Class: MCP::Client::HTTP

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

Overview

TODO: HTTP GET for SSE streaming is not yet implemented.

https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#listening-for-messages-from-the-server

TODO: Resumability and redelivery with Last-Event-ID is not yet implemented.

https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#resumability-and-redelivery

Constant Summary collapse

ACCEPT_HEADER = 
"application/json, text/event-stream"
SESSION_ID_HEADER = 
"Mcp-Session-Id"
PROTOCOL_VERSION_HEADER = 
"MCP-Protocol-Version"

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(url:, headers: {}, &block) ⇒ HTTP

Returns a new instance of HTTP.



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# File 'lib/mcp/client/http.rb', line 22

def initialize(url:, headers: {}, &block)
  @url = url
  @headers = headers
  @faraday_customizer = block
  @session_id = nil
  @protocol_version = nil
  @server_info = nil
  @connected = false
end

Instance Attribute Details

#protocol_version ⇒ Object (readonly)

Returns the value of attribute protocol_version.



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# File 'lib/mcp/client/http.rb', line 20

def protocol_version
  @protocol_version
end

#server_info ⇒ Object (readonly)

Returns the value of attribute server_info.



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# File 'lib/mcp/client/http.rb', line 20

def server_info
  @server_info
end

#session_id ⇒ Object (readonly)

Returns the value of attribute session_id.



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# File 'lib/mcp/client/http.rb', line 20

def session_id
  @session_id
end

#url ⇒ Object (readonly)

Returns the value of attribute url.



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# File 'lib/mcp/client/http.rb', line 20

def url
  @url
end

Instance Method Details

#close ⇒ Object

Terminates the session by sending an HTTP DELETE to the MCP endpoint with the current ‘Mcp-Session-Id` header, and clears locally tracked session state afterward. No-op when no session has been established.

Per spec, the server MAY respond with HTTP 405 Method Not Allowed when it does not support client-initiated termination, and returns 404 for a session it has already terminated. Both mean the session is gone —the desired end state. Other errors surface to the caller; local session state is cleared either way. modelcontextprotocol.io/specification/2025-11-25/basic/transports#session-management



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# File 'lib/mcp/client/http.rb', line 199

def close
  unless @session_id
    clear_session
    return
  end

  begin
    client.delete("", nil, session_headers)
  rescue Faraday::ClientError => e
    raise unless [404, 405].include?(e.response&.dig(:status))
  ensure
    clear_session
  end
end

#connect(client_info: nil, protocol_version: nil, capabilities: {}) ⇒ Hash

Performs the MCP ‘initialize` handshake: sends an `initialize` request followed by the required `notifications/initialized` notification. The server’s ‘InitializeResult` (protocol version, capabilities, server info, instructions) is cached on the transport and returned.

Idempotent: a second call returns the cached ‘InitializeResult` without contacting the server. After `close`, state is cleared and `connect` will handshake again.

modelcontextprotocol.io/specification/2025-11-25/basic/lifecycle#initialization

Parameters:

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

    ‘{ name:, version: }` identifying the client. Defaults to `{ name: “mcp-ruby-client”, version: MCP::VERSION }`.

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

    Protocol version to offer. Defaults to ‘MCP::Configuration::LATEST_STABLE_PROTOCOL_VERSION`.

  • capabilities (Hash) (defaults to: {}) —

    Capabilities advertised by the client. Defaults to ‘{}`.

Returns:

  • (Hash) —

    The server’s ‘InitializeResult`.

Raises:

  • (RequestHandlerError) —

    If the server responds with a JSON-RPC error or a malformed result.



