execjs/lib/execjs/external_runtime.rb

require "execjs/runtime"
require "tmpdir"
require "json"

module ExecJS
  class ExternalRuntime < Runtime
    class Context < Runtime::Context
      def initialize(runtime, source = "", options = {})
        source = source.encode(Encoding::UTF_8)

        @runtime = runtime
        @source  = source

        # Test compile context source
        exec("")
      end

      def eval(source, options = {})
        source = source.encode(Encoding::UTF_8)

        if /\S/ =~ source
          exec("return eval(#{::JSON.generate("(#{source})", quirks_mode: true)})")
        end
      end

      def exec(source, options = {})
        source = source.encode(Encoding::UTF_8)
        source = "#{@source}\n#{source}" if @source != ""
        source = @runtime.compile_source(source)

        tmpfile = write_to_tempfile(source)

        if ExecJS.cygwin?
          filepath = `cygpath -m #{tmpfile.path}`.rstrip
        else
          filepath = tmpfile.path
        end

        begin
          extract_result(@runtime.exec_runtime(filepath), filepath)
        ensure
          File.unlink(tmpfile)
        end
      end

      def call(identifier, *args)
        eval "#{identifier}.apply(this, #{::JSON.generate(args)})"
      end

      protected
        # See Tempfile.create on Ruby 2.1
        def create_tempfile(basename)
          tmpfile = nil
          Dir::Tmpname.create(basename) do |tmpname|
            mode    = File::WRONLY | File::CREAT | File::EXCL
            tmpfile = File.open(tmpname, mode, 0600)
          end
          tmpfile
        end

        def write_to_tempfile(contents)
          tmpfile = create_tempfile(['execjs', 'js'])
          tmpfile.write(contents)
          tmpfile.close
          tmpfile
        end

        def extract_result(output, filename)
          status, value, stack = output.empty? ? [] : ::JSON.parse(output, create_additions: false)
          if status == "ok"
            value
          else
            stack ||= ""
            real_filename = File.realpath(filename)
            stack = stack.split("\n").map do |line|
              line.sub(" at ", "")
                  .sub(real_filename, "(execjs)")
                  .sub(filename, "(execjs)")
                  .strip
            end
            stack.reject! { |line| ["eval code", "eval@[native code]"].include?(line) }
            stack.shift unless stack[0].to_s.include?("(execjs)")
            error_class = value =~ /SyntaxError:/ ? RuntimeError : ProgramError
            error = error_class.new(value)
            error.set_backtrace(stack + caller)
            raise error
          end
        end
    end

    attr_reader :name

    def initialize(options)
      @name        = options[:name]
      @command     = options[:command]
      @runner_path = options[:runner_path]
      @encoding    = options[:encoding]
      @deprecated  = !!options[:deprecated]
      @binary      = nil

      @popen_options = {}
      @popen_options[:external_encoding] = @encoding if @encoding
      @popen_options[:internal_encoding] = ::Encoding.default_internal || 'UTF-8'

      if @runner_path
        instance_eval <<~RUBY, __FILE__, __LINE__
          def compile_source(source)
            <<-RUNNER
            #{IO.read(@runner_path)}
            RUNNER
          end
        RUBY
      end
    end

    def available?
      require 'json'
      binary ? true : false
    end

    def deprecated?
      @deprecated
    end

    private
      def binary
        @binary ||= which(@command)
      end

      def locate_executable(command)
        commands = Array(command)
        if ExecJS.windows? && File.extname(command) == ""
          ENV['PATHEXT'].split(File::PATH_SEPARATOR).each { |p|
            commands << (command + p)
          }
        end

        commands.find { |cmd|
          if File.executable? cmd
            cmd
          else
            path = ENV['PATH'].split(File::PATH_SEPARATOR).find { |p|
              full_path = File.join(p, cmd)
              File.executable?(full_path) && File.file?(full_path)
            }
            path && File.expand_path(cmd, path)
          end
        }
      end

    protected

      def json2_source
        @json2_source ||= IO.read(ExecJS.root + "/support/json2.js")
      end

      def encode_source(source)
        encoded_source = encode_unicode_codepoints(source)
        ::JSON.generate("(function(){ #{encoded_source} })()", quirks_mode: true)
      end

      def encode_unicode_codepoints(str)
        str.gsub(/[\u0080-\uffff]/) do |ch|
          "\\u%04x" % ch.codepoints.to_a
        end
      end

      if ExecJS.windows?
        def exec_runtime(filename)
          path = Dir::Tmpname.create(['execjs', 'json']) {}
          begin
            command = binary.split(" ") << filename
            `#{shell_escape(*command)} 2>&1 > #{path}`
            output = File.open(path, 'rb', **@popen_options) { |f| f.read }
          ensure
            File.unlink(path) if path
          end

          if $?.success?
            output
          else
            raise exec_runtime_error(output)
          end
        end

        def shell_escape(*args)
          # see http://technet.microsoft.com/en-us/library/cc723564.aspx#XSLTsection123121120120
          args.map { |arg|
            arg = %Q("#{arg.gsub('"','""')}") if arg.match(/[&|()<>^ "]/)
            arg
          }.join(" ")
        end
      elsif RUBY_ENGINE == 'jruby'
        require 'shellwords'

        def exec_runtime(filename)
          command = "#{Shellwords.join(binary.split(' ') << filename)} 2>&1"
          io = IO.popen(command, **@popen_options)
          output = io.read
          io.close

          if $?.success?
            output
          else
            raise exec_runtime_error(output)
          end
        end
      else
        def exec_runtime(filename)
          io = IO.popen(binary.split(' ') << filename, **(@popen_options.merge({err: [:child, :out]})))
          output = io.read
          io.close

          if $?.success?
            output
          else
            raise exec_runtime_error(output)
          end
        end
      end
      # Internally exposed for Context.
      public :exec_runtime

      def exec_runtime_error(output)
        error = RuntimeError.new(output)
        lines = output.split("\n")
        lineno = lines[0][/:(\d+)$/, 1] if lines[0]
        lineno ||= 1
        error.set_backtrace(["(execjs):#{lineno}"] + caller)
        error
      end

      def which(command)
        Array(command).find do |name|
          name, args = name.split(/\s+/, 2)
          path = locate_executable(name)

          next unless path

          args ? "#{path} #{args}" : path
        end
      end
  end
end