NODERAWSOCKETS: make setsockopt/getsockopt symmetric by guybedford · Pull Request #27921 · emscripten-core/emscripten

guybedford · 2026-10-07T23:43:37Z

This makes setsockopt and getsockopt consistent under -sNODERAWSOCKETS, resolves #27888.

Previously setsockopt accepted any unknown option silently while getsockopt returned ENOPROTOOPT for it, so a value that had just been set successfully could not be read back (e.g. SO_RCVTIMEO). SO_REUSEADDR also always read back as 1 but was never actually applied to UDP binds.

SO_RCVTIMEO/SO_SNDTIMEO are stored and reported as a struct timeval, validated as the kernel does (EINVAL on a short length, EDOM on an out-of-range tv_usec). Nothing blocks in this backend, so this matches kernel semantics for an O_NONBLOCK socket, where the timeout is stored but never fires.
SO_REUSEADDR and SO_REUSEPORT are now passed to the UDP bind (both the public dgram and udp_wrap paths), so datagram sockets can share a port. IPV6_V6ONLY is passed through for UDP too.
SO_ACCEPTCONN, SO_DOMAIN and SO_PROTOCOL are reported.
Options that are not modelled now fail with ENOPROTOOPT in setsockopt as well, so everything accepted can be read back.

test_socket_options.c is extended to cover the above and a new test_udp_reuseaddr.c checks that two UDP sockets with the option can bind the same port while a third without it gets EADDRINUSE. Both tests also pass natively on Linux.

Made with AI assistance under my review

Store and report SO_RCVTIMEO/SO_SNDTIMEO (struct timeval); report SO_ACCEPTCONN, SO_DOMAIN and SO_PROTOCOL; reject options that are not modelled with ENOPROTOOPT instead of accepting them silently. SO_REUSEADDR/SO_REUSEPORT are now actually applied to UDP binds so datagram sockets can share a port. Fixes emscripten-core#27888

This adds UDP multicast group membership to `-sNODERAWSOCKETS`. Since #27921, `setsockopt` rejects options it doesn't model, so `IP_ADD_MEMBERSHIP` and its IPv6 equivalent now fail with `ENOPROTOOPT`. Before, they were silently accepted and had no effect. Group membership is now modelled on both the dgram and udp_wrap backends, which both expose `addMembership`/`dropMembership`: * `IP_ADD_MEMBERSHIP`/`IP_DROP_MEMBERSHIP` (`struct ip_mreq`, or `ip_mreqn` with an interface address) and `IPV6_JOIN_GROUP`/`IPV6_LEAVE_GROUP` * a join made before `bind()` is applied once the socket is bound, since otherwise libuv would auto-bind it to an ephemeral port * groups are joined again on the new socket that a UDP re-connect swaps in (#28146) * node picks the interface by address (IPv4) or by name (IPv6), so an interface given only by index returns `ENODEV` * as on Linux, the options are set-only, and `getsockopt` rejects them `test_noderawsockets_udp_multicast_membership` covers join and leave, the kernel's `EADDRINUSE` on a duplicate join and `EADDRNOTAVAIL` on leaving a group that wasn't joined, a join before `bind()`, and a short `optlen`. The IPv6 part is skipped on hosts without an IPv6 multicast route.