Clarify ceiling, add tests, fix doc, fix python3

- bad class doc
- explicit ceil
- python3 encoding issue
- improve edns testing

dns/edns.py

@@ -17,7 +17,9 @@
 
 from __future__ import absolute_import
 
+import math
 import struct
+import sys
 
 import dns.inet
 
@@ -145,9 +147,10 @@ def __init__(self, address, srclen=None, scopelen=0):
         @ivar srclen: prefix length, leftmost number of bits of the address
         to be used for the lookup. Sent by client, mirrored by server in
         responses. If not provided at init, will use /24 for v4 and /56 for v6
-        @ivar srclen: int
+        @type srclen: int
         @ivar scopelen: prefix length, leftmost number of bits of the address
         that the response covers. 0 in queries, set by server.
+        @type scopelen: int
         """
         super(ECSOption, self).__init__(ECS)
         af = dns.inet.af_for_address(address)
@@ -167,13 +170,16 @@ def __init__(self, address, srclen=None, scopelen=0):
         self.scopelen = scopelen
         self.address = address
 
-        self.addrdata = dns.inet.inet_pton(af, address)
+        addrdata = dns.inet.inet_pton(af, address)
+        nbytes = int(math.ceil(srclen/8.0))
 
         # Truncate to srclen and pad to the end of the last octet needed
         # See RFC section 6
-        self.addrdata = self.addrdata[:-(-srclen//8)]
-        last = ord(self.addrdata[-1:]) & (0xff << srclen % 8)
-        self.addrdata = self.addrdata[:-1] + chr(last).encode('latin1')
+        self.addrdata = addrdata[:nbytes]
+        last = chr(ord(self.addrdata[-1:]) & (0xff << srclen % 8))
+        if sys.version_info >= (3,):
+            last = last.encode('latin1')
+        self.addrdata = self.addrdata[:-1] + last
 
     def to_text(self):
         return "ECS %s/%s scope/%s" % (self.address, self.srclen,
@@ -191,7 +197,7 @@ def from_wire(cls, otype, wire, cur, olen):
         family, src, scope = struct.unpack('!HBB', wire[cur:cur+4])
         cur += 4
 
-        addrlen = -(-src//8)
+        addrlen = int(math.ceil(src/8.0))
 
         if family == 1:
             af = dns.inet.AF_INET
@@ -202,7 +208,7 @@ def from_wire(cls, otype, wire, cur, olen):
         else:
             raise ValueError('unsupported family')
 
-        addr = dns.inet.inet_ntop(af, wire[cur:cur+addrlen] + '\x00' * pad)
+        addr = dns.inet.inet_ntop(af, wire[cur:cur+addrlen] + b'\x00' * pad)
         return cls(addr, src, scope)
 
     def _cmp(self, other):

tests/test_option.py → tests/test_edns.py

@@ -33,6 +33,21 @@ def testGenericOption(self):
         data = io.getvalue()
         self.assertEqual(data, b'data')
 
+    def testECSOption_prefix_length(self):
+        opt = dns.edns.ECSOption('1.2.255.33', 20)
+        io = BytesIO()
+        opt.to_wire(io)
+        data = io.getvalue()
+        self.assertEqual(data, b'\x00\x01\x14\x00\x01\x02\xf0')
+
+    def testECSOption_from_wire(self):
+        opt = dns.edns.option_from_wire(8, b'\x00\x01\x14\x00\x01\x02\xf0',
+                                        0, 7)
+        self.assertEqual(opt.otype, dns.edns.ECS)
+        self.assertEqual(opt.address, b'1.2.240.0')
+        self.assertEqual(opt.srclen, 20)
+        self.assertEqual(opt.scopelen, 0)
+
     def testECSOption(self):
         opt = dns.edns.ECSOption('1.2.3.4', 24)
         io = BytesIO()