~tribaal/txaws/xss-hardening

# Copyright (C) 2009 Robert Collins <robertc@robertcollins.net>
# Copyright (C) 2009 Canonical Ltd
# Copyright (C) 2009 Duncan McGreggor <oubiwann@adytum.us>
# Licenced under the txaws licence available at /LICENSE in the txaws source.

"""EC2 client support."""

from datetime import datetime
from urllib import quote
from base64 import b64encode

from txaws import version
from txaws.client.base import BaseClient, BaseQuery, error_wrapper
from txaws.ec2 import model
from txaws.ec2.exception import EC2Error
from txaws.util import iso8601time, XML


__all__ = ["EC2Client", "Query", "Parser"]


def ec2_error_wrapper(error):
    error_wrapper(error, EC2Error)


class EC2Client(BaseClient):
    """A client for EC2."""

    def __init__(self, creds=None, endpoint=None, query_factory=None,
                 parser=None):
        if query_factory is None:
            query_factory = Query
        if parser is None:
            parser = Parser()
        super(EC2Client, self).__init__(creds, endpoint, query_factory, parser)

    def describe_instances(self, *instance_ids):
        """Describe current instances."""
        instances = {}
        for pos, instance_id in enumerate(instance_ids):
            instances["InstanceId.%d" % (pos + 1)] = instance_id
        query = self.query_factory(
            action="DescribeInstances", creds=self.creds,
            endpoint=self.endpoint, other_params=instances)
        d = query.submit()
        return d.addCallback(self.parser.describe_instances)

    def run_instances(self, image_id, min_count, max_count,
        security_groups=None, key_name=None, instance_type=None,
        user_data=None, availability_zone=None, kernel_id=None,
        ramdisk_id=None):
        """Run new instances."""
        params = {"ImageId": image_id, "MinCount": str(min_count),
                  "MaxCount": str(max_count)}
        if security_groups is not None:
            for i, name in enumerate(security_groups):
                params["SecurityGroup.%d" % (i + 1)] = name
        if key_name is not None:
            params["KeyName"] = key_name
        if user_data is not None:
            params["UserData"] = b64encode(user_data)
        if instance_type is not None:
            params["InstanceType"] = instance_type
        if availability_zone is not None:
            params["Placement.AvailabilityZone"] = availability_zone
        if kernel_id is not None:
            params["KernelId"] = kernel_id
        if ramdisk_id is not None:
            params["RamdiskId"] = ramdisk_id
        query = self.query_factory(
            action="RunInstances", creds=self.creds, endpoint=self.endpoint,
            other_params=params)
        d = query.submit()
        return d.addCallback(self.parser.run_instances)

    def terminate_instances(self, *instance_ids):
        """Terminate some instances.

        @param instance_ids: The ids of the instances to terminate.
        @return: A deferred which on success gives an iterable of
            (id, old-state, new-state) tuples.
        """
        instances = {}
        for pos, instance_id in enumerate(instance_ids):
            instances["InstanceId.%d" % (pos + 1)] = instance_id
        query = self.query_factory(
            action="TerminateInstances", creds=self.creds,
            endpoint=self.endpoint, other_params=instances)
        d = query.submit()
        return d.addCallback(self.parser.terminate_instances)

    def describe_security_groups(self, *names):
        """Describe security groups.

        @param names: Optionally, a list of security group names to describe.
            Defaults to all security groups in the account.
        @return: A C{Deferred} that will fire with a list of L{SecurityGroup}s
            retrieved from the cloud.
        """
        group_names = {}
        if names:
            group_names = dict([("GroupName.%d" % (i + 1), name)
                                for i, name in enumerate(names)])
        query = self.query_factory(
            action="DescribeSecurityGroups", creds=self.creds,
            endpoint=self.endpoint, other_params=group_names)
        d = query.submit()
        return d.addCallback(self.parser.describe_security_groups)

    def create_security_group(self, name, description):
        """Create security group.

