lib: Add initial flow liveness monitoring

This adds flow liveness monitoring for flows, with a fixed timeout of
120s. I will make it configurable at flow allocation later on (timeout
needs to be communicated to the peer). If one peer dies, or doesn't
call any IPC calls (flow_write/flow_read/fevent) it will stop sending
keepalives and the other peer's read/writes will error on an
-EFLOWDOWN after the timeout expires.

Packets without a payload (0 length packets) are interpreted as
keepalive packets for the flow. They can be sent from any application,
but they will not trigger a message read at the receiver side (0 as a
return value on flow_read indicates a previous partial read has
completed at exactly the buffer size).

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/lib/frct.c b/src/lib/frct.c
index ff938aec..e9741aaf 100644
--- a/src/lib/frct.c
+++ b/src/lib/frct.c
@@ -667,6 +667,7 @@ static int __frcti_snd(struct frcti *       frcti,
         bool              rtx;
 
         assert(frcti);
+        assert(shm_du_buff_head(sdb) != shm_du_buff_tail(sdb));
 
         snd_cr = &frcti->snd_cr;
         rcv_cr = &frcti->rcv_cr;