1 files changed, 119 insertions, 0 deletions
diff --git a/cloudinit/net/dhcp.py b/cloudinit/net/dhcp.py
new file mode 100644
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--- /dev/null
+++ b/cloudinit/net/dhcp.py
@@ -0,0 +1,119 @@
+# Copyright (C) 2017 Canonical Ltd.
+#
+# Author: Chad Smith <chad.smith@canonical.com>
+#
+# This file is part of cloud-init. See LICENSE file for license information.
+
+import logging
+import os
+import re
+
+from cloudinit.net import find_fallback_nic, get_devicelist
+from cloudinit import util
+
+LOG = logging.getLogger(__name__)
+
+
+class InvalidDHCPLeaseFileError(Exception):
+    """Raised when parsing an empty or invalid dhcp.leases file.
+
+    Current uses are DataSourceAzure and DataSourceEc2 during ephemeral
+    boot to scrape metadata.
+    """
+    pass
+
+
+def maybe_perform_dhcp_discovery(nic=None):
+    """Perform dhcp discovery if nic valid and dhclient command exists.
+
+    If the nic is invalid or undiscoverable or dhclient command is not found,
+    skip dhcp_discovery and return an empty dict.
+
+    @param nic: Name of the network interface we want to run dhclient on.
+    @return: A dict of dhcp options from the dhclient discovery if run,
+        otherwise an empty dict is returned.
+    """
+    if nic is None:
+        nic = find_fallback_nic()
+        if nic is None:
+            LOG.debug(
+                'Skip dhcp_discovery: Unable to find fallback nic.')
+            return {}
+    elif nic not in get_devicelist():
+        LOG.debug(
+            'Skip dhcp_discovery: nic %s not found in get_devicelist.', nic)
+        return {}
+    dhclient_path = util.which('dhclient')
+    if not dhclient_path:
+        LOG.debug('Skip dhclient configuration: No dhclient command found.')
+        return {}
+    with util.tempdir(prefix='cloud-init-dhcp-') as tmpdir:
+        return dhcp_discovery(dhclient_path, nic, tmpdir)
+
+
+def parse_dhcp_lease_file(lease_file):
+    """Parse the given dhcp lease file for the most recent lease.
+
+    Return a dict of dhcp options as key value pairs for the most recent lease
+    block.
+
+    @raises: InvalidDHCPLeaseFileError on empty of unparseable leasefile
+        content.
+    """
+    lease_regex = re.compile(r"lease {(?P<lease>[^}]*)}\n")
+    dhcp_leases = []
+    lease_content = util.load_file(lease_file)
+    if len(lease_content) == 0:
+        raise InvalidDHCPLeaseFileError(
+            'Cannot parse empty dhcp lease file {0}'.format(lease_file))
+    for lease in lease_regex.findall(lease_content):
+        lease_options = []
+        for line in lease.split(';'):
+            # Strip newlines, double-quotes and option prefix
+            line = line.strip().replace('"', '').replace('option ', '')
+            if not line:
+                continue
+            lease_options.append(line.split(' ', 1))
+        dhcp_leases.append(dict(lease_options))
+    if not dhcp_leases:
+        raise InvalidDHCPLeaseFileError(
+            'Cannot parse dhcp lease file {0}. No leases found'.format(
+                lease_file))
+    return dhcp_leases
+
+
+def dhcp_discovery(dhclient_cmd_path, interface, cleandir):
+    """Run dhclient on the interface without scripts or filesystem artifacts.
+
+    @param dhclient_cmd_path: Full path to the dhclient used.
+    @param interface: Name of the network inteface on which to dhclient.
+    @param cleandir: The directory from which to run dhclient as well as store
+        dhcp leases.
+
+    @return: A dict of dhcp options parsed from the dhcp.leases file or empty
+        dict.
+    """
+    LOG.debug('Performing a dhcp discovery on %s', interface)
+
+    # XXX We copy dhclient out of /sbin/dhclient to avoid dealing with strict
+    # app armor profiles which disallow running dhclient -sf <our-script-file>.
+    # We want to avoid running /sbin/dhclient-script because of side-effects in
+    # /etc/resolv.conf any any other vendor specific scripts in
+    # /etc/dhcp/dhclient*hooks.d.
+    sandbox_dhclient_cmd = os.path.join(cleandir, 'dhclient')
+    util.copy(dhclient_cmd_path, sandbox_dhclient_cmd)
+    pid_file = os.path.join(cleandir, 'dhclient.pid')
+    lease_file = os.path.join(cleandir, 'dhcp.leases')
+
+    # ISC dhclient needs the interface up to send initial discovery packets.
+    # Generally dhclient relies on dhclient-script PREINIT action to bring the
+    # link up before attempting discovery. Since we are using -sf /bin/true,
+    # we need to do that "link up" ourselves first.
+    util.subp(['ip', 'link', 'set', 'dev', interface, 'up'], capture=True)
+    cmd = [sandbox_dhclient_cmd, '-1', '-v', '-lf', lease_file,
+           '-pf', pid_file, interface, '-sf', '/bin/true']
+    util.subp(cmd, capture=True)
+    return parse_dhcp_lease_file(lease_file)
+
+
+# vi: ts=4 expandtab