        @param name: Name of the new security group.
        @param description: Description of the new security group.
        @return: A C{Deferred} that will fire with a truth value for the
            success of the operation.
        """
        parameters = {"GroupName":  name, "GroupDescription": description}
        query = self.query_factory(
            action="CreateSecurityGroup", creds=self.creds,
            endpoint=self.endpoint, other_params=parameters)
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def delete_security_group(self, name):
        """
        @param name: Name of the new security group.
        @return: A C{Deferred} that will fire with a truth value for the
            success of the operation.
        """
        parameter = {"GroupName":  name}
        query = self.query_factory(
            action="DeleteSecurityGroup", creds=self.creds,
            endpoint=self.endpoint, other_params=parameter)
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def authorize_security_group(
        self, group_name, source_group_name="", source_group_owner_id="",
        ip_protocol="", from_port="", to_port="", cidr_ip=""):
        """
        There are two ways to use C{authorize_security_group}:
            1) associate an existing group (source group) with the one that you
            are targeting (group_name) with an authorization update; or
            2) associate a set of IP permissions with the group you are
            targeting with an authorization update.

        @param group_name: The group you will be modifying with a new
            authorization.

        Optionally, the following parameters:
        @param source_group_name: Name of security group to authorize access to
            when operating on a user/group pair.
        @param source_group_owner_id: Owner of security group to authorize
            access to when operating on a user/group pair.

        If those parameters are not specified, then the following must be:
        @param ip_protocol: IP protocol to authorize access to when operating
            on a CIDR IP.
        @param from_port: Bottom of port range to authorize access to when
            operating on a CIDR IP. This contains the ICMP type if ICMP is
            being authorized.
        @param to_port: Top of port range to authorize access to when operating
            on a CIDR IP. This contains the ICMP code if ICMP is being
            authorized.
        @param cidr_ip: CIDR IP range to authorize access to when operating on
            a CIDR IP.

        @return: A C{Deferred} that will fire with a truth value for the
            success of the operation.
        """
        if source_group_name and source_group_owner_id:
            parameters = {
                "SourceSecurityGroupName": source_group_name,
                "SourceSecurityGroupOwnerId": source_group_owner_id,
                }
        elif ip_protocol and from_port and to_port and cidr_ip:
            parameters = {
                "IpProtocol": ip_protocol,
                "FromPort": from_port,
                "ToPort": to_port,
                "CidrIp": cidr_ip,
                }
        else:
            msg = ("You must specify either both group parameters or "
                   "all the ip parameters.")
            raise ValueError(msg)
        parameters["GroupName"] = group_name
        query = self.query_factory(
            action="AuthorizeSecurityGroupIngress", creds=self.creds,
            endpoint=self.endpoint, other_params=parameters)
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def authorize_group_permission(
        self, group_name, source_group_name, source_group_owner_id):
        """
        This is a convenience function that wraps the "authorize group"
        functionality of the C{authorize_security_group} method.

        For an explanation of the parameters, see C{authorize_security_group}.
        """
        d = self.authorize_security_group(
            group_name,
            source_group_name=source_group_name,
            source_group_owner_id=source_group_owner_id)
        return d

    def authorize_ip_permission(
        self, group_name, ip_protocol, from_port, to_port, cidr_ip):
        """
        This is a convenience function that wraps the "authorize ip
        permission" functionality of the C{authorize_security_group} method.

        For an explanation of the parameters, see C{authorize_security_group}.
        """
        d = self.authorize_security_group(
            group_name,
            ip_protocol=ip_protocol, from_port=from_port, to_port=to_port,
            cidr_ip=cidr_ip)
        return d

    def revoke_security_group(
        self, group_name, source_group_name="", source_group_owner_id="",
        ip_protocol="", from_port="", to_port="", cidr_ip=""):
        """
        There are two ways to use C{revoke_security_group}:
            1) associate an existing group (source group) with the one that you
            are targeting (group_name) with the revoke update; or
            2) associate a set of IP permissions with the group you are
            targeting with a revoke update.

        @param group_name: The group you will be modifying with an
            authorization removal.

        Optionally, the following parameters:
        @param source_group_name: Name of security group to revoke access from
            when operating on a user/group pair.
        @param source_group_owner_id: Owner of security group to revoke
            access from when operating on a user/group pair.

        If those parameters are not specified, then the following must be:
        @param ip_protocol: IP protocol to revoke access from when operating
            on a CIDR IP.
        @param from_port: Bottom of port range to revoke access from when
            operating on a CIDR IP. This contains the ICMP type if ICMP is
            being revoked.
        @param to_port: Top of port range to revoke access from when operating
            on a CIDR IP. This contains the ICMP code if ICMP is being
            revoked.
        @param cidr_ip: CIDR IP range to revoke access from when operating on
            a CIDR IP.

