Optimize ACK and window updates

src/pcbuf.c

@@ -173,7 +173,7 @@ size_t W32_CALL sock_setbuf (sock_type *s, BYTE *rx_buf, size_t rx_len)
   }
   else
   {
-    size_t len = min (rx_len, USHRT_MAX-1) - 8;
+    size_t len = min (rx_len, 2 * USHRT_MAX) - 8;
 
     *(DWORD*)rx_buf         = SAFETY_TCP;
     *(DWORD*)(rx_buf+4+len) = SAFETY_TCP;

src/pctcp.c

@@ -144,7 +144,6 @@ W32_CLANG_PACK_WARN_DEF()
 
   static void tcp_no_arp   (_tcp_Socket *s);
   static void tcp_rtt_win  (_tcp_Socket *s);
-  static void tcp_upd_win  (_tcp_Socket *s, unsigned line);
   static BOOL tcp_checksum (const in_Header *ip, const tcp_Header *tcp, int len);
 #endif
 
@@ -826,8 +825,7 @@ _tcp_Socket *_tcp_handler (const in_Header *ip, BOOL broadcast)
   }
 
   if (flags & tcp_FlagPUSH)       /* EE 2002.2.28 */
-       s->locflags |= LF_GOT_PUSH;
-  else s->locflags &= ~LF_GOT_PUSH;
+     s->locflags |= LF_GOT_PUSH;
 
   tcp_rtt_win (s);        /* update retrans timer, windows etc. */
 
@@ -1273,17 +1271,6 @@ void tcp_Retransmitter (BOOL force)
       continue;
     }
 
-    /* Need to send a window update? Because we advertised a 0 window
-     * in a previous _tcp_send() (but only in ESTAB state).
-     */
-    if ((s->locflags & LF_WINUPDATE) && sock_rbleft((sock_type*)s) > 0)
-    {
-      STAT (tcpstats.tcps_sndwinup++);
-      s->locflags &= ~LF_WINUPDATE;
-      s->flags |= tcp_FlagACK;
-      TCP_SEND (s);
-    }
-
     else if (s->tx_datalen > 0 || s->unhappy || s->karn_count == 1)
     {
       if (chk_timeout(s->rtt_time))  /* retransmission timeout */
@@ -1844,13 +1831,30 @@ static int tcp_read (_tcp_Socket *s, BYTE *buf, int maxlen)
        to_move += s->missed_seq[1] - s->recv_next;
 
     if (to_move > 0)
-    {
-      memmove (s->rx_data, s->rx_data + len, to_move);
+       memmove (s->rx_data, s->rx_data + len, to_move);
 
-      TCP_SENDSOON (s);     /* delayed ACK */
+    /* Delay ACK until we can advertise maximum window size.
+     */
+    if (s->max_rx_data - s->rx_datalen >= s->max_rx_data / 2)
+    {
+      /* Update window if it becomes too small.
+       */
+      if (s->recv_win <= (int)s->max_seg * 2)
+         TCP_SEND (s);
+      else if (s->locflags & LF_NEED_ACK)
+      {
+        /* Normal "fast" ACK condition, except we do it slower.
+         * Try to ACK every second segment, or when PUSH received.
+         * Otherwise, delay further to avoid empty packets.
+         */
+        if ((s->locflags & LF_GOT_PUSH) ||
+            s->adv_win - s->recv_win >= 2 * s->max_seg)
+           TCP_SEND (s);
+        else
+           TCP_SENDSOON (s);
+      }
+      s->locflags &= ~LF_GOT_PUSH;
     }
-    else
-      tcp_upd_win (s, __LINE__);
   }
   else if (s->state == tcp_StateCLOSWT)
           _tcp_close (s);
@@ -1981,7 +1985,7 @@ static void tcp_sockreset (_tcp_Socket *s, BOOL proxy)
     s->unhappy  = FALSE;
     s->hisport  = 0;
     s->hisaddr  = 0UL;
-    s->locflags &= ~(LF_WINUPDATE | LF_KEEPALIVE | LF_GOT_FIN | LF_GOT_ICMP);
+    s->locflags &= ~(LF_NEED_ACK | LF_KEEPALIVE | LF_GOT_FIN | LF_GOT_ICMP);
 
     s->datatimer   = 0UL;
     s->inactive_to = 0;
@@ -2145,20 +2149,6 @@ static void tcp_rtt_win (_tcp_Socket *s)
   s->datatimer = 0UL; /* resetting tx-timer, EE 99.08.23 */
 }
 
