lua dissector from XML file

You may want to have a look at this project. It is not fed by xml directly but you may use a script to convert your xml descriptions into the syntax required by this project.

Other approach would be to somewhat duplicate that project by using Lua to read your xml description of the protocol and create protocol fields at startup, but I am not really sure you can read from a file during the initialisation phase. In Lua, you can use constructs like

all_my_fields = {} local n=0

and then, for each protocol field description extracted from XML:

all_my_fields[n] = ProtoField.uint8(field_abbr_from_XML,field_name_from_XML,base.HEX, all_my_field_values_table_from_XML[n],field_bit_mask_from_XML) n=n+1

choosing the right ProtoField type (uint8 in this case) and base (base.HEX in this case) which I suspect must be literals, and then probably (I've never tested it so a different syntax may be necessary) you can use

my_proto.fields = all_my_fields

The tables for translation of numeric values to text strings must be complete before you use them to create a ProtoField as for some reason they are copied, not referred to.