Hi,

I'm using tcp_send() to send responses to incoming RPC requests over TCP. This works fine when responses are small, but tends to fail on larger responses on somewhat slower links or clients (it fails whenever the links is not on the loopback interface, even on sub-ms RTT links).

The error message thrown in the logs is:

ERROR: <core> [core/tcp_main.c:618]: _wbufq_add(): (32007 bytes): write queue full or timeout (18042, total 18042, last write 0 s ago)

I verified the error is due to a full buffer, not a timeout.

I would like the tcp_send() not to fail on a full send buffer. Instead of failing, it should wait until there is enough space in the buffer again and send the data. Timeout should still be honoured though.

From the code this looks like a "feature", but I would classify this as

a bug. The receiver is still receiving, the timeout is not hit but Kamailio just decides not to send any more data because its (by default small) buffer is full. If the buffer is full, it should wait until enough space becomes free again, not fail before the timeout triggers.

The chunks of data that are sent via tcp_send() are always smaller than tcpconn_wq_max, so they should fit in an empty write buffer. I'd prefer not to increase tcpconn_wq_max as this will be a never ending story, the responses will keep growing over time. They're already in the 10's of MB at this time.

Retrying tcp_send() is not an option. After the first failure, the connection is closed and there is no way for the server (Kamailio) to open a new connection to the RPC client.

tcp_async is enabled, as that's needed/preferred for the SIP processing.

Is there a way around the (full) write buffer for the caller of tcp_send()?