        @return: A C{Deferred} that will fire with a truth value for the
            success of the operation.
        """
        if source_group_name and source_group_owner_id:
            parameters = {
                "SourceSecurityGroupName": source_group_name,
                "SourceSecurityGroupOwnerId": source_group_owner_id,
                }
        elif ip_protocol and from_port and to_port and cidr_ip:
            parameters = {
                "IpProtocol": ip_protocol,
                "FromPort": from_port,
                "ToPort": to_port,
                "CidrIp": cidr_ip,
                }
        else:
            msg = ("You must specify either both group parameters or "
                   "all the ip parameters.")
            raise ValueError(msg)
        parameters["GroupName"] = group_name
        query = self.query_factory(
            action="RevokeSecurityGroupIngress", creds=self.creds,
            endpoint=self.endpoint, other_params=parameters)
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def revoke_group_permission(
        self, group_name, source_group_name, source_group_owner_id):
        """
        This is a convenience function that wraps the "authorize group"
        functionality of the C{authorize_security_group} method.

        For an explanation of the parameters, see C{revoke_security_group}.
        """
        d = self.revoke_security_group(
            group_name,
            source_group_name=source_group_name,
            source_group_owner_id=source_group_owner_id)
        return d

    def revoke_ip_permission(
        self, group_name, ip_protocol, from_port, to_port, cidr_ip):
        """
        This is a convenience function that wraps the "authorize ip
        permission" functionality of the C{authorize_security_group} method.

        For an explanation of the parameters, see C{revoke_security_group}.
        """
        d = self.revoke_security_group(
            group_name,
            ip_protocol=ip_protocol, from_port=from_port, to_port=to_port,
            cidr_ip=cidr_ip)
        return d

    def describe_volumes(self, *volume_ids):
        """Describe available volumes."""
        volumeset = {}
        for pos, volume_id in enumerate(volume_ids):
            volumeset["VolumeId.%d" % (pos + 1)] = volume_id
        query = self.query_factory(
            action="DescribeVolumes", creds=self.creds, endpoint=self.endpoint,
            other_params=volumeset)
        d = query.submit()
        return d.addCallback(self.parser.describe_volumes)

    def create_volume(self, availability_zone, size=None, snapshot_id=None):
        """Create a new volume."""
        params = {"AvailabilityZone": availability_zone}
        if ((snapshot_id is None and size is None) or
            (snapshot_id is not None and size is not None)):
            raise ValueError("Please provide either size or snapshot_id")
        if size is not None:
            params["Size"] = str(size)
        if snapshot_id is not None:
            params["SnapshotId"] = snapshot_id
        query = self.query_factory(
            action="CreateVolume", creds=self.creds, endpoint=self.endpoint,
            other_params=params)
        d = query.submit()
        return d.addCallback(self.parser.create_volume)

    def delete_volume(self, volume_id):
        query = self.query_factory(
            action="DeleteVolume", creds=self.creds, endpoint=self.endpoint,
            other_params={"VolumeId": volume_id})
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def describe_snapshots(self, *snapshot_ids):
        """Describe available snapshots."""
        snapshot_set = {}
        for pos, snapshot_id in enumerate(snapshot_ids):
            snapshot_set["SnapshotId.%d" % (pos + 1)] = snapshot_id
        query = self.query_factory(
            action="DescribeSnapshots", creds=self.creds,
            endpoint=self.endpoint, other_params=snapshot_set)
        d = query.submit()
        return d.addCallback(self.parser.snapshots)

    def create_snapshot(self, volume_id):
        """Create a new snapshot of an existing volume."""
        query = self.query_factory(
            action="CreateSnapshot", creds=self.creds, endpoint=self.endpoint,
            other_params={"VolumeId": volume_id})
        d = query.submit()
        return d.addCallback(self.parser.create_snapshot)

    def delete_snapshot(self, snapshot_id):
        """Remove a previously created snapshot."""
        query = self.query_factory(
            action="DeleteSnapshot", creds=self.creds, endpoint=self.endpoint,
            other_params={"SnapshotId": snapshot_id})
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def attach_volume(self, volume_id, instance_id, device):
        """Attach the given volume to the specified instance at C{device}."""
        query = self.query_factory(
            action="AttachVolume", creds=self.creds, endpoint=self.endpoint,
            other_params={"VolumeId": volume_id, "InstanceId": instance_id,
                          "Device": device})
        d = query.submit()
        return d.addCallback(self.parser.attach_volume)

