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https://github.com/thoughtbot/paperclip

Easy file attachment management for ActiveRecord
https://github.com/thoughtbot/paperclip

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Easy file attachment management for ActiveRecord

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README 

        
Paperclip

=========



# Deprecated



**[Paperclip is deprecated]**.



For new projects, we recommend Rails' own [ActiveStorage].



For existing projects, please consult and contribute to the migration guide,

available [in English], [en español], and as [a video] recorded at RailsConf

2019. You may also prefer [an alternative migration tutorial used by

Doorkeeper][].



Alternatively, for existing projects, [Kreeti] is maintaining [kt-paperclip],

an ongoing [fork of Paperclip].



We will leave the Issues open as a discussion forum _only_. We do _not_

guarantee a response from us in the Issues. All bug reports should go to

kt-paperclip.



We are no longer accepting pull requests _except_ pull requests against the

migration guide. All other pull requests will be closed without merging.



[Paperclip is deprecated]: https://robots.thoughtbot.com/closing-the-trombone

[ActiveStorage]: http://guides.rubyonrails.org/active_storage_overview.html

[in English]: https://github.com/thoughtbot/paperclip/blob/master/MIGRATING.md

[en español]: https://github.com/thoughtbot/paperclip/blob/master/MIGRATING-ES.md

[a video]: https://www.youtube.com/watch?v=tZ_WNUytO9o

[Kreeti]: https://www.kreeti.com/

[kt-paperclip]: https://rubygems.org/gems/kt-paperclip

[fork of Paperclip]: https://github.com/kreeti/kt-paperclip

[an alternative migration tutorial used by Doorkeeper]: https://www.tokyodev.com/2021/03/23/paperclip-activestorage/



# Existing documentation



## Documentation valid for `master` branch



Please check the documentation for the paperclip version you are using:

https://github.com/thoughtbot/paperclip/releases



---



[![Build Status](https://secure.travis-ci.org/thoughtbot/paperclip.svg?branch=master)](http://travis-ci.org/thoughtbot/paperclip)

[![Dependency Status](https://gemnasium.com/thoughtbot/paperclip.svg?travis)](https://gemnasium.com/thoughtbot/paperclip)

[![Code Climate](https://codeclimate.com/github/thoughtbot/paperclip.svg)](https://codeclimate.com/github/thoughtbot/paperclip)

[![Inline docs](http://inch-ci.org/github/thoughtbot/paperclip.svg)](http://inch-ci.org/github/thoughtbot/paperclip)

[![Security](https://hakiri.io/github/thoughtbot/paperclip/master.svg)](https://hakiri.io/github/thoughtbot/paperclip/master)



- [Requirements](#requirements)

  - [Ruby and Rails](#ruby-and-rails)

  - [Image Processor](#image-processor)

  - [`file`](#file)

- [Installation](#installation)

- [Quick Start](#quick-start)

  - [Models](#models)

  - [Migrations](#migrations)

  - [Edit and New Views](#edit-and-new-views)

  - [Edit and New Views with Simple Form](#edit-and-new-views-with-simple-form)

  - [Controller](#controller)

  - [View Helpers](#view-helpers)

  - [Checking a File Exists](#checking-a-file-exists)

  - [Deleting an Attachment](#deleting-an-attachment)

- [Usage](#usage)

- [Validations](#validations)

- [Internationalization (I18n)](#internationalization-i18n)

- [Security Validations](#security-validations)

- [Defaults](#defaults)

- [Migrations](#migrations-1)

  - [Add Attachment Column To A Table](#add-attachment-column-to-a-table)

  - [Schema Definition](#schema-definition)

  - [Vintage Syntax](#vintage-syntax)

- [Storage](#storage)

  - [Understanding Storage](#understanding-storage)

- [IO Adapters](#io-adapters)

- [Post Processing](#post-processing)

- [Custom Attachment Processors](#custom-attachment-processors)

- [Events](#events)

- [URI Obfuscation](#uri-obfuscation)

- [Checksum / Fingerprint](#checksum--fingerprint)

- [File Preservation for Soft-Delete](#file-preservation-for-soft-delete)

- [Dynamic Configuration](#dynamic-configuration)

  - [Dynamic Styles:](#dynamic-styles)

  - [Dynamic Processors:](#dynamic-processors)

- [Logging](#logging)

- [Deployment](#deployment)

  - [Attachment Styles](#attachment-styles)

