codeocean/lib/runner/connection.rb

# frozen_string_literal: true

require 'faye/websocket/client'
require 'json_schemer'

class Runner::Connection
  # These are events for which callbacks can be registered.
  EVENTS = %i[start exit stdout stderr].freeze
  WEBSOCKET_MESSAGE_TYPES = %i[start stdout stderr error timeout exit].freeze
  BACKEND_OUTPUT_SCHEMA = JSONSchemer.schema(JSON.parse(File.read('lib/runner/backend-output.schema.json')))

  # @!attribute start_callback
  # @!attribute exit_callback
  # @!attribute stdout_callback
  # @!attribute stderr_callback
  attr_writer :status
  attr_reader :error

  def initialize(url, strategy, event_loop, locale = I18n.locale)
    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Opening connection to #{url}" }
    # The `ping` value is measured in seconds and specifies how often a Ping frame should be sent.
    # Internally, Faye::WebSocket uses EventMachine and the `ping` value is used to wake the EventMachine thread
    # The `tls` option is used to customize the validation of TLS connections.
    # Passing `nil` as a `root_cert_file` is okay and done so for the DockerContainerPool.
    @socket = Faye::WebSocket::Client.new(url, [], strategy.class.websocket_header.merge(ping: 0.1))
    @strategy = strategy
    @status = :established
    @event_loop = event_loop
    @locale = locale
    @stdout_buffer = Buffer.new
    @stderr_buffer = Buffer.new

    # For every event type of Faye WebSockets, the corresponding
    # RunnerConnection method starting with `on_` is called.
    %i[open message error close].each do |event_type|
      @socket.on(event_type) do |event|
        # The initial locale when establishing the connection is used for all callbacks
        I18n.with_locale(@locale) { __send__(:"on_#{event_type}", event) }
      end
    end

    # This registers empty default callbacks.
    EVENTS.each {|event_type| instance_variable_set(:"@#{event_type}_callback", ->(e) {}) }
    @start_callback = -> {}
    # Fail if no exit status was returned.
    @exit_code = 1
  end

  # Register a callback based on the event type received from runner management
  def on(event, &block)
    return unless EVENTS.include? event

    instance_variable_set(:"@#{event}_callback", block)
  end

  # Send arbitrary data in the WebSocket connection
  def send_data(raw_data)
    encoded_message = encode(raw_data)
    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Sending to #{@socket.url}: #{encoded_message.inspect}" }
    @socket.send(encoded_message)
  end

  # Close the WebSocket connection
  def close(status)
    return unless active?

    @status = status
    @socket.close
  end

  # Check if the WebSocket connection is currently established
  def active?
    @status == :established
  end

  private

  def decode(_raw_event)
    raise NotImplementedError
  end

  def encode(_data)
    raise NotImplementedError
  end

  def flush_buffers
    @stdout_callback.call @stdout_buffer.flush unless @stdout_buffer.empty?
    @stderr_callback.call @stderr_buffer.flush unless @stderr_buffer.empty?
  end

  def ignored_sequence?(event_data)
    case event_data
      when "#exit\r", "{\"cmd\": \"exit\"}\r"
        # Do not forward. We will wait for the confirmed exit sent by the runner management.
        true
      else
        false
    end
  end

  # === WebSocket Callbacks
  # These callbacks are executed based on events indicated by Faye WebSockets and are
  # independent of the JSON specification that is used within the WebSocket once established.

  def on_message(raw_event)
    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Receiving from #{@socket.url}: #{raw_event.data.inspect}" }
    event = decode(raw_event.data)
    return unless BACKEND_OUTPUT_SCHEMA.valid?(event)

    event = event.deep_symbolize_keys
    message_type = event[:type].to_sym
    if WEBSOCKET_MESSAGE_TYPES.include?(message_type)
      __send__("handle_#{message_type}", event)
    else
      @error = Runner::Error::UnexpectedResponse.new("Unknown WebSocket message type: #{message_type}")
      close(:error)
    end
  end

  def on_open(_event)
    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Established connection to #{@socket.url}" }
    @start_callback.call
  end

  def on_error(event)
    # In case of an WebSocket error, the connection will be closed by Faye::WebSocket::Client automatically.
    # Thus, no further handling is required here (the user will get notified).
    Sentry.set_extras(event: event.inspect)
    Sentry.capture_message("The WebSocket connection to #{@socket.url} was closed with an error.")
  end

  def on_close(_event)
    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Closing connection to #{@socket.url} with status: #{@status}" }
    flush_buffers

    # Depending on the status, we might want to destroy the runner at management.
    # This ensures we get a new runner on the next request.
    # All failing runs, those cancelled by the user or those hitting a timeout or error are subject to this mechanism.

    case @status
      when :timeout
        @strategy.destroy_at_management
        @error = Runner::Error::ExecutionTimeout.new('Execution exceeded its time limit')
      when :terminated_by_codeocean, :terminated_by_management
        @exit_callback.call @exit_code
      when :terminated_by_client, :error
        @strategy.destroy_at_management
      else # :established
        # If the runner is killed by the DockerContainerPool after the maximum allowed time per user and
        # while the owning user is running an execution, the command execution stops and log output is incomplete.
        @strategy.destroy_at_management
        @error = Runner::Error::Unknown.new('Execution terminated with an unknown reason')
    end
    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Closed connection to #{@socket.url} with status: #{@status}" }
    @event_loop.stop
  end

  # === Message Handlers
  # Each message type indicated by the +type+ attribute in the JSON
  # sent be the runner management has a dedicated method.
  # Context:: All registered handlers are executed in the scope of
  #           the bindings they had where they were registered.
  #           Information not stored in the binding, such as the
  #           locale or call stack are not available during execution!

  def handle_exit(event)
    @status = :terminated_by_management
    @exit_code = event[:data]
  end

  def handle_stdout(event)
    @stdout_buffer.store event[:data]
    @stdout_buffer.events.each do |event_data|
      @stdout_callback.call event_data unless ignored_sequence? event_data
    end
  end

  def handle_stderr(event)
    @stderr_buffer.store event[:data]
    @stderr_buffer.events.each do |event_data|
      @stderr_callback.call event_data unless ignored_sequence? event_data
    end
  end

  def handle_error(event)
    # In case of a (Nomad) error during execution, the runner management will notify us with an error message here.
    # This shouldn't happen to often and can be considered an internal server error by the runner management.
    # More information is available in the logs of the runner management or the orchestrator (e.g., Nomad).
    Sentry.set_extras(event: event.inspect)
    Sentry.capture_message("An error occurred during code execution while being connected to #{@socket.url}.")
  end

  def handle_start(_event)
    # The execution just started as requested. This is an informal message and no further processing is required.
  end

  def handle_timeout(_event)
    @status = :timeout
    # The runner management stopped the execution as the permitted execution time was exceeded.
    # We set the status here and wait for the connection to be closed (by the runner management).
  end
end