Added tut 10

Author: chewett

README.md

@@ -14,17 +14,18 @@ Later we will get onto more complicated topics such as reaching a consensus of w
 
 Questions comments and suggestions can be raised the specific blog post or by using issues here.
 
-## Tutorial 9 - Multi Slave Master
+## Tutorial 10 - More Advanced Connection Handling
 
-This tutorial focuses on changing the master so that it accepts
-multiple slaves connecting to it.
+This tutorial focuses on improving the master and slaves connection
+handling code. Here I am going to add a custom exception that can
+be used in the event of disconnection.
 
-Currently there is no error handling for nodes connecting and disconnecting.
-The next tutorial will focus on hardening the master and slaves connection/disconnection code.
+In the next tutorial we will look at improving the slave so that if
+the master goes down, it will rejoin at the next opportunity.
 
 The full details for
-[Tutorial 09 - Multi Slave Master is available on my blog](
-https://chewett.co.uk/blog/1872/raspberry-pi-cluster-node-09-multi-slave-master/
+[Tutorial 10 - More Advanced Connection Handling is available on my blog](
+https://chewett.co.uk/blog/1913/raspberry-pi-cluster-node-10-more-advanced-connection-handling/
 )
 
 ## Requirements

RpiCluster/DataPackager.py

@@ -1,5 +1,6 @@
 import socket
 import json
+from RpiClusterExceptions import DisconnectionException
 
 MESSAGE_SEPARATOR = "\r"
 
@@ -42,7 +43,8 @@ def get_message(clientsocket):
         try:
             data = clientsocket.recv(512) #Get at max 512 bytes of data from the client
         except socket.error: #If we failed to get data, assume they have disconnected
-            return None
+            raise DisconnectionException("Failed to receive messages, client has disconnected")
+
         data_len = len(data)
         if data_len > 0: #Do something if we got data
             _buffered_string += data #Keep track of our buffered stored data
@@ -52,4 +54,13 @@ def get_message(clientsocket):
             if message_in_buffer:
                 return message_in_buffer
         else:
-            return None
+            raise DisconnectionException("No further messages received, client has disconnected")
+
+
+def send_message(clientsocket, payload):
+    try:
+        clientsocket.send(payload)
+        return True
+    except socket.error:
+        raise DisconnectionException("Failed to send message")
+

RpiCluster/RpiClusterClient.py

@@ -1,6 +1,8 @@
 import json
 import threading
-from DataPackager import get_message, create_payload
+import time
+from DataPackager import get_message, create_payload, send_message
+from RpiClusterExceptions import DisconnectionException
 from MachineInfo import get_base_machine_info
 from MainLogger import logger
 
@@ -13,21 +15,20 @@ def __init__(self, clientsocket, address):
         self.address = address
 
     def run(self):
-        message = True
-        while message:
-            message = get_message(self.clientsocket)
-            if message:
+        try:
+            message = True
+            while message:
+                message = get_message(self.clientsocket)
                 if message['type'] == 'message':
                     logger.info("Received message: " + message['payload'])
                 elif message['type'] == 'computer_details':
                     logger.info("Computer specifications: " + json.dumps(message['payload']))
                 elif message['type'] == 'info':
                     logger.info("Slave wants to know my info about " + message['payload'])
                     if message['payload'] == 'computer_details':
-                        self.clientsocket.send(create_payload(get_base_machine_info(), "master_info"))
+                        send_message(self.clientsocket, create_payload(get_base_machine_info(), "master_info"))
                     else:
-                        self.clientsocket.send(create_payload("unknown", "bad_message"))
-
-            else:
-                logger.info("Client disconnected at address {addr}".format(addr=self.address))
-
+                        send_message(self.clientsocket, create_payload("unknown", "bad_message"))
+        except DisconnectionException as e:
+            logger.info("Got disconnection exception with message: " + e.message)
+            logger.info("Shutting down slave connection handler")

RpiCluster/RpiClusterExceptions.py

@@ -0,0 +1,5 @@
+
+
+class DisconnectionException(Exception):
+    pass
+

basic_slave.py

@@ -6,8 +6,9 @@
 import socket
 import json
 from RpiCluster.MainLogger import add_file_logger, logger
-from RpiCluster.DataPackager import create_payload, get_message
+from RpiCluster.DataPackager import create_payload, get_message, send_message
 from RpiCluster.MachineInfo import get_base_machine_info
+from RpiCluster.RpiClusterExceptions import DisconnectionException
 
 config = ConfigParser.ConfigParser()
 config.read('rpicluster.cfg')
@@ -27,14 +28,19 @@
 
 client_number = random.randint(1, 100000)
 
-logger.info("Sending an initial hello to master")
-sock.send(create_payload(get_base_machine_info(), 'computer_details'))
-sock.send(create_payload("computer_details", "info"))
+try:
+    logger.info("Sending an initial hello to master")
+    send_message(sock, create_payload(get_base_machine_info(), 'computer_details'))
+    send_message(sock, create_payload("computer_details", "info"))
 
-message = get_message(sock)
-logger.info("We have information about the master " + json.dumps(message['payload']))
+    message = get_message(sock)
+    logger.info("We have information about the master " + json.dumps(message['payload']))
 
-while True:
-    logger.info("Now sending a keepalive to the master")
-    sock.send(create_payload("I am still alive, client: {num}".format(num=client_number)))
-    time.sleep(5)
+    while True:
+        logger.info("Now sending a keepalive to the master")
+        send_message(sock, create_payload("I am still alive, client: {num}".format(num=client_number)))
+        time.sleep(5)
+
+except DisconnectionException as e:
+    logger.info("Got disconnection exception with message: " + e.message)
+    logger.info("Shutting down slave")