- [Testing](#testing)

- [Contributing](#contributing)

- [License](#license)

- [About thoughtbot](#about-thoughtbot)



Paperclip is intended as an easy file attachment library for ActiveRecord. The

intent behind it was to keep setup as easy as possible and to treat files as

much like other attributes as possible. This means they aren't saved to their

final locations on disk, nor are they deleted if set to nil, until

ActiveRecord::Base#save is called. It manages validations based on size and

presence, if required. It can transform its assigned image into thumbnails if

needed, and the prerequisites are as simple as installing ImageMagick (which,

for most modern Unix-based systems, is as easy as installing the right

packages). Attached files are saved to the filesystem and referenced in the

browser by an easily understandable specification, which has sensible and

useful defaults.



See the documentation for `has_attached_file` in [`Paperclip::ClassMethods`](http://www.rubydoc.info/gems/paperclip/Paperclip/ClassMethods) for

more detailed options.



The complete [RDoc](http://www.rubydoc.info/gems/paperclip) is online.



---



Requirements

------------



### Ruby and Rails



Paperclip now requires Ruby version **>= 2.1** and Rails version **>= 4.2**

(only if you're going to use Paperclip with Ruby on Rails).



### Image Processor



[ImageMagick](http://www.imagemagick.org) must be installed and Paperclip must have access to it. To ensure

that it does, on your command line, run `which convert` (one of the ImageMagick

utilities). This will give you the path where that utility is installed. For

example, it might return `/usr/local/bin/convert`.



Then, in your environment config file, let Paperclip know to look there by adding that

directory to its path.



In development mode, you might add this line to `config/environments/development.rb)`:



```ruby

Paperclip.options[:command_path] = "/usr/local/bin/"

```



If you're on Mac OS X, you'll want to run the following with [Homebrew](http://www.brew.sh):



    brew install imagemagick



If you are dealing with pdf uploads or running the test suite, you'll also need

to install GhostScript. On Mac OS X, you can also install that using Homebrew:



    brew install gs



If you are on Ubuntu (or any Debian base Linux distribution), you'll want to run

the following with apt-get:



    sudo apt-get install imagemagick -y



### `file`



The Unix [`file` command](https://en.wikipedia.org/wiki/File_(command)) is required for content-type checking.

This utility isn't available in Windows, but comes bundled with Ruby [Devkit](https://github.com/oneclick/rubyinstaller/wiki/Development-Kit),

so Windows users must make sure that the devkit is installed and added to the system `PATH`.



**Manual Installation**



If you're using Windows 7+ as a development environment, you may need to install the `file.exe` application manually. The `file spoofing` system in Paperclip 4+ relies on this; if you don't have it working, you'll receive `Validation failed: Upload file has an extension that does not match its contents.` errors.



To manually install, you should perform the following:



> **Download & install `file` from [this URL](http://gnuwin32.sourceforge.net/packages/file.htm)**



To test, you can use the image below:

![untitled](https://cloud.githubusercontent.com/assets/1104431/4524452/a1f8cce4-4d44-11e4-872e-17adb96f79c9.png)



Next, you need to integrate with your environment - preferably through the `PATH` variable, or by changing your `config/environments/development.rb` file



**PATH**



    1. Click "Start"

    2. On "Computer", right-click and select "Properties"

    3. In Properties, select "Advanced System Settings"

    4. Click the "Environment Variables" button

    5. Locate the "PATH" var - at the end, add the path to your newly installed `file.exe` (typically `C:\Program Files (x86)\GnuWin32\bin`)

    6. Restart any CMD shells you have open & see if it works



OR



**Environment**



    1. Open `config/environments/development.rb`

    2. Add the following line: `Paperclip.options[:command_path] = 'C:\Program Files (x86)\GnuWin32\bin'`

    3. Restart your Rails server



Either of these methods will give your Rails setup access to the `file.exe` functionality, thus providing the ability to check the contents of a file (fixing the spoofing problem)



---



Installation

------------



Paperclip is distributed as a gem, which is how it should be used in your app.



Include the gem in your Gemfile:



```ruby

gem "paperclip", "~> 6.0.0"

```



Or, if you want to get the latest, you can get master from the main paperclip repository:



```ruby

gem "paperclip", git: "git://github.com/thoughtbot/paperclip.git"

```



If you're trying to use features that don't seem to be in the latest released gem, but are

mentioned in this README, then you probably need to specify the master branch if you want to

use them. This README is probably ahead of the latest released version if you're reading it

on GitHub.



