Port forwarding

[wlandau]

Related to #22 (reply in thread): is there a port forwarding mechanism for server() in which a server can use a different port number than the client? Like SSH port forwarding where ports can listen to each other even though the port numbers do not have to agree? That would allow me to use parallelly::freePort() on the server as well as the client in order to be 100% sure all ports I attempt to use are free. This could come up in cases I have seen where jobs on a cluster share the same node. Say the client has port 5000 free, but someone else's job on a remote cluster node is already using port 5000, and an error or worse happens because figurative wires get crossed.

[shikokuchuo]

NNG always uses an ephemeral port for outbound dialers, this is assigned automatically by the IP stack, so one less thing you need to worry about.

Crossed wires is not possible - as we are using TCP, which is a bytestream - it is for ordered transmission and not lossy like UDP. Further NNG adds much stricter guarantees through its own scalability protocols on top of the transport layer.

On the client, instead of using parallelly::freePort(), you can also just specify port 0 on the client e.g. daemons("tcp://xx.xxx.xxx.175:0"). To retrieve the actual port used, you can on the socket:

nanonext::parse_url(nanonext::opt(sock[["listener"]][[1]], "url"))[["port"]]

[shikokuchuo]

You're in luck, I've implemented this in 8a31123. Now you can supply a zero port for NNG to auto-assign as per the above e.g. daemons("tcp://:0") or daemons(c("tcp://:0", "tcp://:0") , nodes = 2) and subsequent calls to daemons() will report the actual assigned port number in the URL.

Note for the active queue, you will need to supply a vector of URLs otherwise it will just assign a contiguous block of ports starting from the random one.

[shikokuchuo]

In case you need to extract the port numbers from the URL, the URL parsing utility in nanonext should be faster than using a regex nanonext::parse_url().

[wlandau]

Wonderful! This completely solves the problem and allows me to go forward with the active queue with more confidence.

[wlandau]

By the way, what port range does NNG use for this exactly?

[shikokuchuo]

It is only documented that it is the ephemeral range. I didn't find any reference to the exact range - but I did find a new way of getting just the port number!

nanonext::opt(sock[["listener"]][[1]], "tcp-bound-port")