ActiveStorage Validator

A Rails gem that makes it easy to add validations such as content_type and file size to ActiveStorage attachments.

• Supports both has_one_attached and has_many_attached of ActiveStorage
• Flexible validations for content type and file size

Installation

Using Bundler

Add this line to your application's Gemfile:

gem 'activestorage-validator'

Then execute:

$ bundle install

Install with gem command

$ gem install activestorage-validator

Usage

You can add validations to models with ActiveStorage attachments using the blob validator.

class User < ApplicationRecord
  has_one_attached :avatar
  has_many_attached :photos

  # Allow only web image files
  validates :avatar, presence: true, blob: { content_type: :web_image }

  # Allow only JPEG/PNG, up to 5MB per file
  validates :photos, presence: true, blob: { content_type: ["image/png", "image/jpg", "image/jpeg"], size_range: 1..(5.megabytes) }

  # You can also use a regular expression for content_type
  # validates :photos, blob: { content_type: %r{^image/}, size_range: 1..(5.megabytes) }

  # Require the filename to have one of the allowed extensions
  # validates :audio, blob: { content_type: "audio/mpeg", extension: %w[mp3] }
end

Note: For has_many_attached, the size validation is applied to each file individually.

Validation Options

Option	Description
content_type	Allowed MIME types. Accepts a symbol (:web_image, :image, :audio, :video, :text), an array of MIME types, a regular expression, or a string (single MIME type).
size_range	Allowed file size range (e.g. 1..5.megabytes)
extension	Allowed file extensions. Accepts a String or an Array of Strings. Case-insensitive, leading dot optional. Files without an extension are rejected.

content_type Examples

• Symbol
  • :web_image ... PNG, JPEG, GIF, WebP (special handling)
  • :image, :audio, :video, :text ... Calls blob.image?, blob.audio?, etc. (ActiveStorage built-in predicate)
• Array
  • ["image/png", "image/jpg", "image/jpeg"] ... Only allow these MIME types
• Regexp
  • %r{^image/} ... Allow any image type (MIME type starts with image/)
• String
  • "application/pdf" ... Only allow PDF files

extension Examples

• String
  • extension: "mp3" ... Only allow .mp3 files
• Array
  • extension: %w[mp3 m4a] ... Allow either .mp3 or .m4a
• Combined with content_type (AND)
  • blob: { content_type: "audio/mpeg", extension: %w[mp3] } ... Reject both my_podcast (no extension) and my_podcast.wav (wrong extension), even when their MIME types match.

The leading dot is optional ("mp3" and ".mp3" behave the same), and matching is case-insensitive (PHOTO.JPG matches extension: "jpg").

I18n Error Message Options

Validation error messages are I18n compatible. The following interpolation keys are available in your translation files, according to the validator's implementation:

Key	Description
filename	The uploaded file's name
min_size	The minimum allowed file size (humanized)
max_size	The maximum allowed file size (humanized)
extension	The list of allowed extensions, joined by ,

The following error types are used:

• content_type (invalid content type)
• min_size_error (file is too small)
• max_size_error (file is too large)
• extension (invalid file extension)

Example (config/locales/en.yml):

en:
  errors:
    messages:
      content_type: "%{filename} has an invalid content type"
      min_size_error: "%{filename} is too small (minimum is %{min_size})"
      max_size_error: "%{filename} is too large (maximum is %{max_size})"
      extension: "%{filename} has an invalid file extension (allowed: %{extension})"

Notes

• Some features may not work depending on your ActiveStorage or Rails version.
• Validation error messages are I18n compatible and support interpolation keys as described above.

Contributing

Bug reports and pull requests are welcome on GitHub via issues or pull requests.

This project adheres to the Contributor Covenant code of conduct.

License

This gem is released under the MIT License. See LICENSE.txt for details.