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 <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/lib/crypt.c b/src/lib/crypt.c
index 070f5113..043eae13 100644
--- a/src/lib/crypt.c
+++ b/src/lib/crypt.c
@@ -217,6 +217,9 @@ static int openssl_encrypt(struct flow *        f,
         in = shm_du_buff_head(sdb);
         in_sz = shm_du_buff_tail(sdb) - in;
 
+        if (in_sz == 0)
+                return 0;
+
         if (random_buffer(iv, IVSZ) < 0)
                 goto fail_iv;