Message

type: module path: "@root/src/PuduLangMcp/Domain/Rpc/Message.pudu" fidelity: Active grammar: "[[grammar/pudu]]" seam: "[[seams/Transport]]" depth_score: 0.6 depth_status: DEEP coupling: 3 interface_stability: 0.9 tags: [module, deep] aliases: [Message]

Purpose

Classify one line of input as a request, a notification, a response from the client, or a refusal carrying the protocol error to answer with.

Interface

Signatures

export type RequestId = NumberId(Int) | TextId(Str)

export type Incoming
  = Request(RequestId, Str, Json.Json)    // id, method, params (an object; {} when absent)
  | Notification(Str, Json.Json)          // method, params
  | ClientResponse                        // has result or error; this server sends no requests
  | Refused(Option[RequestId], RpcError.ProtocolError)

export fn parse(line: Str) -> Incoming
export fn idJson(id: &RequestId) -> Json.Json

Governance

• Only a request is ever answered; a Refused without an id is answered with "id": null.

Linkage

• Requires: [[src/PuduLangMcp/Errors/RpcError]], [[src/PuduLangMcp/Constants/Protocol]], [[src/PuduLangMcp/Utils/JsonAccess]].
• Consumed by: [[src/PuduLangMcp/App/Dispatch]].

Algorithm

1. Decode; failure is Refused(None, ParseError(reason)).
2. A JSON array is Refused(None, InvalidRequest): batching is not part of MCP.
3. A non-object is Refused(None, InvalidRequest).
4. Read id when present: an integer or string is kept; null, a fraction, or any other kind is Refused(None, InvalidRequest).
5. jsonrpc must be the string "2.0", else Refused(id, InvalidRequest).
6. No method but result or error present is ClientResponse.
7. method must be a string, else Refused(id, InvalidRequest).
8. params, when present, must be an object; else Refused(id, InvalidParams) for a request and a notification with {} params otherwise (a notification is never answered).
9. With an id: Request; without: Notification.

Negative Logic (Prohibited Paths)

• Never answers a notification whose envelope is valid, whatever its params. A line that is not a valid JSON-RPC envelope is refused even without an id, as JSON-RPC 2.0 requires.
• Never treats a string id "1" and integer id 1 as the same id.

Edge Cases

• Leading or trailing whitespace around the JSON is accepted.
• An empty line is a parse error.
• params: null on a request is invalid params.

Depth

DEPTH 0.6 (DEEP). Nine rules behind one function.

Grill Log

• Q: Accept params as an array (JSON-RPC by-position)? A: No; every MCP method takes an object. _Rejected:_ positional parameters.
• Q: Answer a line whose id is null? A: Yes, with -32600 and id: null; the sender broke the rule that ids must not be null and deserves to learn it.

Referenced by

[[src/PuduLangMcp/Domain/Rpc/_MOC]] · [[src/PuduLangMcp/Domain/Rpc/Reply]]