    def describe_keypairs(self, *keypair_names):
        """Returns information about key pairs available."""
        keypairs = {}
        for index, keypair_name in enumerate(keypair_names):
            keypairs["KeyPair.%d" % (index + 1)] = keypair_name
        query = self.query_factory(
            action="DescribeKeyPairs", creds=self.creds,
            endpoint=self.endpoint, other_params=keypairs)
        d = query.submit()
        return d.addCallback(self.parser.describe_keypairs)

    def create_keypair(self, keypair_name):
        """
        Create a new 2048 bit RSA key pair and return a unique ID that can be
        used to reference the created key pair when launching new instances.
        """
        query = self.query_factory(
            action="CreateKeyPair", creds=self.creds, endpoint=self.endpoint,
            other_params={"KeyName": keypair_name})
        d = query.submit()
        return d.addCallback(self.parser.create_keypair)

    def delete_keypair(self, keypair_name):
        """Delete a given keypair."""
        query = self.query_factory(
            action="DeleteKeyPair", creds=self.creds, endpoint=self.endpoint,
            other_params={"KeyName": keypair_name})
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def import_keypair(self, keypair_name, key_material):
        """
        Import an existing SSH key into EC2. It supports:
            * OpenSSH public key format (e.g., the format in
              ~/.ssh/authorized_keys)
            * Base64 encoded DER format
            * SSH public key file format as specified in RFC4716

        @param keypair_name: The name of the key to create.
        @param key_material: The material in one of the supported format.

        @return: A L{Deferred} firing with a L{model.Keypair} instance if
            successful.
        """
        query = self.query_factory(
            action="ImportKeyPair", creds=self.creds, endpoint=self.endpoint,
            other_params={"KeyName": keypair_name,
                          "PublicKeyMaterial": b64encode(key_material)})
        d = query.submit()
        return d.addCallback(self.parser.import_keypair, key_material)

    def allocate_address(self):
        """
        Acquire an elastic IP address to be attached subsequently to EC2
        instances.

        @return: the IP address allocated.
        """
        # XXX remove empty other_params
        query = self.query_factory(
            action="AllocateAddress", creds=self.creds, endpoint=self.endpoint,
            other_params={})
        d = query.submit()
        return d.addCallback(self.parser.allocate_address)

    def release_address(self, address):
        """
        Release a previously allocated address returned by C{allocate_address}.

        @return: C{True} if the operation succeeded.
        """
        query = self.query_factory(
            action="ReleaseAddress", creds=self.creds, endpoint=self.endpoint,
            other_params={"PublicIp": address})
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def associate_address(self, instance_id, address):
        """
        Associate an allocated C{address} with the instance identified by
        C{instance_id}.

        @return: C{True} if the operation succeeded.
        """
        query = self.query_factory(
            action="AssociateAddress", creds=self.creds,
            endpoint=self.endpoint,
            other_params={"InstanceId": instance_id, "PublicIp": address})
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def disassociate_address(self, address):
        """
        Disassociate an address previously associated with
        C{associate_address}. This is an idempotent operation, so it can be
        called several times without error.
        """
        query = self.query_factory(
            action="DisassociateAddress", creds=self.creds,
            endpoint=self.endpoint, other_params={"PublicIp": address})
        d = query.submit()
        return d.addCallback(self.parser.truth_return)

    def describe_addresses(self, *addresses):
        """
        List the elastic IPs allocated in this account.

        @param addresses: if specified, the addresses to get information about.

        @return: a C{list} of (address, instance_id). If the elastic IP is not
            associated currently, C{instance_id} will be C{None}.
        """
        address_set = {}
        for pos, address in enumerate(addresses):
            address_set["PublicIp.%d" % (pos + 1)] = address
        query = self.query_factory(
            action="DescribeAddresses", creds=self.creds,
            endpoint=self.endpoint, other_params=address_set)
        d = query.submit()
        return d.addCallback(self.parser.describe_addresses)

    def describe_availability_zones(self, names=None):
        zone_names = None
        if names:
            zone_names = dict([("ZoneName.%d" % (i + 1), name)
                                for i, name in enumerate(names)])
        query = self.query_factory(
            action="DescribeAvailabilityZones", creds=self.creds,
            endpoint=self.endpoint, other_params=zone_names)
        d = query.submit()
        return d.addCallback(self.parser.describe_availability_zones)


class Parser(object):
    """A parser for EC2 responses"""

    def instances_set(self, root, reservation):
        """Parse instance data out of an XML payload.

