Class: MCPClient::ServerSSE

Inherits:
ServerBase show all
Includes:
JsonRpcTransport, ReconnectMonitor, SseParser
Defined in:
lib/mcp_client/server_sse.rb,
lib/mcp_client/server_sse/sse_parser.rb,
lib/mcp_client/server_sse/reconnect_monitor.rb,
lib/mcp_client/server_sse/json_rpc_transport.rb

Overview

Implementation of MCP server that communicates via Server-Sent Events (SSE) Useful for communicating with remote MCP servers over HTTP

Defined Under Namespace

Modules: JsonRpcTransport, ReconnectMonitor, SseParser

Constant Summary collapse

CLOSE_AFTER_PING_RATIO =

Ratio of close_after timeout to ping interval

2.5
DEFAULT_MAX_PING_FAILURES =

Default values for connection monitoring

3
DEFAULT_MAX_RECONNECT_ATTEMPTS = 
5
BASE_RECONNECT_DELAY =

Reconnection backoff constants

0.5
MAX_RECONNECT_DELAY = 
30
JITTER_FACTOR = 
0.25

Instance Attribute Summary collapse

Attributes inherited from ServerBase

#name

Instance Method Summary collapse

Methods included from ReconnectMonitor

#activity_monitor_loop, #attempt_ping, #attempt_reconnection, #connection_active?, #handle_ping_failure, #handle_sse_auth_error, #record_activity, #reset_connection_state, #setup_sse_connection, #start_activity_monitor, #wait_for_connection

Methods included from JsonRpcTransport

#rpc_notify, #rpc_request

Methods included from JsonRpcCommon

#build_jsonrpc_notification, #build_jsonrpc_request, #initialization_params, #ping, #process_jsonrpc_response, #with_retry

Methods included from SseParser

#handle_endpoint_event, #handle_message_event, #parse_and_handle_sse_event, #parse_sse_event, #process_error_in_message, #process_notification?, #process_response?

Methods inherited from ServerBase

#on_notification, #ping, #rpc_notify, #rpc_request

Constructor Details

#initialize(base_url:, headers: {}, read_timeout: 30, ping: 10, retries: 0, retry_backoff: 1, name: nil, logger: nil) ⇒ ServerSSE

Returns a new instance of ServerSSE.

Parameters:

  • base_url (String) —

    The base URL of the MCP server

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

    Additional headers to include in requests

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

    Read timeout in seconds (default: 30)

  • ping (Integer) (defaults to: 10) —

    Time in seconds after which to send ping if no activity (default: 10)

  • 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

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

    optional name for this server

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

    optional logger



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# File 'lib/mcp_client/server_sse.rb', line 63

def initialize(base_url:, headers: {}, read_timeout: 30, ping: 10,
               retries: 0, retry_backoff: 1, name: nil, logger: nil)
  super(name: name)
  initialize_logger(logger)
  @max_retries = retries
  @retry_backoff = retry_backoff
  # Normalize base_url: preserve trailing slash if explicitly provided for SSE endpoints
  @base_url = base_url
  @headers = headers.merge({
                             'Accept' => 'text/event-stream',
                             'Cache-Control' => 'no-cache',
                             'Connection' => 'keep-alive'
                           })
  # HTTP client is managed via Faraday
  @tools = nil
  @read_timeout = read_timeout
  @ping_interval = ping
  # Set close_after to a multiple of the ping interval
  @close_after = (ping * CLOSE_AFTER_PING_RATIO).to_i

  # SSE-provided JSON-RPC endpoint path for POST requests
  @rpc_endpoint = nil
  @tools_data = nil
  @request_id = 0
  @sse_results = {}
  @mutex = Monitor.new
  @buffer = ''
  @sse_connected = false
  @connection_established = false
  @connection_cv = @mutex.new_cond
  @initialized = false
  @auth_error = nil
  # Whether to use SSE transport; may disable if handshake fails
  @use_sse = true

  # Time of last activity
  @last_activity_time = Time.now
  @activity_timer_thread = nil
end

Instance Attribute Details

#base_url ⇒ String (readonly)

Returns The base URL of the MCP server.