For Non-Rails usage:



```ruby

class ModuleName < ActiveRecord::Base

  include Paperclip::Glue

  ...

end

```



---



Quick Start

-----------



### Models



```ruby

class User < ActiveRecord::Base

  has_attached_file :avatar, styles: { medium: "300x300>", thumb: "100x100>" }, default_url: "/images/:style/missing.png"

  validates_attachment_content_type :avatar, content_type: /\Aimage\/.*\z/

end

```



### Migrations



Assuming you have a `users` table, add an `avatar` column to the `users` table:

```ruby

class AddAvatarColumnsToUsers < ActiveRecord::Migration

  def up

    add_attachment :users, :avatar

  end



  def down

    remove_attachment :users, :avatar

  end

end

```



(Or you can use the Rails migration generator: `rails generate paperclip user avatar`)



### Edit and New Views

Make sure you have corresponding methods in your controller:

```erb

<%= form_for @user, url: users_path, html: { multipart: true } do |form| %>

  <%= form.file_field :avatar %>

  <%= form.submit %>

<% end %>

```



### Edit and New Views with [Simple Form](https://github.com/plataformatec/simple_form)



```erb

<%= simple_form_for @user, url: users_path do |form| %>

  <%= form.input :avatar, as: :file %>

  <%= form.submit %>

<% end %>

```



### Controller



```ruby

def create

  @user = User.create(user_params)

end



private



# Use strong_parameters for attribute whitelisting

# Be sure to update your create() and update() controller methods.



def user_params

  params.require(:user).permit(:avatar)

end

```



### View Helpers

Add these to the view where you want your images displayed:

```erb

<%= image_tag @user.avatar.url %>

<%= image_tag @user.avatar.url(:medium) %>

<%= image_tag @user.avatar.url(:thumb) %>

```



### Checking a File Exists



There are two methods for checking if a file exists:



- `file?` and `present?` checks if the `_file_name` field is populated

- `exists?` checks if the file exists (will perform a TCP connection if stored in the cloud)



Keep this in mind if you are checking if files are present in a loop. The first

version is significantly more performant, but has different semantics.



### Deleting an Attachment



Set the attribute to `nil` and save.



```ruby

@user.avatar = nil

@user.save

```

---



Usage

-----



The basics of Paperclip are quite simple: Declare that your model has an

attachment with the `has_attached_file` method, and give it a name.



Paperclip will wrap up to four attributes (all prefixed with that attachment's name,

so you can have multiple attachments per model if you wish) and give them a

friendly front end. These attributes are:



* `_file_name`

* `_file_size`

* `_content_type`

* `_updated_at`



By default, only `_file_name` is required for Paperclip to operate.

You'll need to add `_content_type` in case you want to use content type

validation.



More information about the options passed to `has_attached_file` is available in the

documentation of [`Paperclip::ClassMethods`](http://www.rubydoc.info/gems/paperclip/Paperclip/ClassMethods).



Validations

-----------



For validations, Paperclip introduces several validators to validate your attachment:



* `AttachmentContentTypeValidator`

* `AttachmentPresenceValidator`

* `AttachmentSizeValidator`



Example Usage:



```ruby

validates :avatar, attachment_presence: true

validates_with AttachmentPresenceValidator, attributes: :avatar

validates_with AttachmentSizeValidator, attributes: :avatar, less_than: 1.megabytes



```



Validators can also be defined using the old helper style:



* `validates_attachment_presence`

* `validates_attachment_content_type`

* `validates_attachment_size`



Example Usage:



```ruby

validates_attachment_presence :avatar

```



Lastly, you can also define multiple validations on a single attachment using `validates_attachment`:



```ruby

validates_attachment :avatar, presence: true,

  content_type: "image/jpeg",

  size: { in: 0..10.kilobytes }

```



_NOTE: Post-processing will not even **start** if the attachment is not valid

according to the validations. Your callbacks and processors will **only** be

called with valid attachments._



```ruby

class Message < ActiveRecord::Base

  has_attached_file :asset, styles: { thumb: "100x100#" }



  before_post_process :skip_for_audio



  def skip_for_audio

    ! %w(audio/ogg application/ogg).include?(asset_content_type)

  end

end

