Class: Phronomy::Tools::Mcp::StdioTransport

Inherits:
Object
  • Object
show all
Defined in:
lib/phronomy/tools/mcp.rb

Overview

Minimal stdio transport implementing a subset of the MCP JSON-RPC protocol. Keeps the child process alive for the lifetime of this transport instance so that session state (registered resources, tool context, etc.) is preserved across multiple calls.

Instance Method Summary collapse

Constructor Details

#initialize(command, read_timeout: 30, env: nil, cwd: nil, startup_timeout: nil) ⇒ StdioTransport

Returns a new instance of StdioTransport.

Parameters:

  • command (String) —

    shell command to spawn the MCP server process

  • read_timeout (Integer) (defaults to: 30) —

    seconds to wait for the server's JSON-RPC response before raising Phronomy::ToolError. Mirrors the read_timeout option on HttpTransport. Defaults to 30 seconds.

  • env (Hash, nil) (defaults to: nil) —

    environment variable overrides for the subprocess. When provided, only these variables are added/overridden; the parent environment is still inherited. Use nil as a value to unset a variable in the child process (e.g. { "SECRET" => nil }). An empty string value (+""+ ) sets the variable to an empty string — it does NOT unset it.

  • cwd (String, nil) (defaults to: nil) —

    working directory for the subprocess. Defaults to the current process's working directory.

  • startup_timeout (Numeric, nil) (defaults to: nil) —

    seconds to wait for the server to emit its first line on stdout before raising Phronomy::ToolError. When nil (default), no startup check is performed.



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# File 'lib/phronomy/tools/mcp.rb', line 134

def initialize(command, read_timeout: 30, env: nil, cwd: nil, startup_timeout: nil)
  # Split the command string into an argv array so that Open3 executes
  # it directly without going through the shell, preventing injection.
  @command = Shellwords.split(command)
  @read_timeout = read_timeout
  @env = env
  @cwd = cwd
  @startup_timeout = startup_timeout
  @stdin = nil
  @stdout = nil
  @stderr = nil
  @wait_thr = nil
  @stderr_thread = nil
  @stderr_op = nil
end

Instance Method Details

#call_tool(tool_name, args) ⇒ Object

Call a tool on the MCP server using the tools/call method.

Parameters:

  • tool_name (String)
  • args (Hash)

Returns:

  • (Object) —

    the tool result



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# File 'lib/phronomy/tools/mcp.rb', line 195

def call_tool(tool_name, args)
  response = rpc_call("tools/call", {name: tool_name, arguments: args})
  if response["error"]
    err_msg = response.dig("error", "message") || response["error"].to_s
    raise Phronomy::ToolError, "MCP server returned error: #{err_msg}"
  end
  content = response.dig("result", "content")

  # MCP content is an array of content blocks; extract text blocks.
  if content.is_a?(Array)
    texts = content.select { |c| c["type"] == "text" }.map { |c| c["text"] }
    (texts.length == 1) ? texts.first : texts
  else
    content
  end
end

#close ⇒ Object

Shut down the child process and close its IO streams.



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# File 'lib/phronomy/tools/mcp.rb', line 151

def close
  @stdin&.close
  @stdout&.close
  @stderr&.close
  @stdin = nil
  @stdout = nil
  @stderr = nil
  stderr_thread = @stderr_thread
  stderr_op = @stderr_op
  wait_thr = @wait_thr
  @stderr_thread = nil
  @stderr_op = nil
  @wait_thr = nil
  stderr_thread&.join(1)
  begin
    stderr_op&.blocking_wait(timeout: 1.0)
  rescue
    nil
  end
  wait_thr&.join(5)
end

#fetch_tool(tool_name) ⇒ Hash

Retrieve the tool definition from the server using the MCP tools/list method.

Parameters:

  • tool_name (String)

Returns:

  • (Hash) —

    { description:, parameters: }

Raises:

  • (ArgumentError) 


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# File 'lib/phronomy/tools/mcp.rb', line 177

def fetch_tool(tool_name)
  response = rpc_call("tools/list", {})
  tools = response.dig("result", "tools") || []
  defn = tools.find { |t| t["name"] == tool_name }
  raise ArgumentError, "Tool #{tool_name.inspect} not found on MCP server #{@command.inspect}" unless defn

  required_names = defn.dig("inputSchema", "required") || []
  {
    description: defn["description"],
    parameters: parse_schema_params(defn.dig("inputSchema", "properties") || {}, required_names: required_names)
  }
end