Returns:

  • (String) —

    The base URL of the MCP server



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# File 'lib/mcp_client/server_sse.rb', line 45

def base_url
  @base_url
end

#capabilities ⇒ Hash? (readonly)

Server capabilities from initialize response

Returns:

  • (Hash, nil) —

    Server capabilities



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# File 'lib/mcp_client/server_sse.rb', line 53

def capabilities
  @capabilities
end

#prompts ⇒ Array<MCPClient::Prompt>? (readonly)

Returns List of available prompts (nil if not fetched yet).

Returns:

  • (Array<MCPClient::Prompt>, nil) —

    List of available prompts (nil if not fetched yet)



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# File 'lib/mcp_client/server_sse.rb', line 45

attr_reader :base_url, :tools, :prompts, :resources

#resources ⇒ Object (readonly)

Returns the value of attribute resources.



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# File 'lib/mcp_client/server_sse.rb', line 45

attr_reader :base_url, :tools, :prompts, :resources

#server_info ⇒ Hash? (readonly)

Server information from initialize response

Returns:

  • (Hash, nil) —

    Server information



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# File 'lib/mcp_client/server_sse.rb', line 49

def server_info
  @server_info
end

#tools ⇒ Array<MCPClient::Tool>? (readonly)

Returns List of available tools (nil if not fetched yet).

Returns:

  • (Array<MCPClient::Tool>, nil) —

    List of available tools (nil if not fetched yet)



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# File 'lib/mcp_client/server_sse.rb', line 45

attr_reader :base_url, :tools, :prompts, :resources

Instance Method Details

#call_tool(tool_name, parameters) ⇒ Object

Call a tool with the given parameters 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

  • 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

  • (Object) —

    the result of the tool invocation (with string keys for backward compatibility)

Raises:



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# File 'lib/mcp_client/server_sse.rb', line 312

def call_tool(tool_name, parameters)
  rpc_request('tools/call', {
                name: tool_name,
                arguments: parameters
              })
rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError
  # Re-raise connection/transport errors directly to match test expectations
  raise
rescue StandardError => e
  # For all other errors, wrap in ToolCallError
  raise MCPClient::Errors::ToolCallError, "Error calling tool '#{tool_name}': #{e.message}"
end

#call_tool_streaming(tool_name, parameters) ⇒ Enumerator

Stream tool call fallback for SSE transport (yields single result)

Parameters:

  • tool_name (String)
  • parameters (Hash)

Returns:

  • (Enumerator) 


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# File 'lib/mcp_client/server_sse.rb', line 107

def call_tool_streaming(tool_name, parameters)
  Enumerator.new do |yielder|
    yielder << call_tool(tool_name, parameters)
  end
end

#cleanup ⇒ Object

Note:

This method preserves ping failure and reconnection metrics between reconnection attempts, allowing the client to track failures across multiple connection attempts. This is essential for proper reconnection logic and exponential backoff.

Clean up the server connection Properly closes HTTP connections and clears cached state



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# File 'lib/mcp_client/server_sse.rb', line 365

def cleanup
  @mutex.synchronize do
    # Set flags first before killing threads to prevent race conditions
    # where threads might check flags after they're set but before they're killed
    @connection_established = false
    @sse_connected = false
    @initialized = false # Reset initialization state for reconnection

    # Log cleanup for debugging
    @logger.debug('Cleaning up SSE connection')

    # Store threads locally to avoid race conditions
    sse_thread = @sse_thread
    activity_thread = @activity_timer_thread

    # Clear thread references first
    @sse_thread = nil
    @activity_timer_thread = nil

    # Kill threads outside the critical section
    begin
      sse_thread&.kill
    rescue StandardError => e
      @logger.debug("Error killing SSE thread: #{e.message}")
    end

    begin
      activity_thread&.kill
    rescue StandardError => e
      @logger.debug("Error killing activity thread: #{e.message}")
    end

    if @http_client
      @http_client.finish if @http_client.started?
      @http_client = nil
    end

