From 774994b951d932d2968305eee4d9b20340a63c71 Mon Sep 17 00:00:00 2001
From: Alexander Lunev <alexanderlunev@mail.ru>
Date: Fri, 11 Feb 2022 17:59:26 +0300
Subject: [PATCH] net/tcp: support for FIN+ACK case in tcp send event handlers

---
 net/tcp/tcp_send_buffered.c   | 54 +++++++++++++++++------------------
 net/tcp/tcp_send_unbuffered.c |  4 +--
 net/tcp/tcp_sendfile.c        |  4 +--
 3 files changed, 28 insertions(+), 34 deletions(-)

diff --git a/net/tcp/tcp_send_buffered.c b/net/tcp/tcp_send_buffered.c
index dfa008b7cb..91312b16c6 100644
--- a/net/tcp/tcp_send_buffered.c
+++ b/net/tcp/tcp_send_buffered.c
@@ -384,45 +384,19 @@ static uint16_t psock_send_eventhandler(FAR struct net_driver_s *dev,
   ninfo("flags: %04x\n", flags);
 
   /* The TCP_ACKDATA, TCP_REXMIT and TCP_DISCONN_EVENTS flags are expected to
-   * appear here strictly one at a time
+   * appear here strictly one at a time, except for the FIN + ACK case.
    */
 
   DEBUGASSERT((flags & TCP_ACKDATA) == 0 ||
               (flags & TCP_REXMIT) == 0);
-  DEBUGASSERT((flags & TCP_DISCONN_EVENTS) == 0 ||
-              (flags & TCP_ACKDATA) == 0);
   DEBUGASSERT((flags & TCP_DISCONN_EVENTS) == 0 ||
               (flags & TCP_REXMIT) == 0);
 
-  /* Check for a loss of connection */
-
-  if ((flags & TCP_DISCONN_EVENTS) != 0)
-    {
-      ninfo("Lost connection: %04x\n", flags);
-
-      /* We could get here recursively through the callback actions of
-       * tcp_lost_connection().  So don't repeat that action if we have
-       * already been disconnected.
-       */
-
-      if (_SS_ISCONNECTED(conn->sconn.s_flags))
-        {
-          /* Report not connected */
-
-          tcp_lost_connection(conn, conn->sndcb, flags);
-        }
-
-      /* Free write buffers and terminate polling */
-
-      psock_lost_connection(conn, !!(flags & NETDEV_DOWN));
-      return flags;
-    }
-
   /* If this packet contains an acknowledgment, then update the count of
    * acknowledged bytes.
    */
 
-  else if ((flags & TCP_ACKDATA) != 0)
+  if ((flags & TCP_ACKDATA) != 0)
     {
       FAR struct tcp_wrbuffer_s *wrb;
       FAR struct tcp_hdr_s *tcp;
@@ -602,6 +576,30 @@ static uint16_t psock_send_eventhandler(FAR struct net_driver_s *dev,
         }
     }
 
+  /* Check for a loss of connection */
+
+  if ((flags & TCP_DISCONN_EVENTS) != 0)
+    {
+      ninfo("Lost connection: %04x\n", flags);
+
+      /* We could get here recursively through the callback actions of
+       * tcp_lost_connection().  So don't repeat that action if we have
+       * already been disconnected.
+       */
+
+      if (_SS_ISCONNECTED(conn->sconn.s_flags))
+        {
+          /* Report not connected */
+
+          tcp_lost_connection(conn, conn->sndcb, flags);
+        }
+
+      /* Free write buffers and terminate polling */
+
+      psock_lost_connection(conn, !!(flags & NETDEV_DOWN));
+      return flags;
+    }
+
   /* Check if we are being asked to retransmit data */
 
   else if ((flags & TCP_REXMIT) != 0)
diff --git a/net/tcp/tcp_send_unbuffered.c b/net/tcp/tcp_send_unbuffered.c
index 10ec05d068..f7dafa39f0 100644
--- a/net/tcp/tcp_send_unbuffered.c
+++ b/net/tcp/tcp_send_unbuffered.c
@@ -210,13 +210,11 @@ static uint16_t tcpsend_eventhandler(FAR struct net_driver_s *dev,
         flags, pstate->snd_acked, pstate->snd_sent);
 
   /* The TCP_ACKDATA, TCP_REXMIT and TCP_DISCONN_EVENTS flags are expected to
-   * appear here strictly one at a time
+   * appear here strictly one at a time, except for the FIN + ACK case.
    */
 
   DEBUGASSERT((flags & TCP_ACKDATA) == 0 ||
               (flags & TCP_REXMIT) == 0);
-  DEBUGASSERT((flags & TCP_DISCONN_EVENTS) == 0 ||
-              (flags & TCP_ACKDATA) == 0);
   DEBUGASSERT((flags & TCP_DISCONN_EVENTS) == 0 ||
               (flags & TCP_REXMIT) == 0);
 
diff --git a/net/tcp/tcp_sendfile.c b/net/tcp/tcp_sendfile.c
index 3af0a7a2db..535dbcc0d8 100644
--- a/net/tcp/tcp_sendfile.c
+++ b/net/tcp/tcp_sendfile.c
@@ -164,13 +164,11 @@ static uint16_t sendfile_eventhandler(FAR struct net_driver_s *dev,
         flags, pstate->snd_acked, pstate->snd_sent);
 
   /* The TCP_ACKDATA, TCP_REXMIT and TCP_DISCONN_EVENTS flags are expected to
-   * appear here strictly one at a time
+   * appear here strictly one at a time, except for the FIN + ACK case.
    */
 
   DEBUGASSERT((flags & TCP_ACKDATA) == 0 ||
               (flags & TCP_REXMIT) == 0);
-  DEBUGASSERT((flags & TCP_DISCONN_EVENTS) == 0 ||
-              (flags & TCP_ACKDATA) == 0);
   DEBUGASSERT((flags & TCP_DISCONN_EVENTS) == 0 ||
               (flags & TCP_REXMIT) == 0);