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Switch to ctypes for sendto

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First, IP level sendto doesn't give the freedom to send 25.255.255.255
out of the interface desired.  So have to go link layer.

Second, while python can do sendto, we have the interface index number
from recvmsg (which was ctypes).  python expects the name instead
(wwhich it promptly turns... back into the index we start with).  I
could have added code to get the name using some syscalls which would
have been work and produced more system calls, or added the code to
directly use sendto, which would also be efficient at runtime.

So I chose to use ctypes for both recvmsg and sendto here.
This commit is contained in:
Jarrod Johnson
2020-03-19 16:20:47 -04:00
parent 22de1153c2
commit b7d85b2166
1 changed files with 27 additions and 2 deletions
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29
confluent_server/confluent/discovery/protocols/pxe.py
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@@ -32,6 +32,15 @@ import struct
libc = ctypes.CDLL(ctypes.util.find_library('c'))
class sockaddr_ll(ctypes.Structure):
_fields_ = [('sll_family', ctypes.c_ushort),
('sll_protocol', ctypes.c_ushort),
('sll_ifindex', ctypes.c_int),
('sll_hatype', ctypes.c_ushort),
('sll_pkttype', ctypes.c_ubyte),
('sll_halen', ctypes.c_ubyte),
('sll_addr', ctypes.c_ubyte * 8)]
class iovec(ctypes.Structure): # from uio.h
_fields_ = [('iov_base', ctypes.c_void_p),
('iov_len', ctypes.c_size_t)]
@@ -65,6 +74,11 @@ class sockaddr_in(ctypes.Structure):
('sin_addr', in_addr)]
sendto = libc.sendto
sendto.argtypes = [ctypes.c_int, ctypes.c_void_p, ctypes.c_size_t,
ctypes.c_int, ctypes.POINTER(sockaddr_ll),
ctypes.c_size_t]
sendto.restype = ctypes.c_size_t
recvmsg = libc.recvmsg
recvmsg.argtypes = [ctypes.c_int, ctypes.POINTER(msghdr), ctypes.c_int]
recvmsg.restype = ctypes.c_size_t
@@ -341,8 +355,19 @@ def check_reply(node, info, packet, sock, cfg, reqview):
repview[245:249] = myipn
repview[249:255] = b'\x33\x04\x00\x00\x00\xf0'
repview[255] = 0xff # end of options, should always be last byte
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_IF, myipn)
sock.sendto(repview[:255], ('255.255.255.255', 68))
tsock = socket.socket(socket.AF_PACKET, socket.SOCK_DGRAM,
socket.htons(0x800))
targ = sockaddr_ll()
bcastaddr = bytearray(8)
bcastaddr[:reqview[2]] = b'\xff' * reqview[2]
targ.sll_addr = (ctypes.c_ubyte * 8).from_buffer(bcastaddr)
targ.sll_family = socket.AF_PACKET
targ.sll_halen = reqview[2]
targ.sll_protocol = socket.htons(0x800)
targ.sll_ifindex = info['netinfo']['ifidx']
pkt = ctypes.byref((ctypes.c_char * 256).from_buffer(repview))
sendto(tsock.fileno(), pkt, 256, 0, ctypes.byref(targ),
ctypes.sizeof(targ))
print('Thinking about reply to {0}'.format(node))