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https://github.com/wader/fq.git
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9b81d4d3ab
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.
67 lines
1.8 KiB
Go
67 lines
1.8 KiB
Go
package inet
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// SLL stands for sockaddr_ll
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// https://www.tcpdump.org/linktypes/LINKTYPE_LINUX_SLL2.html
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import (
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"github.com/wader/fq/format"
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"github.com/wader/fq/pkg/decode"
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"github.com/wader/fq/pkg/interp"
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"github.com/wader/fq/pkg/scalar"
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)
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var sllPacket2InetPacketGroup decode.Group
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func init() {
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interp.RegisterFormat(decode.Format{
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Name: format.SLL2_PACKET,
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Description: "Linux cooked capture encapsulation v2",
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Groups: []string{format.LINK_FRAME},
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Dependencies: []decode.Dependency{
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{Names: []string{format.INET_PACKET}, Group: &sllPacket2InetPacketGroup},
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},
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DecodeFn: decodeSLL2,
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})
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}
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func decodeSLL2(d *decode.D, in any) any {
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if lfi, ok := in.(format.LinkFrameIn); ok {
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if lfi.Type != format.LinkTypeLINUX_SLL2 {
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d.Fatalf("wrong link type %d", lfi.Type)
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}
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}
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protcolType := d.FieldU16("protocol_type", format.EtherTypeMap, scalar.UintHex)
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d.FieldU16("reserved")
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d.FieldU32("interface_index")
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arpHdrType := d.FieldU16("arphdr_type", arpHdrTypeMAp)
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d.FieldU8("packet_type", sllPacketTypeMap)
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addressLength := d.FieldU8("link_address_length", d.UintValidateRange(0, 8))
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// "If there are more than 8 bytes, only the first 8 bytes are present"
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if addressLength > 8 {
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addressLength = 8
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}
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// TODO: maybe skip padding and always read 8 bytes?
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d.FieldU("link_address", int(addressLength)*8)
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addressDiff := 8 - addressLength
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if addressDiff > 0 {
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d.FieldRawLen("padding", int64(addressDiff)*8)
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}
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// TODO: handle other arphdr types
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switch arpHdrType {
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case arpHdrTypeLoopback, arpHdrTypeEther:
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_ = d.FieldMustGet("link_address").TryUintScalarFn(mapUToEtherSym, scalar.UintHex)
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d.FieldFormatOrRawLen(
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"payload",
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d.BitsLeft(),
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sllPacket2InetPacketGroup,
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format.LinkFrameIn{Type: int(protcolType)},
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)
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default:
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d.FieldRawLen("payload", d.BitsLeft())
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}
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return nil
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}
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