def nla_parse(msg, l, mtype, stream, idx):
"""
parses attributes in stream, putting them in msg
:param msg: current message
:param l: total length of message
:param mtype: message content
:param stream: byte stream
:param idx: current index in stream
"""
# get policy family NOTE: cheating here, we know it's either generic or nl80211
pol = 'ctrl_attr' if mtype == nlh.NETLINK_GENERIC else 'nl80211_attr'
attrlen = nlh.NLATTRHDRLEN # pull out these to avoid
attrhdr = nlh.nl_nlattrhdr # doing so in each iteration
# eat the stream until the end
while idx < l:
a = atype = alen = None # shut pycharm up about unitialized variable
try:
alen, atype = struct.unpack_from(attrhdr, stream,
idx) # get length, type
idx += attrlen # move to attr start
alen -= attrlen # attr length (w/ padding)
a = stream[idx:idx + alen] # attr value
dt = nla_datatype(pol, atype) # attr datatype
# Note: we use unpack_from which will ignore the null bytes in numeric
# datatypes & for strings, strip trailing null bytes
# dt == nlh.NLA_UNSPEC: ignore
if _PY3_ and (dt == nlh.NLA_STRING or dt == nlh.NLA_UNSPEC):
# python 3 returns a bytes object, convert to string
try:
a = a.decode('ascii')
except UnicodeDecodeError:
pass # F**k You Python 3
if dt == nlh.NLA_STRING: a = _nla_strip_(a)
elif dt == nlh.NLA_U8: a = struct.unpack_from("B", a, 0)[0]
elif dt == nlh.NLA_U16: a = struct.unpack_from("H", a, 0)[0]
elif dt == nlh.NLA_U32: a = struct.unpack_from("I", a, 0)[0]
elif dt == nlh.NLA_U64: a = struct.unpack_from("Q", a, 0)[0]
elif dt == nlh.NLA_FLAG: a = '' # flags should be 0 size
elif dt == nlh.NLA_MSECS: a = struct.unpack_from("Q", a, 0)[0]
elif dt == nlh.NLA_SET_U8: a = nla_parse_set(a, nlh.NLA_U8)
elif dt == nlh.NLA_SET_U16: a = nla_parse_set(a, nlh.NLA_U16)
elif dt == nlh.NLA_SET_U32: a = nla_parse_set(a, nlh.NLA_U32)
elif dt == nlh.NLA_SET_U64: a = nla_parse_set(a, nlh.NLA_U64)
elif dt == nlh.NLA_NESTED: a = nla_parse_nested(a)
nla_put(msg, a, atype, dt)
except struct.error: # append as Error, stripping null bytes
nla_put(msg, _nla_strip_(a), atype, nlh.NLA_ERROR)
except error as e:
if e.errno == errno.EINVAL: # a nested or set failed to parse correctly
nla_put(msg, _nla_strip_(a), atype, nlh.NLA_ERROR)
else:
raise
except MemoryError as e: # hopefully don't get here
raise error(
-1,
"Attr type {0} of pol {1} failed: {2}".format(atype, pol, e))
idx = nlh.NLMSG_ALIGN(idx + alen) # move index to next attr
def nla_parse_nested(nested):
"""
:param nested: the nested attribute with attribute header removed
:returns: list of tuples (index, data) where index is the index
into an enum structure and attribute is the packed attribute)
Callers must parse these themselves - see below for details
From libnl (Thomas Graf)
When nesting attributes, the nested attributes are included as payload of
a container attribute. Attributes are nested by surrounding them with calls
to nla_nest_start() and nla_nest_end().
<-------- nla_attr_size(payload) --------->
+------------------+-----+------------------+-----+
| Attribute Header | Pad | Payload | Pad |
+------------------+-----+------------------+-----+
Nested attributes (after removing the Attribute header) should have the
form:
+--------+--------+-----+
| Length |Payload | Pad |
+--------+--------+-----+
<-- 2 --><- var ->< var >
where:
Length (u16) is the length of the nested attribute (excluding padding
affixed to the end to align the attribute). The size of padding is
determined by NLMSG_ALIGN
Payload has the format:
+-------+--------+-----+
| Index | Data | Pad |
+-------+--------+-----+
<-- 2 --><- var ->< var >
where index is the index into an enum structure as determined by the
attribute type of the nested attribute which is found in the Attribute
Header
"""
ns = []
idx = 0
l = len(nested)
while idx < l:
# first two bytes define length, including these bytes, length does not
# include pad byte(s) affixed to end for proper alignment
alen = struct.unpack_from("H", nested, idx)[0]
if alen == 0:
raise EnvironmentError(errno.EINVAL, "Invalid nesting")
# ns.append(nested[idx+2:idx+alen]) # don't include the length bytes
nattr = nested[idx + 2 : idx + alen]
ns.append((struct.unpack_from("H", nattr, 0)[0], nattr[2:]))
idx += nlh.NLMSG_ALIGN(alen)
return ns
