A2UICore.MCP.Client behaviour (A2UICore v0.1.1)

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A connection to a Model Context Protocol server, as the MCP catalog's functions use it.

A2UICore makes no MCP connections itself: the host implements this behaviour over whatever MCP client it uses and passes the client as {module, state} (see A2UICore.Catalog.MCP.catalog/2). Every callback receives the state; values are MCP's JSON objects with string keys.

  • call_tool/3 sends tools/call and returns the CallToolResult.
  • read_resource/2 sends resources/read and returns its result (%{"contents" => [...]}); without it, the UI resources a tool names are not read.
  • list_tools/1 sends tools/list and returns the tools; without it, a tool's declared UI resource (_meta.ui.resourceUri in its descriptor) is not looked up.

A callback returns {:error, reason} on failure; reason is a string, an exception or any term, and becomes part of the function's error message. Results are not cached between calls; a client that wants caching (tools/list rarely changes) does it itself.

Summary

Types

t()

A client: its module and the state passed to every callback.

Callbacks

call_tool(state, name, arguments)

Calls the tool name with arguments.

list_tools(state)

Lists the server's tools.

read_resource(state, uri)

Reads the resource at uri.

Types

t()

(since 0.1.0) 
@type t() :: {module(), term()}

A client: its module and the state passed to every callback.

Callbacks

call_tool(state, name, arguments)

(since 0.1.0) 
@callback call_tool(state :: term(), name :: String.t(), arguments :: map()) ::
  {:ok, map() | nil} | {:error, term()}

Calls the tool name with arguments.

list_tools(state)

(since 0.1.0) (optional) 
@callback list_tools(state :: term()) :: {:ok, [map()]} | {:error, term()}

Lists the server's tools.

read_resource(state, uri)

(since 0.1.0) (optional) 
@callback read_resource(state :: term(), uri :: String.t()) ::
  {:ok, map()} | {:error, term()}

Reads the resource at uri.