def build_ip_header():
ihl = 5
ver = 4
tos = 0
id_of_ip_pkt = 54321
fragm_off = 0
ttl = 225
protocol = socket.IPPROTO_TCP
checksum_for_ip = 0
source_add_for_ip = socket.inet_aton(global_data.get_value("local_ip"))
dest_add_for_ip = socket.inet_aton(global_data.get_value("server_ip"))
ihl_ver = (ver << 4) + ihl
tot_length = 4 * ihl + len(global_data.get_value("tcp_header"))
ip_header = struct.pack('!BBHHHBBH4s4s', ihl_ver, tos, tot_length,
id_of_ip_pkt, fragm_off, ttl, protocol,
checksum_for_ip, source_add_for_ip,
dest_add_for_ip)
checksum = util.ip_checksum(ip_header)
""" add checksum into ip header """
ip_header = struct.pack('!BBHHHBBH4s4s', ihl_ver, tos, tot_length,
id_of_ip_pkt, fragm_off, ttl, protocol, checksum,
source_add_for_ip, dest_add_for_ip)
ip_header = ''.join([ip_header, global_data.get_value("tcp_header")])
global_data.set_value("ip_header", ip_header)
def get_gateway_mac_binary():
interface = global_data.get_value("interface")
main_socket = global_data.get_value("main_socket")
# simulate a broadcast address to find the gateway mac address
arp_header = ethernet.build_arp_header()
ethernet_header = ethernet.build_ethernet_header_for_arp()
ethernet_packet = ''.join([ethernet_header, arp_header])
# bind with interface
main_socket.bind((interface, socket.SOCK_RAW))
# send ethernet packet, so that MAC address of gateway can be retrieved from its response.
main_socket.send(ethernet_packet)
# we store the size of struct, will be used while unpacking the packets, corresponding to the given format.
ethernet_header_length = struct.calcsize('!6s6sH')
arp_header_length = struct.calcsize('!HHBBH6s4s6s4s')
while True:
packet = main_socket.recv(65565)
# unpack the ethernet_packet
fields = struct.unpack('!6s6sH', packet[:ethernet_header_length])
if fields[2] == 2054:
break
# unpack arp packet from eth packet
arp_fields = struct.unpack(
'!HHBBH6s4s6s4s', packet[ethernet_header_length:][:arp_header_length])
gateway_mac_binary = arp_fields[5]
print "gateway_mac_binary:", gateway_mac_binary
return gateway_mac_binary
def send_ack_to_server(seq_no):
http.build_empty_http_header()
tcp.build_tcp_header(global_data.get_value("local_port"), 80,
1 + global_data.get_value("http_request_length"),
seq_no + 1, 5, 0, 0, 0, 0, 1)
ip.build_ip_header()
ethernet.build_ethernet_header_for_ip()
send_packet_to_server()
def handshake_step_three():
http.build_empty_http_header()
tcp.build_tcp_header(global_data.get_value("local_port"), 80, 1,
global_data.get_value("sequence_number") + 1, 5, 0, 0,
0, 0, 1)
ip.build_ip_header()
ethernet.build_ethernet_header_for_ip()
data_transfer.send_packet_to_server()
def build_tcp_header(source_of_tcp_p, dest_of_tcp_p, seq_of_tcp_p,
ack_seq_of_tcp_p, d_off_tcp_p, fin_p, syn_p, rst_p, psh_p,
ack_p):
# TCP Header Section
# source port
source_port = source_of_tcp_p
# destination port
destination_port = dest_of_tcp_p
seq_num = seq_of_tcp_p
ack_num = ack_seq_of_tcp_p
d_offset = 5
# flags
fin = fin_p
syn = syn_p
rst = rst_p
psh = psh_p
ack = ack_p
urg = 0
# size of max allowed window size
window_size = socket.htons(5840)
checksum = 0
urg_pointer = 0
offset_res_of_tcp = (d_offset << 4) + 0
flags = fin + (syn << 1) + (rst << 2) + (psh << 3) + (ack << 4) + (
urg << 5)
tcp_header_p = struct.pack("!HHLLBBHHH", source_port, destination_port,
seq_num, ack_num, offset_res_of_tcp, flags,
window_size, checksum, urg_pointer)
source_address = socket.inet_aton(global_data.get_value("local_ip"))
dest_address = socket.inet_aton(global_data.get_value("server_ip"))
placeholder = 0
protocol = socket.IPPROTO_TCP
tcp_length = len(tcp_header_p) + len(global_data.get_value("http_request"))
psh = struct.pack('!4s4sBBH', source_address, dest_address, placeholder,
protocol, tcp_length)
psh = psh + tcp_header_p + global_data.get_value("http_request")
