Class: MCPClient::ServerStdio

Inherits:
ServerBase show all
Defined in:
lib/mcp_client/server_stdio.rb

Overview

JSON-RPC implementation of MCP server over stdio.

Constant Summary collapse

READ_TIMEOUT =

Timeout in seconds for responses

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Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(command:, retries: 0, retry_backoff: 1, logger: nil) ⇒ ServerStdio

Returns a new instance of ServerStdio.

Parameters:

  • command (String, Array) —

    the stdio command to launch the MCP JSON-RPC server

  • retries (Integer) (defaults to: 0) —

    number of retry attempts on transient errors

  • retry_backoff (Numeric) (defaults to: 1) —

    base delay in seconds for exponential backoff

  • logger (Logger, nil) (defaults to: nil) —

    optional logger



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# File 'lib/mcp_client/server_stdio.rb', line 20

def initialize(command:, retries: 0, retry_backoff: 1, logger: nil)
  super()
  @command = command.is_a?(Array) ? command.join(' ') : command
  @mutex = Mutex.new
  @cond = ConditionVariable.new
  @next_id = 1
  @pending = {}
  @initialized = false
  @logger = logger || Logger.new($stdout, level: Logger::WARN)
  @max_retries = retries
  @retry_backoff = retry_backoff
end

Instance Attribute Details

#command ⇒ Object (readonly)

Returns the value of attribute command.



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# File 'lib/mcp_client/server_stdio.rb', line 11

def command
  @command
end

Instance Method Details

#call_tool(tool_name, parameters) ⇒ Object

Call a tool with the given parameters

Parameters:

  • tool_name (String) —

    the name of the tool to call

  • parameters (Hash) —

    the parameters to pass to the tool

Returns:

  • (Object) —

    the result of the tool invocation

Raises:



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# File 'lib/mcp_client/server_stdio.rb', line 97

def call_tool(tool_name, parameters)
  ensure_initialized
  req_id = next_id
  # JSON-RPC method for calling a tool
  req = {
    'jsonrpc' => '2.0',
    'id' => req_id,
    'method' => 'tools/call',
    'params' => { 'name' => tool_name, 'arguments' => parameters }
  }
  send_request(req)
  res = wait_response(req_id)
  if (err = res['error'])
    raise MCPClient::Errors::ServerError, err['message']
  end

  res['result']
rescue StandardError => e
  raise MCPClient::Errors::ToolCallError, "Error calling tool '#{tool_name}': #{e.message}"
end

#cleanup ⇒ Object

Clean up the server connection Closes all stdio handles and terminates any running processes and threads



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# File 'lib/mcp_client/server_stdio.rb', line 120

def cleanup
  return unless @stdin

  @stdin.close unless @stdin.closed?
  @stdout.close unless @stdout.closed?
  @stderr.close unless @stderr.closed?
  if @wait_thread&.alive?
    Process.kill('TERM', @wait_thread.pid)
    @wait_thread.join(1)
  end
  @reader_thread&.kill
rescue StandardError
  # Clean up resources during unexpected termination
ensure
  @stdin = @stdout = @stderr = @wait_thread = @reader_thread = nil
end

#connect ⇒ Boolean

Connect to the MCP server by launching the command process via stdout/stdin

Returns:

  • (Boolean) —

    true if connection was successful

Raises:



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# File 'lib/mcp_client/server_stdio.rb', line 36

def connect
  @stdin, @stdout, @stderr, @wait_thread = Open3.popen3(@command)
  true
rescue StandardError => e
  raise MCPClient::Errors::ConnectionError, "Failed to connect to MCP server: #{e.message}"
end

#handle_line(line) ⇒ Object

Handle a line of output from the stdio server Parses JSON-RPC messages and adds them to pending responses

Parameters:

  • line (String) —

    line of output to parse



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# File 'lib/mcp_client/server_stdio.rb', line 57

def handle_line(line)
  msg = JSON.parse(line)
  @logger.debug("Received line: #{line.chomp}")
  id = msg['id']
  return unless id

  @mutex.synchronize do
    @pending[id] = msg
    @cond.broadcast
  end
rescue JSON::ParserError
  # Skip non-JSONRPC lines in the output stream
end

#list_tools ⇒ Array<MCPClient::Tool>

List all tools available from the MCP server

Returns:

Raises:



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# File 'lib/mcp_client/server_stdio.rb', line 75

def list_tools
  ensure_initialized
  req_id = next_id
  # JSON-RPC method for listing tools
  req = { 'jsonrpc' => '2.0', 'id' => req_id, 'method' => 'tools/list', 'params' => {} }
  send_request(req)
  res = wait_response(req_id)
  if (err = res['error'])
    raise MCPClient::Errors::ServerError, err['message']
  end

  (res.dig('result', 'tools') || []).map { |td| MCPClient::Tool.from_json(td) }
rescue StandardError => e
  raise MCPClient::Errors::ToolCallError, "Error listing tools: #{e.message}"
end

#start_reader ⇒ Object

Spawn a reader thread to collect JSON-RPC responses



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# File 'lib/mcp_client/server_stdio.rb', line 44

def start_reader
  @reader_thread = Thread.new do
    @stdout.each_line do |line|
      handle_line(line)
    end
  rescue StandardError
    # Reader thread aborted unexpectedly
  end
end