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---
-- Facilities for manipulating raw packets.
--
-- @author Marek Majkowski <majek04+nse@gmail.com>
-- @copyright Same as Nmap--See http://nmap.org/book/man-legal.html
module(... or "packet" ,package.seeall)
local bit = require "bit"
local stdnse = require "stdnse"
----------------------------------------------------------------------------------------------------------------
--- Get an 8-bit integer at a 0-based byte offset in a byte string.
-- @param b A byte string.
-- @param i Offset.
-- @return An 8-bit integer.
function u8(b, i)
return string.byte(b, i+1)
end
--- Get a 16-bit integer at a 0-based byte offset in a byte string.
-- @param b A byte string.
-- @param i Offset.
-- @return A 16-bit integer.
function u16(b, i)
local b1,b2
b1, b2 = string.byte(b, i+1), string.byte(b, i+2)
-- 2^8 2^0
return b1*256 + b2
end
--- Get a 32-bit integer at a 0-based byte offset in a byte string.
-- @param b A byte string.
-- @param i Offset.
-- @return A 32-bit integer.
function u32(b,i)
local b1,b2,b3,b4
b1, b2 = string.byte(b, i+1), string.byte(b, i+2)
b3, b4 = string.byte(b, i+3), string.byte(b, i+4)
-- 2^24 2^16 2^8 2^0
return b1*16777216 + b2*65536 + b3*256 + b4
end
--- Set an 8-bit integer at a 0-based byte offset in a byte string
-- (big-endian).
-- @param b A byte string.
-- @param i Offset.
-- @param num Integer to store.
function set_u8(b, i, num)
local s = string.char(bit.band(num, 0xff))
return b:sub(0+1, i+1-1) .. s .. b:sub(i+1+1)
end
--- Set a 16-bit integer at a 0-based byte offset in a byte string
-- (big-endian).
-- @param b A byte string.
-- @param i Offset.
-- @param num Integer to store.
function set_u16(b, i, num)
local s = string.char(bit.band(bit.rshift(num, 8), 0xff)) .. string.char(bit.band(num, 0xff))
return b:sub(0+1, i+1-1) .. s .. b:sub(i+1+2)
end
--- Set a 32-bit integer at a 0-based byte offset in a byte string
-- (big-endian).
-- @param b A byte string.
-- @param i Offset.
-- @param num Integer to store.
function set_u32(b,i, num)
local s = string.char(bit.band(bit.rshift(num,24), 0xff)) ..
string.char(bit.band(bit.rshift(num,16), 0xff)) ..
string.char(bit.band(bit.rshift(num,8), 0xff)) ..
string.char(bit.band(num, 0xff))
return b:sub(0+1, i+1-1) .. s .. b:sub(i+1+4)
end
--- Calculate a standard Internet checksum.
-- @param b Data to checksum.
-- @return Checksum.
function in_cksum(b)
local sum = 0
local i
-- Note we are using 0-based indexes here.
i = 0
while i < b:len() - 1 do
sum = sum + u16(b, i)
i = i + 2
end
if i < b:len() then
sum = sum + u8(b, i) * 256
end
sum = bit.rshift(sum, 16) + bit.band(sum, 0xffff)
sum = sum + bit.rshift(sum, 16)
sum = bit.bnot(sum)
sum = bit.band(sum, 0xffff) -- trunctate to 16 bits
return sum
end
-- ip protocol field
IPPROTO_IP = 0 -- Dummy protocol for TCP
IPPROTO_ICMP = 1 -- Internet Control Message Protocol
IPPROTO_IGMP = 2 -- Internet Group Management Protocol
IPPROTO_IPIP = 4 -- IPIP tunnels (older KA9Q tunnels use 94)
IPPROTO_TCP = 6 -- Transmission Control Protocol
IPPROTO_EGP = 8 -- Exterior Gateway Protocol
IPPROTO_PUP = 12 -- PUP protocol
IPPROTO_UDP = 17 -- User Datagram Protocol
IPPROTO_IDP = 22 -- XNS IDP protocol
IPPROTO_DCCP = 33 -- Datagram Congestion Control Protocol
IPPROTO_RSVP = 46 -- RSVP protocol
IPPROTO_GRE = 47 -- Cisco GRE tunnels (rfc 1701,1702)
IPPROTO_IPV6 = 41 -- IPv6-in-IPv4 tunnelling
IPPROTO_ESP = 50 -- Encapsulation Security Payload protocol
IPPROTO_AH = 51 -- Authentication Header protocol
IPPROTO_BEETPH = 94 -- IP option pseudo header for BEET
IPPROTO_PIM = 103 -- Protocol Independent Multicast
IPPROTO_COMP = 108 -- Compression Header protocol
IPPROTO_SCTP = 132 -- Stream Control Transport Protocol
IPPROTO_UDPLITE = 136 -- UDP-Lite (RFC 3828)
----------------------------------------------------------------------------------------------------------------
-- Packet is a class
Packet = {}
--- Create a new Packet object.
