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.

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