        @param root: The root node of the XML payload.
        @param reservation: The L{Reservation} associated with the instances
            from the response.
        @return: A C{list} of L{Instance}s.
        """
        instances = []
        for instance_data in root.find("instancesSet"):
            instances.append(self.instance(instance_data, reservation))
        return instances

    def instance(self, instance_data, reservation):
        """Parse instance data out of an XML payload.

        @param instance_data: An XML node containing instance data.
        @param reservation: The L{Reservation} associated with the instance.
        @return: An L{Instance}.
        """
        instance_id = instance_data.findtext("instanceId")
        instance_state = instance_data.find(
            "instanceState").findtext("name")
        instance_type = instance_data.findtext("instanceType")
        image_id = instance_data.findtext("imageId")
        private_dns_name = instance_data.findtext("privateDnsName")
        dns_name = instance_data.findtext("dnsName")
        key_name = instance_data.findtext("keyName")
        ami_launch_index = instance_data.findtext("amiLaunchIndex")
        launch_time = instance_data.findtext("launchTime")
        placement = instance_data.find("placement").findtext(
            "availabilityZone")
        products = []
        product_codes = instance_data.find("productCodes")
        if product_codes is not None:
            for product_data in instance_data.find("productCodes"):
                products.append(product_data.text)
        kernel_id = instance_data.findtext("kernelId")
        ramdisk_id = instance_data.findtext("ramdiskId")
        instance = model.Instance(
            instance_id, instance_state, instance_type, image_id,
            private_dns_name, dns_name, key_name, ami_launch_index,
            launch_time, placement, products, kernel_id, ramdisk_id,
            reservation=reservation)
        return instance

    def describe_instances(self, xml_bytes):
        """
        Parse the reservations XML payload that is returned from an AWS
        describeInstances API call.

        Instead of returning the reservations as the "top-most" object, we
        return the object that most developers and their code will be
        interested in: the instances. In instances reservation is available on
        the instance object.

        The following instance attributes are optional:
            * ami_launch_index
            * key_name
            * kernel_id
            * product_codes
            * ramdisk_id
            * reason

        @param xml_bytes: raw XML payload from AWS.
        """
        root = XML(xml_bytes)
        results = []
        # May be a more elegant way to do this:
        for reservation_data in root.find("reservationSet"):
            # Get the security group information.
            groups = []
            for group_data in reservation_data.find("groupSet"):
                group_id = group_data.findtext("groupId")
                groups.append(group_id)
            # Create a reservation object with the parsed data.
            reservation = model.Reservation(
                reservation_id=reservation_data.findtext("reservationId"),
                owner_id=reservation_data.findtext("ownerId"),
                groups=groups)
            # Get the list of instances.
            instances = self.instances_set(
                reservation_data, reservation)
            results.extend(instances)
        return results

    def run_instances(self, xml_bytes):
        """
        Parse the reservations XML payload that is returned from an AWS
        RunInstances API call.

        @param xml_bytes: raw XML payload from AWS.
        """
        root = XML(xml_bytes)
        # Get the security group information.
        groups = []
        for group_data in root.find("groupSet"):
            group_id = group_data.findtext("groupId")
            groups.append(group_id)
        # Create a reservation object with the parsed data.
        reservation = model.Reservation(
            reservation_id=root.findtext("reservationId"),
            owner_id=root.findtext("ownerId"),
            groups=groups)
        # Get the list of instances.
        instances = self.instances_set(root, reservation)
        return instances

    def terminate_instances(self, xml_bytes):
        """Parse the XML returned by the C{TerminateInstances} function.

        @param xml_bytes: XML bytes with a C{TerminateInstancesResponse} root
            element.
        @return: An iterable of C{tuple} of (instanceId, previousState,
            shutdownState) for the ec2 instances that where terminated.
        """
        root = XML(xml_bytes)
        result = []
        # May be a more elegant way to do this:
        for instance in root.find("instancesSet"):
            instanceId = instance.findtext("instanceId")
            previousState = instance.find("previousState").findtext(
                "name")
            shutdownState = instance.find("shutdownState").findtext(
                "name")
            result.append((instanceId, previousState, shutdownState))
        return result

    def describe_security_groups(self, xml_bytes):
        """Parse the XML returned by the C{DescribeSecurityGroups} function.