checksum = util.tcp_checksum(psh)
# add correct tcp header checksum
tcp_header = struct.pack(
'!HHLLBBH', source_port, destination_port, seq_num,
ack_num, offset_res_of_tcp, flags, window_size) + struct.pack(
'H', checksum) + struct.pack('!H', urg_pointer)
tcp_header = ''.join([tcp_header, global_data.get_value("http_request")])
# save into global data value
global_data.set_value("tcp_header", tcp_header)
def send_fin_ack_to_server():
http.build_empty_http_header()
tcp.build_tcp_header(global_data.get_value("local_port"), 80,
global_data.get_value("acknowledge_number"),
int(global_data.get_value("sequence_number")) + 1, 5,
1, 0, 0, 0, 1)
ip.build_ip_header()
ethernet.build_ethernet_header_for_ip()
send_packet_to_server()
def send_data_to_server():
"""
send http request to server
"""
http.build_http_header()
tcp.build_tcp_header(global_data.get_value("local_port"), 80, 1,
int(global_data.get_value("sequence_number")), 5, 0,
0, 0, 1, 1)
ip.build_ip_header()
ethernet.build_ethernet_header_for_ip()
send_packet_to_server()
def build_arp_header():
hardware_type = 1
protocol_type = 2048
hardware_length = 6
protocol_length = 4
broadcast_mac_address = struct.pack('!6B', 255, 255, 255, 255, 255, 255)
operation = 1
arp_pkt = struct.pack('!HHBBH6s4s6s4s', hardware_type, protocol_type, hardware_length, protocol_length, operation,
global_data.get_value("local_mac_binary"), global_data.get_value("local_ip_binary"), broadcast_mac_address,
global_data.get_value("gateway_ip_binary"))
return arp_pkt
def build_ethernet_header_for_arp():
ether_type = 2054 # 0x0806
broadcast_mac_address = struct.pack('!6B', 255, 255, 255, 255, 255, 255)
header_of_eth = struct.pack('!6s6sH', broadcast_mac_address, global_data.get_value("local_mac_binary"), ether_type)
eth_pkt = header_of_eth
return eth_pkt
def handshake_step_one():
http.build_empty_http_header()
tcp.build_tcp_header(global_data.get_value("local_port"), 80, 0, 0, 5, 0,
1, 0, 0, 0)
ip.build_ip_header()
ethernet.build_ethernet_header_for_ip()
data_transfer.send_packet_to_server()
def build_http_header():
http_header = "GET " + global_data.get_value("url") + " HTTP/1.0\r\n\r\n"
http_request = http_header
global_data.set_value("http_request", http_request)
http_request_length = len(http_header)
global_data.set_value("http_request_length", http_request_length)
def send_packet_to_server():
global_data.get_value("main_socket").bind(
(global_data.get_value("interface"), 0))
global_data.get_value("main_socket").send(
global_data.get_value("eth_header"))
last_packet_sent_time = time.time()
global_data.set_value("last_packet_sent_time", last_packet_sent_time)
def build_ethernet_header_for_ip():
ether_type = 2048
header_of_eth = struct.pack('!6s6sH', global_data.get_value("gateway_mac_binary"), global_data.get_value("local_mac_binary"), ether_type)
eth_header = ''.join([header_of_eth, global_data.get_value("ip_header")])
global_data.set_value("eth_header", eth_header)
def get_local_ip_binary():
local_ip = global_data.get_value("local_ip")
local_ip_binary = socket.inet_aton(local_ip)
print "local_ip_binary:", local_ip_binary
return local_ip_binary
def receive_data_from_server():
"""
receive data from the server, for three way handshake and for receive http response data
"""
downloaded_file_name = global_data.get_value("downloaded_file_name")
main_socket = global_data.get_value("main_socket")
local_port = global_data.get_value("local_port")
server_ip = global_data.get_value("server_ip")
local_ip = global_data.get_value("local_ip")
f = open(downloaded_file_name, 'a')
while True:
if (time.time() -
global_data.get_value("last_packet_sent_time")) > 180:
print "Program, rawhttpget, does not receive any data from the remote server for three minutes. Please retry again."
