Handling Amazon SNS notifications with a Tastypie Resource
Using Django and Tastypie, we automagically respond to SNS subscription requests. After that part is handled, the notification messages start coming in and those are used to trigger an SQS polling cycle (trying to do a thorough job there which may seem like an overkill but it's not). A received SQS message is parsed and contents are passed to an external program that forks and exits which keeps the request from blocking.
from django.conf import settings
from tastypie import fields, http
from tastypie.resources import Resource
from tastypie.bundle import Bundle
from tastypie.authentication import Authentication
from tastypie.authorization import Authorization
from tastypie.throttle import BaseThrottle
import boto.sq
from boto.sqs.message import Message
from urlparse import urlparse
import base64, httplib, tempfile, subprocess, time, json, os, sys, syslog
# Http://django-tastypie.readthedocs.org/en/latest/non_orm_data_sources.html
class NotificationObject(object):
def __init__(self, initial=None):
self.__dict__['_data'] = {}
if hasattr(initial, 'items'):
self.__dict__['_data'] = initial
def __getattr__(self, name):
return self._data.get(name, None)
def __setattr__(self, name, value):
self.__dict__['_data'][name] = value
class NotificationResource(Resource):
sns_messageid = fields.CharField(attribute='MessageId')
sns_timestamp = fields.CharField(attribute='Timestamp')
sns_topicarn = fields.CharField(attribute='TopicArn')
sns_type = fields.CharField(attribute='Type')
sns_unsubscribeurl = fields.CharField(attribute='UnsubscribeURL')
sns_subscribeurl = fields.CharField(attribute='SubscribeURL')
sns_token = fields.CharField(attribute='Token')
sns_message = fields.CharField(attribute='Message')
sns_subject = fields.CharField(attribute='Subject')
sns_signature = fields.CharField(attribute='Signature')
sns_signatureversion = fields.CharField(attribute='SignatureVersion')
sns_signingcerturl = fields.CharField(attribute='SigningCertURL')
class Meta:
resource_name = 'notification'
object_class = NotificationObject
fields = ['sns_messageid']
list_allowed_methods = ['post']
authentication = Authentication()
authorization = Authorization()
def get_resource_uri(self, bundle_or_obj):
return ''
def obj_create(self, bundle, request=None, **kwargs):
bundle.obj = NotificationObject(initial={ 'MessageId': '', 'Timestamp': '', 'TopicArn': '', 'Type': '', 'UnsubscribeURL': '', 'SubscribeURL': '', 'Token': '', 'Message': '', 'Subject': '', 'Signature': '', 'SignatureVersion': '', 'SigningCertURL': '' })
bundle = self.full_hydrate(bundle)
o = urlparse(bundle.data['SigningCertURL'])
if not o.hostname.endswith('.amazonaws.com'):
return bundle
topicarn = bundle.data['TopicArn']
if topicarn != settings.SNS_TOPIC:
return bundle
if not self.verify_message(bundle):
return bundle
if bundle.data['Type'] == 'SubscriptionConfirmation':
self.process_subscription(bundle)
elif bundle.data['Type'] == 'Notification':
self.process_notification(bundle)
return bundle
def process_subscription(self, bundle):
syslog.syslog('SNS Subscription ' + bundle.data['SubscribeURL'])
o = urlparse(bundle.data['SubscribeURL'])
conn = httplib.HTTPSConnection(o.hostname)
conn.putrequest('GET', o.path + '?' + o.query)
conn.endheaders()
response = conn.getresponse()
subscription = response.read()
def process_notification(self, bundle):
sqs = boto.sqs.connect_to_region(settings.SQS_REGION)
queue = sqs.lookup(settings.SQS_QUEUE)
retries = 5
done = False
while True:
if retries < 1:
