Add basicList support

[ogasser]

Add support for basicList.

Results can be displayed using ipfixcat. Example:

{"name":"basicList","field":291,"value":"(semantic=4,fieldID=190,fieldLen=2)[60,52,367,52]"}

See RFC 6313 for more info on basicList.

[calmh]

Hi! Thanks!

At first glance I don't think this should interpret into a string. I would expect the interpretation to return a slice of the relevant data type?

[ogasser]

If we are using a "pure" slice we would lose information such as the list semantic. This could be captured in a struct. What do you think @calmh ?

[calmh]

I don't know. How are these things used?

[ogasser]

You can use basicList to encode multiple values of an IE for a single one flow. An example would be to export the length of each packet within a flow. The following example flow

{"name":"basicList","field":291,"value":"(semantic=4,fieldID=190,fieldLen=2)[60,52,367,52]"}

contains four packets, the first has size 60 bytes, second has size 52 bytes, then 367B, and finally 52B.

The semantic specifies the relation of the list elements, e.g. semantic=4 means ordered, i.e. the first list element corresponds to the first packet in the flow.

[calmh]

Given that we’ve managed to stick to just returning basic types for the other things being interpreted, and that I expect the receiving side will already have to know things like whether the list is ordered or not in order to use it, I think returning an []interface{} is the right thing here. If the type of fields can’t vary within the same list, having the slice be of the element type to begin with would be neater.

[ogasser]

basicList types now return []interface{} and support PEN.