How to validate a binary field using Ruby on Rails?

Question

I want to ensure that a binary field has always value. I added a validation code like below.

class Foo < ActiveRecord::Base
  validates :b, presence: true
end

However, the change seems to cause the error.

$ rails c
> Foo.create(b:File.read('b.jpg'))

ArgumentError: invalid byte sequence in UTF-8

The error doesn't always appear. Only when the binary data has non-ascii codes.

How can I validate the binary field?

I made the environment like below. A image file(b.jpg, less than 16KB) is also needed.

$ rails --version
Rails 4.2.0
$ rails new test_binary --database=mysql
$ cd test_binary/
$ rails g model foo b:binary
$ rake db:create db:migrate

mu is too short · Accepted Answer · 2019-03-18 02:26:23Z

2

File.read returns a String that will claim to have UTF-8 encoding by default. That means that this:

Foo.create(b: File.read('b.jpg'))

is really:

some_utf8_string = File.read('b.jpg')
Foo.create(b: some_utf8_string)

But a JPEG will rarely be a valid UTF-8 string so you're going to get that ArgumentError whenever someone tries to treat it as UTF-8.

You can specify an encoding when you read your JPEG:

Foo.create(b: File.read('b.jpeg', encoding: 'binary'))

That should get past your encoding problem.

answered Apr 29, 2015 at 0:13

mu is too short

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