server_cdp.rb

# frozen_string_literal: true

require 'json'
require 'digest/sha1'
require 'base64'
require 'securerandom'
require 'stringio'
require 'open3'
require 'tmpdir'

module DEBUGGER__
  module UI_CDP
    SHOW_PROTOCOL = ENV['RUBY_DEBUG_CDP_SHOW_PROTOCOL'] == '1'

    class << self
      def setup_chrome addr
        return if CONFIG[:chrome_path] == ''

        port, path, pid = run_new_chrome
        begin
          s = Socket.tcp '127.0.0.1', port
        rescue Errno::ECONNREFUSED, Errno::EADDRNOTAVAIL
          return
        end

        ws_client = WebSocketClient.new(s)
        ws_client.handshake port, path
        ws_client.send id: 1, method: 'Target.getTargets'

        loop do
          res = ws_client.extract_data
          case
          when res['id'] == 1 && target_info = res.dig('result', 'targetInfos')
            page = target_info.find{|t| t['type'] == 'page'}
            ws_client.send id: 2, method: 'Target.attachToTarget',
                          params: {
                            targetId: page['targetId'],
                            flatten: true
                          }
          when res['id'] == 2
            s_id = res.dig('result', 'sessionId')
            ws_client.send sessionId: s_id, id: 3,
                          method: 'Page.enable'
          when res['id'] == 3
            s_id = res['sessionId']
            ws_client.send sessionId: s_id, id: 4,
                          method: 'Page.getFrameTree'
          when res['id'] == 4
            s_id = res['sessionId']
            f_id = res.dig('result', 'frameTree', 'frame', 'id')
            ws_client.send sessionId: s_id, id: 5,
                          method: 'Page.navigate',
                          params: {
                            url: "devtools://devtools/bundled/inspector.html?v8only=true&panel=sources&ws=#{addr}/#{SecureRandom.uuid}",
                            frameId: f_id
                          }
          when res['method'] == 'Page.loadEventFired'
            break
          end
        end
        pid
      rescue Errno::ENOENT
        nil
      end

      def get_chrome_path
        return CONFIG[:chrome_path] if CONFIG[:chrome_path]

        # The process to check OS is based on `selenium` project.
        case RbConfig::CONFIG['host_os']
        when /mswin|msys|mingw|cygwin|emc/
          'C:\Program Files (x86)\Google\Chrome\Application\chrome.exe'
        when /darwin|mac os/
          '/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome'
        when /linux/
          'google-chrome'
        else
          raise "Unsupported OS"
        end
      end

      def run_new_chrome
        dir = Dir.mktmpdir
        # The command line flags are based on: https://developer.mozilla.org/en-US/docs/Tools/Remote_Debugging/Chrome_Desktop#connecting
        stdin, stdout, stderr, wait_thr = *Open3.popen3("#{get_chrome_path} --remote-debugging-port=0 --no-first-run --no-default-browser-check --user-data-dir=#{dir}")
        stdin.close
        stdout.close

        data = stderr.readpartial 4096
        if data.match /DevTools listening on ws:\/\/127.0.0.1:(\d+)(.*)/
          port = $1
          path = $2
        end
        stderr.close

        at_exit{
          CONFIG[:skip_path] = [//] # skip all
          FileUtils.rm_rf dir
        }

        [port, path, wait_thr.pid]
      end
    end

    module WebSocketUtils
      class Frame
        attr_reader :b

        def initialize
          @b = ''.b
        end

        def << obj
          case obj
          when String
            @b << obj.b
          when Enumerable
            obj.each{|e| self << e}
          end
        end

        def char bytes
          @b << bytes
        end

        def ulonglong bytes
          @b << [bytes].pack('Q>')
        end

        def uint16 bytes
          @b << [bytes].pack('n*')
        end
      end

      def show_protocol dir, msg
        if DEBUGGER__::UI_CDP::SHOW_PROTOCOL
          $stderr.puts "\#[#{dir}] #{msg}"
        end
      end
    end