-- @param packet Binary string with packet data.
-- @param packet_len Packet length. It could be more than
-- <code>string.len(packet)</code>.
-- @param force_continue whether an error in parsing headers should be fatal or
-- not. This is especially useful when parsing ICMP packets, where a small ICMP
-- payload could be a TCP header. The problem is that parsing this payload
-- normally would fail because the TCP header is too small.
-- @return A new Packet.
function Packet:new(packet, packet_len, force_continue)
local o = setmetatable({}, {__index = Packet})
o.buf = packet
o.packet_len = packet_len
if not o:ip_parse(force_continue) then
return nil
end
if o.ip_p == IPPROTO_TCP then
if not o:tcp_parse(force_continue) then
stdnse.print_debug("Error while parsing TCP packet\n")
end
elseif o.ip_p == IPPROTO_UDP then
if not o:udp_parse(force_continue) then
stdnse.print_debug("Error while parsing UDP packet\n")
end
elseif o.ip_p == IPPROTO_ICMP then
if not o:icmp_parse(force_continue) then
stdnse.print_debug("Error while parsing ICMP packet\n")
end
end
return o
end
-- Helpers
--- Convert a dotted-quad IP address string (like <code>"1.2.3.4"</code>) to a
-- raw string four bytes long.
-- @param str IP address string.
-- @return Four-byte string.
function iptobin(str)
local ret = ""
for c in string.gmatch(str, "[0-9]+") do
ret = ret .. string.char(c+0) -- automatic conversion to int
end
return ret
end
--- Convert a four-byte raw string to a dotted-quad IP address string.
-- @param raw_ip_addr Four-byte string.
-- @return IP address string.
function toip(raw_ip_addr)
if not raw_ip_addr then
return "?.?.?.?"
end
return string.format("%i.%i.%i.%i", string.byte(raw_ip_addr,1,4))
end
--- Get an 8-bit integer at a 0-based byte offset in the packet.
-- @param index Offset.
-- @return An 8-bit integer.
function Packet:u8(index)
return u8(self.buf, index)
end
--- Get a 16-bit integer at a 0-based byte offset in the packet.
-- @param index Offset.
-- @return A 16-bit integer.
function Packet:u16(index)
return u16(self.buf, index)
end
--- Get a 32-bit integer at a 0-based byte offset in the packet.
-- @param index Offset.
-- @return An 32-bit integer.
function Packet:u32(index)
return u32(self.buf, index)
end
--- Return part of the packet contents as a byte string.
-- @param index The beginning of the part of the packet to extract.
-- @param length The length of the part of the packet to extract.
-- @return A string.
function Packet:raw(index, length)
return string.char(string.byte(self.buf, index+1, index+1+length-1))
end
--- Set an 8-bit integer at a 0-based byte offset in the packet.
-- (big-endian).
-- @param index Offset.
-- @param num Integer to store.
function Packet:set_u8(index, num)
self.buf = set_u8(self.buf, index, num)
return self.buf
end
--- Set a 16-bit integer at a 0-based byte offset in the packet.
-- (big-endian).
-- @param index Offset.
-- @param num Integer to store.
function Packet:set_u16(index, num)
self.buf = set_u16(self.buf, index, num)
return self.buf
end
--- Set a 32-bit integer at a 0-based byte offset in the packet.
-- (big-endian).
-- @param index Offset.
-- @param num Integer to store.
function Packet:set_u32(index, num)
self.buf = set_u32(self.buf, index, num)
return self.buf
end
--- Parse an IP packet header.
-- @param force_continue Ignored.
