Assumed value implies length

[mgenereu]

I wrote some test code to learn bindata and I got an error I wasn't expecting.
I had assumed, as the documentation had implied for value (and therefore implied for asserted_value), that the identity string was a fixed length constant of three letters for the purposes of reading, writing, and asserting. Writing went great but reading resulted in a length of zero. I know adding the "read_length" attirbute will fix the issue but it took a trace of the code to figure that out. Doesn't seem intuitive. I would be happy to write a patch if you agree that this is not the expected behavior. Thank you for your review. Here's the code:

require 'bindata'

class TestFormat < BinData::Record
  endian :big
  string :identity, :asserted_value => "xyz"
  uint8 :version, :initial_value => 1
end

test1 = TestFormat.new
test1.version = 65
File.open 'test.bin', 'wb' do |file|
  test1.write( file )
end

test2 = TestFormat.new
File.open 'test.bin', 'rb' do |file|
  test2.read( file )
end

puts test2

[dmendel]

Thanks for the report.

The length should be explicit so the format is understandable when reading the code. If an :asserted_value contains multibyte characters then the length can not be inferred by a casual reader.

A runtime warning if :length is missing would be appropriate. I'll add one in the next release.

[mgenereu]

I can't think of a scenario where a static zero is ever an okay length to file read on a fixed string. Setting a runtime warning for :length would be great. I can code if you like. Thank you!

[dmendel]

Note the length should be specified with :read_length not :length. I realised the mistake while reviewing the code this morning. The code is updated in the repository.