Length of uploaded file in Ruby on Rails decreases after UploadedFile.read - ruby-on-rails

Question

On a RoR app that i've inherited, a test is failing that involves a file upload. The assertion that fails looks like so:
assert_equal File.size("#{RAILS_ROOT}/test/fixtures/#{filename}"), #candidate.picture.length
It fails with (the test file is 69 bytes):
<69> expected but was <5>.
This is after a post using:
fixture_file_upload(filename, content_type, :binary)
In the candidate model, the uploaded file is assigned to a property that is then saved to a mediumblob in MySQL. It looks to me like the uploaded file is 69 bytes, but after it is assigned to the model property (using UploadedFile.read), the length is showing as only 5 bytes.
So this code:
puts "file.length=" + file.length.to_s
self.picture = file.read
puts "self.picture.length=" + self.picture.length.to_s
results in this output:
file.length=69
self.picture.length=5
I'm at a bit of a loss as to why this is, any ideas?

Answer 1

This came down to a Windows/Ruby idiosyncrasy, where reading the file appeared to be happening in text mode. There is an extension in this app in test_helper, something like:
class ActionController::TestUploadedFile
# Akward but neccessary for testing since an ActionController::UploadedFile subtype is expected
include ActionController::UploadedFile
def read
tempfile = File.new(self.path)
tempfile.read
end
end
And apparently, on Windows, there is a specific IO method that can be called to force the file into binary mode. Calling this method on the tempfile, like so:
tempfile.binmode
caused everything to work as expected, with the read from the UploadedFile matching the size of the fixture file on disk.