go-profinet v0.4.0

Date: 2026-10-28
Previous release: v0.3.0

Independent interoperability and production readiness: MRP and the SNMP
agent tested against independent implementations, persistence,
re-parameterization of a running AR, an allocation-free Linux transport, and
synthetic GSDML fixtures. What each feature covers, how it is tested and
what limits it is in docs/FEATURE-STATUS.md; the
program's outcome, blockers and roadmap in
docs/research/NEXT-PROGRAM-REPORT.md.
Feature coverage is not conformance: go-profinet is not certified, and no
measured time is a real-time claim.

No incompatible API change (apidiff against v0.3.0). One behaviour change:
snmp.LLDPRemote.TimeMark is the time of a row's last change; walks list
every row at TimeFilter 0 and a Get answers any filter value up to it
(before, a row appeared at its TimeMark only).

• Persistence: package store (Store; Memory; Dir: CRC-32C-checked
  files replaced atomically, the previous version kept and used after a
  crash or corruption) and device.Config.Store/StoreKey: the permanent
  station name and IP suite, DHCP options, I&M1–4 and resets survive a
  restart; a temporary DCP Set clears the stored value; a failing store
  refuses the change; Device.StoreError.
• controller.Device.Reparameterize: PrmBegin, writes, PrmEnd and the
  device's ApplicationReady on a running AR; the parameters are kept for
  reconnects. Verified with profinet-py re-parameterizing go-profinet's
  device; p-net and pnio-rs refuse PrmBegin in Data.
• SNMP: lldpRemIndex is kept per neighbor (lldp.Neighbor.Index,
  Changed); lldpRemTimeMark is a TimeFilter. Verified with Net-SNMP:
  walks, errors, limits, malformed datagrams, a flood, changing neighbors.
• MRP verified against umrp as manager and as client (profinet-interop
  v0.3.0); microchip-ung/mrp could not run (the kernels available refuse
  MRP on a software bridge); the interop suite builds MRP rings of veth
  cables (otfnode mrp).
• l2/afpacket: reads, writes and LinkUp allocate nothing; flood
  throughput ×11, losses gone, 35 → 1 garbage collection per 30 s of a 1 ms
  exchange (docs/BENCHMARKS.md, scripts/l2-bench.sh); the cyclic intervals
  in a VM are unchanged.
• GSDML: synthetic MIT fixtures (gsdml/testdata/fixtures: two device
  access points with one and two ports, shared device, a compact device),
  run as devices and controllers and parsed by profinet-py; an evidence file
  for engineering-tool imports (none run yet).
• Fixes: device: a Connect counted twice against MaxARs while its AR was
  being established, so a second IO controller connecting at that moment was
  refused "out of AR resources"; l2/bridge: statistics counted a frame
  after it could be read.
• Docs: docs/research/INDEPENDENT-CONTROLLER.md (CODESYS manual recipe),
  docs/research/GSDML-TOOLS.md; a correction of v0.3.0's report: scapy has
  no MRP dissector.
• Interop: profinet-interop v0.3.0 (193 pass, 0 fail, 8 n/a, 8 attributed
  deviations).