Improve error resilience and handling

Timeouts are now handled correctly and the Runner automatically
creates the execution environment if it could not be found in
Poseidon. The runner is deleted locally if Poseidon returns
a bad request error.

app/controllers/submissions_controller.rb

@@ -150,6 +150,10 @@ class SubmissionsController < ApplicationController
     end
 
     socket.on :exit do |exit_code|
+      # As this is sometimes called before the timeout is handled, we must not close the
+      # socket to the user here. The socket will be closed after handling the timeout.
+      next if exit_code == Runner::Connection::TIMEOUT_EXIT_STATUS
+
       EventMachine.stop_event_loop
       if @output.empty?
         tubesock.send_data JSON.dump({cmd: :write, stream: :stdout, data: "#{t('exercises.implement.no_output', timestamp: l(Time.zone.now, format: :short))}\n"})

app/models/runner.rb

@@ -39,8 +39,8 @@ class Runner < ApplicationRecord
     define_method(method) do |*args, &block|
       @strategy.send(method, *args, &block)
     rescue Runner::Error::NotFound
-      update(runner_id: self.class.strategy_class.request_from_management(execution_environment))
-      @strategy = self.class.strategy_class.new(runner_id, execution_environment)
+      request_new_id
+      save
       @strategy.send(method, *args, &block)
     end
   end
@@ -48,10 +48,22 @@ class Runner < ApplicationRecord
   private
 
   def request_id
-    return if runner_id.present?
+    request_new_id if runner_id.blank?
+  end
 
+  def request_new_id
     strategy_class = self.class.strategy_class
     self.runner_id = strategy_class.request_from_management(execution_environment)
     @strategy = strategy_class.new(runner_id, execution_environment)
+  rescue Runner::Error::NotFound
+    if strategy_class.sync_environment(execution_environment)
+      raise Runner::Error::NotFound.new(
+        "The execution environment with id #{execution_environment.id} was not found and was successfully synced with the runner management"
+      )
+    else
+      raise Runner::Error::NotFound.new(
+        "The execution environment with id #{execution_environment.id} was not found and could not be synced with the runner management"
+      )
+    end
   end
 end

db/migrate/20210602071834_clean_exposed_ports_in_execution_environment.rb

@@ -3,7 +3,7 @@
 class CleanExposedPortsInExecutionEnvironment < ActiveRecord::Migration[6.1]
   def change
     ExecutionEnvironment.all.each do |execution_environment|
-      continue if execution_environment.exposed_ports.nil?
+      next if execution_environment.exposed_ports.nil?
 
       cleaned = execution_environment.exposed_ports.gsub(/[[:space:]]/, '')
       list = cleaned.split(',').map(&:to_i).uniq

lib/runner/connection.rb

@@ -7,6 +7,7 @@ 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')))
+  TIMEOUT_EXIT_STATUS = -100
 
   def initialize(url)
     @socket = Faye::WebSocket::Client.new(url, [], ping: 5)
@@ -20,7 +21,8 @@ class Runner::Connection
     # This registers empty default callbacks.
     EVENTS.each {|event_type| instance_variable_set(:"@#{event_type}_callback", ->(e) {}) }
     @start_callback = -> {}
-    @exit_code = 0
+    # Fail if no exit status was returned.
+    @exit_code = 1
   end
 
   def on(event, &block)
@@ -80,6 +82,7 @@ class Runner::Connection
   def handle_start(_event); end
 
   def handle_timeout(_event)
+    @exit_code = TIMEOUT_EXIT_STATUS
     raise Runner::Error::ExecutionTimeout.new('Execution exceeded its time limit')
   end
 end

lib/runner/strategy/poseidon.rb

@@ -10,6 +10,10 @@ class Runner::Strategy::Poseidon < Runner::Strategy
     end
   end
 
