Fix IPv6 generation for taps.

Each tap will have a subnetwork with 16 more bits than the interface.
The IPv6 of the tap is the last of the subnetwork.

Note: the example IPv6 address is the address used in documentation (see https://en.wikipedia.org/wiki/IPv6_address#Documentation)

slapos/format.py

@@ -58,6 +58,8 @@ import xml_marshaller.xml_marshaller
 
 import slapos.util
 from slapos.util import mkdir_p
+from slapos.util import ipv6FromBin
+from slapos.util import binFromIpv6
 import slapos.slap as slap
 from slapos import version
 from slapos import manager as slapmanager
@@ -443,6 +445,10 @@ class Computer(object):
         tap.ipv4_netmask = partition_dict['tap'].get('ipv4_netmask', '')
         tap.ipv4_gateway = partition_dict['tap'].get('ipv4_gateway', '')
         tap.ipv4_network = partition_dict['tap'].get('ipv4_network', '')
+        tap.ipv6_addr = partition_dict['tap'].get('ipv6_addr', '')
+        tap.ipv6_netmask = partition_dict['tap'].get('ipv6_netmask', '')
+        tap.ipv6_gateway = partition_dict['tap'].get('ipv6_gateway', '')
+        tap.ipv6_network = partition_dict['tap'].get('ipv6_network', '')
       else:
         tap = Tap(partition_dict['reference'])
 
@@ -613,9 +619,9 @@ class Computer(object):
               partition.tap.ipv4_network = gateway_addr_dict['network']
 
             if not partition.tap.ipv6_addr:
-              ipv6_addr = self.interface.addIPv6Address(tap=partition.tap)
-              partition.tap.ipv6_addr = ""
-              partition.tap.ipv6_netmask = ""
+              ipv6_dict = self.interface.addIPv6Address(tap=partition.tap)
+              partition.tap.ipv6_addr = ipv6_dict['addr']
+              partition.tap.ipv6_netmask = ipv6_dict['netmask']
               partition.tap.ipv6_gateway = ""
               partition.tap.ipv6_network = ""
 
@@ -1115,7 +1121,7 @@ class Interface(object):
       tap: tap interface
 
     Returns:
-      Tuple of (address, netmask).
+      dict(addr=address, netmask=netmask).
 
     Raises:
       AddressGenerationError: Couldn't construct valid address with existing
@@ -1157,15 +1163,24 @@ class Interface(object):
     # Try 10 times to add address, raise in case if not possible
     try_num = 10
     netmask = address_dict['netmask']
-    while try_num > 0:
     if tap:
-        cut = -3
-        if "::" in address_dict['addr']:
-          cut = -2
+      netmask_len = len(binFromIpv6(netmask).rstrip('0'))
+      prefix = binFromIpv6(address_dict['addr'])[:netmask_len]
+      netmask_len += 16
+      # we generate a subnetwork for the tap
+      # the subnetwork has 16 bits more than the interface network
+      # make sure we have at least 2 IPs in the subnetwork
+      if netmask_len >= 128:
+        self._logger.error('Interface {} has netmask {} which is too big for generating IPv6 on taps.'.format(
+            interface_name, netmask))
+        raise AddressGenerationError(addr)
+      netmask = ipv6FromBin('1'*netmask_len)
 
-        addr = ':'.join(address_dict['addr'].split(':')[:cut] + ['%x' % (
-          random.randint(1, 65000), )] + ["ff", "ff"])
-        netmask = "ffff:ffff:ffff:ffff:ffff:ffff::"
+    while try_num > 0:
+      if tap:
+        addr = ipv6FromBin(prefix
+          + bin(random.randint(1, 65000))[2:].zfill(16)
+          + '1' * (128 - netmask_len))
       else:
         addr = ':'.join(address_dict['addr'].split(':')[:-1] + ['%x' % (
           random.randint(1, 65000), )])