    class WebSocketClient
      include WebSocketUtils

      def initialize s
        @sock = s
      end

      def handshake port, path
        key = SecureRandom.hex(11)
        req = "GET #{path} HTTP/1.1\r\nHost: 127.0.0.1:#{port}\r\nConnection: Upgrade\r\nUpgrade: websocket\r\nSec-WebSocket-Version: 13\r\nSec-WebSocket-Key: #{key}==\r\n\r\n"
        show_protocol :>, req
        @sock.print req
        res = @sock.readpartial 4092
        show_protocol :<, res

        if res.match /^Sec-WebSocket-Accept: (.*)\r\n/
          correct_key = Base64.strict_encode64 Digest::SHA1.digest "#{key}==258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
          raise "The Sec-WebSocket-Accept value: #{$1} is not valid" unless $1 == correct_key
        else
          raise "Unknown response: #{res}"
        end
      end

      def send **msg
        msg = JSON.generate(msg)
        show_protocol :>, msg
        frame = Frame.new
        fin = 0b10000000
        opcode = 0b00000001
        frame.char fin + opcode

        mask = 0b10000000 # A client must mask all frames in a WebSocket Protocol.
        bytesize = msg.bytesize
        if bytesize < 126
          payload_len = bytesize
          frame.char mask + payload_len
        elsif bytesize < 2 ** 16
          payload_len = 0b01111110
          frame.char mask + payload_len
          frame.uint16 bytesize
        elsif bytesize < 2 ** 64
          payload_len = 0b01111111
          frame.char mask + payload_len
          frame.ulonglong bytesize
        else
          raise 'Bytesize is too big.'
        end

        masking_key = 4.times.map{
          key = rand(1..255)
          frame.char key
          key
        }
        msg.bytes.each_with_index do |b, i|
          frame.char(b ^ masking_key[i % 4])
        end

        @sock.print frame.b
      end

      def extract_data
        first_group = @sock.getbyte
        fin = first_group & 0b10000000 != 128
        raise 'Unsupported' if fin
        opcode = first_group & 0b00001111
        raise "Unsupported: #{opcode}" unless opcode == 1

        second_group = @sock.getbyte
        mask = second_group & 0b10000000 == 128
        raise 'The server must not mask any frames' if mask
        payload_len = second_group & 0b01111111
        # TODO: Support other payload_lengths
        if payload_len == 126
          payload_len = @sock.read(2).unpack('n*')[0]
        end

        msg = @sock.read payload_len
        show_protocol :<, msg
        JSON.parse msg
      end
    end

    class Detach < StandardError
    end

    class WebSocketServer
      include WebSocketUtils

      def initialize s
        @sock = s
      end

      def handshake
        req = @sock.readpartial 4096
        show_protocol '>', req

        if req.match /^Sec-WebSocket-Key: (.*)\r\n/
          accept = Base64.strict_encode64 Digest::SHA1.digest "#{$1}258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
          res = "HTTP/1.1 101 Switching Protocols\r\nUpgrade: websocket\r\nConnection: Upgrade\r\nSec-WebSocket-Accept: #{accept}\r\n\r\n"
          @sock.print res
          show_protocol :<, res
        else
          "Unknown request: #{req}"
        end
      end

      def send **msg
        msg = JSON.generate(msg)
        show_protocol :<, msg
        frame = Frame.new
        fin = 0b10000000
        opcode = 0b00000001
        frame.char fin + opcode

        mask = 0b00000000 # A server must not mask any frames in a WebSocket Protocol.
        bytesize = msg.bytesize
        if bytesize < 126
          payload_len = bytesize
          frame.char mask + payload_len
        elsif bytesize < 2 ** 16
          payload_len = 0b01111110
          frame.char mask + payload_len
          frame.uint16 bytesize
        elsif bytesize < 2 ** 64
          payload_len = 0b01111111
          frame.char mask + payload_len
          frame.ulonglong bytesize
        else
          raise 'Bytesize is too big.'
        end