-- @return Whether the parsing succeeded.
function Packet:ip_parse(force_continue)
self.ip_offset = 0
if string.len(self.buf) < 20 then -- too short
return false
end
self.ip_v = bit.rshift(bit.band(self:u8(self.ip_offset + 0), 0xF0), 4)
self.ip_hl = bit.band(self:u8(self.ip_offset + 0), 0x0F) -- header_length or data_offset
if self.ip_v ~= 4 then -- not ip
return false
end
self.ip = true
self.ip_tos = self:u8(self.ip_offset + 1)
self.ip_len = self:u16(self.ip_offset + 2)
self.ip_id = self:u16(self.ip_offset + 4)
self.ip_off = self:u16(self.ip_offset + 6)
self.ip_rf = bit.band(self.ip_off, 0x8000)~=0 -- true/false
self.ip_df = bit.band(self.ip_off, 0x4000)~=0
self.ip_mf = bit.band(self.ip_off, 0x2000)~=0
self.ip_off = bit.band(self.ip_off, 0x1FFF) -- fragment offset
self.ip_ttl = self:u8(self.ip_offset + 8)
self.ip_p = self:u8(self.ip_offset + 9)
self.ip_sum = self:u16(self.ip_offset + 10)
self.ip_bin_src = self:raw(self.ip_offset + 12,4) -- raw 4-bytes string
self.ip_bin_dst = self:raw(self.ip_offset + 16,4)
self.ip_src = toip(self.ip_bin_src) -- formatted string
self.ip_dst = toip(self.ip_bin_dst)
self.ip_opt_offset = self.ip_offset + 20
self.ip_options = self:parse_options(self.ip_opt_offset, ((self.ip_hl*4)-20))
self.ip_data_offset = self.ip_offset + self.ip_hl*4
return true
end
--- Set the header length field.
function Packet:ip_set_hl(len)
self:set_u8(self.ip_offset + 0, bit.bor(bit.lshift(self.ip_v, 4), bit.band(len, 0x0F)))
self.ip_v = bit.rshift(bit.band(self:u8(self.ip_offset + 0), 0xF0), 4)
self.ip_hl = bit.band(self:u8(self.ip_offset + 0), 0x0F) -- header_length or data_offset
end
--- Set the packet length field.
-- @param len Packet length.
function Packet:ip_set_len(len)
self:set_u16(self.ip_offset + 2, len)
self.ip_len = len
end
--- Set the TTL.
-- @param ttl TTL.
function Packet:ip_set_ttl(ttl)
self:set_u8(self.ip_offset + 8, ttl)
self.ip_ttl = ttl
end
--- Set the checksum.
-- @param checksum Checksum.
function Packet:ip_set_checksum(checksum)
self:set_u16(self.ip_offset + 10, checksum)
self.ip_sum = checksum
end
--- Count checksum for packet and save it.
function Packet:ip_count_checksum()
self:ip_set_checksum(0)
local csum = in_cksum( self.buf:sub(0, self.ip_offset + self.ip_hl*4) )
self:ip_set_checksum(csum)
end
--- Set the source IP address.
-- @param binip The source IP address as a byte string.
function Packet:ip_set_bin_src(binip)
local nrip = u32(binip, 0)
self:set_u32(self.ip_offset + 12, nrip)
self.ip_bin_src = self:raw(self.ip_offset + 12,4) -- raw 4-bytes string
end
--- Set the destination IP address.
-- @param binip The destination IP address as a byte string.
function Packet:ip_set_bin_dst(binip)
local nrip = u32(binip, 0)
self:set_u32(self.ip_offset + 16, nrip)
self.ip_bin_dst = self:raw(self.ip_offset + 16,4)
end
--- Set the IP options field (and move the data, count new length,
-- etc.).
-- @param ipoptions IP options.
function Packet:ip_set_options(ipoptions)
-- packet = <ip header> + ipoptions + <payload>
local buf = self.buf:sub(0+1,self.ip_offset + 20) .. ipoptions .. self.buf:sub(self.ip_data_offset+1)
self.buf = buf
-- set ip_len
self:ip_set_len(self.buf:len())
-- set ip_hl
self:ip_set_hl(5 + ipoptions:len()/4)
-- set data offset correctly
self.ip_options = self:parse_options(self.ip_opt_offset, ((self.ip_hl*4)-20))
self.ip_data_offset = self.ip_offset + self.ip_hl*4
if self.tcp then
self.tcp_offset = self.ip_data_offset
elseif self.icmp then
self.icmp_offset = self.ip_data_offset
end
end
--- Get a short string representation of the IP header.
-- @return A string representation of the IP header.
function Packet:ip_tostring()
return string.format(
"IP %s -> %s",
self.ip_src,
self.ip_dst)
end
--- Parse IP/TCP options into a table.
