How do I start reading at an offset in binary data?

Question

I have a C-like struct like this:

SomeStruct << BinData::Record
endian :little

uint32 :offsetOfName
uint32 :offsetOfLastname
#...
uint32 :lenVars
struct :Person, :length => :lenVars
    string :name
    string :lname
    #...
end

I have a bunch of offsets and lengths before :Person. All the offsets and lengths describe the data within the :Person struct.

How can I start reading data at a specified offset, for the given length, or until the next offset?

Answer 1

Seek to offset 1234 and then read 32 bytes into String s:

open 'some-binary-file', 'r' do |f|
  f.seek 1234
  s = f.read 32
  # tho in your case, something like:
  o = aBinData_object.read f
  p s
end

Update: It looks like BinData understands records that encode the lengths of their own fields, but I doubt if there is any way to make it seek for you, unless you are willing to essentially encode dummy fields the size of the seeked-over space, and then ignore forever the data that it's skipping.

I suspect that a good solution will involve an explicit seek and then someBinDataObject.read(f) to get the record.