Send transfer frames that fit in the window for a larger delivery

No frames were sent to the open window for a delivery that was larger than
the recipient was ready to receive.

Author: kohtala

lib/session.js

@@ -159,6 +159,7 @@ Outgoing.prototype.send = function (sender, tag, data, format) {
         'link':sender,
         'data': fragments,
         'format':format ? format : 0,
+        'next_to_send': 0,
         'sent': false,
         'settled': false,
         'state': undefined,
@@ -229,20 +230,27 @@ Outgoing.prototype.process = function() {
         d = this.deliveries.by_id(this.next_pending_delivery);
         if (d) {
             if (d.link.has_credit()) {
-                if (this.transfer_window() >= d.data.length) {
-                    this.window -= d.data.length;
-                    for (var i = 0; i < d.data.length; i++) {
+                const num_to_send = Math.min(this.transfer_window(), d.data.length - d.next_to_send);
+                if (num_to_send > 0) {
+                    this.window -= num_to_send;
+                    const end_of_send = d.next_to_send + num_to_send;
+                    for (var i = d.next_to_send; i < end_of_send; i++) {
                         this.next_transfer_id++;
                         var more = (i+1) < d.data.length;
                         var transfer = frames.transfer({'handle':d.link.local.handle,'message_format':d.format,'delivery_id':d.id, 'delivery_tag':d.tag, 'settled':d.settled, 'more':more});
                         d.link.session.output(transfer, d.data[i]);
+                    }
+                    if (end_of_send < d.data.length) {
+                        d.next_to_send = end_of_send;
+                        break;
+                    } else {
                         if (d.settled) {
                             d.remote_settled = true;//if sending presettled, it can now be cleaned up
                         }
+                        d.link.credit--;
+                        d.link.delivery_count++;
+                        this.next_pending_delivery++;
                     }
-                    d.link.credit--;
-                    d.link.delivery_count++;
-                    this.next_pending_delivery++;
                 } else {
                     log.flow('[%s] Incoming window of peer preventing sending further transfers: remote_window=%d, remote_next_transfer_id=%d, next_transfer_id=%d',
                         this.connection.options.id, this.remote_window, this.remote_next_transfer_id, this.next_transfer_id);