Crate sim_codec_mcp 

MCP JSON-RPC envelope codec for SIM.

This crate provides codec:mcp, a pure data codec for one MCP JSON-RPC envelope per frame. It owns only envelope validation and conversion; routing, transport, and callable execution live in later MCP libraries. As a domain codec it round-trips only MCP envelopes and fails closed outside them.

Module map (all modules are private; the public surface is re-exported from this crate root):

• canonical: the McpCodec decoder/encoder and the McpCodecLib host lib bridging MCP JSON-RPC text and the envelope model.
• envelope: the envelope types (McpEnvelope and its request, notification, response, and error variants) and their class symbols.
• error: the JSON-RPC and MCP error-code constants and the codec error helper.
• expr: conversion between envelopes and checked Expr values (envelope_to_expr, expr_to_envelope).

Structs

McpCodec

The codec:mcp decoder/encoder.

McpCodecLib

The host-registered Lib that installs McpCodec as the domain codec codec:mcp.

McpError

The error object inside an McpErrorEnvelope.

McpErrorEnvelope

A JSON-RPC error response for a prior request.

McpNotification

A JSON-RPC notification: a method call with no id and no response.

McpRequest

A JSON-RPC request: an addressed method call expecting a response.

McpResponse

A JSON-RPC successful response for a prior request.

Enums

McpEnvelope

One MCP JSON-RPC 2.0 envelope: the typed payload carried by a single frame.

Constants

CANCELLED

MCP cancelled: the request was cancelled before completion (-32003).

CAPABILITY_DENIED

MCP capability denied: a required capability was not granted (-32001).

EXECUTION_ERROR

MCP execution error: a tool or method failed while executing (-32002).

INTERNAL_ERROR

JSON-RPC internal error: an internal failure occurred (-32603).

INVALID_PARAMS

JSON-RPC invalid params: the method parameters are invalid (-32602).

INVALID_REQUEST

JSON-RPC invalid request: the payload is not a valid request object (-32600).

METHOD_NOT_FOUND

JSON-RPC method not found: the requested method does not exist (-32601).

NOT_FOUND

MCP not found: the addressed resource does not exist (-32004).

PARSE_ERROR

JSON-RPC parse error: invalid JSON was received (-32700).

RATE_LIMITED

MCP rate limited: the request was throttled (-32005).

Functions

envelope_to_expr

Project an McpEnvelope into its canonical Expr map, with the mcp version field and the variant-specific fields.

expr_to_envelope

Validate a canonical Expr map back into a typed McpEnvelope.

mcp_error_class_symbol

The stable class symbol mcp/Error for McpError.

mcp_error_envelope_class_symbol

The stable class symbol mcp/ErrorEnvelope for McpErrorEnvelope.

mcp_notification_class_symbol

The stable class symbol mcp/Notification for McpNotification.

mcp_request_class_symbol

The stable class symbol mcp/Request for McpRequest.

mcp_response_class_symbol

The stable class symbol mcp/Response for McpResponse.