slow.Reader{}

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)
+   }
+}