Make ScanForLinks non-recursive

This way, we can't blow out our stack.

utils.go

@@ -17,11 +17,8 @@ const maxCidLength = 100
 const maxHeaderSize = 9
 
 func ScanForLinks(br io.Reader, cb func(cid.Cid)) error {
-	buf := make([]byte, maxCidLength)
-	return scanForLinksRec(br, cb, buf)
-}
-
-func scanForLinksRec(br io.Reader, cb func(cid.Cid), scratch []byte) error {
+	scratch := make([]byte, maxCidLength)
+	for remaining := uint64(1); remaining > 0; remaining-- {
 		maj, extra, err := CborReadHeaderBuf(br, scratch)
 		if err != nil {
 			return err
@@ -60,25 +57,16 @@ func scanForLinksRec(br io.Reader, cb func(cid.Cid), scratch []byte) error {
 				cb(c)
 
 			} else {
-			if err := scanForLinksRec(br, cb, scratch); err != nil {
-				return err
-			}
+				remaining++
 			}
 		case MajArray:
-		for i := 0; i < int(extra); i++ {
-			if err := scanForLinksRec(br, cb, scratch); err != nil {
-				return err
-			}
-		}
+			remaining += extra
 		case MajMap:
-		for i := 0; i < int(extra*2); i++ {
-			if err := scanForLinksRec(br, cb, scratch); err != nil {
-				return err
-			}
-		}
+			remaining += (extra * 2)
 		default:
 			return fmt.Errorf("unhandled cbor type: %d", maj)
 		}
+	}
 	return nil
 }