Class: MCPClient::Client

Inherits:
Object
  • Object
show all
Defined in:
lib/mcp_client/client.rb

Overview

MCP Client for integrating with the Model Context Protocol This is the main entry point for using MCP tools

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(mcp_server_configs: [], logger: nil) ⇒ Client

Initialize a new MCPClient::Client

Parameters:

  • mcp_server_configs (Array<Hash>) (defaults to: []) —

    configurations for MCP servers

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

    optional logger, defaults to STDOUT



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

def initialize(mcp_server_configs: [], logger: nil)
  @logger = logger || Logger.new($stdout, level: Logger::WARN)
  @logger.progname = self.class.name
  @logger.formatter = proc { |severity, _datetime, progname, msg| "#{severity} [#{progname}] #{msg}\n" }
  @servers = mcp_server_configs.map do |config|
    @logger.debug("Creating server with config: #{config.inspect}")
    MCPClient::ServerFactory.create(config, logger: @logger)
  end
  @tool_cache = {}
  # JSON-RPC notification listeners
  @notification_listeners = []
  # Register default and user-defined notification handlers on each server
  @servers.each do |server|
    server.on_notification do |method, params|
      # Default notification processing (e.g., cache invalidation, logging)
      process_notification(server, method, params)
      # Invoke user-defined listeners
      @notification_listeners.each { |cb| cb.call(server, method, params) }
    end
  end
end

Instance Attribute Details

#logger ⇒ Object (readonly)

Returns the value of attribute logger.



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# File 'lib/mcp_client/client.rb', line 15

attr_reader :servers, :tool_cache, :logger

#servers ⇒ Array<MCPClient::ServerBase> (readonly)

Returns list of servers.

Returns:



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# File 'lib/mcp_client/client.rb', line 15

def servers
  @servers
end

#tool_cache ⇒ Hash<String, MCPClient::Tool> (readonly)

Returns cache of tools by name.

Returns:



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# File 'lib/mcp_client/client.rb', line 15

attr_reader :servers, :tool_cache, :logger

Instance Method Details

#call_tool(tool_name, parameters, server: nil) ⇒ Object

Calls a specific tool by name with the given parameters

Parameters:

  • tool_name (String) —

    the name of the tool to call

  • parameters (Hash) —

    the parameters to pass to the tool

  • server (String, Symbol, Integer, MCPClient::ServerBase, nil) (defaults to: nil) —

    optional server to use

Returns:

  • (Object) —

    the result of the tool invocation

Raises:



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# File 'lib/mcp_client/client.rb', line 84

def call_tool(tool_name, parameters, server: nil)
  tools = list_tools

  if server
    # Use the specified server
    srv = select_server(server)
    # Find the tool on this specific server
    tool = tools.find { |t| t.name == tool_name && t.server == srv }
    unless tool
      raise MCPClient::Errors::ToolNotFound,
            "Tool '#{tool_name}' not found on server '#{srv.name || srv.class.name}'"
    end
  else
    # Find the tool across all servers
    matching_tools = tools.select { |t| t.name == tool_name }

    if matching_tools.empty?
      raise MCPClient::Errors::ToolNotFound, "Tool '#{tool_name}' not found"
    elsif matching_tools.size > 1
      # If multiple matches, disambiguate with server names
      server_names = matching_tools.map { |t| t.server&.name || 'unnamed' }
      raise MCPClient::Errors::AmbiguousToolName,
            "Multiple tools named '#{tool_name}' found across servers (#{server_names.join(', ')}). " \
            "Please specify a server using the 'server' parameter."
    end

    tool = matching_tools.first
  end

  # Validate parameters against tool schema
  validate_params!(tool, parameters)

  # Use the tool's associated server
  server = tool.server
  raise MCPClient::Errors::ServerNotFound, "No server found for tool '#{tool_name}'" unless server

  begin
    server.call_tool(tool_name, parameters)
  rescue MCPClient::Errors::ConnectionError => e
    # Add server identity information to the error for better context
    server_id = server.name ? "#{server.class}[#{server.name}]" : server.class.name
    raise MCPClient::Errors::ToolCallError, "Error calling tool '#{tool_name}': #{e.message} (Server: #{server_id})"
  end
end

#call_tool_streaming(tool_name, parameters, server: nil) ⇒ Enumerator

Stream call of a specific tool by name with the given parameters. Returns an Enumerator yielding streaming updates if supported.

