[#149] client: Do not finish on empty ID list in ObjectListReader

In previous implementation `ObjectListReader.Read` returned `false` on
server responded with empty ID list. This could cause premature end of
reading since the protocol does not forbid intermediate empty lists.

Do not stop if ID list from response body is empty.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

client/object_search.go

@@ -136,34 +136,42 @@ func (x *ObjectListReader) Read(buf []oid.ID) (int, bool) {
 		return read, true
 	}
 
-	// receive next message
-	ok := x.ctxCall.readResponse()
-	if !ok {
-		return read, false
+	var ok bool
+	var ids []*v2refs.ObjectID
+	var i, ln, rem int
+
+	for {
+		// receive next message
+		ok = x.ctxCall.readResponse()
+		if !ok {
+			return read, false
+		}
+
+		// read new chunk of objects
+		ids = x.bodyResp.GetIDList()
+
+		ln = len(ids)
+		if ln == 0 {
+			// just skip empty lists since they are not prohibited by protocol
+			continue
+		}
+
+		if rem = len(buf) - read; ln > rem {
+			ln = rem
+		}
+
+		for i = 0; i < ln; i++ {
+			buf[read+i] = *oid.NewIDFromV2(ids[i]) // need smth better
+		}
+
+		read += ln
+
+		// save the tail and break
+		x.tail = append(x.tail, ids[ln:]...)
+
+		break
 	}
 
-	// read new chunk of objects
-	ids := x.bodyResp.GetIDList()
-	ln := len(ids)
-	if ln == 0 {
-		x.ctxCall.err = io.EOF
-		return read, false
-	}
-
-	buf = buf[read:]
-	if ln > len(buf) {
-		ln = len(buf)
-	}
-
-	for i := 0; i < ln; i++ {
-		buf[i] = *oid.NewIDFromV2(ids[i]) // need smth better
-	}
-
-	read += ln
-
-	// save the tail
-	x.tail = append(x.tail, ids[ln:]...)
-
 	return read, true
 }