doing first steps in kaitai struct, i've been trying bson parser excercise. .ksy code parses bson element looks that:
element: seq: - id: el_type type: u1 enum: bson_type - id: el_name type: strz encoding: utf-8 if: el_type != bson_type::end_of_document - id: el_string type: bson_string if: el_type == bson_type::string - id: el_document type: bson_document if: el_type == bson_type::document - id: el_boolean type: u1 if: el_type == bson_type::boolean - id: el_int32 type: s4 if: el_type == bson_type::int32 - id: el_int64 type: s4 if: el_type == bson_type::int64 enums: bson_type: 0: end_of_document 1: double 2: string 3: document 8: boolean 0x10: int32 0x12: int64 as might have noticed, there's lots of repetition. 1 have go duplicate if block every time 1 wants additional element type. worse, have duplicate stuff 3 times in every such field, i.e.:
- id: el_string # <= string! type: bson_string # <= string! if: el_type == bson_type::string # <= string! my target language java. before kaitai, i've tried preon, , there had clauses such as:
@choices(prefixsize = 8, alternatives = { @choice(condition = "prefix==0x01", type = floatnamedelement.class), @choice(condition = "prefix==0x02", type = utf8namedelement.class) } private namedelement elements; there automatically these 2 elements based on value of "prefix". possible in kaitai?
well, you're right, , feature requested 3 or 4 times ;) i've filed issue that.
i can't agree on preon's implementation, though, seems limited me. can have single "prefix", integer, , must preceed point of choice.
i want implement little more generic switch style statement, that:
- id: value switch: code cases: string: type: bson_string document: type: bson_document boolean: type: u1 int32: type: s4 int64: type: s8 what think of that?
note chances won't "proper" oop object hierarchy, though, you're getting preon. because preon's classes made hand , can common superclass , inherit both floatnamedelement , utf8namedelement it, can't think of method in current ks model now.
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