Qt: add graph of unacked (outstanding) bytes to window scale graph

This metric is commonly used as an estimate of the sender's congestion window.
[ when examining a capture taken from the sender ]

Change-Id: I812d5556cef477c08ef1e5d396fbdddda9a6751e
Reviewed-on: https://code.wireshark.org/review/19661
Petri-Dish: Roland Knall <rknall@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Roland Knall <rknall@gmail.com>

2 files changed, 52 insertions, 10 deletions

diff --git a/ui/qt/tcp_stream_dialog.cpp b/ui/qt/tcp_stream_dialog.cpp
index 800b02adcb..4230b3820f 100644
--- a/ui/qt/tcp_stream_dialog.cpp
+++ b/ui/qt/tcp_stream_dialog.cpp
@@ -931,23 +931,50 @@ void TCPStreamDialog::fillWindowScale()
     title_->setText(dlg_title);
 
     QCustomPlot *sp = ui->streamPlot;
-    base_graph_->setLineStyle(QCPGraph::lsLine);
+    // use base_graph_ to represent unacked window size
+    //  (estimate of congestion window)
+    base_graph_->setLineStyle(QCPGraph::lsStepLeft);
+    // use rwin_graph_ here to show rwin window scale
+    //  (derived from ACK packets)
+    rwin_graph_->setVisible(true);
 
     QVector<double> rel_time, win_size;
+    QVector<double> cwnd_time, cwnd_size;
+    guint32 last_ack = 0;
+    bool found_first_ack = false;
     for (struct segment *seg = graph_.segments; seg != NULL; seg = seg->next) {
-        if (!compareHeaders(seg)) {
-            continue;
-        }
-
         double ts = seg->rel_secs + seg->rel_usecs / 1000000.0;
-        guint16 flags = seg->th_flags;
 
-        if ((flags & (TH_SYN|TH_RST)) == 0) {
-            rel_time.append(ts - ts_offset_);
-            win_size.append(seg->th_win);
+        // The receive window that applies to this flow comes
+        //   from packets in the opposite direction
+        if (compareHeaders(seg)) {
+            // compute bytes_in_flight for cwnd graph
+            guint32 end_seq = seg->th_seq + seg->th_seglen;
+            if (found_first_ack &&
+                tcp_seq_eq_or_after(end_seq, last_ack)) {
+                cwnd_time.append(ts - ts_offset_);
+                cwnd_size.append((double)(end_seq - last_ack));
+            }
+        } else {
+            // packet in opposite direction - has advertised rwin
+            guint16 flags = seg->th_flags;
+
+            if ((flags & (TH_SYN|TH_RST)) == 0) {
+                rel_time.append(ts - ts_offset_);
+                win_size.append(seg->th_win);
+            }
+            if ((flags & (TH_ACK)) != 0) {
+                // use this to update last_ack
+                if (!found_first_ack ||
+                    tcp_seq_eq_or_after(seg->th_ack, last_ack)) {
+                    last_ack = seg->th_ack;
+                    found_first_ack = true;
+                }
+            }
         }
     }
-    base_graph_->setData(rel_time, win_size);
+    base_graph_->setData(cwnd_time, cwnd_size);
+    rwin_graph_->setData(rel_time, win_size);
     sp->yAxis->setLabel(window_size_label_);
 }
 
diff --git a/ui/tap-tcp-stream.h b/ui/tap-tcp-stream.h
index f430fa5fa5..360f4af016 100644
--- a/ui/tap-tcp-stream.h
+++ b/ui/tap-tcp-stream.h
@@ -114,6 +114,21 @@ struct unack *rtt_get_new_unack(double , unsigned int );
 void rtt_put_unack_on_list(struct unack ** , struct unack * );
 void rtt_delete_unack_from_list(struct unack ** , struct unack * );
 
+static inline int
+tcp_seq_before(guint32 s1, guint32 s2) {
+    return (gint32)(s1 - s2) < 0;
+}
+
+static inline int
+tcp_seq_eq_or_after(guint32 s1, guint32 s2) {
+    return !tcp_seq_before(s1, s2);
+}
+
+static inline int
+tcp_seq_after(guint32 s1, guint32 s2) {
+    return (s1 != s2) && !tcp_seq_before(s1, s2);
+}
+
 
 #ifdef __cplusplus
 }