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# Copyright (C) 2009 Robert Collins <robertc@robertcollins.net>
# Licenced under the txaws licence available at /LICENSE in the txaws source.
"""EC2 client support."""
__all__ = ['EC2Client']
from base64 import b64encode
from urllib import quote
from twisted.web.client import getPage
from txaws import credentials
from txaws.util import iso8601time, XML
class Instance(object):
"""An Amazon EC2 Instance.
:attrib instanceId: The instance ID of this instance.
:attrib instanceState: The state of this instance.
"""
def __init__(self, instanceId, instanceState):
self.instanceId = instanceId
self.instanceState = instanceState
class EC2Client(object):
"""A client for EC2."""
NS = '{http://ec2.amazonaws.com/doc/2008-12-01/}'
def __init__(self, creds=None, query_factory=None):
"""Create an EC2Client.
:param creds: Explicit credentials to use. If None, credentials are
inferred as per txaws.credentials.AWSCredentials.
"""
if creds is None:
self.creds = credentials.AWSCredentials()
else:
self.creds = creds
if query_factory is None:
self.query_factory = Query
else:
self.query_factory = query_factory
def describe_instances(self):
"""Describe current instances."""
q = self.query_factory('DescribeInstances', self.creds)
d = q.submit()
return d.addCallback(self._parse_Reservation)
def _parse_Reservation(self, xml_bytes):
root = XML(xml_bytes)
result = []
# May be a more elegant way to do this:
for reservation in root.find(self.NS + 'reservationSet'):
for instance in reservation.find(self.NS + 'instancesSet'):
instanceId = instance.findtext(self.NS + 'instanceId')
instanceState = instance.find(
self.NS + 'instanceState').findtext(self.NS + 'name')
result.append(Instance(instanceId, instanceState))
return result
class Query(object):
"""A query that may be submitted to EC2."""
def __init__(self, action, creds, other_params=None, time_tuple=None):
"""Create a Query to submit to EC2."""
# Require params (2008-12-01 API):
# Version, SignatureVersion, SignatureMethod, Action, AWSAccessKeyId,
# Timestamp || Expires, Signature,
self.params = {'Version': '2008-12-01',
'SignatureVersion': '2',
'SignatureMethod': 'HmacSHA1',
'Action': action,
'AWSAccessKeyId': creds.access_key,
'Timestamp': iso8601time(time_tuple),
}
if other_params:
self.params.update(other_params)
self.method = 'GET'
self.host = 'ec2.amazonaws.com'
self.uri = '/'
self.creds = creds
def canonical_query_params(self):
"""Return the canonical query params (used in signing)."""
result = []
for key, value in self.sorted_params():
result.append('%s=%s' % (self.encode(key), self.encode(value)))
return '&'.join(result)
def encode(self, a_string):
"""Encode a_string as per the canonicalisation encoding rules.
See the AWS dev reference page 90 (2008-12-01 version).
:return: a_string encoded.
"""
return quote(a_string, safe='~')
def signing_text(self):
"""Return the text to be signed when signing the query."""
result = "%s\n%s\n%s\n%s" % (self.method, self.host, self.uri,
self.canonical_query_params())
return result
def sign(self):
"""Sign this query using its built in credentials.
This prepares it to be sent, and should be done as the last step before
submitting the query. Signing is done automatically - this is a public
method to facilitate testing.
"""
self.params['Signature'] = self.creds.sign(self.signing_text())
def sorted_params(self):
"""Return the query params sorted appropriately for signing."""
return sorted(self.params.items())
def submit(self):
"""Submit this query.
:return: A deferred from twisted.web.client.getPage
"""
self.sign()
url = 'http://%s%s?%s' % (self.host, self.uri,
self.canonical_query_params())
return getPage(url, method=self.method)
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