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mirror of https://github.com/wader/fq.git synced 2024-12-23 05:13:30 +03:00
fq/format/inet/sll2_packet.go
Mattias Wadman 9b81d4d3ab decode: More type safe API and split scalar into multiple types
Preparation to make decoder use less memory and API more type safe.
Now each scalar type has it's own struct type so it can store different
things and enables to have a scalar interface.
Also own types will enable experimenting with decode DLS designs like
using chained methods that are type aware.
2022-12-14 16:23:58 +01:00

67 lines
1.8 KiB
Go

package inet
// SLL stands for sockaddr_ll
// https://www.tcpdump.org/linktypes/LINKTYPE_LINUX_SLL2.html
import (
"github.com/wader/fq/format"
"github.com/wader/fq/pkg/decode"
"github.com/wader/fq/pkg/interp"
"github.com/wader/fq/pkg/scalar"
)
var sllPacket2InetPacketGroup decode.Group
func init() {
interp.RegisterFormat(decode.Format{
Name: format.SLL2_PACKET,
Description: "Linux cooked capture encapsulation v2",
Groups: []string{format.LINK_FRAME},
Dependencies: []decode.Dependency{
{Names: []string{format.INET_PACKET}, Group: &sllPacket2InetPacketGroup},
},
DecodeFn: decodeSLL2,
})
}
func decodeSLL2(d *decode.D, in any) any {
if lfi, ok := in.(format.LinkFrameIn); ok {
if lfi.Type != format.LinkTypeLINUX_SLL2 {
d.Fatalf("wrong link type %d", lfi.Type)
}
}
protcolType := d.FieldU16("protocol_type", format.EtherTypeMap, scalar.UintHex)
d.FieldU16("reserved")
d.FieldU32("interface_index")
arpHdrType := d.FieldU16("arphdr_type", arpHdrTypeMAp)
d.FieldU8("packet_type", sllPacketTypeMap)
addressLength := d.FieldU8("link_address_length", d.UintValidateRange(0, 8))
// "If there are more than 8 bytes, only the first 8 bytes are present"
if addressLength > 8 {
addressLength = 8
}
// TODO: maybe skip padding and always read 8 bytes?
d.FieldU("link_address", int(addressLength)*8)
addressDiff := 8 - addressLength
if addressDiff > 0 {
d.FieldRawLen("padding", int64(addressDiff)*8)
}
// TODO: handle other arphdr types
switch arpHdrType {
case arpHdrTypeLoopback, arpHdrTypeEther:
_ = d.FieldMustGet("link_address").TryUintScalarFn(mapUToEtherSym, scalar.UintHex)
d.FieldFormatOrRawLen(
"payload",
d.BitsLeft(),
sllPacket2InetPacketGroup,
format.LinkFrameIn{Type: int(protcolType)},
)
default:
d.FieldRawLen("payload", d.BitsLeft())
}
return nil
}