```



If you have other validations that depend on assignment order, the recommended

course of action is to prevent the assignment of the attachment until

afterwards, then assign manually:



```ruby

class Book < ActiveRecord::Base

  has_attached_file :document, styles: { thumbnail: "60x60#" }

  validates_attachment :document, content_type: "application/pdf"

  validates_something_else # Other validations that conflict with Paperclip's

end



class BooksController < ApplicationController

  def create

    @book = Book.new(book_params)

    @book.document = params[:book][:document]

    @book.save

    respond_with @book

  end



  private



  def book_params

    params.require(:book).permit(:title, :author)

  end

end

```



**A note on content_type validations and security**



You should ensure that you validate files to be only those MIME types you

explicitly want to support.  If you don't, you could be open to

XSS attacks

if a user uploads a file with a malicious HTML payload.



If you're only interested in images, restrict your allowed content_types to

image-y ones:



```ruby

validates_attachment :avatar,

  content_type: ["image/jpeg", "image/gif", "image/png"]

```



`Paperclip::ContentTypeDetector` will attempt to match a file's extension to an

inferred content_type, regardless of the actual contents of the file.



---



Internationalization (I18n)

---------------------------



For using or adding locale files in different languages, check the project

https://github.com/thoughtbot/paperclip-i18n.



Security Validations

====================



Thanks to a report from [Egor Homakov](http://homakov.blogspot.com/) we have

taken steps to prevent people from spoofing Content-Types and getting data

you weren't expecting onto your server.



NOTE: Starting at version 4.0.0, all attachments are *required* to include a

content_type validation, a file_name validation, or to explicitly state that

they're not going to have either. *Paperclip will raise an error* if you do not

do this.



```ruby

class ActiveRecord::Base

  has_attached_file :avatar

  # Validate content type

  validates_attachment_content_type :avatar, content_type: /\Aimage/

  # Validate filename

  validates_attachment_file_name :avatar, matches: [/png\z/, /jpe?g\z/]

  # Explicitly do not validate

  do_not_validate_attachment_file_type :avatar

end

```



This keeps Paperclip secure-by-default, and will prevent people trying to mess

with your filesystem.



NOTE: Also starting at version 4.0.0, Paperclip has another validation that

cannot be turned off. This validation will prevent content type spoofing. That

is, uploading a PHP document (for example) as part of the EXIF tags of a

well-formed JPEG. This check is limited to the media type (the first part of the

MIME type, so, 'text' in `text/plain`). This will prevent HTML documents from

being uploaded as JPEGs, but will not prevent GIFs from being uploaded with a

`.jpg` extension. This validation will only add validation errors to the form. It

will not cause errors to be raised.



This can sometimes cause false validation errors in applications that use custom

file extensions. In these cases you may wish to add your custom extension to the

list of content type mappings by creating `config/initializers/paperclip.rb`:



```ruby

# Allow ".foo" as an extension for files with the MIME type "text/plain".

Paperclip.options[:content_type_mappings] = {

  foo: %w(text/plain)

}

```



---



Defaults

--------

Global defaults for all your Paperclip attachments can be defined by changing the Paperclip::Attachment.default_options Hash. This can be useful for setting your default storage settings per example so you won't have to define them in every `has_attached_file` definition.



If you're using Rails, you can define a Hash with default options in `config/application.rb` or in any of the `config/environments/*.rb` files on config.paperclip_defaults. These will get merged into `Paperclip::Attachment.default_options` as your Rails app boots. An example:



```ruby

module YourApp

  class Application < Rails::Application

    # Other code...



    config.paperclip_defaults = { storage: :fog, fog_credentials: { provider: "Local", local_root: "#{Rails.root}/public"}, fog_directory: "", fog_host: "localhost"}

  end

end

```



Another option is to directly modify the `Paperclip::Attachment.default_options` Hash - this method works for non-Rails applications or is an option if you prefer to place the Paperclip default settings in an initializer.



