From ae52e9a1d1f120d358830a3d2ef68fa7683bde2f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?D=C4=81vis=20Mos=C4=81ns?= <davispuh@gmail.com>
Date: Tue, 3 Dec 2024 18:17:49 +0200
Subject: [PATCH] Make `send()` more robust by handling previous ACK

---
 lib/tftp/tftp.rb | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/lib/tftp/tftp.rb b/lib/tftp/tftp.rb
index 86ee945..8d0dd86 100644
--- a/lib/tftp/tftp.rb
+++ b/lib/tftp/tftp.rb
@@ -129,15 +129,18 @@ def send(tag, sock, io)
               log :warn, "#{tag} Timeout at block ##{seq}"
               return
             end
-            msg, _ = sock.recvfrom(4, 0)
-            pkt = Packet.parse(msg)
-            if pkt.class != Packet::ACK
-              log :warn, "#{tag} Expected ACK but got: #{pkt.class}"
-              return
-            end
-            if pkt.seq != seq
-              log :warn, "#{tag} Seq mismatch: #{seq} != #{pkt.seq}"
-              return
+            loop do
+              msg, _ = sock.recvfrom(4, 0)
+              pkt = Packet.parse(msg)
+              if pkt.class != Packet::ACK
+                log :warn, "#{tag} Expected ACK but got: #{pkt.class}"
+                return
+              end
+              break if pkt.seq == seq
+              if pkt.seq > seq
+                log :warn, "#{tag} Seq mismatch: #{seq} != #{pkt.seq}"
+                return
+              end
             end
             # Increment with wrap around at 16 bit boundary,
             # because of tftp block number field size limit.