From 7933149acf5a629e611a007cbe7c2c46a4a0d154 Mon Sep 17 00:00:00 2001
From: Jack O'Sullivan <jackos1998@gmail.com>
Date: Mon, 26 Aug 2019 22:46:54 +0100
Subject: [PATCH] Send hostname with persistent DHCP requests

---
 net-dhcp/network.py | 11 +++++++++--
 net-dhcp/udhcpc.py  | 20 ++++++++++++++++++--
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/net-dhcp/network.py b/net-dhcp/network.py
index 0e830d3..0a93fea 100644
--- a/net-dhcp/network.py
+++ b/net-dhcp/network.py
@@ -91,6 +91,12 @@ def await_endpoint_container_iface(n, e, timeout=5):
         raise NetDhcpError('Timed out waiting for container to become availabile')
     return iface
 
+def endpoint_container_name(n, e):
+    for info in client.networks.get(n).attrs['Containers'].values():
+        if info['EndpointID'] == e:
+            return info['Name']
+    return None
+
 @app.route('/NetworkDriver.GetCapabilities', methods=['POST'])
 def net_get_capabilities():
     return jsonify({
@@ -340,13 +346,14 @@ class ContainerDHCPManager:
     def run(self):
         try:
             iface = await_endpoint_container_iface(self.network, self.endpoint)
+            hostname = endpoint_container_name(self.network, self.endpoint)
 
-            self.dhcp = udhcpc.DHCPClient(iface, event_listener=self._on_event)
+            self.dhcp = udhcpc.DHCPClient(iface, event_listener=self._on_event, hostname=hostname)
             logger.info('Starting DHCPv4 client on %s in container namespace %s', iface['ifname'], \
                 self.dhcp.netns)
 
             if self.ipv6:
-                self.dhcp6 = udhcpc.DHCPClient(iface, v6=True, event_listener=self._on_event)
+                self.dhcp6 = udhcpc.DHCPClient(iface, v6=True, event_listener=self._on_event, hostname=hostname)
                 logger.info('Starting DHCPv6 client on %s in container namespace %s', iface['ifname'], \
                     self.dhcp6.netns)
         except Exception as e:
diff --git a/net-dhcp/udhcpc.py b/net-dhcp/udhcpc.py
index cefab3e..ebbfb38 100644
--- a/net-dhcp/udhcpc.py
+++ b/net-dhcp/udhcpc.py
@@ -1,6 +1,8 @@
 from enum import Enum
 import ipaddress
 import json
+import struct
+import binascii
 import os
 from os import path
 from select import select
@@ -30,7 +32,7 @@ class DHCPClientError(Exception):
 def _nspopen_wrapper(netns):
     return lambda *args, **kwargs: NSPopen(netns, *args, **kwargs)
 class DHCPClient:
-    def __init__(self, iface, v6=False, once=False, event_listener=None):
+    def __init__(self, iface, v6=False, once=False, hostname=None, event_listener=None):
         self.iface = iface
         self.v6 = v6
         self.once = once
@@ -47,6 +49,18 @@ class DHCPClient:
         bin_path = '/usr/bin/udhcpc6' if v6 else '/sbin/udhcpc'
         cmdline = [bin_path, '-s', HANDLER_SCRIPT, '-i', iface['ifname'], '-f']
         cmdline.append('-q' if once else '-R')
+        if hostname:
+            cmdline.append('-x')
+            if v6:
+                # TODO: We encode the fqdn for DHCPv6 because udhcpc6 seems to be broken
+                # flags: S bit set (see RFC4704)
+                enc_hostname = hostname.encode('utf-8')
+                enc_hostname = struct.pack('BB', 0b0001, len(enc_hostname)) + enc_hostname
+                enc_hostname = binascii.hexlify(enc_hostname).decode('ascii')
+                hostname_opt = f'0x27:{enc_hostname}'
+            else:
+                hostname_opt = f'hostname:{hostname}'
+            cmdline.append(hostname_opt)
         if not v6:
             cmdline += ['-V', VENDOR_ID]
 
@@ -54,6 +68,8 @@ class DHCPClient:
         self._event_queue = posix_ipc.MessageQueue(f'/udhcpc{self._suffix}_{iface["address"].replace(":", "_")}', \
             flags=os.O_CREAT | os.O_EXCL)
         self.proc = Popen(cmdline, env={'EVENT_QUEUE': self._event_queue.name})
+        if hostname:
+            logger.debug('[udhcpc%s#%d] using hostname "%s"', self._suffix, self.proc.pid, hostname)
 
         self._has_lease = threading.Event()
         self.ip = None
@@ -110,7 +126,7 @@ class DHCPClient:
         if self._shutdown_event.is_set():
             return
 
-        if self.proc.returncode != None and (not self.once or self.proc.returncode != 0):
+        if self.proc.returncode is not None and (not self.once or self.proc.returncode != 0):
             raise DHCPClientError(f'udhcpc{self._suffix} exited early with code {self.proc.returncode}')
         if self.once:
             self.await_ip()