slapos/tests/slapformat.py

@@ -464,7 +464,7 @@ class TestComputer(SlapformatMixin):
     self.assertEqual([
         'ip tuntap add dev tap mode tap user testuser',
         'ip link set tap up',
-        'ip addr add ip/ffff:ffff:ffff:ffff:ffff:ffff:: dev tap',
+        'ip addr add ip/ffff:ffff:ffff:ffff:ffff:: dev tap',
         'ip -6 addr list tap',
         'ip route show 10.0.0.2',
         'ip route add 10.0.0.2 dev tap',
@@ -493,7 +493,7 @@ class TestComputer(SlapformatMixin):
     INTERFACE_DICT['iface'] = {
       socket.AF_INET: [{'addr': '192.168.242.77', 'broadcast': '127.0.0.1',
         'netmask': '255.255.255.0'}],
-      socket.AF_INET6: [{'addr': '2a01:e35:2e27::e59c', 'netmask': 'ffff:ffff:ffff:ffff::'}]
+      socket.AF_INET6: [{'addr': '2a01:e35:2e27:3456::e59c', 'netmask': 'ffff:ffff:ffff:ffff:ffff::'}]
     }
     INTERFACE_DICT['eth1'] = {
       socket.AF_INET: [{'addr': '10.8.0.1', 'broadcast': '10.8.0.254',
@@ -501,7 +501,7 @@ class TestComputer(SlapformatMixin):
     }
 
     INTERFACE_DICT['tap'] = {
-      socket.AF_INET6: [{'addr': '2a01:e35:2e27::e59c', 'netmask': 'ffff:ffff:ffff:ffff::'}]
+      socket.AF_INET6: [{'addr': '2a01:e35:2e27:3456::e59c', 'netmask': 'ffff:ffff:ffff:ffff:ffff::'}]
     }
 
     computer.format(alter_user=False)
@@ -521,7 +521,7 @@ class TestComputer(SlapformatMixin):
         'ip route show 10.8.0.2',
         'ip route add 10.8.0.2 dev tap',
         'ip addr add ip/255.255.255.255 dev iface',
-        'ip addr add ip/ffff:ffff:ffff:ffff:: dev iface',
+        'ip addr add ip/ffff:ffff:ffff:ffff:ffff:: dev iface',
         'ip -6 addr list iface'
       ],
       self.fakeCallAndRead.external_command_list)

slapos/util.py

@@ -29,6 +29,8 @@
 
 import errno
 import os
+import socket
+import struct
 import subprocess
 import sqlite3
 
@@ -104,3 +106,32 @@ def sqlite_connect(dburi, timeout=None):
   conn = sqlite3.connect(dburi, **connect_kw)
   conn.text_factory = str       # allow 8-bit strings
   return conn
+
+# The 3 functions below were imported from re6st:
+# https://lab.nexedi.com/nexedi/re6stnet/blob/master/re6st/utils.py
+def binFromRawIpv6(ip):
+  ip1, ip2 = struct.unpack('>QQ', ip)
+  return bin(ip1)[2:].rjust(64, '0') + bin(ip2)[2:].rjust(64, '0')
+
+def binFromIpv6(ip):
+  """
+  convert an IPv6  to a 128 characters string containing 0 and 1
+  e.g.: '2001:db8::'-> '001000000000000100001101101110000000000...000'
+  """
+  return binFromRawIpv6(socket.inet_pton(socket.AF_INET6, ip))
+
+def ipv6FromBin(ip, suffix=''):
+  """
+  convert a string containing 0 and 1 to an IPv6
+  if the string is less than 128 characters:
+   * consider the string is the first bits
+   * optionnaly can replace the last bits of the IP with a suffix (in binary string format)
+  """
+  suffix_len = 128 - len(ip)
+  if suffix_len > 0:
+    ip += suffix.rjust(suffix_len, '0')
+  elif suffix_len:
+    sys.exit("Prefix exceeds 128 bits")
+  return socket.inet_ntop(socket.AF_INET6,
+    struct.pack('>QQ', int(ip[:64], 2), int(ip[64:], 2)))
+