This re-works the persist timer to have the following behavior:
1) Only start persist timer when a buffered segment doesn't fit within
the current window and there is no in-fligh data. Previously, the
persist timer was always started when the window went to zero even
if there was no buffered data (since timer was managed in receive
pathway rather than transmit pathway)
2) Upon first fire of persist timer, fill the remaining window if
non-zero by splitting the unsent segment. If split segment is sent,
persist timer is stopped, RTO timer is now ensuring reliable window
updates
3) If window is already zero when persist timer fires, send 1 byte probe
4) Persist timer and zero window probe should only be active when the
following are true:
* no in-flight data (pcb->unacked == NULL)
* when there is buffered data (pcb->unsent != NULL)
* when pcb->unsent->len > pcb->snd_wnd
- add a better-documented static function tcp_output_segment_busy
- try to reduce the number of checks
- tcp_rexmit_rto: iterate pcb->unacked only once
- no need to check for ref==1 in tcp_rexmit_fast when tcp_rexmit does
- call tcp_rexmit_fast if dupacks >= 3 (not == 3) and use TF_INFR flag to guard the fast-rexmit case (that way, it's triggered again on the next dupack)
- added `altcp_tls_free_config()`.
- added `altcp_tls_context()` function to allow mbedtls parameter tweak.
Since state structure isn't exported, this allow application to get
internal context (port dependent) to tweak it.
- free altcp_pcb when lower error callback called.
- expose `altcp_tcp_setup()` so we can wrap altcp over existing tcp pcb.
- avoid calling tcp_close() with NULL pcb.
- free altcp_pcb struct when error callback called.
According to `mqtt_tcp_err_cb()` in src/apps/mqtt/mqtt.c, altcp socket should
work the same way than raw tcp socket. So freeing altcp_pcb ensure this.
The new functions both take size_t as increment/decrement argument instead of s16_t (which needed to be range-checked before conversion everywhere) - in most places, the direction (increment or decrement) is known anyway, so no need to encode it in a sign bit
These are now defined to return != SYS_ARCH_TIMEOUT on success rather than the time
waiting. The returned times were unused by lwip and this simplifies at
least some implementations.
Signed-off-by: goldsimon <goldsimon@gmx.de>