An example Rails initializer would look something like this:



```ruby

Paperclip::Attachment.default_options[:storage] = :fog

Paperclip::Attachment.default_options[:fog_credentials] = { provider: "Local", local_root: "#{Rails.root}/public"}

Paperclip::Attachment.default_options[:fog_directory] = ""

Paperclip::Attachment.default_options[:fog_host] = "http://localhost:3000"

```

---



Migrations

----------



Paperclip defines several migration methods which can be used to create the necessary columns in your

model. There are two types of helper methods to aid in this, as follows:



### Add Attachment Column To A Table



The `attachment` helper can be used when creating a table:



```ruby

class CreateUsersWithAttachments < ActiveRecord::Migration

  def up

    create_table :users do |t|

      t.attachment :avatar

    end

  end



  # This is assuming you are only using the users table for Paperclip attachment. Drop with care!

  def down

    drop_table :users

  end

end

```



You can also use the `change` method, instead of the `up`/`down` combination above, as shown below:



```ruby

class CreateUsersWithAttachments < ActiveRecord::Migration

  def change

    create_table :users do |t|

      t.attachment :avatar

    end

  end

end

```



### Schema Definition



Alternatively, the `add_attachment` and `remove_attachment` methods can be used to add new Paperclip columns to an existing table:



```ruby

class AddAttachmentColumnsToUsers < ActiveRecord::Migration

  def up

    add_attachment :users, :avatar

  end



  def down

    remove_attachment :users, :avatar

  end

end

```



Or you can do this with the `change` method:



```ruby

class AddAttachmentColumnsToUsers < ActiveRecord::Migration

  def change

    add_attachment :users, :avatar

  end

end

```



### Vintage Syntax



Vintage syntax (such as `t.has_attached_file` and `drop_attached_file`) is still supported in

Paperclip 3.x, but you're advised to update those migration files to use this new syntax.



---



Storage

-------



Paperclip ships with 3 storage adapters:



* File Storage

* S3 Storage (via `aws-sdk-s3`)

* Fog Storage



If you would like to use Paperclip with another storage, you can install these

gems along side with Paperclip:



* [paperclip-azure](https://github.com/supportify/paperclip-azure)

* [paperclip-azure-storage](https://github.com/gmontard/paperclip-azure-storage)

* [paperclip-dropbox](https://github.com/janko-m/paperclip-dropbox)



### Understanding Storage



The files that are assigned as attachments are, by default, placed in the

directory specified by the `:path` option to `has_attached_file`. By default, this

location is `:rails_root/public/system/:class/:attachment/:id_partition/:style/:filename`.

This location was chosen because, on standard Capistrano deployments, the

`public/system` directory can be symlinked to the app's shared directory, meaning it

survives between deployments. For example, using that `:path`, you may have a

file at



    /data/myapp/releases/20081229172410/public/system/users/avatar/000/000/013/small/my_pic.png



_**NOTE**: This is a change from previous versions of Paperclip, but is overall a

safer choice for the default file store._



You may also choose to store your files using Amazon's S3 service. To do so, include

the `aws-sdk-s3` gem in your Gemfile:



```ruby

gem 'aws-sdk-s3'

```



And then you can specify using S3 from `has_attached_file`.

You can find more information about configuring and using S3 storage in

[the `Paperclip::Storage::S3` documentation](http://www.rubydoc.info/gems/paperclip/Paperclip/Storage/S3).



Files on the local filesystem (and in the Rails app's public directory) will be

available to the internet at large. If you require access control, it's

possible to place your files in a different location. You will need to change

both the `:path` and `:url` options in order to make sure the files are unavailable

to the public. Both `:path` and `:url` allow the same set of interpolated

variables.



---



IO Adapters

-----------



When a file is uploaded or attached, it can be in one of a few different input

forms, from Rails' UploadedFile object to a StringIO to a Tempfile or even a

simple String that is a URL that points to an image.



Paperclip will accept, by default, many of these sources. It also is capable of

handling even more with a little configuration. The IO Adapters that handle

images from non-local sources are not enabled by default. They can be enabled by

adding a line similar to the following into `config/initializers/paperclip.rb`:



```ruby

Paperclip::DataUriAdapter.register

```



It's best to only enable a remote-loading adapter if you need it. Otherwise

there's a chance that someone can gain insight into your internal network

structure using it as a vector.



The following adapters are *not* loaded by default:



* `Paperclip::UriAdapter` - which accepts a `URI` instance.

* `Paperclip::HttpUrlProxyAdapter` - which accepts a `http` string.

* `Paperclip::DataUriAdapter` - which accepts a Base64-encoded `data:` string.



