/*Unshim removes the shim layer from an IPv4 packet, if it's present.*/
func Unshim(ipLayer *layers.IPv4) *RouteRecord {
if Shimmed(ipLayer) {
/*Remove the route record from the payload*/
ipPayload := bytes.NewBuffer(ipLayer.LayerPayload())
var rr RouteRecord
rr.ReadFrom(ipPayload)
ipLayer.Length -= uint16(rr.Len())
ipLayer.Protocol = layers.IPProtocol(rr.Protocol)
ipLayer.Checksum = 0
ipLayer.Payload = ipPayload.Bytes()
return &rr
}
return nil
}
/*Shim inserts the given router into the shim layer route record of the given
IPv4 packet, creating a new route record if it's not already present.*/
func Shim(ipLayer *layers.IPv4, r Router) {
ipPayload := bytes.NewBuffer(ipLayer.LayerPayload())
var modifiedIPPayload bytes.Buffer
var rr RouteRecord
if Shimmed(ipLayer) {
rr.ReadFrom(ipPayload)
ipLayer.Length -= uint16(rr.Len())
} else {
rr.Protocol = uint8(ipLayer.Protocol)
}
/*Add the specified router to the route record and put the record at the
beginning of the payload.*/
rr.AddRouter(r)
rr.WriteTo(&modifiedIPPayload)
ipPayload.WriteTo(&modifiedIPPayload)
ipLayer.Length += uint16(rr.Len())
ipLayer.Protocol = layers.IPProtocol(IPProtocolAITFRouteRecord)
ipLayer.Checksum = 0
ipLayer.Payload = modifiedIPPayload.Bytes()
}