class ActiveStorage::Blob
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:
-
Subsequent to the file being uploaded server-side to the service via
create_after_upload!
. -
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.
Public Class Methods
Returns a new, unsaved blob instance after the io
has been uploaded to the service.
# File activestorage/app/models/active_storage/blob.rb, line 35 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
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.
# File activestorage/app/models/active_storage/blob.rb, line 48 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
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.
# File activestorage/app/models/active_storage/blob.rb, line 57 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
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.
# File activestorage/app/models/active_storage/blob.rb, line 30 def find_signed(id) find ActiveStorage.verifier.verify(id, purpose: :blob_id) end
Public Instance Methods
Returns true if the content_type of this blob is in the audio range, like audio/mpeg.
# File activestorage/app/models/active_storage/blob.rb, line 90 def audio? content_type.start_with?("audio") end
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.
# File activestorage/app/models/active_storage/blob.rb, line 171 def delete service.delete key end
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.
# File activestorage/app/models/active_storage/blob.rb, line 163 def download(&block) service.download key, &block end
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.
# File activestorage/app/models/active_storage/blob.rb, line 80 def filename ActiveStorage::Filename.new(self[:filename]) end
Returns true if the content_type of this blob is in the image range, like image/png.
# File activestorage/app/models/active_storage/blob.rb, line 85 def image? content_type.start_with?("image") end
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 Quails
. 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.
# File activestorage/app/models/active_storage/blob.rb, line 72 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
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.
# File activestorage/app/models/active_storage/blob.rb, line 178 def purge delete destroy end
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.
# File activestorage/app/models/active_storage/blob.rb, line 185 def purge_later ActiveStorage::PurgeJob.perform_later(self) end
Returns a Hash
of headers for service_url_for_direct_upload
requests.
# File activestorage/app/models/active_storage/blob.rb, line 140 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
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.
# File activestorage/app/models/active_storage/blob.rb, line 129 def service_url(expires_in: 5.minutes, disposition: :inline) service.url key, expires_in: expires_in, disposition: "#{disposition}; #{filename.parameters}", filename: filename, content_type: content_type end
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.
# File activestorage/app/models/active_storage/blob.rb, line 135 def service_url_for_direct_upload(expires_in: 5.minutes) service.url_for_direct_upload key, expires_in: expires_in, content_type: content_type, content_length: byte_size, checksum: checksum end
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.
# File activestorage/app/models/active_storage/blob.rb, line 65 def signed_id ActiveStorage.verifier.generate(id, purpose: :blob_id) end
Returns true if the content_type of this blob is in the text range, like text/plain.
# File activestorage/app/models/active_storage/blob.rb, line 100 def text? content_type.start_with?("text") end
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!
.
# File activestorage/app/models/active_storage/blob.rb, line 154 def upload(io) self.checksum = compute_checksum_in_chunks(io) self.byte_size = io.size service.upload(key, io, checksum: checksum) end
Returns an ActiveStorage::Variant
instance with the set of transformations
passed in. This is only relevant for image files, and it allows any image to be transformed for size, colors, and the like. Example:
avatar.variant(resize: "100x100").processed.service_url
This will create and process a variant of the avatar blob that's constrained to a height and width of 100. Then it'll upload said variant to the service according to a derivative key of the blob and the transformations.
Frequently, though, you don't actually want to transform the variant right away. But rather simply refer to a specific variant that can be created by a controller on-demand. Like so:
<%= image_tag url_for(Current.user.avatar.variant(resize: "100x100")) %>
This will create a URL for that specific blob with that specific variant, which the ActiveStorage::VariantsController
can then produce on-demand.
# File activestorage/app/models/active_storage/blob.rb, line 120 def variant(transformations) ActiveStorage::Variant.new(self, ActiveStorage::Variation.new(transformations)) end
Returns true if the content_type of this blob is in the video range, like video/mp4.
# File activestorage/app/models/active_storage/blob.rb, line 95 def video? content_type.start_with?("video") end
Private Instance Methods
# File activestorage/app/models/active_storage/blob.rb, line 190 def compute_checksum_in_chunks(io) Digest::MD5.new.tap do |checksum| while chunk = io.read(5.megabytes) checksum << chunk end io.rewind end.base64digest end