---



Post Processing

---------------



Paperclip supports an extensible selection of post-processors. When you define

a set of styles for an attachment, by default it is expected that those

"styles" are actually "thumbnails." These are processed by

`Paperclip::Thumbnail`.  For backward compatibility reasons you can pass either

a single geometry string, or an array containing a geometry and a format that

the file will be converted to, like so:



```ruby

has_attached_file :avatar, styles: { thumb: ["32x32#", :png] }

```



This will convert the "thumb" style to a 32x32 square in PNG format, regardless

of what was uploaded. If the format is not specified, it is kept the same (e.g.

JPGs will remain JPGs). `Paperclip::Thumbnail` uses ImageMagick to process

images; [ImageMagick's geometry documentation](http://www.imagemagick.org/script/command-line-processing.php#geometry)

has more information on the accepted style formats.



For more fine-grained control of the conversion process, `source_file_options` and `convert_options` can be used to pass flags and settings directly to ImageMagick's powerful Convert tool, [documented here](https://www.imagemagick.org/script/convert.php). For example:



```ruby

has_attached_file :image, styles: { regular: ['800x800>', :png]}, 

    source_file_options: { regular: "-density 96 -depth 8 -quality 85" },

    convert_options: { regular: "-posterize 3"}

```



ImageMagick supports a number of environment variables for controlling its resource limits. For example, you can enforce memory or execution time limits by setting the following variables in your application's process environment:



* `MAGICK_MEMORY_LIMIT=128MiB`

* `MAGICK_MAP_LIMIT=64MiB`

* `MAGICK_TIME_LIMIT=30`



For a full list of variables and description, see [ImageMagick's resources documentation](http://www.imagemagick.org/script/resources.php).



---



Custom Attachment Processors

-------



You can write your own custom attachment processors to carry out tasks like

adding watermarks, compressing images, or encrypting files. Custom processors

must be defined within the `Paperclip` module, inherit from

`Paperclip::Processor` (see [`lib/paperclip/processor.rb`](https://github.com/thoughtbot/paperclip/blob/master/lib/paperclip/processor.rb)),

and implement a `make` method that returns a `File`. All files in your Rails

app's `lib/paperclip` and `lib/paperclip_processors` directories will be

automatically loaded by Paperclip. Processors are specified using the

`:processors` option to `has_attached_file`:



```ruby

has_attached_file :scan, styles: { text: { quality: :better } },

                         processors: [:ocr]

```



This would load the hypothetical class `Paperclip::Ocr`, and pass it the

options hash `{ quality: :better }`, along with the uploaded file.



Multiple processors can be specified, and they will be invoked in the order

they are defined in the `:processors` array. Each successive processor is given

the result from the previous processor. All processors receive the same

parameters, which are defined in the `:styles` hash.  For example, assuming we

had this definition:



```ruby

has_attached_file :scan, styles: { text: { quality: :better } },

                         processors: [:rotator, :ocr]

```



Both the `:rotator` processor and the `:ocr` processor would receive the

options `{ quality: :better }`. If a processor receives an option it doesn't

recognise, it's expected to ignore it.



_NOTE: Because processors operate by turning the original attachment into the

styles, no processors will be run if there are no styles defined._



If you're interested in caching your thumbnail's width, height and size in the

database, take a look at the [paperclip-meta](https://github.com/teeparham/paperclip-meta)

gem.



Also, if you're interested in generating the thumbnail on-the-fly, you might want

to look into the [attachment_on_the_fly](https://github.com/drpentode/Attachment-on-the-Fly)

gem.



Paperclip's thumbnail generator (see [`lib/paperclip/thumbnail.rb`](lib/paperclip/thumbnail.rb))

is implemented as a processor, and may be a good reference for writing your own

processors.



---



Events

------



Before and after the Post Processing step, Paperclip calls back to the model

with a few callbacks, allowing the model to change or cancel the processing

step. The callbacks are `before_post_process` and `after_post_process` (which

are called before and after the processing of each attachment), and the

attachment-specific `before__post_process` and

`after__post_process`. The callbacks are intended to be as close to

normal ActiveRecord callbacks as possible, so if you return false (specifically

\- returning nil is not the same) in a `before_filter`, the post processing step

will halt. Returning false in an `after_filter` will not halt anything, but you

can access the model and the attachment if necessary.



_NOTE: Post processing will not even **start** if the attachment is not valid

according to the validations. Your callbacks and processors will **only** be

called with valid attachments._



```ruby

class Message < ActiveRecord::Base

  has_attached_file :asset, styles: { thumb: "100x100#" }



  before_post_process :skip_for_audio



  def skip_for_audio

    ! %w(audio/ogg application/ogg).include?(asset_content_type)

  end

end

```



---



URI Obfuscation

---------------



Paperclip has an interpolation called `:hash` for obfuscating filenames of

publicly-available files.



