setsockopt(2) and reuse

Issue by AngusL
Sunday Jul 20, 2014 at 17:56 GMT

For earlier discussion, see https://github.com/rust-lang/rust/issues/15835

This issue was labelled with: A-libs in the Rust repository

I see there's been discussion of SO_REUSEADDR in the past. Mooted was that Windows allows later sockets to set the option and bind to endpoints which already have sockets without the option set, permitting a partial denial of service. (Later mitigated somewhat by SO_EXCLUSIVEADDRUSE.) TcpListener::bind currently uses this option to ignore the TIME_WAIT state, allowing faster re-binding. This introduces more-or-less the same problem in exchange for a benefit that's probably more useful in development than production.

There are other platform variations which make it difficult to find a unifying interface, particularly for TCP. In lieu of such an interface, I'd suggest exposing setsockopt(2) - even from an obviously platform-specific namespace. My motivation is a multicast discovery protocol, where I'd like multiple agents on one machine to be able to see each other. As far as I can tell, I need to either handle this separately or reinvent much of the UdpSocket wheel - which would be a shame.

Start with the earlier discussion in rust-lang/rust#15835, then examine TcpListener::bind, UdpSocket, and the setsockopt(2) behavior described for SO_REUSEADDR. A complete contribution would define a cross-platform or explicitly platform-specific interface that supports the multicast discovery use case while addressing the stated TCP and Windows differences.