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# File 'lib/mcp/client/http.rb', line 50

def connect(client_info: nil, protocol_version: nil, capabilities: {})
  return @server_info if connected?

  client_info ||= { name: "mcp-ruby-client", version: MCP::VERSION }
  protocol_version ||= MCP::Configuration::LATEST_STABLE_PROTOCOL_VERSION

  response = send_request(request: {
    jsonrpc: JsonRpcHandler::Version::V2_0,
    id: SecureRandom.uuid,
    method: MCP::Methods::INITIALIZE,
    params: {
      protocolVersion: protocol_version,
      capabilities: capabilities,
      clientInfo: client_info,
    },
  })

  if response.is_a?(Hash) && response.key?("error")
    clear_session
    error = response["error"]
    raise RequestHandlerError.new(
      "Server initialization failed: #{error["message"]}",
      { method: MCP::Methods::INITIALIZE },
      error_type: :internal_error,
    )
  end

  unless response.is_a?(Hash) && response["result"].is_a?(Hash)
    clear_session
    raise RequestHandlerError.new(
      "Server initialization failed: missing result in response",
      { method: MCP::Methods::INITIALIZE },
      error_type: :internal_error,
    )
  end

  @server_info = response["result"]
  negotiated_protocol_version = @server_info["protocolVersion"]
  unless MCP::Configuration::SUPPORTED_STABLE_PROTOCOL_VERSIONS.include?(negotiated_protocol_version)
    clear_session
    raise RequestHandlerError.new(
      "Server initialization failed: unsupported protocol version #{negotiated_protocol_version.inspect}",
      { method: MCP::Methods::INITIALIZE },
      error_type: :internal_error,
    )
  end

  begin
    send_request(request: {
      jsonrpc: JsonRpcHandler::Version::V2_0,
      method: MCP::Methods::NOTIFICATIONS_INITIALIZED,
    })
  rescue StandardError
    clear_session
    raise
  end

  @connected = true
  @server_info
end

#connected? ⇒ Boolean

Returns true once ‘connect` has completed the full handshake (`initialize` response received and `notifications/initialized` sent). Returns false before the first handshake and after `close`.

Returns:

  • (Boolean) 


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# File 'lib/mcp/client/http.rb', line 114

def connected?
  @connected
end

#send_request(request:) ⇒ Object

Sends a JSON-RPC request and returns the parsed response body. After a successful ‘initialize` handshake, the session ID and protocol version returned by the server are captured and automatically included on subsequent requests.



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# File 'lib/mcp/client/http.rb', line 122

def send_request(request:)
  method = request[:method] || request["method"]
  params = request[:params] || request["params"]

  response = client.post("", request, session_headers)
  body = parse_response_body(response, method, params)

  capture_session_info(method, response, body)

  body
rescue Faraday::BadRequestError => e
  raise RequestHandlerError.new(
    "The #{method} request is invalid",
    { method: method, params: params },
    error_type: :bad_request,
    original_error: e,
  )
rescue Faraday::UnauthorizedError => e
  raise RequestHandlerError.new(
    "You are unauthorized to make #{method} requests",
    { method: method, params: params },
    error_type: :unauthorized,
    original_error: e,
  )
rescue Faraday::ForbiddenError => e
  raise RequestHandlerError.new(
    "You are forbidden to make #{method} requests",
    { method: method, params: params },
    error_type: :forbidden,
    original_error: e,
  )
rescue Faraday::ResourceNotFound => e
  # Per spec, 404 is the session-expired signal only when the request
  # actually carried an `Mcp-Session-Id`. A 404 without a session attached
  # (e.g. wrong URL or a stateless server) surfaces as a generic not-found.
  # https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#session-management
  if @session_id
    clear_session
    raise SessionExpiredError.new(
      "The #{method} request is not found",
      { method: method, params: params },
      original_error: e,
    )
  else
    raise RequestHandlerError.new(
      "The #{method} request is not found",
      { method: method, params: params },
      error_type: :not_found,
      original_error: e,
    )
  end
rescue Faraday::UnprocessableEntityError => e
  raise RequestHandlerError.new(
    "The #{method} request is unprocessable",
    { method: method, params: params },
    error_type: :unprocessable_entity,
    original_error: e,
  )
rescue Faraday::Error => e # Catch-all
  raise RequestHandlerError.new(
    "Internal error handling #{method} request",
    { method: method, params: params },
    error_type: :internal_error,
    original_error: e,
  )
end