Introduce new error types for runners

The errors are raised in the runner model and in the runner connection
class. In the submission controller the errors are rescued and,
depending on the error, the status timeout / container depleted is
sent to the client.

app/controllers/submissions_controller.rb

@@ -133,7 +133,7 @@ class SubmissionsController < ApplicationController
   end
 
   def handle_websockets(tubesock, runner, socket)
-    tubesock.send_data JSON.dump({'cmd' => 'status', 'status' => :container_running})
+    tubesock.send_data JSON.dump({cmd: :status, status: :container_running})
     @output = +''
 
     socket.on :output do |data|
@@ -182,21 +182,21 @@ class SubmissionsController < ApplicationController
 
   def run
     hijack do |tubesock|
-      if @embed_options[:disable_run]
-        kill_socket(tubesock)
-      else
-        begin
-          @container_execution_time = @submission.run(sanitize_filename) do |runner, socket|
-            @waiting_for_container_time = runner.waiting_time
-            handle_websockets(tubesock, runner, socket)
-          end
-          save_run_output
-        rescue RunnerNotAvailableError
-          tubesock.send_data JSON.dump({cmd: :timeout})
-          kill_socket(tubesock)
-          Rails.logger.debug('Runner not available')
-        end
+      return kill_socket(tubesock) if @embed_options[:disable_run]
+
+      @container_execution_time = @submission.run(sanitize_filename) do |runner, socket|
+        @waiting_for_container_time = runner.waiting_time
+        handle_websockets(tubesock, runner, socket)
       end
+      save_run_output
+    rescue Runner::Error::ExecutionTimeout => e
+      tubesock.send_data JSON.dump({cmd: :status, status: :timeout})
+      kill_socket(tubesock)
+      Rails.logger.debug { "Running a submission failed: #{e.message}" }
+    rescue Runner::Error => e
+      tubesock.send_data JSON.dump({cmd: :status, status: :container_depleted})
+      kill_socket(tubesock)
+      Rails.logger.debug { "Runner error while running a submission: #{e.message}" }
     end
   end
 
@@ -244,8 +244,15 @@ class SubmissionsController < ApplicationController
         tubesock.send_data(@submission.calculate_score)
         # To enable hints when scoring a submission, uncomment the next line:
         # send_hints(tubesock, StructuredError.where(submission: @submission))
-
-        tubesock.send_data JSON.dump({'cmd' => 'exit'})
+      rescue Runner::Error::ExecutionTimeout => e
+        tubesock.send_data JSON.dump({cmd: :status, status: :timeout})
+        Rails.logger.debug { "Running a submission failed: #{e.message}" }
+      rescue Runner::Error => e
+        tubesock.send_data JSON.dump({cmd: :status, status: :container_depleted})
+        Rails.logger.debug { "Runner error while scoring a submission: #{e.message}" }
+      ensure
+        tubesock.send_data JSON.dump({cmd: :exit})
+        tubesock.close
       end
     ensure
       ActiveRecord::Base.connection_pool.release_connection

app/errors/runner/error.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class Runner::Error < ApplicationError; end

app/errors/runner/error/bad_request.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class Runner::Error::BadRequest < Runner::Error; end

app/errors/runner/error/execution_timeout.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class Runner::Error::ExecutionTimeout < Runner::Error; end

app/errors/runner/error/internal_server_error.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class Runner::Error::InternalServerError < Runner::Error; end

app/errors/runner/error/not_available.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class Runner::Error::NotAvailable < Runner::Error; end

app/errors/runner/error/not_found.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class Runner::Error::NotFound < Runner::Error; end

app/errors/runner/error/unauthorized.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class Runner::Error::Unauthorized < Runner::Error; end

app/errors/runner/error/unknown.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class Runner::Error::Unknown < Runner::Error; end

app/errors/runner_not_available_error.rb

@@ -1,4 +0,0 @@
-# frozen_string_literal: true
-
-class RunnerNotAvailableError < ApplicationError
-end

app/models/runner.rb

@@ -4,51 +4,60 @@ class Runner < ApplicationRecord
   BASE_URL = CodeOcean::Config.new(:code_ocean).read[:runner_management][:url]
   HEADERS = {'Content-Type' => 'application/json'}.freeze
   UNUSED_EXPIRATION_TIME = CodeOcean::Config.new(:code_ocean).read[:runner_management][:unused_runner_expiration_time].seconds
+  ERRORS = %w[NOMAD_UNREACHABLE NOMAD_OVERLOAD NOMAD_INTERNAL_SERVER_ERROR UNKNOWN].freeze
+
+  ERRORS.each do |error|
+    define_singleton_method :"error_#{error.downcase}" do
+      error
+    end
+  end
 
   belongs_to :execution_environment
   belongs_to :user, polymorphic: true
 
-  before_create :new_runner
-  before_destroy :destroy_runner
+  before_validation :request_remotely
 
-  validates :execution_environment, presence: true
-  validates :user, presence: true
+  validates :execution_environment, :user, :runner_id, presence: true
 
   def self.for(user, exercise)
     execution_environment = ExecutionEnvironment.find(exercise.execution_environment_id)
     runner = find_or_create_by(user: user, execution_environment: execution_environment)
 
-    return runner if runner.save
+    unless runner.persisted?
+      # runner was not saved in the database (was not valid)
+      raise Runner::Error::InternalServerError.new("Provided runner could not be saved: #{runner.errors.inspect}")
+    end
 
