zhhyu7 commented on code in PR #20627:
URL: https://github.com/apache/nuttx/pull/20627#discussion_r4259596220
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net/tcp/tcp_send_buffered.c:
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@@ -1135,6 +1147,24 @@ static uint32_t psock_send_eventhandler(FAR struct
net_driver_s *dev,
return flags;
}
+#ifdef CONFIG_NET_TCPURGDATA
+ if (wrb->wb_urg > 0)
+ {
+ uint16_t urg_offset = wrb->wb_urg;
Review Comment:
```wb_urg``` is an offset from the start of the wrb. On a partial ACK,
```TCP_WBTRIM()``` removes the acknowledged bytes from the head of the wrb and
decreases ```TCP_WBSENT()```, but wb_urg keeps its old value. The urgent
pointer then moves forward by the trimmed amount in every following segment,
and the fast-retransmit path at line 803 uses the same stale value. Reproduced
with a 3000-byte OOB send over loopback (every segment is ACKed before the next
is sent): the pointer always points past the segment, so the receiver never
finds the urgent byte. A Linux receiver would treat a later byte of the stream
as urgent.
Also, when ```wb_urg < TCP_WBSENT(wrb)``` (the urgent byte was already
sent), the code keeps ```urg_offset = wb_urg``` instead of not setting
```URG```.
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