        frame << msg
        @sock.print frame.b
      end

      def extract_data
        first_group = @sock.getbyte
        fin = first_group & 0b10000000 != 128
        raise 'Unsupported' if fin

        opcode = first_group & 0b00001111
        raise Detach if opcode == 8
        raise "Unsupported: #{opcode}" unless opcode == 1

        second_group = @sock.getbyte
        mask = second_group & 0b10000000 == 128
        raise 'The client must mask all frames' unless mask
        payload_len = second_group & 0b01111111
        # TODO: Support other payload_lengths
        if payload_len == 126
          payload_len = @sock.gets(2).unpack('n*')[0]
        end

        masking_key = []
        4.times { masking_key << @sock.getbyte }
        unmasked = []
        payload_len.times do |n|
          masked = @sock.getbyte
          unmasked << (masked ^ masking_key[n % 4])
        end
        msg = unmasked.pack 'c*'
        show_protocol :>, msg
        JSON.parse msg
      end
    end

    def send_response req, **res
      if res.empty?
        @ws_server.send id: req['id'], result: {}
      else
        @ws_server.send id: req['id'], result: res
      end
    end

    def send_fail_response req, **res
      @ws_server.send id: req['id'], error: res
    end

    def send_event method, **params
      if params.empty?
        @ws_server.send method: method, params: {}
      else
        @ws_server.send method: method, params: params
      end
    end

    INVALID_REQUEST = -32600

    def process
      bps = {}
      @src_map = {}
      loop do
        req = @ws_server.extract_data

        case req['method']

        ## boot/configuration
        when 'Debugger.getScriptSource'
          @q_msg << req
        when 'Debugger.enable'
          send_response req
          @q_msg << req
        when 'Runtime.enable'
          send_response req
          send_event 'Runtime.executionContextCreated',
                      context: {
                        id: SecureRandom.hex(16),
                        origin: "http://#{@local_addr.inspect_sockaddr}",
                        name: ''
                      }
        when 'Runtime.getIsolateId'
          send_response req,
                        id: SecureRandom.hex
        when 'Runtime.terminateExecution'
          send_response req
          exit
        when 'Page.startScreencast', 'Emulation.setTouchEmulationEnabled', 'Emulation.setEmitTouchEventsForMouse',
          'Runtime.compileScript', 'Page.getResourceContent', 'Overlay.setPausedInDebuggerMessage',
          'Runtime.releaseObjectGroup', 'Runtime.discardConsoleEntries', 'Log.clear', 'Runtime.runIfWaitingForDebugger'
          send_response req

        ## control
        when 'Debugger.resume'
          send_response req
          send_event 'Debugger.resumed'
          @q_msg << 'c'
          @q_msg << req
        when 'Debugger.stepOver'
          begin
            @session.check_postmortem
            send_response req
            send_event 'Debugger.resumed'
            @q_msg << 'n'
          rescue PostmortemError
            send_fail_response req,
                              code: INVALID_REQUEST,
                              message: "'stepOver' is not supported while postmortem mode"
          ensure
            @q_msg << req
          end
        when 'Debugger.stepInto'
          begin
            @session.check_postmortem
            send_response req
            send_event 'Debugger.resumed'
            @q_msg << 's'
          rescue PostmortemError
            send_fail_response req,
                              code: INVALID_REQUEST,
                              message: "'stepInto' is not supported while postmortem mode"
          ensure
            @q_msg << req
          end
        when 'Debugger.stepOut'
          begin
            @session.check_postmortem
            send_response req
            send_event 'Debugger.resumed'
            @q_msg << 'fin'
          rescue PostmortemError
            send_fail_response req,
                              code: INVALID_REQUEST,
                              message: "'stepOut' is not supported while postmortem mode"
          ensure
            @q_msg << req
          end
        when 'Debugger.setSkipAllPauses'
          skip = req.dig('params', 'skip')
          if skip
            deactivate_bp
          else
            activate_bp bps
          end
          send_response req