-- @param offset Offset at which options start.
-- @param length Length of options.
-- @return Table of options.
function Packet:parse_options(offset, length)
local options = {}
local op = 1
local opt_ptr = 0
while opt_ptr < length do
local t, l, d
options[op] = {}
t = self:u8(offset + opt_ptr)
options[op].type = t
if t==0 or t==1 then
l = 1
d = nil
else
l = self:u8(offset + opt_ptr + 1)
if l > 2 then
d = self:raw(offset + opt_ptr + 2, l-2)
end
end
options[op].len = l
options[op].data = d
opt_ptr = opt_ptr + l
op = op + 1
end
return options
end
--- Get a short string representation of the packet.
-- @return A string representation of the packet.
function Packet:tostring()
if self.tcp then
return self:tcp_tostring()
elseif self.udp then
return self:udp_tostring()
elseif self.icmp then
return self:icmp_tostring()
elseif self.ip then
return self:ip_tostring()
end
return "<no tostring!>"
end
----------------------------------------------------------------------------------------------------------------
--- Parse an ICMP packet header.
-- @param force_continue Ignored.
-- @return Whether the parsing succeeded.
function Packet:icmp_parse(force_continue)
self.icmp_offset = self.ip_data_offset
if string.len(self.buf) < self.icmp_offset + 8 then -- let's say 8 bytes minimum
return false
end
self.icmp = true
self.icmp_type = self:u8(self.icmp_offset + 0)
self.icmp_code = self:u8(self.icmp_offset + 1)
self.icmp_sum = self:u16(self.icmp_offset + 2)
if self.icmp_type == 3 or self.icmp_type == 4 or self.icmp_type == 11 or self.icmp_type == 12 then
self.icmp_payload = true
self.icmp_r0 = self:u32(self.icmp_offset + 4)
self.icmp_payload_offset = self.icmp_offset + 8
if string.len(self.buf) < self.icmp_payload_offset + 24 then
return false
end
self.icmp_payload = Packet:new(self.buf:sub(self.icmp_payload_offset+1), self.packet_len - self.icmp_payload_offset, true)
end
return true
end
--- Get a short string representation of the ICMP header.
-- @return A string representation of the ICMP header.
function Packet:icmp_tostring()
return self:ip_tostring() .. " ICMP(" .. self.icmp_payload:tostring() .. ")"
end
----------------------------------------------------------------------------------------------------------------
-- Parse a TCP packet header.
-- @param force_continue Whether a short packet causes parsing to fail.
-- @return Whether the parsing succeeded.
function Packet:tcp_parse(force_continue)
self.tcp = true
self.tcp_offset = self.ip_data_offset
if string.len(self.buf) < self.tcp_offset + 4 then
return false
end
self.tcp_sport = self:u16(self.tcp_offset + 0)
self.tcp_dport = self:u16(self.tcp_offset + 2)
if string.len(self.buf) < self.tcp_offset + 20 then
if force_continue then
return true
else
return false
end
end
self.tcp_seq = self:u32(self.tcp_offset + 4)
self.tcp_ack = self:u32(self.tcp_offset + 8)
self.tcp_hl = bit.rshift(bit.band(self:u8(self.tcp_offset+12), 0xF0), 4) -- header_length or data_offset
self.tcp_x2 = bit.band(self:u8(self.tcp_offset+12), 0x0F)
self.tcp_flags = self:u8(self.tcp_offset + 13)
self.tcp_th_fin = bit.band(self.tcp_flags, 0x01)~=0 -- true/false
self.tcp_th_syn = bit.band(self.tcp_flags, 0x02)~=0
self.tcp_th_rst = bit.band(self.tcp_flags, 0x04)~=0
self.tcp_th_push = bit.band(self.tcp_flags, 0x08)~=0
self.tcp_th_ack = bit.band(self.tcp_flags, 0x10)~=0
self.tcp_th_urg = bit.band(self.tcp_flags, 0x20)~=0
self.tcp_th_ece = bit.band(self.tcp_flags, 0x40)~=0
self.tcp_th_cwr = bit.band(self.tcp_flags, 0x80)~=0
self.tcp_win = self:u16(self.tcp_offset + 14)
self.tcp_sum = self:u16(self.tcp_offset + 16)
self.tcp_urp = self:u16(self.tcp_offset + 18)
self.tcp_opt_offset = self.tcp_offset + 20
self.tcp_options = self:parse_options(self.tcp_opt_offset, ((self.tcp_hl*4)-20))
self.tcp_data_offset = self.tcp_offset + self.tcp_hl*4
self.tcp_data_length = self.ip_len - self.tcp_offset - self.tcp_hl*4
self:tcp_parse_options()
return true
end
--- Get a short string representation of the TCP packet.