        @param xml_bytes: XML bytes with a C{DescribeSecurityGroupsResponse}
            root element.
        @return: A list of L{SecurityGroup} instances.
        """
        root = XML(xml_bytes)
        result = []
        for group_info in root.findall("securityGroupInfo/item"):
            name = group_info.findtext("groupName")
            description = group_info.findtext("groupDescription")
            owner_id = group_info.findtext("ownerId")
            allowed_groups = []
            allowed_ips = []
            ip_permissions = group_info.find("ipPermissions")
            if ip_permissions is None:
                ip_permissions = ()
            for ip_permission in ip_permissions:

                # openstack doesn't handle self authorized groups properly
                # XXX this is an upstream problem and should be addressed there
                # lp bug #829609
                ip_protocol = ip_permission.findtext("ipProtocol")
                from_port = ip_permission.findtext("fromPort")
                to_port = ip_permission.findtext("toPort")

                if from_port:
                    from_port = int(from_port)

                if to_port:
                    to_port = int(to_port)

                for groups in ip_permission.findall("groups/item") or ():
                    user_id = groups.findtext("userId")
                    group_name = groups.findtext("groupName")
                    if user_id and group_name:
                        if (user_id, group_name) not in allowed_groups:
                            allowed_groups.append((user_id, group_name))
                for ip_ranges in ip_permission.findall("ipRanges/item") or ():
                    cidr_ip = ip_ranges.findtext("cidrIp")
                    allowed_ips.append(
                        model.IPPermission(
                            ip_protocol, from_port, to_port, cidr_ip))

            allowed_groups = [model.UserIDGroupPair(user_id, group_name)
                              for user_id, group_name in allowed_groups]

            security_group = model.SecurityGroup(
                name, description, owner_id=owner_id,
                groups=allowed_groups, ips=allowed_ips)
            result.append(security_group)
        return result

    def truth_return(self, xml_bytes):
        """Parse the XML for a truth value.

        @param xml_bytes: XML bytes.
        @return: True if the node contains "return" otherwise False.
        """
        root = XML(xml_bytes)
        return root.findtext("return") == "true"

    def describe_volumes(self, xml_bytes):
        """Parse the XML returned by the C{DescribeVolumes} function.

        @param xml_bytes: XML bytes with a C{DescribeVolumesResponse} root
            element.
        @return: A list of L{Volume} instances.
        """
        root = XML(xml_bytes)
        result = []
        for volume_data in root.find("volumeSet"):
            volume_id = volume_data.findtext("volumeId")
            size = int(volume_data.findtext("size"))
            status = volume_data.findtext("status")
            availability_zone = volume_data.findtext("availabilityZone")
            snapshot_id = volume_data.findtext("snapshotId")
            create_time = volume_data.findtext("createTime")
            create_time = datetime.strptime(
                create_time[:19], "%Y-%m-%dT%H:%M:%S")
            volume = model.Volume(
                volume_id, size, status, create_time, availability_zone,
                snapshot_id)
            result.append(volume)
            for attachment_data in volume_data.find("attachmentSet"):
                instance_id = attachment_data.findtext("instanceId")
                status = attachment_data.findtext("status")
                device = attachment_data.findtext("device")
                attach_time = attachment_data.findtext("attachTime")
                attach_time = datetime.strptime(
                    attach_time[:19], "%Y-%m-%dT%H:%M:%S")
                attachment = model.Attachment(
                    instance_id, device, status, attach_time)
                volume.attachments.append(attachment)
        return result

    def create_volume(self, xml_bytes):
        """Parse the XML returned by the C{CreateVolume} function.

        @param xml_bytes: XML bytes with a C{CreateVolumeResponse} root
            element.
        @return: The L{Volume} instance created.
        """
        root = XML(xml_bytes)
        volume_id = root.findtext("volumeId")
        size = int(root.findtext("size"))
        status = root.findtext("status")
        create_time = root.findtext("createTime")
        availability_zone = root.findtext("availabilityZone")
        snapshot_id = root.findtext("snapshotId")
        create_time = datetime.strptime(
            create_time[:19], "%Y-%m-%dT%H:%M:%S")
        volume = model.Volume(
            volume_id, size, status, create_time, availability_zone,
            snapshot_id)
        return volume

    def snapshots(self, xml_bytes):
        """Parse the XML returned by the C{DescribeSnapshots} function.

