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Checksum simplification proposal (#29)

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* Simplified checksum calculation and verification

* Fixed tests

* UDP: using NewBoundedFrame to create a Frame instance limited to the actual frame size.

* Minor: renamed some functions

* Commented and made more readable consecutive SetCRC calls.

* Fixed icmp checksum calculation after rebase

* Replaced NewBoundedFrame with explicit validation
This commit is contained in:
ddirect
2026-02-05 22:35:42 +02:00
committed by GitHub
parent cd51bd6c3f
commit fba97c990a
13 changed files with 139 additions and 228 deletions
Download Patch File Download Diff File Expand all files Collapse all files
internet/pcap/capture.go
+33 -53
View File
@@ -161,27 +161,26 @@ func (pc *PacketBreakdown) CaptureIPv6(dst []Frame, pkt []byte, bitOffset int) (
end := bitOffset + 40*octet
var protoErrs []error
var crc lneto.CRC791
if proto == lneto.IPProtoTCP {
ifrm6.CRCWritePseudo(&crc)
tfrm, err := tcp.NewFrame(ifrm6.Payload())
if err == nil {
tfrm.CRCWrite(&crc)
wantSum := crc.Sum16()
gotSum := tfrm.CRC()
if wantSum != gotSum {
protoErrs = append(protoErrs, &crcError16{protocol: "ipv6+tcp", want: wantSum, got: gotSum})
}
ifrm6.CRCWritePseudo(&crc)
switch proto {
case lneto.IPProtoTCP:
if crc.PayloadSum16(ifrm6.Payload()) != 0 {
protoErrs = append(protoErrs, lneto.ErrBadCRC)
}
} else if proto == lneto.IPProtoUDP || proto == lneto.IPProtoUDPLite {
ifrm6.CRCWritePseudo(&crc)
case lneto.IPProtoUDP, lneto.IPProtoUDPLite:
ufrm, err := udp.NewFrame(ifrm6.Payload())
if err == nil {
ufrm.CRCWriteIPv6(&crc)
wantSum := crc.Sum16()
gotSum := ufrm.CRC()
if wantSum != gotSum {
protoErrs = append(protoErrs, &crcError16{protocol: "ipv6+udp", want: wantSum, got: gotSum})
}
if err != nil {
protoErrs = append(protoErrs, err)
break
}
ufrm.ValidateSize(pc.validator())
if err = pc.validator().ErrPop(); err != nil {
protoErrs = append(protoErrs, err)
break
}
frameLen := ufrm.Length()
if crc.PayloadSum16(ufrm.RawData()[:frameLen]) != 0 {
protoErrs = append(protoErrs, lneto.ErrBadCRC)
}
}
return pc.captureIPProto(proto, dst, pkt, end, protoErrs...)
@@ -214,57 +213,48 @@ func (pc *PacketBreakdown) CaptureIPv4(dst []Frame, pkt []byte, bitOffset int) (
BitLength: octet * len(options),
})
}
gotSum := ifrm4.CRC()
wantSum := ifrm4.CalculateHeaderCRC()
if gotSum != wantSum {
finfo.Errors = append(finfo.Errors, &crcError16{protocol: "ipv4", want: wantSum, got: gotSum})
if ifrm4.CalculateHeaderCRC() != 0 {
finfo.Errors = append(finfo.Errors, lneto.ErrBadCRC)
}
dst = append(dst, finfo)
proto := ifrm4.Protocol()
end := bitOffset + octet*ifrm4.HeaderLength()
var protoErrs []error
var crc lneto.CRC791
payload := ifrm4.Payload()
switch proto {
case lneto.IPProtoTCP:
ifrm4.CRCWriteTCPPseudo(&crc)
tfrm, err := tcp.NewFrame(ifrm4.Payload())
tfrm, err := tcp.NewFrame(payload)
if err == nil {
tfrm.ValidateSize(pc.validator())
if pc.vld.HasError() {
println("BAD TCP")
return dst, pc.vld.ErrPop()
}
tfrm.CRCWrite(&crc)
wantSum := crc.Sum16()
gotSum := tfrm.CRC()
if wantSum != gotSum {
protoErrs = append(protoErrs, &crcError16{protocol: "ipv4+tcp", want: wantSum, got: gotSum})
ifrm4.CRCWriteTCPPseudo(&crc)
if crc.PayloadSum16(payload) != 0 {
protoErrs = append(protoErrs, lneto.ErrBadCRC)
}
}
case lneto.IPProtoUDP:
ifrm4.CRCWriteUDPPseudo(&crc)
ufrm, err := udp.NewFrame(ifrm4.Payload())
ufrm, err := udp.NewFrame(payload)
if err == nil {
ufrm.ValidateSize(pc.validator())
if pc.vld.HasError() {
println("BAD UDP")
return dst, pc.vld.ErrPop()
}
ufrm.CRCWriteIPv4(&crc)
wantSum := crc.Sum16()
gotSum := ufrm.CRC()
if wantSum != gotSum {
protoErrs = append(protoErrs, &crcError16{protocol: "ipv4+udp", want: wantSum, got: gotSum})
frameLen := ufrm.Length()
ifrm4.CRCWriteUDPPseudo(&crc, frameLen)
if crc.PayloadSum16(ufrm.RawData()[:frameLen]) != 0 {
protoErrs = append(protoErrs, lneto.ErrBadCRC)
}
}
case lneto.IPProtoICMP:
ifrm, err := icmpv4.NewFrame(ifrm4.Payload())
_, err := icmpv4.NewFrame(payload)
if err == nil {
ifrm.CRCWrite(&crc)
wantSum := crc.Sum16()
gotSum := ifrm.CRC()
if wantSum != gotSum {
protoErrs = append(protoErrs, &crcError16{protocol: "icmpv4", want: wantSum, got: gotSum})
if crc.PayloadSum16(payload) != 0 {
protoErrs = append(protoErrs, lneto.ErrBadCRC)
}
}
}
@@ -1309,13 +1299,3 @@ func remainingFrameInfo(proto any, class FieldClass, pktBitOffset, pktBitLen int
}},
}
}
type crcError16 struct {
protocol string
want uint16
got uint16
}
func (cerr *crcError16) Error() string {
return fmt.Sprintf("%s:incorrect checksum. want 0x%x, got 0x%x", cerr.protocol, cerr.want, cerr.got)
}
internet/pcap/capture_test.go
+1
View File
@@ -447,6 +447,7 @@ func ExampleFormatter_dhcp() {
totalLen := ipv4Size + udpSize + dhcpLen
ifrm.SetTotalLength(uint16(totalLen))
ufrm.SetLength(uint16(udpSize + dhcpLen))
// The CRC field is already zero here.
ifrm.SetCRC(ifrm.CalculateHeaderCRC())
pkt = pkt[:ethSize+totalLen]