        # breakpoint
        when 'Debugger.getPossibleBreakpoints'
          @q_msg << req
        when 'Debugger.setBreakpointByUrl'
          line = req.dig('params', 'lineNumber')
          if regexp = req.dig('params', 'urlRegex')
            path = regexp.match(/(.*)\|/)[1].gsub("\\", "")
            cond = req.dig('params', 'condition')
            src = get_source_code path
            end_line = src.lines.count
            line = end_line  if line > end_line
            b_id = "1:#{line}:#{regexp}"
            if cond != ''
              SESSION.add_line_breakpoint(path, line + 1, cond: cond)
            else
              SESSION.add_line_breakpoint(path, line + 1)
            end
            bps[b_id] = bps.size
            # Because we need to return scriptId, responses are returned in SESSION thread.
            req['params']['scriptId'] = path
            req['params']['lineNumber'] = line
            req['params']['breakpointId'] = b_id
            @q_msg << req
          elsif url = req.dig('params', 'url')
            b_id = "#{line}:#{url}"
            send_response req,
                          breakpointId: b_id,
                          locations: []
          elsif hash = req.dig('params', 'scriptHash')
            b_id = "#{line}:#{hash}"
            send_response req,
                          breakpointId: b_id,
                          locations: []
          else
            raise 'Unsupported'
          end
        when 'Debugger.removeBreakpoint'
          b_id = req.dig('params', 'breakpointId')
          bps = del_bp bps, b_id
          send_response req
        when 'Debugger.setBreakpointsActive'
          active = req.dig('params', 'active')
          if active
            activate_bp bps
          else
            deactivate_bp # TODO: Change this part because catch breakpoints should not be deactivated.
          end
          send_response req
        when 'Debugger.setPauseOnExceptions'
          state = req.dig('params', 'state')
          ex = 'Exception'
          case state
          when 'none'
            @q_msg << 'config postmortem = false'
            bps = del_bp bps, ex
          when 'uncaught'
            @q_msg << 'config postmortem = true'
            bps = del_bp bps, ex
          when 'all'
            @q_msg << 'config postmortem = false'
            SESSION.add_catch_breakpoint ex
            bps[ex] = bps.size
          end
          send_response req

        when 'Debugger.evaluateOnCallFrame', 'Runtime.getProperties'
          @q_msg << req
        end
      end
    rescue Detach
      @q_msg << 'continue'
    end

    def del_bp bps, k
      return bps unless idx = bps[k]

      bps.delete k
      bps.each_key{|i| bps[i] -= 1 if bps[i] > idx}
      @q_msg << "del #{idx}"
      bps
    end

    def get_source_code path
      return @src_map[path] if @src_map[path]

      src = File.read(path)
      @src_map[path] = src
      src
    end

    def activate_bp bps
      bps.each_key{|k|
        if k.match /^\d+:(\d+):(.*)/
          line = $1
          path = $2
          SESSION.add_line_breakpoint(path, line.to_i + 1)
        else
          SESSION.add_catch_breakpoint 'Exception'
        end
      }
    end

    def deactivate_bp
      @q_msg << 'del'
      @q_ans << 'y'
    end

    def cleanup_reader
      super
      Process.kill :KILL, @chrome_pid if @chrome_pid
    end

    ## Called by the SESSION thread

    def readline prompt
      return 'c' unless @q_msg

      @q_msg.pop || 'kill!'
    end

    def respond req, **result
      send_response req, **result
    end

    def respond_fail req, **result
      send_fail_response req, **result
    end

    def fire_event event, **result
      if result.empty?
        send_event event
      else
        send_event event, **result
      end
    end

    def sock skip: false
      yield $stderr
    end

    def puts result
      # STDERR.puts "puts: #{result}"
      # send_event 'output', category: 'stderr', output: "PUTS!!: " + result.to_s
    end
  end

  class Session
    def fail_response req, **result
      @ui.respond_fail req, **result
      return :retry
    end

