Sarthak-Pandey commented on code in PR #20627:
URL: https://github.com/apache/nuttx/pull/20627#discussion_r4282040730
##########
net/tcp/tcp_input.c:
##########
@@ -1570,38 +1573,57 @@ static void tcp_input(FAR struct net_driver_s *dev,
uint8_t domain,
if ((tcp->flags & TCP_URG) != 0)
{
- dev->d_urglen = (tcp->urgp[0] << 8) | tcp->urgp[1];
- if (dev->d_urglen > dev->d_len)
+ uint16_t urgp = (tcp->urgp[0] << 8) | tcp->urgp[1];
+
+ /* BSD/Linux default semantics (tcp_stdurg=0):
+ * The urgent pointer points ONE BYTE PAST the urgent byte.
+ * The single urgent byte is at payload[urgp - 1].
+ *
+ * If urgp is within the current segment (1 <= urgp <= d_len):
+ * - Extract the single urgent byte into conn->urg_data from
+ * the IOB chain.
+ * - Record state as TCP_URG_VALID.
+ * - Signal urgent data availability (flags |= TCP_URGDATA).
+ *
+ * If urgp > d_len:
+ * - The urgent byte is located in a future segment not yet
+ * received; mark state as TCP_URG_AWAITING.
+ * - Signal urgent data (flags |= TCP_URGDATA).
+ */
+
+ if (urgp >= 1 && urgp <= dev->d_len)
{
- /* There is more urgent data in the next segment to come. */
+ int app_offset;
+
+ /* Payload is stored in an IOB chain starting at dev->d_iob.
+ * Calculate the offset of d_appdata within dev->d_iob.
+ */
- dev->d_urglen = dev->d_len;
+ app_offset = (dev->d_appdata - dev->d_iob->io_data) -
+ dev->d_iob->io_offset;
+
+ /* Copy the urgent byte safely from the IOB chain */
+
+ iob_copyout(&conn->urg_data, dev->d_iob, 1,
+ app_offset + urgp - 1);
Review Comment:
Thanks for pointing this out. When SO_OOBINLINE is not enabled, the urgent
byte should not appear in the normal data stream. I have added
tcp_remove_urgbyte() to strip the urgent byte from the IOB chain payload and
advanced conn->rcvseq by 1 to acknowledge it. This ensures the application only
reads the urgent byte via recv(..., MSG_OOB) and does not receive it twice in
the normal stream. If SO_OOBINLINE is enabled, the urgent byte remains inline
in the normal stream as expected.
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