Class: ActiveStorage::Blob

Inherits:
ActiveRecord::Base
  • Object
show all
Includes:
Analyzable, Identifiable, Representable
Defined in:
app/models/active_storage/blob.rb

Overview

A blob is a record that contains the metadata about a file and a key for where that file resides on the service. Blobs can be created in two ways:

  1. Subsequent to the file being uploaded server-side to the service via create_after_upload!.

  2. Ahead of the file being directly uploaded client-side to the service via create_before_direct_upload!.

The first option doesn't require any client-side JavaScript integration, and can be used by any other back-end service that deals with files. The second option is faster, since you're not using your own server as a staging point for uploads, and can work with deployments like Heroku that do not provide large amounts of disk space.

Blobs are intended to be immutable in as-so-far as their reference to a specific file goes. You're allowed to update a blob's metadata on a subsequent pass, but you should not update the key or change the uploaded file. If you need to create a derivative or otherwise change the blob, simply create a new blob and purge the old one.

Defined Under Namespace

Modules: Analyzable, Identifiable, Representable

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Representable

#preview, #previewable?, #representable?, #representation, #variable?, #variant

Methods included from Identifiable

#identified?, #identify

Methods included from Analyzable

#analyze, #analyze_later, #analyzed?

Class Method Details

.build_after_upload(io:, filename:, content_type: nil, metadata: nil) ⇒ Object

Returns a new, unsaved blob instance after the io has been uploaded to the service.



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# File 'app/models/active_storage/blob.rb', line 51

def build_after_upload(io:, filename:, content_type: nil, metadata: nil)
  new.tap do |blob|
    blob.filename     = filename
    blob.content_type = content_type
    blob.metadata     = metadata

    blob.upload io
  end
end

.create_after_upload!(io:, filename:, content_type: nil, metadata: nil) ⇒ Object

Returns a saved blob instance after the io has been uploaded to the service. Note, the blob is first built, then the io is uploaded, then the blob is saved. This is done this way to avoid uploading (which may take time), while having an open database transaction.



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# File 'app/models/active_storage/blob.rb', line 64

def create_after_upload!(io:, filename:, content_type: nil, metadata: nil)
  build_after_upload(io: io, filename: filename, content_type: content_type, metadata: metadata).tap(&:save!)
end

.create_before_direct_upload!(filename:, byte_size:, checksum:, content_type: nil, metadata: nil) ⇒ Object

Returns a saved blob without uploading a file to the service. This blob will point to a key where there is no file yet. It's intended to be used together with a client-side upload, which will first create the blob in order to produce the signed URL for uploading. This signed URL points to the key generated by the blob. Once the form using the direct upload is submitted, the blob can be associated with the right record using the signed ID.



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# File 'app/models/active_storage/blob.rb', line 73

def create_before_direct_upload!(filename:, byte_size:, checksum:, content_type: nil, metadata: nil)
  create! filename: filename, byte_size: byte_size, checksum: checksum, content_type: content_type, metadata: metadata
end

.find_signed(id) ⇒ Object

You can used the signed ID of a blob to refer to it on the client side without fear of tampering. This is particularly helpful for direct uploads where the client-side needs to refer to the blob that was created ahead of the upload itself on form submission.

The signed ID is also used to create stable URLs for the blob through the BlobsController.



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# File 'app/models/active_storage/blob.rb', line 46

def find_signed(id)
  find ActiveStorage.verifier.verify(id, purpose: :blob_id)
end

Instance Method Details

#audio? ⇒ Boolean

Returns true if the content_type of this blob is in the audio range, like audio/mpeg.

Returns:

  • (Boolean) 


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# File 'app/models/active_storage/blob.rb', line 105

def audio?
  content_type.start_with?("audio")
end

#delete ⇒ Object

Deletes the file on the service that's associated with this blob. This should only be done if the blob is going to be deleted as well or you will essentially have a dead reference. It's recommended to use the #purge and #purge_later methods in most circumstances.



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# File 'app/models/active_storage/blob.rb', line 172

def delete
  service.delete(key)
  service.delete_prefixed("variants/#{key}/") if image?
end

#download(&block) ⇒ Object

Downloads the file associated with this blob. If no block is given, the entire file is read into memory and returned. That'll use a lot of RAM for very large files. If a block is given, then the download is streamed and yielded in chunks.



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# File 'app/models/active_storage/blob.rb', line 164

def download(&block)
  service.download key, &block
end

#filename ⇒ Object

Returns an ActiveStorage::Filename instance of the filename that can be queried for basename, extension, and a sanitized version of the filename that's safe to use in URLs.



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# File 'app/models/active_storage/blob.rb', line 95

def filename
  ActiveStorage::Filename.new(self[:filename])
end

#image? ⇒ Boolean

Returns true if the content_type of this blob is in the image range, like image/png.