-- @return A string representation of the TCP header.
function Packet:tcp_tostring()
return string.format(
"TCP %s:%i -> %s:%i",
self.ip_src, self.tcp_sport,
self.ip_dst, self.tcp_dport
)
end
--- Parse options for TCP header.
function Packet:tcp_parse_options()
local eoo = false
for _,opt in ipairs(self.tcp_options) do
if eoo then
self.tcp_opt_after_eol = true
end
if opt.type == 0 then -- end of options
eoo = true
elseif opt.type == 2 then -- MSS
self.tcp_opt_mss = u16(opt.data, 0)
self.tcp_opt_mtu = self.tcp_opt_mss + 40
elseif opt.type == 3 then -- widow scaling
self.tcp_opt_ws = u8(opt.data, 0)
elseif opt.type == 8 then -- timestamp
self.tcp_opt_t1 = u32(opt.data, 0)
self.tcp_opt_t2 = u32(opt.data, 4)
end
end
end
--- Set the TCP source port.
-- @param port Source port.
function Packet:tcp_set_sport(port)
self:set_u16(self.tcp_offset + 0, port)
self.tcp_sport = port
end
--- Set the TCP destination port.
-- @param port Destination port.
function Packet:tcp_set_dport(port)
self:set_u16(self.tcp_offset + 2, port)
self.tcp_dport = port
end
--- Set the TCP sequence field.
-- @param new_seq Sequence.
function Packet:tcp_set_seq(new_seq)
self:set_u32(self.tcp_offset + 4, new_seq)
self.tcp_seq = new_seq
end
--- Set the TCP flags field (like SYN, ACK, RST).
-- @param new_flags Flags, represented as an 8-bit number.
function Packet:tcp_set_flags(new_flags)
self:set_u8(self.tcp_offset + 13, new_flags)
self.tcp_flags = new_flags
end
--- Set the urgent pointer field.
-- @param urg_ptr Urgent pointer.
function Packet:tcp_set_urp(urg_ptr)
self:set_u16(self.tcp_offset + 18, urg_ptr)
self.tcp_urp = urg_ptr
end
--- Set the TCP checksum field.
-- @param checksum Checksum.
function Packet:tcp_set_checksum(checksum)
self:set_u16(self.tcp_offset + 16, checksum)
self.tcp_sum = checksum
end
--- Count and save the TCP checksum field.
function Packet:tcp_count_checksum()
self:tcp_set_checksum(0)
local proto = self.ip_p
local length = self.buf:len() - self.tcp_offset
local b = self.ip_bin_src ..
self.ip_bin_dst ..
string.char(0) ..
string.char(proto) ..
set_u16("..", 0, length) ..
self.buf:sub(self.tcp_offset+1)
self:tcp_set_checksum(in_cksum(b))
end
--- Map an MTU to a link type string. Stolen from p0f.
-- @return A string describing the link type.
