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net/tcp: In tcp_input(), add the logic to detect, decode, and respond to TCP Keep-Alive packets. In tcp_timer(), fix some problems with the way that TCP Keep-Alive probes were being formatted.

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This commit is contained in:
Gregory Nutt 2018-03-12 15:54:21 -06:00
parent 1f52c13814
commit ae399b9b62
2 changed files with 88 additions and 12 deletions
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66
net/tcp/tcp_input.c
View File

@ -385,11 +385,58 @@ found:
dev->d_len -= (len + iplen);
/* First, check if the sequence number of the incoming packet is
* what we're expecting next. If not, we send out an ACK with the
* correct numbers in, unless we are in the SYN_RCVD state and
* receive a SYN, in which case we should retransmit our SYNACK
* (which is done further down).
#ifdef CONFIG_NET_TCP_KEEPALIVE
/* Check for a to KeepAlive probes. These packets have these properties:
*
* - TCP_ACK flag is set. SYN/FIN/RST never appear in a Keepalive probe.
* - Sequence number is the sequence number of previously ACKed data, i.e.,
* the expected sequence number minus one.
* - The data payload is one or two bytes.
*
* We would expect a KeepAlive only in the ESTABLISHED state and only after
* some time has elapsed with no network activity. If there is un-ACKed data,
* then we will let the normal TCP re-transmission logic handle that case.
*/
if ((tcp->flags & TCP_ACK) != 0 &&
(tcp->flags & (TCP_SYN | TCP_FIN | TCP_RST)) == 0 &&
(conn->tcpstateflags & TCP_STATE_MASK) == TCP_ESTABLISHED &&
(dev->d_len == 0 || dev->d_len == 1) &&
conn->unacked <= 0)
{
uint32_t ackseq;
uint32_t rcvseq;
/* Get the sequence number of that has just been acknowledged by this
* incoming packet.
*/
ackseq = tcp_getsequence(tcp->seqno);
rcvseq = tcp_getsequence(conn->rcvseq);
if (ackseq < rcvseq)
{
if (dev->d_len > 0)
{
/* Increment the received sequence number (perhaps including the
* discarded dummy byte in the probe).
*/
net_incr32(conn->rcvseq, dev->d_len);
}
/* And send a "normal" acknowledgment of the KeepAlive probe */
tcp_send(dev, conn, TCP_ACK, tcpiplen);
return;
}
}
#endif
/* Check if the sequence number of the incoming packet is what we are
* expecting next. If not, we send out an ACK with the correct numbers
* in, unless we are in the SYN_RCVD state and receive a SYN, in which
* case we should retransmit our SYNACK (which is done further down).
*/
if (!((((conn->tcpstateflags & TCP_STATE_MASK) == TCP_SYN_SENT) &&
@ -405,10 +452,9 @@ found:
}
}
/* Next, check if the incoming segment acknowledges any outstanding
* data. If so, we update the sequence number, reset the length of
* the outstanding data, calculate RTT estimations, and reset the
* retransmission timer.
/* Check if the incoming segment acknowledges any outstanding data. If so,
* we update the sequence number, reset the length of the outstanding
* data, calculate RTT estimations, and reset the retransmission timer.
*/
if ((tcp->flags & TCP_ACK) != 0 && conn->unacked > 0)
@ -764,7 +810,7 @@ found:
#endif /* CONFIG_NET_TCPURGDATA */
}
#ifdef NET_TCP_KEEPALIVE
#ifdef CONFIG_NET_TCP_KEEPALIVE
/* If the established socket receives an ACK or any kind of data
* from the remote peer (whether we accept it or not), then reset
* the keep alive timer.

34
net/tcp/tcp_timer.c
View File

@ -364,6 +364,7 @@ void tcp_timer(FAR struct net_driver_s *dev, FAR struct tcp_conn_s *conn,
if (conn->keepalive)
{
socktimeo_t timeo;
uint32_t saveseq;
/* If this is the first probe, then the keepstart time is
* the time that the last ACK or data was received from the
@ -381,6 +382,7 @@ void tcp_timer(FAR struct net_driver_s *dev, FAR struct tcp_conn_s *conn,
{
timeo = (socktimeo_t)conn->keepidle;
}
/* Yes... has the idle period elapsed with no data or ACK
* received from the remote peer?
*/
@ -422,10 +424,38 @@ void tcp_timer(FAR struct net_driver_s *dev, FAR struct tcp_conn_s *conn,
}
#endif
/* And send the probe */
/* And send the probe (along with a garbage byte).
* The packet we sned must have these properties:
*
* - TCP_ACK flag (only) is set.
* - Sequence number is the sequence number of
* previously ACKed data, i.e., the expected
* sequence number minus one.
* - The data payload is one or two bytes.
*
* tcp_send() will send the TCP sequence number as
* conn->sndseq. Rather than creating a new
* interface, we spoof tcp_end() here:
*/
tcp_send(dev, conn, TCP_ACK, tcpiplen);
saveseq = tcp_getsequence(conn->sndseq);
tcp_setsequence(conn->sndseq, saveseq - 1);
tcp_send(dev, conn, TCP_ACK, tcpiplen + 1);
tcp_setsequence(conn->sndseq, saveseq);
/* Increment the number of un-ACKed bytes due to the dummy
* byte that we just sent.
*/
conn->unacked++;
#ifdef CONFIG_NET_TCP_WRITE_BUFFERS
/* Increment the un-ACKed sequence number */
conn->sndseq_max++;
#endif
/* Update for the next probe */
conn->keeptime = clock_systimer();