go-mms v1.2.0

Date: 2026-10-28
Previous release: v1.1.0

Summary

Operability and quality release. Errors are classified so errors.Is /
errors.As work across every failure path; a pluggable Metrics interface,
configurable retry with backoff and jitter, Server.Shutdown, association and
handshake timeouts and Client.Done / Client.Err are added. A cancelled
request no longer tears down its association, and a silent peer can no longer
block iso.Listener.Accept. Fuzzing found and this release fixes several
codec bugs (Cancel PDU tags, BinaryTime, UTCTime fractions, long-form tags).
Every package now has ≥90% test coverage, enforced in CI. All API changes are
additive.

Interop runs against three MMS peers from the mms-interop
v0.3.0 images,
pinned by digest: libiec61850 (120 pass), dscsystems/go-iec61850 (112 pass,
8 skipped peer limitations) and iec61850-rust (120 pass).

Changes

Added

• Errors — ErrServerClosed, ErrInvalidArgument; PhaseSession, PhasePresentation, PhaseACSE, PhaseMMS; RejectType (with String) and RejectError for MMS Reject PDUs (it unwraps to the previous *ProtocolError, so errors.Is(err, ErrProtocol) still holds); ServiceError.CodeName() (ISO 9506-2 code names). Failures carry sentinel kinds without changing their messages: association → ErrAssociationFailed, negotiation → ErrNegotiationFailed, connection loss → ErrClosed (+ ErrDecodeFailed / ErrInvalidPDU), request deadline → ErrInvokeTimeout + context.DeadlineExceeded, argument validation → ErrInvalidArgument.
• Metrics — Metrics interface (ObserveRequest, ObserveConnection), NopMetrics, Role, Service, RequestEvent, ConnectionState, ConnectionEvent; set via DialOptions.Metrics and ServerOptions.Metrics. OBSERVABILITY.md has a Prometheus adapter example.
• Retry — RetryPolicy (attempts, exponential backoff, jitter, Retryable, OnRetry), DefaultRetryPolicy, IsRetryable, Retry; iso.WithRetry retries DialTCP and Dial (connect, TLS, COTP and association), honouring the context.
• Lifecycle — Client.Done, Client.Err, DialOptions.RequestTimeout, Server.Shutdown(ctx) (closes listeners, waits for in-flight handlers, aborts associations; Serve / ListenAndServe then return ErrServerClosed), ServerOptions.AssociationTimeout, iso.WithHandshakeTimeout, iso.WithDialer.
• RawHookSend / RawHookRecv constants for the raw PDU hook direction.

Changed

• Request cancellation — a request whose context ends mid-write returns at once; the write completes in the background (an unstarted one is skipped) instead of closing the association.
• Association timeout — Serve aborts an association that has not completed its handshake within 30s by default (ServerOptions.AssociationTimeout; negative disables). Serve also closes the transport when its context is cancelled.
• iso.Listener — TLS and COTP handshakes run concurrently (up to 64 pending) with a 10s default timeout, so a peer that connects and stays silent no longer blocks other connections. Temporary accept errors (such as EMFILE) are retried with backoff.
• ServiceError.Error() includes the code name, e.g. (object-non-existent). Compare with errors.As and the Class / Code fields, never the string.
• Server error mapping — a *DataAccessError returned by a Read/Write callback is sent with its code (other errors: temporarily-unavailable, as before); a *ServiceError from a handler is sent as returned; a malformed Status request gets the invalid-request service error.
• Value.Equal compares floats bitwise (all NaNs equal, +0 ≠ -0).
• Logs carry role and remote_addr; requests are logged at debug level with service, invoke_id, duration and error. Messages are prefixed mms: / iso:.

Fixed

• Cancel PDUs — cancel-Request/Response/Error use tags [5], [6], [7] (the tag constants were wrong).
• BinaryTime — values below one day encode in the 4-octet TimeOfDay form (previously not re-encodable after decoding); the decoder rejects a millisecond-of-day ≥ 86 400 000.
• UTCTime — the fraction of a second round-trips losslessly.
• GeneralizedTime — a fractional second accepted on decode is kept on encode (it was dropped); whole seconds encode as before.
• Long-form tags — MMS PDUs with a long-form outer tag are rejected; tag numbers above 30 encode correctly.
• Deadline classification — an I/O timeout caused by a context deadline is reported as context.DeadlineExceeded even when the connection deadline fires just before the context's timer (association timeout, ISO transport).
• Full-duplex deadlines — go-cotp v1.0.4 arms a both-direction deadline around each read and write; a write deadline could cut a concurrent read (read tpkt header: i/o timeout). transport/iso now uses per-direction deadlines.
• Client.Abort honours its context; closing a transport whose deadline already fired no longer returns a timeout error.
• Server callback errors that are not wire errors no longer reach the error-code encoder (possible panic path).

Tests

• Coverage ≥90% in every package and in total, enforced by scripts/coverage-gate.sh (make coverage, CI quality job).
• internal/chaos: fault-injecting net.Conn / net.Listener (delays, chunked I/O, bandwidth limit, drops, resets, stalls). e2e chaos tests (lossy, drops with reconnect via Retry, slow peer) and a concurrent stress test under -race; make chaos.
• 57 fuzz targets, including FuzzValueCodec, FuzzServerDispatch, FuzzServerSession and new session/presentation/ACSE, codec and BER targets; scripts/fuzz.sh discovers them (make fuzz, make fuzz-short in make check and CI).
• Interop is stack-parametrized (MMS_INTEROP_STACK, make interop-all): one test body per scenario, run in CI against libiec61850, dscsystems/go-iec61850 and iec61850-rust from mms-interop v0.3.0. Peer limitations are explicit per-stack quirks or skips with reasons (INTEROP.md). New TestClient_PeerDisconnect (Done/Err) and TestServer_Shutdown.

Docs

• ERRORS.md, OBSERVABILITY.md, TIMEOUT_AND_CLOSE.md, API.md, README.md, LIMITS.md, KNOWN_LIMITATIONS.md, COMPLIANCE.md, INTEROP.md, RACE_NOTES.md and RELEASE_CHECKLIST.md updated; PROGRESS.md replaced by a current-status summary. Removed stale PLAN.md, REQUIREMENTS.md, extract_c_functions.py and mms_functions.csv.