function Packet:tcp_lookup_link()
local mtu_def = {
{["mtu"]=256, ["txt"]= "radio modem"},
{["mtu"]=386, ["txt"]= "ethernut"},
{["mtu"]=552, ["txt"]= "SLIP line / encap ppp"},
{["mtu"]=576, ["txt"]= "sometimes modem"},
{["mtu"]=1280, ["txt"]= "gif tunnel"},
{["mtu"]=1300, ["txt"]= "PIX, SMC, sometimes wireless"},
{["mtu"]=1362, ["txt"]= "sometimes DSL (1)"},
{["mtu"]=1372, ["txt"]= "cable modem"},
{["mtu"]=1400, ["txt"]= "(Google/AOL)"},
{["mtu"]=1415, ["txt"]= "sometimes wireless"},
{["mtu"]=1420, ["txt"]= "GPRS, T1, FreeS/WAN"},
{["mtu"]=1423, ["txt"]= "sometimes cable"},
{["mtu"]=1440, ["txt"]= "sometimes DSL (2)"},
{["mtu"]=1442, ["txt"]= "IPIP tunnel"},
{["mtu"]=1450, ["txt"]= "vtun"},
{["mtu"]=1452, ["txt"]= "sometimes DSL (3)"},
{["mtu"]=1454, ["txt"]= "sometimes DSL (4)"},
{["mtu"]=1456, ["txt"]= "ISDN ppp"},
{["mtu"]=1458, ["txt"]= "BT DSL (?)"},
{["mtu"]=1462, ["txt"]= "sometimes DSL (5)"},
{["mtu"]=1470, ["txt"]= "(Google 2)"},
{["mtu"]=1476, ["txt"]= "IPSec/GRE"},
{["mtu"]=1480, ["txt"]= "IPv6/IPIP"},
{["mtu"]=1492, ["txt"]= "pppoe (DSL)"},
{["mtu"]=1496, ["txt"]= "vLAN"},
{["mtu"]=1500, ["txt"]= "ethernet/modem"},
{["mtu"]=1656, ["txt"]= "Ericsson HIS"},
{["mtu"]=2024, ["txt"]= "wireless/IrDA"},
{["mtu"]=2048, ["txt"]= "Cyclom X.25 WAN"},
{["mtu"]=2250, ["txt"]= "AiroNet wireless"},
{["mtu"]=3924, ["txt"]= "loopback"},
{["mtu"]=4056, ["txt"]= "token ring (1)"},
{["mtu"]=4096, ["txt"]= "Sangoma X.25 WAN"},
{["mtu"]=4352, ["txt"]= "FDDI"},
{["mtu"]=4500, ["txt"]= "token ring (2)"},
{["mtu"]=9180, ["txt"]= "FORE ATM"},
{["mtu"]=16384, ["txt"]= "sometimes loopback (1)"},
{["mtu"]=16436, ["txt"]= "sometimes loopback (2)"},
{["mtu"]=18000, ["txt"]= "token ring x4"},
}
if not self.tcp_opt_mss or self.tcp_opt_mss==0 then
return "unspecified"
end
for _,x in ipairs(mtu_def) do
local mtu = x["mtu"]
local txt = x["txt"]
if self.tcp_opt_mtu == mtu then
return txt
end
if self.tcp_opt_mtu < mtu then
return string.format("unknown-%i", self.tcp_opt_mtu)
end
end
return string.format("unknown-%i", self.tcp_opt_mtu)
end
----------------------------------------------------------------------------------------------------------------
-- Parse a UDP packet header.
-- @param force_continue Whether a short packet causes parsing to fail.
-- @return Whether the parsing succeeded.
function Packet:udp_parse(force_continue)
self.udp = true
self.udp_offset = self.ip_data_offset
if string.len(self.buf) < self.udp_offset + 4 then
return false
end
self.udp_sport = self:u16(self.udp_offset + 0)
self.udp_dport = self:u16(self.udp_offset + 2)
if string.len(self.buf) < self.udp_offset + 8 then
if force_continue then
return true
else
return false
end
end
self.udp_len = self:u16(self.udp_offset + 4)
self.udp_sum = self:u16(self.udp_offset + 6)
return true
end
--- Get a short string representation of the UDP packet.
-- @return A string representation of the UDP header.
function Packet:udp_tostring()
return string.format(
"UDP %s:%i -> %s:%i",
self.ip_src, self.udp_sport,
self.ip_dst, self.udp_dport
)
end
---
-- Set the UDP source port.
-- @param port Source port.
function Packet:udp_set_sport(port)
self:set_u16(self.udp_offset + 0, port)
self.udp_sport = port
end
---
-- Set the UDP destination port.
-- @param port Destination port.
function Packet:udp_set_dport(port)
self:set_u16(self.udp_offset + 2, port)
self.udp_dport = port
end
---
-- Set the UDP payload length.
-- @param len UDP payload length.
function Packet:udp_set_length(len)
self:set_u16(self.udp_offset + 4, len)
self.udp_len = len
end
---
-- Set the UDP checksum field.
-- @param checksum Checksum.
function Packet:udp_set_checksum(checksum)
self:set_u16(self.udp_offset + 6, checksum)
self.udp_sum = checksum
end
---
-- Count and save the UDP checksum field.
function Packet:udp_count_checksum()
self:udp_set_checksum(0)
local proto = self.ip_p
local length = self.buf:len() - self.udp_offset
local b = self.ip_bin_src ..
self.ip_bin_dst ..
string.char(0) ..
string.char(proto) ..
set_u16("..", 0, length) ..
self.buf:sub(self.udp_offset+1)
self:udp_set_checksum(in_cksum(b))
end
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