Comments (3)
I banged away at my keyboard and eventually ended up with this:
module BinData
class Base
def real_abs_offset
if @params[:adjust_offset].nil?
parent.real_abs_offset + parent.offset_of(self)
else
@lazy.lazy_eval @params[:adjust_offset]
end
end
end
end
I can't really explain how/why it works (and I feel like a monkey at a typewriter) or it's terribly wrong, but it's allowed me to continue on with my current task. I thought it would be worth posting here to see your thoughts on it.
from bindata.
:adjust_offset
is an experimental feature (which is why it is undocumented see #52). I'm still working out how to achieve seeking fuctionality in a structured way. :adjust_offset
, as it currently stands, is analogous to using goto to achieve looping.
:adjust_offset
will eventually be replaced with a better solution. Your above monkey patch looks like a good fix to your problem.
Do be aware that :adjust_offset
is only in effect when reading. It will not automatically do any seeking when writing.
from bindata.
BinData::Skip
now has the :to_abs_offset
option. This is the official way to perform seeking in a stream. Skip
will ensure that #abs_offset
is calculated correctly.
:adjust_offset
remains for backwards compatibility.
Your example can be written as:
class KeychainFile < BinData::Record
endian :big
string :magic, length: 4, asserted_value: 'kych'
string :padding, read_length: 8
uint32 :schema_offset # in this example, the value is 20
skip to_abs_offset: lambda { schema_offset + 4 }
uint32 :table_count
end
from bindata.
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from bindata.