        @param xml_bytes: XML bytes with a C{DescribeSnapshotsResponse} root
            element.
        @return: A list of L{Snapshot} instances.
        """
        root = XML(xml_bytes)
        result = []
        for snapshot_data in root.find("snapshotSet"):
            snapshot_id = snapshot_data.findtext("snapshotId")
            volume_id = snapshot_data.findtext("volumeId")
            status = snapshot_data.findtext("status")
            start_time = snapshot_data.findtext("startTime")
            start_time = datetime.strptime(
                start_time[:19], "%Y-%m-%dT%H:%M:%S")
            progress = snapshot_data.findtext("progress")[:-1]
            progress = float(progress or "0") / 100.
            snapshot = model.Snapshot(
                snapshot_id, volume_id, status, start_time, progress)
            result.append(snapshot)
        return result

    def create_snapshot(self, xml_bytes):
        """Parse the XML returned by the C{CreateSnapshot} function.

        @param xml_bytes: XML bytes with a C{CreateSnapshotResponse} root
            element.
        @return: The L{Snapshot} instance created.
        """
        root = XML(xml_bytes)
        snapshot_id = root.findtext("snapshotId")
        volume_id = root.findtext("volumeId")
        status = root.findtext("status")
        start_time = root.findtext("startTime")
        start_time = datetime.strptime(
            start_time[:19], "%Y-%m-%dT%H:%M:%S")
        progress = root.findtext("progress")[:-1]
        progress = float(progress or "0") / 100.
        return model.Snapshot(
            snapshot_id, volume_id, status, start_time, progress)

    def attach_volume(self, xml_bytes):
        """Parse the XML returned by the C{AttachVolume} function.

        @param xml_bytes: XML bytes with a C{AttachVolumeResponse} root
            element.
        @return: a C{dict} with status and attach_time keys.
        """
        root = XML(xml_bytes)
        status = root.findtext("status")
        attach_time = root.findtext("attachTime")
        attach_time = datetime.strptime(
            attach_time[:19], "%Y-%m-%dT%H:%M:%S")
        return {"status": status, "attach_time": attach_time}

    def describe_keypairs(self, xml_bytes):
        """Parse the XML returned by the C{DescribeKeyPairs} function.

        @param xml_bytes: XML bytes with a C{DescribeKeyPairsResponse} root
            element.
        @return: a C{list} of L{Keypair}.
        """
        results = []
        root = XML(xml_bytes)
        keypairs = root.find("keySet")
        if keypairs is None:
            return results
        for keypair_data in keypairs:
            key_name = keypair_data.findtext("keyName")
            key_fingerprint = keypair_data.findtext("keyFingerprint")
            results.append(model.Keypair(key_name, key_fingerprint))
        return results

    def create_keypair(self, xml_bytes):
        """Parse the XML returned by the C{CreateKeyPair} function.

        @param xml_bytes: XML bytes with a C{CreateKeyPairResponse} root
            element.
        @return: The L{Keypair} instance created.
        """
        keypair_data = XML(xml_bytes)
        key_name = keypair_data.findtext("keyName")
        key_fingerprint = keypair_data.findtext("keyFingerprint")
        key_material = keypair_data.findtext("keyMaterial")
        return model.Keypair(key_name, key_fingerprint, key_material)

    def import_keypair(self, xml_bytes, key_material):
        """Extract the key name and the fingerprint from the result."""
        keypair_data = XML(xml_bytes)
        key_name = keypair_data.findtext("keyName")
        key_fingerprint = keypair_data.findtext("keyFingerprint")
        return model.Keypair(key_name, key_fingerprint, key_material)

    def allocate_address(self, xml_bytes):
        """Parse the XML returned by the C{AllocateAddress} function.

        @param xml_bytes: XML bytes with a C{AllocateAddress} root element.
        @return: The public ip address as a string.
        """
        address_data = XML(xml_bytes)
        return address_data.findtext("publicIp")

    def describe_addresses(self, xml_bytes):
        """Parse the XML returned by the C{DescribeAddresses} function.

        @param xml_bytes: XML bytes with a C{DescribeAddressesResponse} root
            element.
        @return: a C{list} of L{tuple} of (publicIp, instancId).
        """
        results = []
        root = XML(xml_bytes)
        for address_data in root.find("addressesSet"):
            address = address_data.findtext("publicIp")
            instance_id = address_data.findtext("instanceId")
            results.append((address, instance_id))
        return results

    def describe_availability_zones(self, xml_bytes):
        """Parse the XML returned by the C{DescribeAvailibilityZones} function.

