[PATCH] net: wget: Support retransmission a dropped packet

[Yasuharu Shibata]

The server sends multiple packets without waiting for an ACK
by window control and if some packets are dropped,
wget will return an ACK including the dropped packets.

Following log indicates this issue.

  wget_handler() wget: Transferring, seq=97bbdd4a, ack=30,len=580
  wget_handler() wget: Transferring, seq=97bbedca, ack=30,len=580

First packet of TCP sequence number is 0x97bbdd4a.
Second packet of TCP sequence number should be 0x97bbe2ca,
however it is 0x97bbedca and returns its ACK, so the server
suppose that 0x97bbe2ca and 0x97bbedca are received appropriately.
In this case, 0x97bbe2ca was lost and the data of wget was broken.

In this patch, next_data_seq_num holds the next expected
TCP sequence number.
If the TCP sequence number different from next_data_seq_num,
trying to retransmit the packet.

Signed-off-by: Yasuharu Shibata <yasuharu.shibata at gmail.com>
---
 net/wget.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/wget.c b/net/wget.c
index 817c5ebd5d..71bac92d84 100644
--- a/net/wget.c
+++ b/net/wget.c
@@ -50,6 +50,7 @@ static unsigned long content_length;
 static unsigned int packets;
 
 static unsigned int initial_data_seq_num;
+static unsigned int next_data_seq_num;
 
 static enum  wget_state current_wget_state;
 
@@ -272,17 +273,18 @@ static void wget_connected(uchar *pkt, unsigned int tcp_seq_num,
 
 		current_wget_state = WGET_TRANSFERRING;
 
+		initial_data_seq_num = tcp_seq_num + hlen;
+		next_data_seq_num    = tcp_seq_num + len;
+
 		if (strstr((char *)pkt, http_ok) == 0) {
 			debug_cond(DEBUG_WGET,
 				   "wget: Connected Bad Xfer\n");
-			initial_data_seq_num = tcp_seq_num + hlen;
 			wget_loop_state = NETLOOP_FAIL;
 			wget_send(action, tcp_seq_num, tcp_ack_num, len);
 		} else {
 			debug_cond(DEBUG_WGET,
 				   "wget: Connctd pkt %p  hlen %x\n",
 				   pkt, hlen);
-			initial_data_seq_num = tcp_seq_num + hlen;
 
 			pos = strstr((char *)pkt, content_len);
 			if (!pos) {
@@ -396,6 +398,12 @@ static void wget_handler(uchar *pkt, u16 dport,
 			   "wget: Transferring, seq=%x, ack=%x,len=%x\n",
 			   tcp_seq_num, tcp_ack_num, len);
 
+		if (next_data_seq_num != tcp_seq_num) {
+			debug_cond(DEBUG_WGET, "wget: seq=%x packet was lost\n", next_data_seq_num);
+			return;
+		}
+		next_data_seq_num = tcp_seq_num + len;
+
 		if (tcp_seq_num >= initial_data_seq_num &&
 		    store_block(pkt, tcp_seq_num - initial_data_seq_num,
 				len) != 0) {
-- 
2.25.1