 0 {
-			cksum, err := Cksum(p)
+			cksum, err := Cksum(ctx, p)
 			if err != nil {
 				return err
 			}
@@ -52,7 +53,7 @@ func One(ctx context.Context, p string) error {
 		return err
 	}
 
-	cksum, err := Cksum(p)
+	cksum, err := Cksum(ctx, p)
 	if err != nil {
 		return err
 	}
@@ -63,7 +64,7 @@ func One(ctx context.Context, p string) error {
 	return checked(ctx, p, cksum, stat.ModTime())
 }
 
-func Cksum(p string) (string, error) {
+func Cksum(ctx context.Context, p string) (string, error) {
 	f, err := os.Open(p)
 	if err != nil {
 		return "", err
@@ -71,6 +72,6 @@ func Cksum(p string) (string, error) {
 	defer f.Close()
 
 	hasher := md5.New()
-	_, err = io.Copy(hasher, f)
+	_, err = io.Copy(hasher, slow.NewReader(ctx, 10_000_000, f))
 	return base64.StdEncoding.EncodeToString(hasher.Sum(nil)), err
 }

src/asses/one_test.go

@@ -17,7 +17,7 @@ func TestOne(t *testing.T) {
 	p := path.Join(d, "f.mkv")
 	os.WriteFile(p, b, os.ModePerm)
 
-	cksum, _ := asses.Cksum(p)
+	cksum, _ := asses.Cksum(context.Background(), p)
 
 	if err := asses.One(ctx, p); err != nil {
 		t.Fatal(err)
@@ -31,7 +31,7 @@ func TestOne(t *testing.T) {
 		t.Fatalf("no new srt: %v", err)
 	}
 
-	newCksum, _ := asses.Cksum(p)
+	newCksum, _ := asses.Cksum(context.Background(), p)
 	if cksum == newCksum {
 		t.Fatalf("cksum unchanged")
 	}

src/slow/reader.go

@@ -0,0 +1,39 @@
+package slow
+
+import (
+	"context"
+	"io"
+
+	"golang.org/x/time/rate"
+)
+
+type Reader struct {
+	ctx     context.Context
+	limiter *rate.Limiter
+	r       io.Reader
+}
+
+var _ io.Reader = Reader{}
+
+func NewReader(ctx context.Context, bps rate.Limit, r io.Reader) Reader {
+	return Reader{
+		ctx:     ctx,
+		limiter: rate.NewLimiter(bps, 8192),
+		r:       r,
+	}
+}
+
+func (r Reader) Read(b []byte) (int, error) {
+	n, err := r.r.Read(b)
+
+	m := 0
+	burst := r.limiter.Burst()
+	for m < n {
+		if err := r.limiter.WaitN(r.ctx, burst); err != nil {
+			return n, err
+		}
+		m += burst
+	}
+
+	return n, err
+}

src/slow/reader_test.go

@@ -0,0 +1,20 @@
+package slow_test
+
+import "show-rss/src/slow"
+import "testing"
+import "context"
+import "bytes"
+import "io"
+
+func TestReader(t *testing.T) {
+   junk := bytes.NewReader(bytes.Repeat([]byte("1"), 256_000))
+
+   slowReader := slow.NewReader(context.Background(), 300_000, junk)
+
+   buff := bytes.NewBuffer(nil)
+   if n, err := io.Copy(buff, slowReader); err != nil {
+      t.Fatal(err)
+   } else if n != 256_000 {
+      t.Fatal(n)
+   }
+}