        @param xml_bytes: XML bytes with a C{DescribeAvailibilityZonesResponse}
            root element.
        @return: a C{list} of L{AvailabilityZone}.
        """
        results = []
        root = XML(xml_bytes)
        for zone_data in root.find("availabilityZoneInfo"):
            zone_name = zone_data.findtext("zoneName")
            zone_state = zone_data.findtext("zoneState")
            results.append(model.AvailabilityZone(zone_name, zone_state))
        return results


class Query(BaseQuery):
    """A query that may be submitted to EC2."""

    timeout = 30

    def __init__(self, other_params=None, time_tuple=None, api_version=None,
                 *args, **kwargs):
        """Create a Query to submit to EC2."""
        super(Query, self).__init__(*args, **kwargs)
        # Currently, txAWS only supports version 2008-12-01
        if api_version is None:
            api_version = version.ec2_api
        self.params = {
            "Version": api_version,
            "SignatureVersion": "2",
            "Action": self.action,
            "AWSAccessKeyId": self.creds.access_key,
            }
        if other_params is None or "Expires" not in other_params:
            # Only add a Timestamp parameter, if Expires isn't used,
            # since both can't be used in the same request.
            self.params["Timestamp"] = iso8601time(time_tuple)
        if other_params:
            self.params.update(other_params)
        self.signature = Signature(self.creds, self.endpoint, self.params)

    def sign(self, hash_type="sha256"):
        """Sign this query using its built in credentials.

        @param hash_type: if the SignatureVersion is 2, specify the type of
            hash to use, either "sha1" or "sha256". It defaults to the latter.

        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.
        """
        version = self.params["SignatureVersion"]
        if version == "2":
            self.params["SignatureMethod"] = "Hmac%s" % hash_type.upper()
        self.params["Signature"] = self.signature.compute()

    def submit(self):
        """Submit this query.

        @return: A deferred from get_page
        """
        self.sign()
        url = self.endpoint.get_uri()
        method = self.endpoint.method
        params = self.signature.get_canonical_query_params()
        headers = {}
        kwargs = {"method": method}
        if method == "POST":
            headers["Content-Type"] = "application/x-www-form-urlencoded"
            kwargs["postdata"] = params
        else:
            url += "?%s" % params
        if self.endpoint.get_host() != self.endpoint.get_canonical_host():
            headers["Host"] = self.endpoint.get_canonical_host()
        if headers:
            kwargs["headers"] = headers
        if self.timeout:
            kwargs["timeout"] = self.timeout
        d = self.get_page(url, **kwargs)
        return d.addErrback(ec2_error_wrapper)


class Signature(object):
    """Compute EC2-compliant signatures for requests.

    @ivar creds: The L{AWSCredentials} to use to compute the signature.
    @ivar endpoint: The {AWSServiceEndpoint} to consider.
    @ivar params: A C{dict} of parameters to consider.
    """

    def __init__(self, creds, endpoint, params):
        """Create a Query to submit to EC2."""
        self.creds = creds
        self.endpoint = endpoint
        self.params = params

    def compute(self):
        """Compute and return the signature according to the given data."""
        if "Signature" in self.params:
            raise RuntimeError("Existing signature in parameters")
        version = self.params["SignatureVersion"]
        if version == "1":
            bytes = self.old_signing_text()
            hash_type = "sha1"
        elif version == "2":
            bytes = self.signing_text()
            hash_type = self.params["SignatureMethod"][len("Hmac"):].lower()
        else:
            raise RuntimeError("Unsupported SignatureVersion: '%s'" % version)
        return self.creds.sign(bytes, hash_type)

    def old_signing_text(self):
        """Return the text needed for signing using SignatureVersion 1."""
        result = []
        lower_cmp = lambda x, y: cmp(x[0].lower(), y[0].lower())
        for key, value in sorted(self.params.items(), cmp=lower_cmp):
            result.append("%s%s" % (key, value))
        return "".join(result)

    def signing_text(self):
        """Return the text to be signed when signing the query."""
        result = "%s\n%s\n%s\n%s" % (self.endpoint.method,
                                     self.endpoint.get_canonical_host(),
                                     self.endpoint.path,
                                     self.get_canonical_query_params())
        return result

    def get_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, 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(string, safe="~")

    def sorted_params(self):
        """Return the query parameters sorted appropriately for signing."""
        return sorted(self.params.items())