break
retries -= 1
time.sleep(5)
messages = queue.get_messages(10, visibility_timeout=60)
if len(messages) < 1:
continue
for message in messages:
try:
m = json.loads(message.get_body())
m['return_sns_region'] = settings.SNS_REGION
m['return_sns_topic'] = settings.SNS_TOPIC
m['return_sqs_region'] = settings.SQS_REGION
m['return_sqs_queue'] = settings.SQS_QUEUE
process = subprocess.Popen(['/usr/bin/nice', '-n', '15', os.path.dirname(os.path.normpath(os.sys.modules[settings.SETTINGS_MODULE].__file__)) + '/process.py', base64.b64encode(json.dumps(m))], shell=False)
process.wait()
except:
e = sys.exc_info()[1]
syslog.syslog(str(e))
queue.delete_message(message)
def verify_message(self, bundle):
message = u''
if bundle.data['Type'] == 'SubscriptionConfirmation':
message += 'Message\n'
message += bundle.data['Message'] + '\n'
message += 'MessageId\n'
message += bundle.data['MessageId'] + '\n'
message += 'SubscribeURL\n'
message += bundle.data['SubscribeURL'] + '\n'
message += 'Timestamp\n'
message += bundle.data['Timestamp'] + '\n'
message += 'Token\n'
message += bundle.data['Token'] + '\n'
message += 'TopicArn\n'
message += bundle.data['TopicArn'] + '\n'
message += 'Type\n'
message += bundle.data['Type'] + '\n'
elif bundle.data['Type'] == 'Notification':
message += 'Message\n'
message += bundle.data['Message'] + '\n'
message += 'MessageId\n'
message += bundle.data['MessageId'] + '\n'
if bundle.data['Subject'] != '':
message += 'Subject\n'
message += bundle.data['Subject'] + '\n'
message += 'Timestamp\n'
message += bundle.data['Timestamp'] + '\n'
message += 'TopicArn\n'
message += bundle.data['TopicArn'] + '\n'
message += 'Type\n'
message += bundle.data['Type'] + '\n'
else:
return False
o = urlparse(bundle.data['SigningCertURL'])
conn = httplib.HTTPSConnection(o.hostname)
conn.putrequest('GET', o.path)
conn.endheaders()
response = conn.getresponse()
cert = response.read()
# ok; attempt to use m2crypto failed, using openssl command line tool instead
file_cert = tempfile.NamedTemporaryFile(mode='w', delete=False)
file_sig = tempfile.NamedTemporaryFile(mode='w', delete=False)
file_mess = tempfile.NamedTemporaryFile(mode='w', delete=False)
file_cert.write(cert)
file_sig.write(bundle.data['Signature'])
file_mess.write(message)
file_cert.close()
file_sig.close()
file_mess.close()
# see: https://async.fi/2011/10/sns-verify-sh/
verify_process = subprocess.Popen(['/usr/local/bin/sns-verify.sh', file_cert.name, file_sig.name, file_mess.name], shell=False)
verify_process.wait()
if verify_process.returncode == 0:
return True
return False
That process.py would be something like:
#!/usr/bin/env python
import boto.sqs
from boto.sqs.message import Message
import base64, json, os, sys, syslog
if len(sys.argv) != 2:
sys.exit('usage: %s <base64 encoded json object>' % (sys.argv[0], ))
m = json.loads(base64.b64decode(sys.argv[1]))
# http://code.activestate.com/recipes/66012-fork-a-daemon-process-on-unix/
try:
pid = os.fork()
if pid > 0:
sys.exit(0)
except OSError, e:
print >>sys.stderr, "fork #1 failed: %d (%s)" % (e.errno, e.strerror)
sys.exit(1)
os.chdir("/")
os.setsid()
os.umask(0)
try:
pid = os.fork()
if pid > 0:
sys.exit(0)
except OSError, e:
sys.exit(1)
syslog.syslog(sys.argv[0] + ': ' + str(m))
# ...
That is, process.py gets the received (and doped) SQS message, Base64 encoded, as it's only command line argument, forks, exits and does what it's supposed to do after that on its own. Control returns to NotificationResource so the request doesn't block unnecessarily.
Categorised as: snippet