+  def self.sync_environment(environment)
+    environment.copy_to_poseidon
+  end
+
   def self.request_from_management(environment)
     url = "#{Runner::BASE_URL}/runners"
     body = {executionEnvironmentId: environment.id, inactivityTimeout: Runner::UNUSED_EXPIRATION_TIME}
@@ -21,10 +25,12 @@ class Runner::Strategy::Poseidon < Runner::Strategy
         runner_id = response_body[:runnerId]
         runner_id.presence || raise(Runner::Error::Unknown.new('Poseidon did not send a runner id'))
       when 404
-        raise Runner::Error::NotFound.new('Execution environment not found')
+        raise Runner::Error::EnvironmentNotFound.new
       else
         handle_error response
     end
+  rescue Faraday::Error => e
+    raise Runner::Error::Unknown.new("Faraday request to runner management failed: #{e.inspect}")
   end
 
   def self.handle_error(response)
@@ -35,7 +41,7 @@ class Runner::Strategy::Poseidon < Runner::Strategy
       when 401
         raise Runner::Error::Unauthorized.new('Authentication with Poseidon failed')
       when 404
-        raise Runner::Error::NotFound.new('Runner not found')
+        raise Runner::Error::RunnerNotFound.new
       when 500
         response_body = parse response
         error_code = response_body[:errorCode]
@@ -60,7 +66,12 @@ class Runner::Strategy::Poseidon < Runner::Strategy
     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)
-    self.class.handle_error response unless response.status == 204
+    return if response.status == 204
+
+    Runner.destroy(@runner_id) if response.status == 400
+    self.class.handle_error response
+  rescue Faraday::Error => e
+    raise Runner::Error::Unknown.new("Faraday request to runner management failed: #{e.inspect}")
   end
 
   def attach_to_execution(command)
@@ -68,7 +79,7 @@ class Runner::Strategy::Poseidon < Runner::Strategy
     websocket_url = execute_command(command)
     EventMachine.run do
       socket = Runner::Connection.new(websocket_url)
-      yield(socket) if block_given?
+      yield(socket)
     end
     Time.zone.now - starting_time # execution duration
   end
@@ -76,6 +87,8 @@ class Runner::Strategy::Poseidon < Runner::Strategy
   def destroy_at_management
     response = Faraday.delete runner_url
     self.class.handle_error response unless response.status == 204
+  rescue Faraday::Error => e
+    raise Runner::Error::Unknown.new("Faraday request to runner management failed: #{e.inspect}")
   end
 
   private
@@ -84,17 +97,22 @@ class Runner::Strategy::Poseidon < Runner::Strategy
     url = "#{runner_url}/execute"
     body = {command: command, timeLimit: @execution_environment.permitted_execution_time}
     response = Faraday.post(url, body.to_json, HEADERS)
-    if response.status == 200
-      response_body = self.class.parse response
-      websocket_url = response_body[:websocketUrl]
-      if websocket_url.present?
-        return websocket_url
-      else
-        raise Runner::Error::Unknown.new('Poseidon did not send websocket url')
-      end
+    case response.status
+      when 200
+        response_body = self.class.parse response
+        websocket_url = response_body[:websocketUrl]
+        if websocket_url.present?
+          return websocket_url
+        else
+          raise Runner::Error::Unknown.new('Poseidon did not send websocket url')
+        end
+      when 400
+        Runner.destroy(@runner_id)
     end
 
     self.class.handle_error response
+  rescue Faraday::Error => e
+    raise Runner::Error::Unknown.new("Faraday request to runner management failed: #{e.inspect}")
   end
 
   def runner_url

spec/lib/runner/strategy/poseidon_spec.rb

@@ -16,11 +16,26 @@ describe Runner::Strategy::Poseidon do
       let(:response_status) { 400 }
 
       it 'raises an error' do
+        allow(Runner).to receive(:destroy).with(runner_id)
         expect { action.call }.to raise_error(Runner::Error::BadRequest, /#{error_message}/)
       end
     end
   end
 
+  # Only #copy_files and #execute_command destroy the runner locally in case
+  # of a BadRequest (400) response.
+  shared_examples 'BadRequest (400) destroys local runner' do
+    context 'when Poseidon returns BadRequest (400)' do
+      let(:response_body) { {message: error_message}.to_json }
+      let(:response_status) { 400 }
+
+      it 'destroys the runner locally' do
+        expect(Runner).to receive(:destroy).with(runner_id)
+        expect { action.call }.to raise_error(Runner::Error::BadRequest)
+      end
+    end
+  end
+
   # All requests handle a Unauthorized (401) response the same way.
   shared_examples 'Unauthorized (401) error handling' do
     context 'when Poseidon returns Unauthorized (401)' do
@@ -193,6 +208,7 @@ describe Runner::Strategy::Poseidon do
     end
 