-/**
- * Check if receive window needs an update.
- */
-static void tcp_upd_win (_tcp_Socket *s, unsigned line)
-{
-  UINT winfree = s->max_rx_data - (UINT)s->rx_datalen;
-
-  if (winfree < s->max_seg/2)
-  {
-    _tcp_send (s, __FILE__, line);  /* update window now */
-    TRACE_CONSOLE (2, "tcp_upd_win(%d): win-free %u\n", line, winfree);
-  }
-}
-
 /**
  * TCP option routines.
  * \note Each of these \b MUST add multiple of 4 bytes of options.
@@ -2364,10 +2354,27 @@ int _tcp_send (_tcp_Socket *s, const char *file, unsigned line)
   int          opt_len;          /* total length of TCP options */
   int          pkt_num;          /* 0 .. s->cwindow-1 */
   int          rtt;
+  int          new_window;
 
   s->recent = 0;
   dst = (_pktserial ? NULL : &s->his_ethaddr);
 
+  new_window = s->max_rx_data - s->rx_datalen;
+  if (s->max_rx_data >= s->max_seg * 4)
+  {
+    new_window = min (new_window, s->max_rx_data / 2);
+    if (new_window > (int)s->max_seg)
+    {
+      new_window -= new_window % s->max_seg;
+      if (s->recv_win < new_window - (int)s->max_seg)
+        s->recv_win = new_window;
+    }
+    else s->recv_win = new_window;
+  }
+  else s->recv_win = new_window;
+
+  s->adv_win = s->recv_win;
+
 #if defined(USE_IPV6)
   if (s->is_ip6)
   {
@@ -2425,7 +2432,6 @@ int _tcp_send (_tcp_Socket *s, const char *file, unsigned line)
     tcp->seqnum   = intel (s->send_next + start_data); /* unacked - no longer send_tot_len */
     tcp->acknum   = intel (s->recv_next);
 
-    s->adv_win    = s->max_rx_data - s->rx_datalen;    /* Our new advertised recv window */
     tcp->window   = intel16 ((WORD)s->adv_win);
     tcp->flags    = (BYTE) (s->flags & ~tcp_FlagPUSH);
     tcp->unused   = 0;
@@ -2461,7 +2467,7 @@ int _tcp_send (_tcp_Socket *s, const char *file, unsigned line)
            memcpy (data, s->tx_queue+start_data, send_data_len);
       else memcpy (data, s->tx_data +start_data, send_data_len);
 
-      if (send_data_len == send_tot_data &&
+      if ((unsigned)start_data + send_data_len == s->tx_datalen &&
           (s->flags & tcp_FlagPUSH))
       {
         /* Set PUSH bit on last segment.
@@ -2524,6 +2530,7 @@ int _tcp_send (_tcp_Socket *s, const char *file, unsigned line)
   }
 
   s->send_una = start_data;  /* relative start of tx_data[] buffer */
+  s->locflags &= ~LF_NEED_ACK;
 
   TRACE_CONSOLE (2, "tcp_send (called from %s/%u): sent %u bytes in %u "
                     "packets with (%ld) unacked. SND.NXT %lu\n",

src/socket.c

@@ -231,7 +231,7 @@ BOOL _sock_dos_fd (int s)
  */
 int _sock_set_rcv_buf (sock_type *s, size_t len)
 {
-  len = min (len+8,USHRT_MAX);  /* add room for head/tail markers */
+  len = 2 * min (len, USHRT_MAX) + 8;  /* add room for head/tail markers */
   return sock_setbuf (s, (BYTE*)malloc(len), len);
 
   /* Note: the ret-val from above malloc() is freed below.

src/tcp_fsm.c

@@ -330,7 +330,6 @@ static int tcp_estab_state (_tcp_Socket **sp, const in_Header *ip,
   _tcp_Socket *s   = *sp;
   int   len;
   long  ldiff;      /* how much still ACK'ed */
-  BOOL  did_tx;
 
   /* handle lost SYN
    */
@@ -364,14 +363,13 @@ static int tcp_estab_state (_tcp_Socket **sp, const in_Header *ip,
        len = intel16 (ip->length) - in_GetHdrLen (ip);
   else len = intel16 (ip6->len);
 
-  if (tcp_process_data (s, tcp, len, &flags) < 0)
+  len = tcp_process_data (s, tcp, len, &flags);
+  if (len < 0)
   {
     TCP_SEND (s);  /* An out-of-order or missing segment; do fast ACK */
     return (1);
   }
 
-  did_tx = FALSE;
-
   if (s->state != tcp_StateCLOSWT  &&
       (flags & tcp_FlagFIN)        &&
       SEQ_GEQ(s->recv_next,seqnum) &&
@@ -385,7 +383,6 @@ static int tcp_estab_state (_tcp_Socket **sp, const in_Header *ip,
       /* Implied CLOSE-WAIT -> LAST-ACK transition here
        */
       TCP_SEND (s);
-      did_tx = TRUE;
 
       TRACE_CONSOLE (2, "tcp_estab_state(): got FIN\n");
 
