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Tagged attributes are a horrible hack that breaks all kinds of things and makes the internal API more complex. e.g. TAG_ANY. The solution appears to be to use re-use groups.

We would create 32 attributes, Tag-0 though Tag-31. These attributes would be of type group, as with Diameter.

The tagged attributes would then be put into the appropriate group by the parser. e.g.

Tunnel-Type:1 := 3

would end up as

Tag-1 {
   Tunnel-Type := 3

We could also leverage named-subattrs, and do:

Tag-1.Tunnel-Type := 3

The encoder could then see that these attributes were of type tag, (or group, with a tag option), and then call a special encoding routine.

The TLV stack used by the RADIUS encoder would remain the same, as it enforces DA / TLV parentage. Using groups would break this, as the VP parentage would be different from the DA / TLV parentage.

The solution to that problem is for the tag encoder to just create it's own TLV stack, and call the normal encoder. Since tagged attributes can only be of type string or integer, the TLV stack will only ever be one entry deep.

The encoder can write the tag, and then call the encode_value() function to do the actual encoding. Or, just do it itself, as it's all pretty simple.