test promised don't get allocated where not wanted

License: MIT
Signed-off-by: Jeromy <jeromyj@gmail.com>

unixfs/io/dagreader_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"io"
 	"io/ioutil"
+	"math/rand"
 	"strings"
 	"testing"
 
@@ -72,6 +73,55 @@ func TestSeekAndRead(t *testing.T) {
 	}
 }
 
+func TestSeekAndReadLarge(t *testing.T) {
+	dserv := testu.GetDAGServ()
+	inbuf := make([]byte, 20000)
+	rand.Read(inbuf)
+
+	node := testu.GetNode(t, dserv, inbuf, testu.UseProtoBufLeaves)
+	ctx, closer := context.WithCancel(context.Background())
+	defer closer()
+
+	reader, err := NewDagReader(ctx, node, dserv)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = reader.Seek(10000, io.SeekStart)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	buf := make([]byte, 100)
+	_, err = io.ReadFull(reader, buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !bytes.Equal(buf, inbuf[10000:10100]) {
+		t.Fatal("seeked read failed")
+	}
+
+	pbdr := reader.(*pbDagReader)
+	var count int
+	for i, p := range pbdr.promises {
+		if i > 20 && i < 30 {
+			if p == nil {
+				t.Fatal("expected index to be not nil: ", i)
+			}
+			count++
+		} else {
+			if p != nil {
+				t.Fatal("expected index to be nil: ", i)
+			}
+		}
+	}
+	// -1 because we read some and it cleared one
+	if count != preloadSize-1 {
+		t.Fatalf("expected %d preloaded promises, got %d", preloadSize-1, count)
+	}
+}
+
 func TestRelativeSeek(t *testing.T) {
 	dserv := testu.GetDAGServ()
 	ctx, closer := context.WithCancel(context.Background())