From 64dd669749707d4476fa5ce602d785a8a2ea7b68 Mon Sep 17 00:00:00 2001
From: Alexander Lunev <alexanderlunev@mail.ru>
Date: Wed, 19 Jan 2022 11:02:33 +0300
Subject: [PATCH] net/tcp/sendfile: retransmit only one the earliest not
 acknowledged segment (according to RFC 6298 (5.4)). The issue is the same as
 it was in tcp_send_unbuffered.c.

---
 net/tcp/tcp.h                 |  3 ++-
 net/tcp/tcp_appsend.c         | 46 +++++++++++++++++++++--------------
 net/tcp/tcp_send_unbuffered.c |  6 +++++
 net/tcp/tcp_sendfile.c        | 45 +++++++++++++++++++++++++++++-----
 4 files changed, 75 insertions(+), 25 deletions(-)

diff --git a/net/tcp/tcp.h b/net/tcp/tcp.h
index 3992d6be0e..60dd1e3b9f 100644
--- a/net/tcp/tcp.h
+++ b/net/tcp/tcp.h
@@ -172,7 +172,8 @@ struct tcp_conn_s
   uint8_t  rcvseq[4];     /* The sequence number that we expect to
                            * receive next */
   uint8_t  sndseq[4];     /* The sequence number that was last sent by us */
-#if !defined(CONFIG_NET_TCP_WRITE_BUFFERS)
+#if !defined(CONFIG_NET_TCP_WRITE_BUFFERS) || \
+    defined(CONFIG_NET_SENDFILE)
   uint32_t rexmit_seq;    /* The sequence number to be retrasmitted */
 #endif
   uint8_t  crefs;         /* Reference counts on this instance */
diff --git a/net/tcp/tcp_appsend.c b/net/tcp/tcp_appsend.c
index 82c7c9f6f7..1e8e58dbc2 100644
--- a/net/tcp/tcp_appsend.c
+++ b/net/tcp/tcp_appsend.c
@@ -322,26 +322,36 @@ void tcp_rexmit(FAR struct net_driver_s *dev, FAR struct tcp_conn_s *conn,
    * new data in it, we must send out a packet.
    */
 
-#ifdef CONFIG_NET_TCP_WRITE_BUFFERS
+#if defined(CONFIG_NET_TCP_WRITE_BUFFERS) && defined(CONFIG_NET_SENDFILE)
+  if (conn->sendfile)
+#endif
+    {
+#if !defined(CONFIG_NET_TCP_WRITE_BUFFERS) || defined(CONFIG_NET_SENDFILE)
+      if ((result & TCP_REXMIT) != 0 &&
+          dev->d_sndlen > 0 && conn->tx_unacked > 0)
+        {
+          uint32_t saveseq;
+
+          /* According to RFC 6298 (5.4), retransmit the earliest segment
+           * that has not been acknowledged by the TCP receiver.
+           */
+
+          saveseq = tcp_getsequence(conn->sndseq);
+          tcp_setsequence(conn->sndseq, conn->rexmit_seq);
+
+          tcp_send(dev, conn, TCP_ACK | TCP_PSH, dev->d_sndlen + hdrlen);
+
+          tcp_setsequence(conn->sndseq, saveseq);
+
+          return;
+        }
+#endif
+    }
+
+#if defined(CONFIG_NET_TCP_WRITE_BUFFERS)
   if (dev->d_sndlen > 0)
 #else
-  if ((result & TCP_REXMIT) != 0 &&
-      dev->d_sndlen > 0 && conn->tx_unacked > 0)
-    {
-      uint32_t saveseq;
-
-      /* According to RFC 6298 (5.4), retransmit the earliest segment
-       * that has not been acknowledged by the TCP receiver.
-       */
-
-      saveseq = tcp_getsequence(conn->sndseq);
-      tcp_setsequence(conn->sndseq, conn->rexmit_seq);
-
-      tcp_send(dev, conn, TCP_ACK | TCP_PSH, dev->d_sndlen + hdrlen);
-
-      tcp_setsequence(conn->sndseq, saveseq);
-    }
-  else if (dev->d_sndlen > 0 && conn->tx_unacked > 0)
+  if (dev->d_sndlen > 0 && conn->tx_unacked > 0)
 #endif
     {
       uint32_t seq;
diff --git a/net/tcp/tcp_send_unbuffered.c b/net/tcp/tcp_send_unbuffered.c
index 26a11ed2d7..41d23023cf 100644
--- a/net/tcp/tcp_send_unbuffered.c
+++ b/net/tcp/tcp_send_unbuffered.c
@@ -311,6 +311,8 @@ static uint16_t tcpsend_eventhandler(FAR struct net_driver_s *dev,
 
   if ((flags & TCP_REXMIT) != 0)
     {
+      nwarn("WARNING: TCP_REXMIT\n");
+
       /* According to RFC 6298 (5.4), retransmit the earliest segment
        * that has not been acknowledged by the TCP receiver.
        */
@@ -430,6 +432,10 @@ static uint16_t tcpsend_eventhandler(FAR struct net_driver_s *dev,
           ninfo("SEND: acked=%" PRId32 " sent=%zd buflen=%zd\n",
                 pstate->snd_acked, pstate->snd_sent, pstate->snd_buflen);
         }
+      else
+        {
+          nwarn("WARNING: Window full, wait for ack\n");
+        }
     }
 
   /* Continue waiting */
diff --git a/net/tcp/tcp_sendfile.c b/net/tcp/tcp_sendfile.c
index 5f4a30275f..9406fa5313 100644
--- a/net/tcp/tcp_sendfile.c
+++ b/net/tcp/tcp_sendfile.c
@@ -276,14 +276,47 @@ static uint16_t sendfile_eventhandler(FAR struct net_driver_s *dev,
     {
       nwarn("WARNING: TCP_REXMIT\n");
 
-      /* Yes.. in this case, reset the number of bytes that have been sent
-       * to the number of bytes that have been ACKed.
+      /* According to RFC 6298 (5.4), retransmit the earliest segment
+       * that has not been acknowledged by the TCP receiver.
        */
 
-      pstate->snd_sent = pstate->snd_acked;
-#ifndef CONFIG_NET_TCP_WRITE_BUFFERS
-      conn->rexmit_seq = pstate->snd_sent + pstate->snd_isn;
-#endif
+      /* Reconstruct the length of the earliest segment to be retransmitted */
+
+      uint32_t sndlen = pstate->snd_flen - pstate->snd_acked;
+
+      if (sndlen > conn->mss)
+        {
+          sndlen = conn->mss;
+        }
+
+      conn->rexmit_seq = pstate->snd_isn + pstate->snd_acked;
+
+      /* Then set-up to send that amount of data. (this won't actually
+       * happen until the polling cycle completes).
+       */
+
+      ret = file_seek(pstate->snd_file,
+                      pstate->snd_foffset + pstate->snd_acked, SEEK_SET);
+      if (ret < 0)
+        {
+          nerr("ERROR: Failed to lseek: %d\n", ret);
+          pstate->snd_sent = ret;
+          goto end_wait;
+        }
+
+      ret = file_read(pstate->snd_file, dev->d_appdata, sndlen);
+      if (ret < 0)
+        {
+          nerr("ERROR: Failed to read from input file: %d\n", (int)ret);
+          pstate->snd_sent = ret;
+          goto end_wait;
+        }
+
+      dev->d_sndlen = sndlen;
+
+      /* Continue waiting */
+
+      return flags;
     }
 
   /* Check for a loss of connection.