Example Usage:



```ruby

has_attached_file :avatar, {

    url: "/system/:hash.:extension",

    hash_secret: "longSecretString"

}

```



The `:hash` interpolation will be replaced with a unique hash made up of whatever

is specified in `:hash_data`. The default value for `:hash_data` is `":class/:attachment/:id/:style/:updated_at"`.



`:hash_secret` is required - an exception will be raised if `:hash` is used without `:hash_secret` present.



For more on this feature, read [the author's own explanation](https://github.com/thoughtbot/paperclip/pull/416)



Checksum / Fingerprint

-------



A checksum of the original file assigned will be placed in the model if it

has an attribute named fingerprint.  Following the user model migration example

above, the migration would look like the following:



```ruby

class AddAvatarFingerprintColumnToUser < ActiveRecord::Migration

  def up

    add_column :users, :avatar_fingerprint, :string

  end



  def down

    remove_column :users, :avatar_fingerprint

  end

end

```



The algorithm can be specified using a configuration option; it defaults to MD5

for backwards compatibility with Paperclip 5 and earlier.



```ruby

has_attached_file :some_attachment, adapter_options: { hash_digest: Digest::SHA256 }

```



Run `CLASS=User ATTACHMENT=avatar rake paperclip:refresh:fingerprints` after

changing the digest on existing attachments to update the fingerprints in the

database.



File Preservation for Soft-Delete

-------



An option is available to preserve attachments in order to play nicely with soft-deleted models. (acts_as_paranoid, paranoia, etc.)



```ruby

has_attached_file :some_attachment, {

    preserve_files: true,

}

```



This will prevent ```some_attachment``` from being wiped out when the model gets destroyed, so it will still exist when the object is restored later.



---



Dynamic Configuration

---------------------



Callable objects (lambdas, Procs) can be used in a number of places for dynamic

configuration throughout Paperclip.  This strategy exists in a number of

components of the library but is most significant in the possibilities for

allowing custom styles and processors to be applied for specific model

instances, rather than applying defined styles and processors across all

instances.



### Dynamic Styles:



Imagine a user model that had different styles based on the role of the user.

Perhaps some users are bosses (e.g. a User model instance responds to `#boss?`)

and merit a bigger avatar thumbnail than regular users. The configuration to

determine what style parameters are to be used based on the user role might

look as follows where a boss will receive a `300x300` thumbnail otherwise a

`100x100` thumbnail will be created.



```ruby

class User < ActiveRecord::Base

  has_attached_file :avatar, styles: lambda { |attachment| { thumb: (attachment.instance.boss? ? "300x300>" : "100x100>") } }

end

```



### Dynamic Processors:



Another contrived example is a user model that is aware of which file processors

should be applied to it (beyond the implied `thumbnail` processor invoked when

`:styles` are defined). Perhaps we have a watermark processor available and it is

only used on the avatars of certain models.  The configuration for this might be

where the instance is queried for which processors should be applied to it.

Presumably some users might return `[:thumbnail, :watermark]` for its

processors, where a defined `watermark` processor is invoked after the

`thumbnail` processor already defined by Paperclip.



```ruby

class User < ActiveRecord::Base

  has_attached_file :avatar, processors: lambda { |instance| instance.processors }

  attr_accessor :processors

end

```



---



Logging

----------



By default, Paperclip outputs logging according to your logger level. If you want to disable logging (e.g. during testing) add this into your environment's configuration:

```ruby

Your::Application.configure do

...

  Paperclip.options[:log] = false

...

end

```



More information in the [rdocs](http://www.rubydoc.info/github/thoughtbot/paperclip/Paperclip.options)



---



Deployment

----------



To make Capistrano symlink the `public/system` directory so that attachments

survive new deployments, set the `linked_dirs` option in your `config/deploy.rb`

file:



```ruby

set :linked_dirs, fetch(:linked_dirs, []).push('public/system')

```



### Attachment Styles



Paperclip is aware of new attachment styles you have added in previous deploys. The only thing you should do after each deployment is to call

`rake paperclip:refresh:missing_styles`.  It will store current attachment styles in `RAILS_ROOT/public/system/paperclip_attachments.yml`

by default. You can change it by:



```ruby

Paperclip.registered_attachments_styles_path = '/tmp/config/paperclip_attachments.yml'

```



Here is an example for Capistrano:



```ruby

namespace :paperclip do

  desc "build missing paperclip styles"

  task :build_missing_styles do

    on roles(:app) do

      within release_path do

        with rails_env: fetch(:rails_env) do

          execute :rake, "paperclip:refresh:missing_styles"

        end

      end

    end

  end

end



after("deploy:compile_assets", "paperclip:build_missing_styles")

```



Now you don't have to remember to refresh thumbnails in production every time you add a new style.

