go-cotp v1.0.1

Improved RFC 1006 Class 0 TPDU size negotiation interoperability with existing industrial protocol stacks while preserving protocol validation for undefined TPDU size codes.

Interoperability

• Expanded the accepted standard Class 0 TPDU size codes to include 0x0C–0x10 (4096–65536 bytes).
  • This aligns with common RFC 1006 implementations used by industrial protocols such as IEC 61850 MMS.
  • Improves interoperability with widely deployed stacks including libIEC61850 and iec61850bean.
  • Undefined TPDU size codes continue to be rejected during connection establishment.
• Improved negotiation when the client omits the TPDU Size parameter.
  • Connection Confirm (CC) responses advertising a larger standard TPDU size are now capped to the local proposal instead of being rejected.
  • This accommodates implementations that negotiate larger RFC 1006 TPDU sizes (for example 0x10 = 65536) while the local endpoint uses the protocol maximum of 65531 bytes.

Validation

• Tightened handshake validation tests to distinguish between:
  • valid extended standard TPDU size codes (0x0C–0x10), and
  • undefined TPDU size codes (for example 0x11), which continue to fail the handshake with ErrHandshake.

Tests

• Updated TPDU size negotiation tests to reflect the extended standard size table.
• Added coverage for negotiation using the newly accepted standard sizes.
• Updated interoperability tests for RFC 1006 compatibility and undefined TPDU size validation.

No API changes. No breaking changes.

Import path remains github.com/otfabric/go-cotp.