    INVALID_PARAMS = -32602
    INTERNAL_ERROR = -32603

    def process_protocol_request req
      case req['method']
      when 'Debugger.stepOver', 'Debugger.stepInto', 'Debugger.stepOut', 'Debugger.resume', 'Debugger.enable'
        request_tc [:cdp, :backtrace, req]
      when 'Debugger.evaluateOnCallFrame'
        frame_id = req.dig('params', 'callFrameId')
        group = req.dig('params', 'objectGroup')
        if fid = @frame_map[frame_id]
          expr = req.dig('params', 'expression')
          request_tc [:cdp, :evaluate, req, fid, expr, group]
        else
          fail_response req,
                        code: INVALID_PARAMS,
                        message: "'callFrameId' is an invalid"
        end
      when 'Runtime.getProperties'
        oid = req.dig('params', 'objectId')
        if ref = @obj_map[oid]
          case ref[0]
          when 'local'
            frame_id = ref[1]
            fid = @frame_map[frame_id]
            request_tc [:cdp, :scope, req, fid]
          when 'properties'
            request_tc [:cdp, :properties, req, oid]
          when 'script', 'global'
            # TODO: Support script and global types
            @ui.respond req, result: []
            return :retry
          else
            raise "Unknown type: #{ref.inspect}"
          end
        else
          fail_response req,
                        code: INVALID_PARAMS,
                        message: "'objectId' is an invalid"
        end
      when 'Debugger.getScriptSource'
        s_id = req.dig('params', 'scriptId')
        if src = @src_map[s_id]
          @ui.respond req, scriptSource: src
        else
          fail_response req,
                        code: INVALID_PARAMS,
                        message: "'scriptId' is an invalid"
        end
        return :retry
      when 'Debugger.getPossibleBreakpoints'
        s_id = req.dig('params', 'start', 'scriptId')
        if src = @src_map[s_id]
          lineno = req.dig('params', 'start', 'lineNumber')
          end_line = src.lines.count
          lineno = end_line  if lineno > end_line
          @ui.respond req,
                      locations: [{
                        scriptId: s_id,
                        lineNumber: lineno
                      }]
        else
          fail_response req,
                        code: INVALID_PARAMS,
                        message: "'scriptId' is an invalid"
        end
        return :retry
      when 'Debugger.setBreakpointByUrl'
        path = req.dig('params', 'scriptId')
        if s_id = @scr_id_map[path]
          lineno = req.dig('params', 'lineNumber')
          b_id = req.dig('params', 'breakpointId')
          @ui.respond req,
                      breakpointId: b_id,
                      locations: [{
                          scriptId: s_id,
                          lineNumber: lineno
                      }]
        else
          fail_response req,
                        code: INTERNAL_ERROR,
                        message: 'The target script is not found...'
        end
        return :retry
      end
    end

    def cdp_event args
      type, req, result = args

      case type
      when :backtrace
        result[:callFrames].each.with_index do |frame, i|
          frame_id = frame[:callFrameId]
          @frame_map[frame_id] = i
          path = frame[:url]
          unless s_id = @scr_id_map[path]
            s_id = (@scr_id_map.size + 1).to_s
            @scr_id_map[path] = s_id
            if path && File.exist?(path)
              src = File.read(path)
            end
            @src_map[s_id] = src
          end
          if src = @src_map[s_id]
            lineno = src.lines.count
          else
            lineno = 0
          end
          frame[:location][:scriptId] = s_id
          frame[:functionLocation][:scriptId] = s_id
          @ui.fire_event 'Debugger.scriptParsed',
                          scriptId: s_id,
                          url: frame[:url],
                          startLine: 0,
                          startColumn: 0,
                          endLine: lineno,
                          endColumn: 0,
                          executionContextId: 1,
                          hash: src.hash.inspect