Unfortunately, it does not work with dynamic styles - it just ignores them.



If you already have a working app and don't want `rake paperclip:refresh:missing_styles` to refresh old pictures, you need to tell

Paperclip about existing styles. Simply create a `paperclip_attachments.yml` file by hand. For example:



```ruby

class User < ActiveRecord::Base

  has_attached_file :avatar, styles: { thumb: 'x100', croppable: '600x600>', big: '1000x1000>' }

end



class Book < ActiveRecord::Base

  has_attached_file :cover, styles: { small: 'x100', large: '1000x1000>' }

  has_attached_file :sample, styles: { thumb: 'x100' }

end

```



Then in `RAILS_ROOT/public/system/paperclip_attachments.yml`:



```yml

---

:User:

  :avatar:

  - :thumb

  - :croppable

  - :big

:Book:

  :cover:

  - :small

  - :large

  :sample:

  - :thumb

```



---



Testing

-------



Paperclip provides rspec-compatible matchers for testing attachments. See the

documentation on [Paperclip::Shoulda::Matchers](http://www.rubydoc.info/gems/paperclip/Paperclip/Shoulda/Matchers)

for more information.



**Parallel Tests**



Because of the default `path` for Paperclip storage, if you try to run tests in

parallel, you may find that files get overwritten because the same path is being

calculated for them in each test process. While this fix works for

parallel_tests, a similar concept should be used for any other mechanism for

running tests concurrently.



```ruby

if ENV['PARALLEL_TEST_GROUPS']

  Paperclip::Attachment.default_options[:path] = ":rails_root/public/system/:rails_env/#{ENV['TEST_ENV_NUMBER'].to_i}/:class/:attachment/:id_partition/:filename"

else

  Paperclip::Attachment.default_options[:path] = ":rails_root/public/system/:rails_env/:class/:attachment/:id_partition/:filename"

end

```



The important part here being the inclusion of `ENV['TEST_ENV_NUMBER']`, or a

similar mechanism for whichever parallel testing library you use.



**Integration Tests**



Using integration tests with FactoryBot may save multiple copies of

your test files within the app. To avoid this, specify a custom path in

the `config/environments/test.rb` like so:



```ruby

Paperclip::Attachment.default_options[:path] = "#{Rails.root}/spec/test_files/:class/:id_partition/:style.:extension"

```



Then, make sure to delete that directory after the test suite runs by adding

this to `spec_helper.rb`.



```ruby

config.after(:suite) do

  FileUtils.rm_rf(Dir["#{Rails.root}/spec/test_files/"])

end

```



**Example of test configuration with Factory Bot**



```ruby

FactoryBot.define do

  factory :user do

    avatar { File.new("#{Rails.root}/spec/support/fixtures/image.jpg") }

  end

end

```

---



Contributing

------------



If you'd like to contribute a feature or bugfix: Thanks! To make sure your

fix/feature has a high chance of being included, please read the following

guidelines:



1. Post a [pull request](https://github.com/thoughtbot/paperclip/compare/).

2. Make sure there are tests! We will not accept any patch that is not tested.

   It's a rare time when explicit tests aren't needed. If you have questions

   about writing tests for paperclip, please open a

   [GitHub issue](https://github.com/thoughtbot/paperclip/issues/new).



Please see [`CONTRIBUTING.md`](./CONTRIBUTING.md) for more details on contributing and running test.



Thank you to all [the contributors](https://github.com/thoughtbot/paperclip/graphs/contributors)!



License

-------



Paperclip is Copyright © 2008-2017 thoughtbot, inc. It is free software, and may be

redistributed under the terms specified in the MIT-LICENSE file.



About thoughtbot

----------------



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Paperclip is maintained and funded by thoughtbot.

The names and logos for thoughtbot are trademarks of thoughtbot, inc.



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