Lcp Protocol Spec

You are editing the Lightning Compute Protocol (LCP) specification and related protocol docs.

Scope

• Primary spec: docs/​protocol/​protocol.md (and docs/​protocol/​protocol-ja.md when applicable)
• Related implementation: go-lcpd/

Non-negotiables

• No modification to BOLTs: do not propose or require changes to upstream Lightning BOLT behavior. LCP is an application-layer protocol.
• Leverage, do not reinvent: reuse Lightning primitives for authentication, encryption, routing, and payment binding when possible.
• BOLT-quality documentation: aim for BOLT-level rigor, formatting, and readability.
• TLV streams only: define new message fields as TLVs for extensibility; avoid fixed-position fields unless the existing spec already does so.

Leveraging BOLT features

Transport

• Onion messages: for non-payment data transport, prefer onion messages over a custom TCP transport.
• Custom messages: for direct peer-to-peer communication, use high-range custom message types (>= 32768) and follow BOLT #1 parity rules.

Data structure

• Extension areas: if attaching to existing messages (init, HTLC-related messages, etc.), use spec-defined extension TLVs.

Privacy

• Blinded paths: if the protocol carries identifiers or route information, use route blinding / blinded paths to protect endpoint privacy.

Specification strictness

Keep message and TLV definitions parseable and consistent. Use a BOLT-style definition shape like:

1. type: <TypeNumber> (`<message_name>`)
2. data:
   * [`<type>`:`<field_name>`]
   * [`<length>`*`<type>`:`<array_name>`]

Workflow

1. Identify the exact section you are changing (message definition, TLV table, state machine, examples).
2. Update the English spec first (docs/​protocol/​protocol.md). If the Japanese page is meant to mirror it, update docs/​protocol/​protocol-ja.md accordingly (it may be a summary).
3. Keep terminology consistent with identifiers used in go-lcpd/ (when they exist).
4. If you introduce new fields:
   • Define them as TLVs with explicit type numbers and clear semantics.
   • Specify validation rules (required/​optional, size limits, encoding, error handling).
5. Add/​adjust examples to match the new behavior.

Validation

• For prose/​spec changes: re-read for consistency and BOLT-style formatting.
• If the change implies implementation changes, ensure go-lcpd/ is updated in the same PR and validated with:
  • cd go-lcpd && make test
  • cd go-lcpd && make lint