ruby-sdk/examples/streamable_http_client.rb

# frozen_string_literal: true

$LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
require "mcp"
require "net/http"
require "uri"
require "json"
require "logger"
require "event_stream_parser"

SERVER_URL = "http://localhost:9393"

def create_logger
  logger = Logger.new($stdout)
  logger.formatter = proc do |severity, datetime, _progname, msg|
    "[CLIENT] #{severity} #{datetime.strftime("%H:%M:%S.%L")} - #{msg}\n"
  end
  logger
end

# The SDK does not yet implement the optional GET SSE stream, so this example
# uses MCP::Client for JSON-RPC requests and raw Net::HTTP for the event stream.
def connect_sse(session_id, logger)
  uri = URI(SERVER_URL)

  logger.info("Connecting to SSE stream...")

  Net::HTTP.start(uri.host, uri.port) do |http|
    request = Net::HTTP::Get.new(uri)
    request["Mcp-Session-Id"] = session_id
    request["Accept"] = "text/event-stream"
    request["Cache-Control"] = "no-cache"

    http.request(request) do |response|
      if response.code == "200"
        logger.info("SSE stream connected successfully")

        parser = EventStreamParser::Parser.new
        response.read_body do |chunk|
          parser.feed(chunk) do |type, data, _id|
            if type.empty?
              logger.info("SSE event: #{data}")
            else
              logger.info("SSE event (#{type}): #{data}")
            end
          end
        end
      else
        logger.error("Failed to connect to SSE: #{response.code} #{response.message}")
      end
    end
  end
rescue Interrupt
  logger.info("SSE connection interrupted")
rescue => e
  logger.error("SSE connection error: #{e.message}")
end

def print_response(response)
  if response.nil?
    puts "Response accepted; watch the SSE stream for the server response."
  else
    puts "Response: #{JSON.pretty_generate(response)}"
  end
end

def main
  logger = create_logger

  puts <<~MESSAGE
    MCP Streamable HTTP Client
    Make sure the server is running (ruby examples/streamable_http_server.rb)
    #{"=" * 60}
  MESSAGE

  http_transport = MCP::Client::HTTP.new(url: SERVER_URL)
  client = MCP::Client.new(transport: http_transport)
  sse_thread = nil

  begin
    puts "=== Initializing session ==="
    server_info = client.connect(
      client_info: { name: "streamable-http-client", version: "1.0" },
    )

    puts <<~MESSAGE
      ID: #{http_transport.session_id}
      Version: #{http_transport.protocol_version}
      Server: #{server_info["serverInfo"]}
    MESSAGE

    unless http_transport.session_id
      logger.error("No session ID received; this example requires a stateful Streamable HTTP session.")
      return
    end

    puts "=== Listing tools ==="
    tools = client.tools
    tools.each { |tool| puts "  - #{tool.name}: #{tool.description}" }

    echo_tool = tools.find { |tool| tool.name == "echo" }
    notification_tool = tools.find { |tool| tool.name == "notification_tool" }

    sse_thread = Thread.new { connect_sse(http_transport.session_id, logger) }
    sleep(1)

    # Once the optional SSE stream is active, POST requests may receive only a
    # 202 ACK while the actual JSON-RPC response is delivered over SSE.
    loop do
      puts <<~MENU.chomp

        === Available Actions ===
        1. Send notification (triggers SSE event)
        2. Echo message
        3. Show cached tools
        0. Exit

        Choose an action:#{" "}
      MENU

      case gets.chomp
      when "1"
        if notification_tool
          print("Enter notification message: ")
          message = gets.chomp
          print("Enter delay in seconds (0 for immediate): ")
          delay = gets.chomp.to_f

          puts "=== Calling tool: notification_tool ==="
          response = client.call_tool(
            tool: notification_tool,
            arguments: { message: message, delay: delay },
          )
          print_response(response)
        else
          puts "notification_tool not available"
        end
      when "2"
        if echo_tool
          print("Enter message to echo: ")
          message = gets.chomp

          puts "=== Calling tool: echo ==="
          response = client.call_tool(tool: echo_tool, arguments: { message: message })
          print_response(response)
        else
          puts "echo tool not available"
        end
      when "3"
        puts "=== Cached tools ==="
        tools.each { |tool| puts "  - #{tool.name}: #{tool.description}" }
      when "0"
        logger.info("Exiting...")
        break
      else
        puts "Invalid choice"
      end
    end
  rescue MCP::Client::SessionExpiredError => e
    logger.error("Session expired: #{e.message}")
  rescue MCP::Client::RequestHandlerError => e
    logger.error("Request error: #{e.message}")
  rescue Interrupt
    logger.info("Client interrupted")
  rescue => e
    logger.error("Error: #{e.message}")
    logger.error(e.backtrace.first(5).join("\n"))
  ensure
    sse_thread.kill if sse_thread&.alive?

    if http_transport.connected?
      puts "=== Closing session ==="
      http_transport.close
      puts "Session closed"
    end
  end
end

main