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udp.go
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udp.go
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package csum
import "github.com/google/gopacket/layers"
func UDPIPv4(srcaddr, dstaddr, udpdata []byte) uint16 {
var csum uint32
var udplen uint32 = uint32(len(udpdata))
// clear checksum bytes
udpdata[6] = 0
udpdata[7] = 0
csum += uint32(srcaddr[0]) << 8
csum += uint32(srcaddr[1])
csum += uint32(srcaddr[2]) << 8
csum += uint32(srcaddr[3])
csum += uint32(dstaddr[0]) << 8
csum += uint32(dstaddr[1])
csum += uint32(dstaddr[2]) << 8
csum += uint32(dstaddr[3])
csum += uint32(layers.IPProtocolUDP)
csum += udplen
end := len(udpdata) - 1
for i := 0; i < end; i += 2 {
csum += uint32(udpdata[i]) << 8
csum += uint32(udpdata[i+1])
}
if len(udpdata)%2 == 1 {
csum += uint32(udpdata[end]) << 8
}
for csum > 0xffff {
csum = (csum >> 16) + (csum & 0xffff)
}
return ^uint16(csum)
}
func UDPIPv6(srcaddr, dstaddr, udpdata []byte) uint16 {
var csum uint32
var udplen uint32 = uint32(len(udpdata))
// clear checksum bytes
udpdata[6] = 0
udpdata[7] = 0
for i := 0; i <= 14; i += 2 {
csum += uint32(srcaddr[i]) << 8
csum += uint32(srcaddr[i+1])
}
for i := 0; i <= 14; i += 2 {
csum += uint32(dstaddr[i]) << 8
csum += uint32(dstaddr[i+1])
}
csum += udplen
csum += uint32(layers.IPProtocolUDP)
end := len(udpdata) - 1
for i := 0; i < end; i += 2 {
csum += uint32(udpdata[i]) << 8
csum += uint32(udpdata[i+1])
}
if len(udpdata)%2 == 1 {
csum += uint32(udpdata[end]) << 8
}
for csum > 0xffff {
csum = (csum >> 16) + (csum & 0xffff)
}
return ^uint16(csum)
}