-    raise RunnerNotAvailableError.new('No runner available')
+    runner
   end
 
   def copy_files(files)
     url = "#{runner_url}/files"
     body = {copy: files.map {|filename, content| {path: filename, content: Base64.strict_encode64(content)} }}
     response = Faraday.patch(url, body.to_json, HEADERS)
-    return unless response.status == 404
-
-    # runner has disappeared for some reason
-    destroy
-    raise RunnerNotAvailableError.new('Runner unavailable')
+    handle_error response unless response.status == 204
   end
 
   def execute_command(command)
     url = "#{runner_url}/execute"
     body = {command: command, timeLimit: execution_environment.permitted_execution_time}
     response = Faraday.post(url, body.to_json, HEADERS)
-    if response.status == 404
-      # runner has disappeared for some reason
-      destroy
-      raise RunnerNotAvailableError.new('Runner unavailable')
+    if response.status == 200
+      response_body = parse response
+      websocket_url = response_body[:websocketUrl]
+      if websocket_url.present?
+        return websocket_url
+      else
+        raise Runner::Error::Unknown.new('Runner management sent unexpected response')
+      end
     end
-    parse response
+
+    handle_error response
   end
 
   def execute_interactively(command)
     starting_time = Time.zone.now
-    websocket_url = execute_command(command)[:websocketUrl]
+    websocket_url = execute_command(command)
     EventMachine.run do
       socket = Runner::Connection.new(websocket_url)
       yield(self, socket) if block_given?
@@ -56,24 +65,64 @@ class Runner < ApplicationRecord
     Time.zone.now - starting_time # execution time
   end
 
-  def destroy_runner
-    Faraday.delete runner_url
-  end
+  # This method is currently not used.
+  # This does *not* destroy the ActiveRecord model.
+  def destroy_remotely
+    response = Faraday.delete runner_url
+    return if response.status == 204
 
-  def status
-    # TODO: return actual state retrieved via websocket
-    :timeouted
+    if response.status == 404
+      raise Runner::Error::NotFound.new('Runner not found')
+    else
+      handle_error response
+    end
   end
 
   private
 
-  def new_runner
+  def request_remotely
+    return if runner_id.present?
+
     url = "#{BASE_URL}/runners"
     body = {executionEnvironmentId: execution_environment.id, inactivityTimeout: UNUSED_EXPIRATION_TIME}
     response = Faraday.post(url, body.to_json, HEADERS)
-    response_body = parse response
-    self.runner_id = response_body[:runnerId]
-    throw :abort unless response.status == 200
+
+    case response.status
+      when 200
+        response_body = parse response
+        runner_id = response_body[:runnerId]
+        throw(:abort) if runner_id.blank?
+        self.runner_id = response_body[:runnerId]
+      when 404
+        raise Runner::Error::NotFound.new('Execution environment not found')
+      else
+        handle_error response
+    end
+  end
+
+  def handle_error(response)
+    case response.status
+      when 400
+        response_body = parse response
+        raise Runner::Error::BadRequest.new(response_body[:message])
+      when 401
+        raise Runner::Error::Unauthorized.new('Authentication with runner management failed')
+      when 404
+        # The runner does not exist in the runner management (e.g. due to an inactivity timeout).
+        # Delete the runner model in this case as it can not be used anymore.
+        destroy
+        raise Runner::Error::NotFound.new('Runner not found')
+      when 500
+        response_body = parse response
+        error_code = response_body[:errorCode]
+        if error_code == Runner.error_nomad_overload
+          raise Runner::Error::NotAvailable.new("No runner available (#{error_code}): #{response_body[:message]}")
+        else
+          raise Runner::Error::InternalServerError.new("#{response_body[:errorCode]}: #{response_body[:message]}")
+        end
+      else
+        raise Runner::Error::Unknown.new('Runner management sent unexpected response')
+    end
   end
 
   def runner_url
@@ -82,5 +131,8 @@ class Runner < ApplicationRecord
 
   def parse(response)
     JSON.parse(response.body).deep_symbolize_keys
+  rescue JSON::ParserError => e
+    # the runner management should not send invalid json
+    raise Runner::Error::Unknown.new("Error parsing response from runner management: #{e.message}")
   end
 end

lib/runner/connection.rb

@@ -4,16 +4,20 @@ require 'faye/websocket/client'
 require 'json_schemer'
 
 class Runner::Connection
+  # These are events for which callbacks can be registered.
   EVENTS = %i[start output exit stdout stderr].freeze
   BACKEND_OUTPUT_SCHEMA = JSONSchemer.schema(JSON.parse(File.read('lib/runner/backend-output.schema.json')))
 
   def initialize(url)
     @socket = Faye::WebSocket::Client.new(url, [], ping: 5)
 
+    # 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) {|event| __send__(:"on_#{event_type}", event) }
     end
 
+    # This registers empty default callbacks.
     EVENTS.each {|event_type| instance_variable_set(:"@#{event_type}_callback", ->(e) {}) }
     @start_callback = -> {}
     @exit_code = 0
@@ -43,6 +47,7 @@ class Runner::Connection
     return unless BACKEND_OUTPUT_SCHEMA.valid?(JSON.parse(event.data))
 
     event = decode(event.data)
+    # There is one `handle_` method for every message type defined in the WebSocket schema.
     __send__("handle_#{event[:type]}", event)
   end
 
@@ -50,7 +55,7 @@ class Runner::Connection
     @start_callback.call
   end
 
-  def on_error(event); end
+  def on_error(_event); end
 
   def on_close(_event)
     @exit_callback.call @exit_code
@@ -70,11 +75,11 @@ class Runner::Connection
     @output_callback.call event[:data]
   end
 
-  def handle_error(event) end
+  def handle_error(_event); end
 
-  def handle_start(event) end
+  def handle_start(_event); end
 
-  def handle_timeout(event)
-    # TODO: set the runner state
+  def handle_timeout(_event)
+    raise Runner::Error::ExecutionTimeout.new('Execution exceeded its time limit')
   end
 end