def make_ipv4_header(size,
src_addr,
dest_addr,
dscp=None,
ecn=None,
identification=None,
flags=None,
frag_offset=None,
ttl=255,
proto=None,
verify_checksum=False):
version = 4 << 4
ihl = IHL
vihl = version + ihl
if dscp is None:
dscp = 0 << 6
if ecn is None:
ecn = 0
dscpecn = dscp + ecn
total_length = twos_comp(size + 20, 16)
if identification is None:
identification = twos_comp(randint(0, 2**16), 16)
if flags is None:
flag_rsv = 0
flag_dtf = 0
flag_mrf = 0
flags = (flag_rsv << 15) | (flag_dtf << 14) | (flag_mrf << 13)
if frag_offset is None:
frag_offset = 0
flags |= frag_offset
ttl = twos_comp(ttl, 8)
if proto is None:
proto = IPPROTO_TCP
checksum = 0
src_addr = str2addr(src_addr)
dest_addr = str2addr(dest_addr)
header = struct.pack('!bbhhhbbh', vihl, dscpecn, total_length,
identification, flags, ttl, proto,
checksum) + src_addr + dest_addr
if verify_checksum:
checksum = twos_comp(calc_checksum(header[:4 * ihl]), 16)
header = struct.pack('!bbhhhbbh', vihl, dscpecn, total_length,
identification, flags, ttl, proto,
checksum) + src_addr + dest_addr
return header
def __raw_recv(self, datagrama):
dscp, ecn, identification, flags, frag_offset, ttl, proto, \
src_addr, dst_addr, payload = read_ipv4_header(datagrama)
if dst_addr == self.meu_endereco:
# atua como host
if proto == IPPROTO_TCP and self.callback:
self.callback(src_addr, dst_addr, payload)
else:
# atua como roteador
next_hop = self._next_hop(dst_addr)
# TODO: Trate corretamente o campo TTL do datagrama
vihl, dscpecn, total_len, identification, flagsfrag, ttl, proto, \
checksum, src_addr, dest_addr = \
struct.unpack('!BBHHHBBHII', datagrama[:20])
ttl -= 1
datagrama2 = struct.pack('!BBHHHBBH', (4 << 4) + 5, 0,
len(datagrama[20:]) + 20, 0, 0, ttl, 6,
0) + datagrama[12:16] + datagrama[16:20]
data_checksum = mytcputils.calc_checksum(datagrama2)
print(ttl)
if ttl > 0:
datagrama2 = struct.pack(
'!BBHHHBBH', (4 << 4) + 5, 0,
len(datagrama[20:]) + 20, 0, 0, ttl, 6,
data_checksum) + datagrama[12:16] + datagrama[16:20]
self.enlace.enviar(datagrama2, next_hop)
else:
#print(self.meu_endereco)
#print(addr2str(datagrama[12:16]))
#print(addr2str(datagrama[16:20]))
#mytcputils.str2addr(self.meu_endereco)
datafake = struct.pack('!BBHHHBBH', (4 << 4) + 5, 0, 20 + 8 + max(28, len(datagrama[20:])), 0, 0, 64, 1, 0) + \
mytcputils.str2addr(self.meu_endereco) + datagrama[12:16]
data_checksum = mytcputils.calc_checksum(datafake)
outro_checksum = mytcputils.calc_checksum(
struct.pack('BBHI', 11, 0, 0, 0) + datagrama[:28])
print(outro_checksum)
print(struct.pack('!BBHI', 11, 0, outro_checksum, 0))
datafake = struct.pack('!BBHHHBBH', (4 << 4) + 5, 0, 20 + 8 + max(28, len(datagrama[20:])), 0, 0, 64, 1, data_checksum) + \
mytcputils.str2addr(self.meu_endereco) + datagrama[12:16] + struct.pack('!BBHI', 11, 0, outro_checksum, 0) + datagrama[:28]
print(len(datafake))
self.enlace.enviar(datafake, next_hop)
def _rdt_rcv(self, src_addr, dst_addr, segment):
src_port, dst_port, seq_no, ack_no, \
flags, _, _, _ = read_header(segment)
if dst_port != self.porta:
# Ignora segmentos que não são destinados à porta do nosso servidor
return
try:
pseudohdr = str2addr(src_addr) + str2addr(dst_addr) + \
struct.pack('!HH', 0x0006, len(segment))
if calc_checksum(pseudohdr + segment) != 0:
print('descartando segmento com checksum incorreto')
return
def enviar(self, segmento, dest_addr):
"""
Envia segmento para dest_addr, onde dest_addr é um endereço IPv4
(string no formato x.y.z.w).
"""
next_hop = self._next_hop(dest_addr)
print("DEST_ADDR {0} NEXT_HOP {1} MEU_END {2}".format(
dest_addr, next_hop, self.meu_endereco))
dest = dest_addr.split('.')
destino = [int(dest[0]), int(dest[1]), int(dest[2]), int(dest[3])]
val = destino[3] << 24
val += destino[2] << 16
val += destino[1] << 8
val += destino[0] << 0
val_dst = val
val_dst = mytcputils.str2addr(dest_addr)
dest = self.meu_endereco.split('.')
destino = [int(dest[0]), int(dest[1]), int(dest[2]), int(dest[3])]
val = destino[3] << 24
val += destino[2] << 16
val += destino[1] << 8
val += destino[0] << 0
val_src = val
val_src = mytcputils.str2addr(self.meu_endereco)
version = 4
ihl = 5
datagrama = struct.pack('!BBHHHBBH', (version << 4) + ihl, 0,
len(segmento) + 20, 0, 0, 64, 6,
0) + val_src + val_dst
data_checksum = mytcputils.calc_checksum(datagrama)
datagrama = struct.pack('!BBHHHBBH', (version << 4) + ihl, 0,
len(segmento) + 20, 0, 0, 64, 6,
data_checksum) + val_src + val_dst + segmento
#datagrama = ((4 << 4) + 5).to_bytes(1, 'little') + (0).to_bytes(7, 'little') + (64).to_bytes(1, 'little') + (0).to_bytes(7, 'little') + datagrama
# TODO: Assumindo que a camada superior é o protocolo TCP, monte o
# datagrama com o cabeçalho IP, contendo como payload o segmento.
self.enlace.enviar(datagrama, next_hop)