          frame[:scopeChain].each {|s|
            oid = s.dig(:object, :objectId)
            @obj_map[oid] = [s[:type], frame_id]
          }
        end

        if oid = result.dig(:data, :objectId)
          @obj_map[oid] = ['properties']
        end
        @ui.fire_event 'Debugger.paused', **result
      when :evaluate
        message = result.delete :message
        if message
          fail_response req,
                        code: INVALID_PARAMS,
                        message: message
        else
          src = req.dig('params', 'expression')
          s_id = (@src_map.size + 1).to_s
          @src_map[s_id] = src
          lineno = src.lines.count
          @ui.fire_event 'Debugger.scriptParsed',
                            scriptId: s_id,
                            url: '',
                            startLine: 0,
                            startColumn: 0,
                            endLine: lineno,
                            endColumn: 0,
                            executionContextId: 1,
                            hash: src.hash.inspect
          if exc = result.dig(:response, :exceptionDetails)
            exc[:stackTrace][:callFrames].each{|frame|
              if frame[:url].empty?
                frame[:scriptId] = s_id
              else
                path = frame[:url]
                unless s_id = @scr_id_map[path]
                  s_id = (@scr_id_map.size + 1).to_s
                  @scr_id_map[path] = s_id
                end
                frame[:scriptId] = s_id
              end
            }
          end
          rs = result.dig(:response, :result)
          [rs].each{|obj|
            if oid = obj[:objectId]
              @obj_map[oid] = ['properties']
            end
          }
          @ui.respond req, **result[:response]

          out = result[:output]
          if out && !out.empty?
            @ui.fire_event 'Runtime.consoleAPICalled',
                            type: 'log',
                            args: [
                              type: out.class,
                              value: out
                            ],
                            executionContextId: 1, # Change this number if something goes wrong.
                            timestamp: Time.now.to_f
          end
        end
      when :scope
        result.each{|obj|
          if oid = obj.dig(:value, :objectId)
            @obj_map[oid] = ['properties']
          end
        }
        @ui.respond req, result: result
      when :properties
        result.each_value{|v|
          v.each{|obj|
            if oid = obj.dig(:value, :objectId)
              @obj_map[oid] = ['properties']
            end
          }
        }
        @ui.respond req, **result
      end
    end
  end

  class ThreadClient
    def process_cdp args
      type = args.shift
      req = args.shift

      case type
      when :backtrace
        exception = nil
        result = {
          reason: 'other',
          callFrames: @target_frames.map.with_index{|frame, i|
            exception = frame.raised_exception if frame == current_frame && frame.has_raised_exception

            path = frame.realpath || frame.path

            if frame.iseq.nil?
              lineno = 0
            else
              lineno = frame.iseq.first_line - 1
            end

            {
              callFrameId: SecureRandom.hex(16),
              functionName: frame.name,
              functionLocation: {
                # scriptId: N, # filled by SESSION
                lineNumber: lineno
              },
              location: {
                # scriptId: N, # filled by SESSION
                lineNumber: frame.location.lineno - 1 # The line number is 0-based.
              },
              url: path,
              scopeChain: [
                {
                  type: 'local',
                  object: {
                    type: 'object',
                    objectId: rand.to_s
                  }
                },
                {
                  type: 'script',
                  object: {
                    type: 'object',
                    objectId: rand.to_s
                  }
                },
                {
                  type: 'global',
                  object: {
                    type: 'object',
                    objectId: rand.to_s
                  }
                }
              ],
              this: {
                type: 'object'
              }
            }
          }
        }

        if exception
          result[:data] = evaluate_result exception
          result[:reason] = 'exception'
        end
        event! :cdp_result, :backtrace, req, result
      when :evaluate
        res = {}
        fid, expr, group = args
        frame = @target_frames[fid]
        message = nil

