DDD.MCP (vicander v0.1.1)

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The application as a Model Context Protocol server: an AI client can call its commands and queries as tools and read its aggregates as resources.

This module is the protocol core. It takes one decoded JSON-RPC message and returns the reply, so a transport (DDD.MCP.Stdio, or an HTTP Plug later) only moves JSON. Use it through a server module (DDD.MCP.Server).

What is exposed

  • Tools. Each listed command and query is a tool. Its input schema is built from the command's fields (DDD.MCP.Schema), its description from description "...". Queries are marked readOnlyHint: true.
  • Resources. Each listed aggregate is read-only: name://<identity> reads one, and name://by/<field>/<value> runs a find_by the repository port declares (at most 100 results). resources/list is empty on purpose: a client is never handed a whole table.

What a client is told about failures

A business error (validation, not found, a precondition) is returned with its code, message and violations, so the client can correct itself. An infrastructure error is a generic "the operation failed" and the details only go to the log. A malformed request gets a JSON-RPC error saying what was wrong.

A read-only server refuses every command tool. An :authorize function is called before every tool call and resource read and may refuse it.

Summary

Functions

handle(registry, message)

Handle one decoded JSON-RPC message: {:reply, response} or :noreply (notifications).

parse_error()

A parse-error response, for a transport that received text that is not JSON.

Functions

handle(registry, message)

@spec handle(DDD.MCP.Registry.t(), term()) :: {:reply, map()} | :noreply

Handle one decoded JSON-RPC message: {:reply, response} or :noreply (notifications).

parse_error()

A parse-error response, for a transport that received text that is not JSON.