     include_examples 'BadRequest (400) error handling'
+    include_examples 'BadRequest (400) destroys local runner'
     include_examples 'Unauthorized (401) error handling'
     include_examples 'NotFound (404) error handling'
     include_examples 'InternalServerError (500) error handling'
@@ -247,6 +263,7 @@ describe Runner::Strategy::Poseidon do
     end
 
     include_examples 'BadRequest (400) error handling'
+    include_examples 'BadRequest (400) destroys local runner'
     include_examples 'Unauthorized (401) error handling'
     include_examples 'NotFound (404) error handling'
     include_examples 'InternalServerError (500) error handling'

spec/models/runner_spec.rb

@@ -61,28 +61,81 @@ describe Runner do
     include_examples 'delegates method sends to its strategy', :attach_to_execution, nil
   end
 
-  describe '#request_id' do
-    it 'requests a runner from the runner management when created' do
+  describe 'creation' do
+    let(:user) { FactoryBot.create :external_user }
+    let(:execution_environment) { FactoryBot.create :ruby }
+    let(:create_action) { -> { described_class.create(user: user, execution_environment: execution_environment) } }
+
+    it 'requests a runner id from the runner management' do
       expect(strategy_class).to receive(:request_from_management)
-      described_class.create
+      create_action.call
     end
 
-    it 'sets the runner id when created' do
+    it 'returns a valid runner' do
       allow(strategy_class).to receive(:request_from_management).and_return(runner_id)
-      runner = described_class.create
-      expect(runner.runner_id).to eq(runner_id)
+      expect(create_action.call).to be_valid
     end
 
-    it 'sets the strategy when created' do
+    it 'sets the strategy' do
       allow(strategy_class).to receive(:request_from_management).and_return(runner_id)
-      runner = described_class.create
-      expect(runner.strategy).to be_present
+      strategy = strategy_class.new(runner_id, execution_environment)
+      allow(strategy_class).to receive(:new).with(runner_id, execution_environment).and_return(strategy)
+      runner = create_action.call
+      expect(runner.strategy).to eq(strategy)
     end
 
-    it 'does not call the runner management again when validating the model' do
+    it 'does not call the runner management again while a runner id is set' do
       expect(strategy_class).to receive(:request_from_management).and_return(runner_id).once
-      runner = described_class.create
-      runner.valid?
+      runner = create_action.call
+      runner.update(user: FactoryBot.create(:external_user))
+    end
+  end
+
+  describe '#request_new_id' do
+    let(:runner) { FactoryBot.create :runner }
+
+    context 'when the environment is available in the runner management' do
+      it 'requests the runner management' do
+        expect(strategy_class).to receive(:request_from_management)
+        runner.send(:request_new_id)
+      end
+
+      it 'updates the runner id' do
+        allow(strategy_class).to receive(:request_from_management).and_return(runner_id)
+        runner.send(:request_new_id)
+        expect(runner.runner_id).to eq(runner_id)
+      end
+
+      it 'updates the strategy' do
+        allow(strategy_class).to receive(:request_from_management).and_return(runner_id)
+        strategy = strategy_class.new(runner_id, runner.execution_environment)
+        allow(strategy_class).to receive(:new).with(runner_id, runner.execution_environment).and_return(strategy)
+        runner.send(:request_new_id)
+        expect(runner.strategy).to eq(strategy)
+      end
+    end
+
+    context 'when the environment could not be found in the runner management' do
+      let(:environment_id) { runner.execution_environment.id }
+
+      before { allow(strategy_class).to receive(:request_from_management).and_raise(Runner::Error::NotFound) }
+
+      it 'syncs the execution environment' do
+        expect(strategy_class).to receive(:sync_environment).with(runner.execution_environment)
+        runner.send(:request_new_id)
+      rescue Runner::Error::NotFound
+        # Ignored because this error is expected (see tests below).
+      end
+
+      it 'raises an error when the environment could be synced' do
+        allow(strategy_class).to receive(:sync_environment).with(runner.execution_environment).and_return(true)
+        expect { runner.send(:request_new_id) }.to raise_error(Runner::Error::NotFound, /#{environment_id}.*successfully synced/)
+      end
+
+      it 'raises an error when the environment could not be synced' do
+        allow(strategy_class).to receive(:sync_environment).with(runner.execution_environment).and_return(false)
+        expect { runner.send(:request_new_id) }.to raise_error(Runner::Error::NotFound, /#{environment_id}.*could not be synced/)
+      end
     end
   end