        if frame && (b = frame.eval_binding)
          special_local_variables frame do |name, var|
            b.local_variable_set(name, var) if /\%/ !~name
          end

          result = nil

          case group
          when 'popover'
            case expr
            # Chrome doesn't read instance variables
            when /\A\$\S/
              global_variables.each{|gvar|
                if gvar.to_s == expr
                  result = eval(gvar.to_s)
                  break false
                end
              } and (message = "Error: Not defined global variable: #{expr.inspect}")
            when /(\A((::[A-Z]|[A-Z])\w*)+)/
              unless result = search_const(b, $1)
                message = "Error: Not defined constant: #{expr.inspect}"
              end
            else
              begin
                result = b.local_variable_get(expr)
              rescue NameError
                # try to check method
                if b.receiver.respond_to? expr, include_all: true
                  result = b.receiver.method(expr)
                else
                  message = "Error: Can not evaluate: #{expr.inspect}"
                end
              end
            end
          when 'console', 'watch-group'
            begin
              orig_stdout = $stdout
              $stdout = StringIO.new
              result = current_frame.binding.eval(expr.to_s, '(DEBUG CONSOLE)')
            rescue Exception => e
              result = e
              b = result.backtrace.map{|e| "    #{e}\n"}
              frames = [
                {
                  columnNumber: 0,
                  functionName: 'eval',
                  lineNumber: 0,
                  url: ''
                }
              ]
              e.backtrace_locations&.each do |loc|
                break if loc.path == __FILE__
                path = loc.absolute_path || loc.path
                frames << {
                  columnNumber: 0,
                  functionName: loc.base_label,
                  lineNumber: loc.lineno - 1,
                  url: path
                }
              end
              res[:exceptionDetails] = {
                exceptionId: 1,
                text: 'Uncaught',
                lineNumber: 0,
                columnNumber: 0,
                exception: evaluate_result(result),
                stackTrace: {
                  callFrames: frames
                }
              }
            ensure
              output = $stdout.string
              $stdout = orig_stdout
            end
          else
            message = "Error: unknown objectGroup: #{group}"
          end
        else
          result = Exception.new("Error: Can not evaluate on this frame")
        end

        res[:result] = evaluate_result(result)
        event! :cdp_result, :evaluate, req, message: message, response: res, output: output
      when :scope
        fid = args.shift
        frame = @target_frames[fid]
        if b = frame.binding
          vars = b.local_variables.map{|name|
            v = b.local_variable_get(name)
            variable(name, v)
          }
          special_local_variables frame do |name, val|
            vars.unshift variable(name, val)
          end
          vars.unshift variable('%self', b.receiver)
        elsif lvars = frame.local_variables
          vars = lvars.map{|var, val|
            variable(var, val)
          }
        else
          vars = [variable('%self', frame.self)]
          special_local_variables frame do |name, val|
            vars.unshift variable(name, val)
          end
        end
        event! :cdp_result, :scope, req, vars
      when :properties
        oid = args.shift
        result = []
        prop = []

        if obj = @obj_map[oid]
          case obj
          when Array
            result = obj.map.with_index{|o, i|
              variable i.to_s, o
            }
          when Hash
            result = obj.map{|k, v|
              variable(k, v)
            }
          when Struct
            result = obj.members.map{|m|
              variable(m, obj[m])
            }
          when String
            prop = [
              internalProperty('#length', obj.length),
              internalProperty('#encoding', obj.encoding)
            ]
          when Class, Module
            result = obj.instance_variables.map{|iv|
              variable(iv, obj.instance_variable_get(iv))
            }
            prop = [internalProperty('%ancestors', obj.ancestors[1..])]
          when Range
            prop = [
              internalProperty('#begin', obj.begin),
              internalProperty('#end', obj.end),
            ]
          end