@@ -394,63 +391,41 @@ static int tcp_estab_state (_tcp_Socket **sp, const in_Header *ip,
       s->unhappy   = TRUE;
       s->timeout   = set_timeout (tcp_LASTACK_TIME); /* Added AGW 6 Jan 2001 */
       s->state     = tcp_StateLASTACK;
+
+      return (0);
     }
     else
     {
       s->unhappy = TRUE;
       TCP_SEND (s);  /* force a retransmit, no state change */
-      did_tx = TRUE;
+      return (0);
     }
   }
 
-  /*
-   * Eliminate the spurious ACK messages bug.
-   * For the window update, the length should be the
-   * data length only, so exclude the TCP header size
-   *  -- Joe <jdhagen@itis.com>
-   */
-  len -= (tcp->offset << 2);
-
   /* Peer ACKed some of our data, continue sending more.
    */
   if (ldiff > 0 && s->tx_datalen > (unsigned long)s->send_una)
-     goto send_now;
+  {
+    s->karn_count = 0;
+    TCP_SEND (s);
+    return (0);
+  }
 
-  /* Send ACK for received data.
+  /* Schedule delayed-ACK for received data, in case
+   * tcp_read() doesn't get to it in time.
    */
   if (len > 0)
   {
-    /* Need to ACK and update window, but how urgent ??
-     * We need a better criteria for doing Fast-ACK.
-     */
-    if (s->adv_win < s->max_seg)
-    {
-    send_now:
-      TRACE_FILE ("tcp_estab_state (%u): FastACK: ldiff %ld, "
-                  "UNA %ld, MS-right %ld\n",
-                  __LINE__, ldiff, s->send_una,
-                  s->missed_seq[0] != s->missed_seq[1] ?
-                  (u_long)(s->missed_seq[0] - s->recv_next) : 0);
-      s->karn_count = 0;
-      TCP_SEND (s);
-      did_tx = TRUE;
-
-      if (s->adv_win == 0)  /* need to open closed window in retransmitter */
-      {
-        s->locflags |= LF_WINUPDATE;
-        s->unhappy = TRUE;
-      }
-    }
-    else
-    {
-      TCP_SENDSOON (s);          /* delayed ACK */
-      did_tx = TRUE;
-    }
+    BOOL do_tx = !(s->locflags & LF_NEED_ACK);
+    s->locflags |= LF_NEED_ACK;
+    if (do_tx)
+       TCP_SENDSOON (s);
+    return (0);
   }
 
   /* Check if we need to reply to keep-alive segment
    */
-  if (!did_tx && (len == 0) && (seqnum == s->recv_next-1) &&
+  if ((seqnum == s->recv_next-1) &&
       ((flags & tcp_FlagACK) == tcp_FlagACK) &&  /* ACK only */
       (s->state == tcp_StateESTAB))
   {
@@ -866,6 +841,7 @@ copy_in_order (_tcp_Socket *s, const BYTE *data, unsigned len)
   memcpy (s->rx_data + s->rx_datalen, data, len);
   s->recv_next  += len;
   s->rx_datalen += len;
+  s->recv_win   -= len;
 }
 
 /*
@@ -907,6 +883,7 @@ data_in_order (_tcp_Socket *s, const BYTE *data, unsigned len, unsigned diff)
     TRACE_FILE ("data_in_order (%u): Use %lu out-of-order bytes\n",
                 __LINE__, (u_long)(s->missed_seq[1] - s->missed_seq[0]));
     s->rx_datalen   += (s->missed_seq[1] - s->missed_seq[0]);
+    s->recv_win     -= (s->missed_seq[1] - s->missed_seq[0]);
     s->recv_next     = s->missed_seq[1];
     s->missed_seq[0] = s->missed_seq[1] = 0;
 
@@ -1117,7 +1094,7 @@ static int tcp_process_data (_tcp_Socket *s, const tcp_Header *tcp,
   {
     data_in_order (s, data, len, ldiff);
     s->unhappy = (s->tx_datalen > 0);
-    return (0);
+    return (len);
   }
 
   STAT (tcpstats.tcps_rcvduppack++);      /* increment dup-ACK count */

src/wattcp.h

@@ -299,7 +299,7 @@ struct ulong_long {
  * UDP/TCP socket local flags (locflags) bits.
  * Mostly used to support the BSD-socket API.
  */
-#define LF_WINUPDATE    0x00001   /**< need to send a window-update */
+#define LF_NEED_ACK     0x00001   /**< need to send ACK for received data */
 #define LF_NOPUSH       0x00002   /**< don't push on write */
 #define LF_NOOPT        0x00004   /**< don't use tcp options */
 #define LF_REUSEADDR    0x00008   /**< \todo Reuse address not supported */
@@ -607,6 +607,7 @@ typedef struct tcp_Socket {
 
         UINT         window;            /**< other guy's window */
         UINT         adv_win;           /**< our last advertised window */
+        long         recv_win;          /**< our current remaining window */
 
         BYTE         cwindow;           /**< Congestion window */
         BYTE         wwindow;           /**< Van Jacobson's algorithm */