Add initial GCE datasource

There are some rough edges here and its missing some test, but
I want to get this pulled in.

ChangeLog

@@ -27,7 +27,8 @@
  - skip config_modules that declare themselves only verified on a set of
    distros.  Add them to 'unverified_modules' list to run anyway.
  - Add CloudSigma datasource [Kiril Vladimiroff]
- - Add intiial support for Gentoo and Arch distributions [Nate House]
+ - Add initial support for Gentoo and Arch distributions [Nate House]
+ - Add GCE datasource [Vaidas Jablonskis]
 0.7.4:
  - fix issue mounting 'ephemeral0' if ephemeral0 was an alias for a
    partitioned block device with target filesystem on ephemeral0.1.

cloudinit/settings.py

@@ -36,6 +36,7 @@ CFG_BUILTIN = {
         'AltCloud',
         'OVF',
         'MAAS',
+        'GCE',
         'Ec2',
         'CloudSigma',
         'CloudStack',

cloudinit/sources/DataSourceGCE.py

@@ -0,0 +1,117 @@
+# vi: ts=4 expandtab
+#
+#    Author: Vaidas Jablonskis <jablonskis@gmail.com>
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License version 3, as
+#    published by the Free Software Foundation.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+from cloudinit import log as logging
+from cloudinit import util
+from cloudinit import sources
+from cloudinit import url_helper
+
+LOG = logging.getLogger(__name__)
+
+BUILTIN_DS_CONFIG = {
+    'metadata_url': 'http://metadata.google.internal./computeMetadata/v1/'
+}
+REQUIRED_FIELDS = ('instance-id', 'availability-zone', 'local-hostname')
+
+
+class DataSourceGCE(sources.DataSource):
+    def __init__(self, sys_cfg, distro, paths):
+        sources.DataSource.__init__(self, sys_cfg, distro, paths)
+        self.metadata = {}
+        self.ds_cfg = util.mergemanydict([
+            util.get_cfg_by_path(sys_cfg, ["datasource", "GCE"], {}),
+            BUILTIN_DS_CONFIG])
+        self.metadata_address = self.ds_cfg['metadata_url']
+
+    # GCE takes sshKeys attribute in the format of '<user>:<public_key>'
+    # so we have to trim each key to remove the username part
+    def _trim_key(self, public_key):
+        try:
+            index = public_key.index(':')
+            if index > 0:
+                return public_key[(index + 1):]
+        except:
+            return public_key
+
+    def get_data(self):
+        # GCE metadata server requires a custom header since v1
+        headers = {'X-Google-Metadata-Request': True}
+
+        url_map = {
+            'instance-id': self.metadata_address + 'instance/id',
+            'availability-zone': self.metadata_address + 'instance/zone',
+            'public-keys': self.metadata_address + 'project/attributes/sshKeys',
+            'local-hostname': self.metadata_address + 'instance/hostname',
+            'user-data': self.metadata_address + 'instance/attributes/user-data',
+        }
+
+        # if we cannot resolve the metadata server, then no point in trying
+        if not util.is_resolvable(self.metadata_address):
+            LOG.debug("%s is not resolvable", self.metadata_address)
+            return False
+
+        for mkey in url_map.iterkeys():
+            try:
+                resp = url_helper.readurl(url=url_map[mkey], headers=headers,
+                                          retries=0)
+            except IOError:
+                return False
+            if resp.ok():
+                if mkey == 'public-keys':
+                    pub_keys = [self._trim_key(k) for k in resp.contents.splitlines()]
+                    self.metadata[mkey] = pub_keys
+                else:
+                    self.metadata[mkey] = resp.contents
+            else:
+                if mkey in REQUIRED_FIELDS:
+                    LOG.warn("required metadata '%s' not found in metadata",
+                        url_map[mkey])
+                    return False
+                        
+                self.metadata[mkey] = None
+                return False
+
+        self.user_data_raw = self.metadata['user-data']
+        return True
+
+    @property
+    def launch_index(self):
+        # GCE does not provide lauch_index property
+        return None
+
+    def get_instance_id(self):
+        return self.metadata['instance-id']
+
+    def get_public_ssh_keys(self):
+        return self.metadata['public-keys']
+
+    def get_hostname(self, fqdn=False):
+        return self.metadata['local-hostname']
+
+    @property
+    def availability_zone(self):
+        return self.metadata['instance-zone']
+
+# Used to match classes to dependencies
+datasources = [
+    (DataSourceGCE, (sources.DEP_FILESYSTEM, sources.DEP_NETWORK)),
+]
+
+
+# Return a list of data sources that match this set of dependencies
+def get_datasource_list(depends):
+    return sources.list_from_depends(depends, datasources)