Parameters:

  • tool_name (String) —

    the name of the tool to call

  • parameters (Hash) —

    the parameters to pass to the tool

  • server (String, Symbol, Integer, MCPClient::ServerBase, nil) (defaults to: nil) —

    optional server to use

Returns:

  • (Enumerator) —

    streaming enumerator or single-value enumerator

Raises:



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# File 'lib/mcp_client/client.rb', line 215

def call_tool_streaming(tool_name, parameters, server: nil)
  tools = list_tools

  if server
    # Use the specified server
    srv = select_server(server)
    # Find the tool on this specific server
    tool = tools.find { |t| t.name == tool_name && t.server == srv }
    unless tool
      raise MCPClient::Errors::ToolNotFound,
            "Tool '#{tool_name}' not found on server '#{srv.name || srv.class.name}'"
    end
  else
    # Find the tool across all servers
    matching_tools = tools.select { |t| t.name == tool_name }

    if matching_tools.empty?
      raise MCPClient::Errors::ToolNotFound, "Tool '#{tool_name}' not found"
    elsif matching_tools.size > 1
      # If multiple matches, disambiguate with server names
      server_names = matching_tools.map { |t| t.server&.name || 'unnamed' }
      raise MCPClient::Errors::AmbiguousToolName,
            "Multiple tools named '#{tool_name}' found across servers (#{server_names.join(', ')}). " \
            "Please specify a server using the 'server' parameter."
    end

    tool = matching_tools.first
  end

  # Validate parameters against tool schema
  validate_params!(tool, parameters)

  # Use the tool's associated server
  server = tool.server
  raise MCPClient::Errors::ServerNotFound, "No server found for tool '#{tool_name}'" unless server

  begin
    # Use the streaming API if it's available
    server.call_tool_streaming(tool_name, parameters)
  rescue MCPClient::Errors::ConnectionError => e
    # Add server identity information to the error for better context
    server_id = server.name ? "#{server.class}[#{server.name}]" : server.class.name
    msg = "Error calling streaming tool '#{tool_name}': #{e.message} (Server: #{server_id})"
    raise MCPClient::Errors::ToolCallError, msg
  end
end

#call_tools(calls) ⇒ Array<Object>

Call multiple tools in batch

Parameters:

  • calls (Array<Hash>) —

    array of calls in the form: { name: tool_name, parameters: …, server: optional_server_name }

Returns:

  • (Array<Object>) —

    array of results for each tool invocation



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# File 'lib/mcp_client/client.rb', line 200

def call_tools(calls)
  calls.map do |call|
    name = call[:name] || call['name']
    params = call[:parameters] || call['parameters'] || {}
    server = call[:server] || call['server']
    call_tool(name, params, server: server)
  end
end

#cleanup ⇒ Object

Clean up all server connections



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# File 'lib/mcp_client/client.rb', line 157

def cleanup
  servers.each(&:cleanup)
end

#clear_cache ⇒ void

This method returns an undefined value.

Clear the cached tools so that next list_tools will fetch fresh data



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# File 'lib/mcp_client/client.rb', line 163

def clear_cache
  @tool_cache.clear
end

#find_server(name) ⇒ MCPClient::ServerBase?

Find a server by name

Parameters:

  • name (String) —

    the name of the server to find

Returns:



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# File 'lib/mcp_client/client.rb', line 177

def find_server(name)
  @servers.find { |s| s.name == name }
end

#find_tool(pattern) ⇒ MCPClient::Tool?

Find the first tool whose name matches the given pattern

Parameters:

  • pattern (String, Regexp) —

    pattern to match tool names

Returns:



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# File 'lib/mcp_client/client.rb', line 192

def find_tool(pattern)
  find_tools(pattern).first
end

#find_tools(pattern) ⇒ Array<MCPClient::Tool>

Find all tools whose name matches the given pattern (String or Regexp)

Parameters:

  • pattern (String, Regexp) —

    pattern to match tool names

Returns:



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# File 'lib/mcp_client/client.rb', line 184

def find_tools(pattern)
  rx = pattern.is_a?(Regexp) ? pattern : /#{Regexp.escape(pattern)}/
  list_tools.select { |t| t.name.match(rx) }
end

#list_tools(cache: true) ⇒ Array<MCPClient::Tool>

Lists all available tools from all connected MCP servers

Parameters:

  • cache (Boolean) (defaults to: true) —

    whether to use cached tools or fetch fresh

Returns:

Raises:



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# File 'lib/mcp_client/client.rb', line 47

def list_tools(cache: true)
  return @tool_cache.values if cache && !@tool_cache.empty?

  tools = []
  connection_errors = []

  servers.each do |server|
    server.list_tools.each do |tool|
      @tool_cache[tool.name] = tool
      tools << tool
    end
  rescue MCPClient::Errors::ConnectionError => e
    # Fast-fail on authorization errors for better user experience
    # If this is the first server or we haven't collected any tools yet,
    # raise the auth error directly to avoid cascading error messages
    raise e if e.message.include?('Authorization failed') && tools.empty?