    # Close Faraday connections if they exist
    @rpc_conn = nil
    @sse_conn = nil

    @tools = nil
    # Don't clear auth error as we need it for reporting the correct error
    # Don't reset @consecutive_ping_failures or @reconnect_attempts as they're tracked across reconnections
  end
end

#connect ⇒ Boolean

Connect to the MCP server over HTTP/HTTPS with SSE

Returns:

  • (Boolean) —

    true if connection was successful

Raises:



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# File 'lib/mcp_client/server_sse.rb', line 328

def connect
  return true if @mutex.synchronize { @connection_established }

  # Check for pre-existing auth error (needed for tests)
  pre_existing_auth_error = @mutex.synchronize { @auth_error }

  begin
    # Don't reset auth error if it's pre-existing
    @mutex.synchronize { @auth_error = nil } unless pre_existing_auth_error

    start_sse_thread
    effective_timeout = [@read_timeout || 30, 30].min
    wait_for_connection(timeout: effective_timeout)
    start_activity_monitor
    true
  rescue MCPClient::Errors::ConnectionError => e
    cleanup
    # Simply pass through any ConnectionError without wrapping it again
    # This prevents duplicate error messages in the stack
    raise e
  rescue StandardError => e
    cleanup
    # Check for stored auth error first as it's more specific
    auth_error = @mutex.synchronize { @auth_error }
    raise MCPClient::Errors::ConnectionError, auth_error if auth_error

    raise MCPClient::Errors::ConnectionError, "Failed to connect to MCP server at #{@base_url}: #{e.message}"
  end
end

#get_prompt(prompt_name, parameters) ⇒ Object

Get a prompt with the given parameters

Parameters:

  • prompt_name (String) —

    the name of the prompt to get

  • parameters (Hash) —

    the parameters to pass to the prompt

Returns:

  • (Object) —

    the result of the prompt interpolation

Raises:



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

def get_prompt(prompt_name, parameters)
  rpc_request('prompts/get', {
                name: prompt_name,
                arguments: parameters
              })
rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError
  # Re-raise connection/transport errors directly to match test expectations
  raise
rescue StandardError => e
  # For all other errors, wrap in PromptGetError
  raise MCPClient::Errors::PromptGetError, "Error get prompt '#{prompt_name}': #{e.message}"
end

#list_prompts ⇒ Array<MCPClient::Prompt>

List all prompts available from the MCP server

Returns:

Raises:



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# File 'lib/mcp_client/server_sse.rb', line 118

def list_prompts
  @mutex.synchronize do
    return @prompts if @prompts
  end

  begin
    ensure_initialized

    prompts_data = request_prompts_list
    @mutex.synchronize do
      @prompts = prompts_data.map do |prompt_data|
        MCPClient::Prompt.from_json(prompt_data, server: self)
      end
    end

    @mutex.synchronize { @prompts }
  rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError, MCPClient::Errors::ServerError
    # Re-raise these errors directly
    raise
  rescue StandardError => e
    raise MCPClient::Errors::PromptGetError, "Error listing prompts: #{e.message}"
  end
end

#list_resource_templates(cursor: nil) ⇒ Hash

List all resource templates available from the MCP server

Parameters:

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

    optional cursor for pagination

Returns:

  • (Hash) —

    result containing resourceTemplates array and optional nextCursor

Raises:



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# File 'lib/mcp_client/server_sse.rb', line 224

def list_resource_templates(cursor: nil)
  ensure_initialized
  params = {}
  params['cursor'] = cursor if cursor
  result = rpc_request('resources/templates/list', params)

  templates = (result['resourceTemplates'] || []).map do |template_data|
    MCPClient::ResourceTemplate.from_json(template_data, server: self)
  end