          result += obj.instance_variables.map{|iv|
            variable(iv, obj.instance_variable_get(iv))
          }
          prop += [internalProperty('#class', obj.class)]
        end
        event! :cdp_result, :properties, req, result: result, internalProperties: prop
      end
    end

    def search_const b, expr
      cs = expr.delete_prefix('::').split('::')
      [Object, *b.eval('::Module.nesting')].reverse_each{|mod|
        if cs.all?{|c|
             if mod.const_defined?(c)
               mod = mod.const_get(c)
             else
               false
             end
           }
          # if-body
          return mod
        end
      }
      false
    end

    def evaluate_result r
      v = variable nil, r
      v[:value]
    end

    def internalProperty name, obj
      v = variable name, obj
      v.delete :configurable
      v.delete :enumerable
      v
    end

    def propertyDescriptor_ name, obj, type, description: nil, subtype: nil
      description = DEBUGGER__.safe_inspect(obj, short: true) if description.nil?
      oid = rand.to_s
      @obj_map[oid] = obj
      prop = {
        name: name,
        value: {
          type: type,
          description: description,
          value: obj,
          objectId: oid
        },
        configurable: true, # TODO: Change these parts because
        enumerable: true    #       they are not necessarily `true`.
      }

      if type == 'object'
        v = prop[:value]
        v.delete :value
        v[:subtype] = subtype if subtype
        v[:className] = obj.class
      end
      prop
    end

    def preview_ value, hash, overflow
      {
        type: value[:type],
        subtype: value[:subtype],
        description: value[:description],
        overflow: overflow,
        properties: hash.map{|k, v|
          pd = propertyDescriptor k, v
          {
            name: pd[:name],
            type: pd[:value][:type],
            value: pd[:value][:description]
          }
        }
      }
    end

    def variable name, obj
      pd = propertyDescriptor name, obj
      case obj
      when Array
        pd[:value][:preview] = preview name, obj
        obj.each_with_index{|item, idx|
          if valuePreview = preview(idx.to_s, item)
            pd[:value][:preview][:properties][idx][:valuePreview] = valuePreview
          end
        }
      when Hash
        pd[:value][:preview] = preview name, obj
        obj.each_with_index{|item, idx|
          key, val = item
          if valuePreview = preview(key, val)
            pd[:value][:preview][:properties][idx][:valuePreview] = valuePreview
          end
        }
      end
      pd
    end

    def preview name, obj
      case obj
      when Array
        pd = propertyDescriptor name, obj
        overflow = false
        if obj.size > 100
          obj = obj[0..99]
          overflow = true
        end
        hash = obj.each_with_index.to_h{|o, i| [i.to_s, o]}
        preview_ pd[:value], hash, overflow
      when Hash
        pd = propertyDescriptor name, obj
        overflow = false
        if obj.size > 100
          obj = obj.to_a[0..99].to_h
          overflow = true
        end
        preview_ pd[:value], obj, overflow
      else
        nil
      end
    end

    def propertyDescriptor name, obj
      case obj
      when Array
        propertyDescriptor_ name, obj, 'object', subtype: 'array'
      when Hash
        propertyDescriptor_ name, obj, 'object', subtype: 'map'
      when String
        propertyDescriptor_ name, obj, 'string', description: obj
      when TrueClass, FalseClass
        propertyDescriptor_ name, obj, 'boolean'
      when Symbol
        propertyDescriptor_ name, obj, 'symbol'
      when Integer, Float
        propertyDescriptor_ name, obj, 'number'
      when Exception
        bt = ''
        if log = obj.backtrace_locations
          log.each do |loc|
            break if loc.path == __FILE__
            bt += "    #{loc}\n"
          end
        end
        propertyDescriptor_ name, obj, 'object', description: "#{obj.inspect}\n#{bt}", subtype: 'error'
      else
        propertyDescriptor_ name, obj, 'object'
      end
    end
  end
end