    # Store the error and try other servers
    connection_errors << e
    @logger.error("Server error: #{e.message}")
  end

  # If we didn't get any tools from any server but have servers configured, report failure
  if tools.empty? && !servers.empty?
    raise connection_errors.first if connection_errors.any?

    @logger.warn('No tools found from any server.')
  end

  tools
end

#on_notification {|server, method, params| ... } ⇒ void

This method returns an undefined value.

Register a callback for JSON-RPC notifications from servers

Yields:

  • (server, method, params) 


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# File 'lib/mcp_client/client.rb', line 170

def on_notification(&block)
  @notification_listeners << block
end

#ping(server_index: nil) ⇒ Object

Ping the MCP server to check connectivity (zero-parameter heartbeat call)

Parameters:

  • server_index (Integer, nil) (defaults to: nil) —

    optional index of a specific server to ping, nil for first available

Returns:

  • (Object) —

    result from the ping request

Raises:



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# File 'lib/mcp_client/client.rb', line 266

def ping(server_index: nil)
  if server_index.nil?
    # Ping first available server
    raise MCPClient::Errors::ServerNotFound, 'No server available for ping' if @servers.empty?

    @servers.first.ping
  else
    # Ping specified server
    if server_index >= @servers.length
      raise MCPClient::Errors::ServerNotFound,
            "Server at index #{server_index} not found"
    end

    @servers[server_index].ping
  end
end

#send_notification(method, params: {}, server: nil) ⇒ void

This method returns an undefined value.

Send a raw JSON-RPC notification to a server (no response expected)

Parameters:

  • method (String) —

    JSON-RPC method name

  • params (Hash) (defaults to: {}) —

    parameters for the notification

  • server (Integer, String, Symbol, MCPClient::ServerBase, nil) (defaults to: nil) —

    server selector



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# File 'lib/mcp_client/client.rb', line 298

def send_notification(method, params: {}, server: nil)
  srv = select_server(server)
  srv.rpc_notify(method, params)
end

#send_rpc(method, params: {}, server: nil) ⇒ Object

Send a raw JSON-RPC request to a server

Parameters:

  • method (String) —

    JSON-RPC method name

  • params (Hash) (defaults to: {}) —

    parameters for the request

  • server (Integer, String, Symbol, MCPClient::ServerBase, nil) (defaults to: nil) —

    server selector

Returns:

  • (Object) —

    result from the JSON-RPC response



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# File 'lib/mcp_client/client.rb', line 288

def send_rpc(method, params: {}, server: nil)
  srv = select_server(server)
  srv.rpc_request(method, params)
end

#to_anthropic_tools(tool_names: nil) ⇒ Array<Hash>

Convert MCP tools to Anthropic Claude tool specifications

Parameters:

  • tool_names (Array<String>, nil) (defaults to: nil) —

    optional list of tool names to include, nil means all tools

Returns:

  • (Array<Hash>) —

    Anthropic Claude tool specifications



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# File 'lib/mcp_client/client.rb', line 141

def to_anthropic_tools(tool_names: nil)
  tools = list_tools
  tools = tools.select { |t| tool_names.include?(t.name) } if tool_names
  tools.map(&:to_anthropic_tool)
end

#to_google_tools(tool_names: nil) ⇒ Array<Hash>

Convert MCP tools to Google Vertex AI tool specifications

Parameters:

  • tool_names (Array<String>, nil) (defaults to: nil) —

    optional list of tool names to include, nil means all tools

Returns:

  • (Array<Hash>) —

    Google Vertex AI tool specifications with cleaned schemas



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# File 'lib/mcp_client/client.rb', line 150

def to_google_tools(tool_names: nil)
  tools = list_tools
  tools = tools.select { |t| tool_names.include?(t.name) } if tool_names
  tools.map(&:to_google_tool)
end

#to_openai_tools(tool_names: nil) ⇒ Array<Hash>

Convert MCP tools to OpenAI function specifications

Parameters:

  • tool_names (Array<String>, nil) (defaults to: nil) —

    optional list of tool names to include, nil means all tools

Returns:

  • (Array<Hash>) —

    OpenAI function specifications



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# File 'lib/mcp_client/client.rb', line 132

def to_openai_tools(tool_names: nil)
  tools = list_tools
  tools = tools.select { |t| tool_names.include?(t.name) } if tool_names
  tools.map(&:to_openai_tool)
end