sys.exit(0)
packet = main_socket.recvfrom(65565)
packet = packet[0]
ethernet_header_length = struct.calcsize('!6s6sH')
ip_header = packet[ethernet_header_length:ethernet_header_length + 20]
global_data.set_value("ip_header", ip_header)
iph = struct.unpack('!BBHHHBBH4s4s', ip_header)
version_ihl = iph[0]
ihl = version_ihl & 0xF
iph_length = ihl * 4
server_as_source_address = socket.inet_ntoa(iph[8])
local_as_destination_address = socket.inet_ntoa(iph[9])
tcp_header = packet[ethernet_header_length +
iph_length:ethernet_header_length + iph_length +
20]
global_data.set_value("tcp_header", tcp_header)
tcph = struct.unpack('!HHLLBBHHH', tcp_header)
server_as_source_port = tcph[0]
local_as_destination_port = tcph[1]
sequence_number = tcph[2]
global_data.set_value("sequence_number", sequence_number)
acknowledge_number = tcph[3]
global_data.set_value("acknowledge_number", acknowledge_number)
data_offset_reserved = tcph[4]
tcp_flags = tcph[5]
flag_fin = tcp_flags & int(hex(1), 16)
flag_syn = (tcp_flags >> 1) & int(hex(1), 16)
flag_ack = (tcp_flags >> 4) & int(hex(1), 16)
tcph_length = data_offset_reserved >> 4
header_size = ethernet_header_length + iph_length + tcph_length * 4
data_size = len(packet) - header_size
data = packet[header_size:]
if local_as_destination_port != local_port or server_as_source_port != 80 \
or server_as_source_address != server_ip or local_as_destination_address != local_ip:
continue
else:
if flag_ack == 1 and flag_syn == 1:
old_sequence_number = sequence_number + 1
global_data.set_value("old_sequence_number",
old_sequence_number)
break
if data_size > 6 and global_data.get_value(
"current_cwnd_size") <= 1000:
if global_data.get_value("old_sequence_number") + global_data.get_value("old_data_length") == \
global_data.get_value("sequence_number") and util.tcp_checksum(global_data.get_value("ip_header")) == 0:
if (time.time() -
global_data.get_value("last_packet_sent_time")
) < 60:
if data.split('\r\n\r\n')[0] == data:
""" directly write data into file """
f.write(data)
else:
data_containing_header = data.split('\r\n\r\n')[0]
http_status = data_containing_header.split(' ')[1]
if http_status == "200":
f.write(data.split('\r\n\r\n')[1])
else:
print "Only 200 will be considered!"
break
old_sequence_number = global_data.get_value(
"sequence_number")
global_data.set_value("old_sequence_number",
old_sequence_number)
old_data_length = data_size
global_data.set_value("old_data_length",
old_data_length)
""" solve the retransmit packet needs to be ACK """
if global_data.get_value(
"number_of_retransmit_packet_to_be_ACK") > 0:
new_number_of_retransmit_packet_to_be_ACK = global_data.get_value(
"number_of_retransmit_packet_to_be_ACK") - 1
global_data.set_value(
"number_of_retransmit_packet_to_be_ACK",
new_number_of_retransmit_packet_to_be_ACK)
""" normal cwnd size """
if 0 < global_data.get_value(
"current_cwnd_size") + 1 < 1000:
new_current_cwnd_size = global_data.get_value(
"current_cwnd_size") + 1
global_data.set_value("current_cwnd_size",
new_current_cwnd_size)
else:
new_current_cwnd_size = 1
global_data.set_value("current_cwnd_size",
new_current_cwnd_size)
send_ack_to_server(
global_data.get_value("sequence_number"))
else:
print "retransmit because the 60 seconds limit"
send_ack_retransmit_to_server(
global_data.get_value("old_sequence_number"))
else:
if global_data.get_value(
"current_cwnd_size"
) + 1 <= 0 or global_data.get_value(
"current_cwnd_size") + 1 >= 1000:
new_current_cwnd_size = 1
global_data.set_value("current_cwnd_size",
new_current_cwnd_size)
else:
new_current_cwnd_size = global_data.get_value(
"current_cwnd_size") + 1
global_data.set_value("current_cwnd_size",
new_current_cwnd_size)
new_number_of_retransmit_packet_to_be_ACK = 1
global_data.set_value(
"number_of_retransmit_packet_to_be_ACK",
new_number_of_retransmit_packet_to_be_ACK)
print "retransmit because sequence number or checksum error"
send_ack_retransmit_to_server(
global_data.get_value("old_sequence_number"))
if flag_fin == 1 and global_data.get_value(
"number_of_retransmit_packet_to_be_ACK") == 0:
f.close()
send_fin_ack_to_server()
break
sys.exit(0)