Returns:

  • (Boolean) 


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# File 'app/models/active_storage/blob.rb', line 100

def image?
  content_type.start_with?("image")
end

#key ⇒ Object

Returns the key pointing to the file on the service that's associated with this blob. The key is in the standard secure-token format from Rails. So it'll look like: XTAPjJCJiuDrLk3TmwyJGpUo. This key is not intended to be revealed directly to the user. Always refer to blobs using the signed_id or a verified form of the key.



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# File 'app/models/active_storage/blob.rb', line 87

def key
  # We can't wait until the record is first saved to have a key for it
  self[:key] ||= self.class.generate_unique_secure_token
end

#purge ⇒ Object

Deletes the file on the service and then destroys the blob record. This is the recommended way to dispose of unwanted blobs. Note, though, that deleting the file off the service will initiate a HTTP connection to the service, which may be slow or prevented, so you should not use this method inside a transaction or in callbacks. Use #purge_later instead.



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# File 'app/models/active_storage/blob.rb', line 180

def purge
  destroy
  delete
rescue ActiveRecord::InvalidForeignKey
end

#purge_later ⇒ Object

Enqueues an ActiveStorage::PurgeJob job that'll call purge. This is the recommended way to purge blobs when the call needs to be made from a transaction, a callback, or any other real-time scenario.



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# File 'app/models/active_storage/blob.rb', line 188

def purge_later
  ActiveStorage::PurgeJob.perform_later(self)
end

#service_headers_for_direct_upload ⇒ Object

Returns a Hash of headers for service_url_for_direct_upload requests.



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# File 'app/models/active_storage/blob.rb', line 138

def service_headers_for_direct_upload
  service.headers_for_direct_upload key, filename: filename, content_type: content_type, content_length: byte_size, checksum: checksum
end

#service_url(expires_in: service.url_expires_in, disposition: :inline, filename: nil, **options) ⇒ Object

Returns the URL of the blob on the service. This URL is intended to be short-lived for security and not used directly with users. Instead, the service_url should only be exposed as a redirect from a stable, possibly authenticated URL. Hiding the service_url behind a redirect also gives you the power to change services without updating all URLs. And it allows permanent URLs that redirect to the service_url to be cached in the view.



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# File 'app/models/active_storage/blob.rb', line 124

def service_url(expires_in: service.url_expires_in, disposition: :inline, filename: nil, **options)
  filename = ActiveStorage::Filename.wrap(filename || self.filename)

  service.url key, expires_in: expires_in, filename: filename, content_type: content_type_for_service_url,
    disposition: forced_disposition_for_service_url || disposition, **options
end

#service_url_for_direct_upload(expires_in: service.url_expires_in) ⇒ Object

Returns a URL that can be used to directly upload a file for this blob on the service. This URL is intended to be short-lived for security and only generated on-demand by the client-side JavaScript responsible for doing the uploading.



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# File 'app/models/active_storage/blob.rb', line 133

def service_url_for_direct_upload(expires_in: service.url_expires_in)
  service.url_for_direct_upload key, expires_in: expires_in, content_type: content_type, content_length: byte_size, checksum: checksum
end

#signed_id ⇒ Object

Returns a signed ID for this blob that's suitable for reference on the client-side without fear of tampering. It uses the framework-wide verifier on ActiveStorage.verifier, but with a dedicated purpose.



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# File 'app/models/active_storage/blob.rb', line 80

def signed_id
  ActiveStorage.verifier.generate(id, purpose: :blob_id)
end

#text? ⇒ Boolean

Returns true if the content_type of this blob is in the text range, like text/plain.

Returns:

  • (Boolean) 


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# File 'app/models/active_storage/blob.rb', line 115

def text?
  content_type.start_with?("text")
end

#upload(io) ⇒ Object

Uploads the io to the service on the key for this blob. Blobs are intended to be immutable, so you shouldn't be using this method after a file has already been uploaded to fit with a blob. If you want to create a derivative blob, you should instead simply create a new blob based on the old one.

Prior to uploading, we compute the checksum, which is sent to the service for transit integrity validation. If the checksum does not match what the service receives, an exception will be raised. We also measure the size of the io and store that in byte_size on the blob record.

Normally, you do not have to call this method directly at all. Use the factory class methods of build_after_upload and create_after_upload!.



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# File 'app/models/active_storage/blob.rb', line 153

def upload(io)
  self.checksum     = compute_checksum_in_chunks(io)
  self.content_type = extract_content_type(io)
  self.byte_size    = io.size
  self.identified   = true

  service.upload key, io, checksum: checksum, **service_metadata
end

#video? ⇒ Boolean

Returns true if the content_type of this blob is in the video range, like video/mp4.

Returns:

  • (Boolean) 


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# File 'app/models/active_storage/blob.rb', line 110

def video?
  content_type.start_with?("video")
end