  { 'resourceTemplates' => templates, 'nextCursor' => result['nextCursor'] }
rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError, MCPClient::Errors::ServerError
  raise
rescue StandardError => e
  raise MCPClient::Errors::ResourceReadError, "Error listing resource templates: #{e.message}"
end

#list_resources(cursor: nil) ⇒ Hash

List all resources available from the MCP server

Parameters:

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

    optional cursor for pagination

Returns:

  • (Hash) —

    result containing resources array and optional nextCursor

Raises:



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# File 'lib/mcp_client/server_sse.rb', line 169

def list_resources(cursor: nil)
  @mutex.synchronize do
    return @resources_result if @resources_result && !cursor
  end

  begin
    ensure_initialized

    params = {}
    params['cursor'] = cursor if cursor
    result = rpc_request('resources/list', params)

    resources = (result['resources'] || []).map do |resource_data|
      MCPClient::Resource.from_json(resource_data, server: self)
    end

    resources_result = { 'resources' => resources, 'nextCursor' => result['nextCursor'] }

    @mutex.synchronize do
      @resources_result = resources_result unless cursor
    end

    resources_result
  rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError, MCPClient::Errors::ServerError
    # Re-raise these errors directly
    raise
  rescue StandardError => e
    raise MCPClient::Errors::ResourceReadError, "Error listing resources: #{e.message}"
  end
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_sse.rb', line 276

def list_tools
  @mutex.synchronize do
    return @tools if @tools
  end

  begin
    ensure_initialized

    tools_data = request_tools_list
    @mutex.synchronize do
      @tools = tools_data.map do |tool_data|
        MCPClient::Tool.from_json(tool_data, server: self)
      end
    end

    @mutex.synchronize { @tools }
  rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError, MCPClient::Errors::ServerError
    # Re-raise these errors directly
    raise
  rescue StandardError => e
    raise MCPClient::Errors::ToolCallError, "Error listing tools: #{e.message}"
  end
end

#read_resource(uri) ⇒ Array<MCPClient::ResourceContent>

Read a resource by its URI

Parameters:

  • uri (String) —

    the URI of the resource to read

Returns:

Raises:



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# File 'lib/mcp_client/server_sse.rb', line 207

def read_resource(uri)
  result = rpc_request('resources/read', { uri: uri })
  contents = result['contents'] || []
  contents.map { |content| MCPClient::ResourceContent.from_json(content) }
rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError
  # Re-raise connection/transport errors directly to match test expectations
  raise
rescue StandardError => e
  # For all other errors, wrap in ResourceReadError
  raise MCPClient::Errors::ResourceReadError, "Error reading resource '#{uri}': #{e.message}"
end

#subscribe_resource(uri) ⇒ Boolean

Subscribe to resource updates

Parameters:

  • uri (String) —

    the URI of the resource to subscribe to

Returns:

  • (Boolean) —

    true if subscription successful

Raises:



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# File 'lib/mcp_client/server_sse.rb', line 246

def subscribe_resource(uri)
  ensure_initialized
  rpc_request('resources/subscribe', { uri: uri })
  true
rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError, MCPClient::Errors::ServerError
  raise
rescue StandardError => e
  raise MCPClient::Errors::ResourceReadError, "Error subscribing to resource '#{uri}': #{e.message}"
end

#unsubscribe_resource(uri) ⇒ Boolean

Unsubscribe from resource updates

Parameters:

  • uri (String) —

    the URI of the resource to unsubscribe from

Returns:

  • (Boolean) —

    true if unsubscription successful

Raises:



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# File 'lib/mcp_client/server_sse.rb', line 261

def unsubscribe_resource(uri)
  ensure_initialized
  rpc_request('resources/unsubscribe', { uri: uri })
  true
rescue MCPClient::Errors::ConnectionError, MCPClient::Errors::TransportError, MCPClient::Errors::ServerError
  raise
rescue StandardError => e
  raise MCPClient::Errors::ResourceReadError, "Error unsubscribing from resource '#{uri}': #{e.message}"
end