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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. Ahead of the file being uploaded server-side to the service, via create_and_upload!. A rewindable io with the file contents must be available at the server for this operation.

  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.

Included Modules
Class Public methods
create_after_upload!(key: nil, io:, filename:, content_type: nil, metadata: nil, service_name: nil, identify: true, record: nil)
Alias for: create_and_upload!
create_and_upload!(key: nil, io:, filename:, content_type: nil, metadata: nil, service_name: nil, identify: true, record: nil)

Creates a new blob instance and then uploads the contents of the given io to the service. The blob instance is going to be saved before the upload begins to prevent the upload clobbering another due to key collisions. When providing a content type, pass identify: false to bypass automatic content type inference.

Also aliased as: create_after_upload!
# File activestorage/app/models/active_storage/blob.rb, line 104
def create_and_upload!(key: nil, io:, filename:, content_type: nil, metadata: nil, service_name: nil, identify: true, record: nil)
  create_after_unfurling!(key: key, io: io, filename: filename, content_type: content_type, metadata: metadata, service_name: service_name, identify: identify).tap do |blob|
create_before_direct_upload!(key: nil, filename:, byte_size:, checksum:, content_type: nil, metadata: nil, service_name: nil, record: nil)

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 118
def create_before_direct_upload!(key: nil, filename:, byte_size:, checksum:, content_type: nil, metadata: nil, service_name: nil, record: nil)
  create! key: key, filename: filename, byte_size: byte_size, checksum: checksum, content_type: content_type, metadata: metadata, service_name: service_name
find_signed!(id, record: nil, purpose: :blob_id)

You can use 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 77
def find_signed!(id, record: nil, purpose: :blob_id)
  super(id, purpose: purpose)
generate_unique_secure_token(length: MINIMUM_TOKEN_LENGTH)

To prevent problems with case-insensitive filesystems, especially in combination with databases which treat indices as case-sensitive, all blob keys generated are going to only contain the base-36 character alphabet and will therefore be lowercase. To maintain the same or higher amount of entropy as in the base-58 encoding used by `has_secure_token` the number of bytes used is increased to 28 from the standard 24

# File activestorage/app/models/active_storage/blob.rb, line 127
def generate_unique_secure_token(length: MINIMUM_TOKEN_LENGTH)
Instance Public 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 172
def audio?

Deletes the files on the service associated with the 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 purge and purge_later methods in most circumstances.

# File activestorage/app/models/active_storage/blob.rb, line 279
def delete
  service.delete_prefixed("variants/#{key}/") if image?

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 250
def download(&block)
  service.download key, &block

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 162
def filename

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 167
def image?

Returns the key pointing to the file on the service that's associated with this blob. The key is the secure-token format from Rails in lower case. So it'll look like: xtapjjcjiudrlk3tmwyjgpuobabd. 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 154
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(length: MINIMUM_TOKEN_LENGTH)
open(tmpdir: nil, &block)

Downloads the blob to a tempfile on disk. Yields the tempfile.

The tempfile's name is prefixed with ActiveStorage- and the blob's ID. Its extension matches that of the blob.

By default, the tempfile is created in Dir.tmpdir. Pass tmpdir: to create it in a different directory:

blob.open(tmpdir: "/path/to/tmp") do |file|
  # ...

The tempfile is automatically closed and unlinked after the given block is executed.

Raises ActiveStorage::IntegrityError if the downloaded data does not match the blob's checksum.

# File activestorage/app/models/active_storage/blob.rb, line 267
def open(tmpdir: nil, &block)
  service.open key, checksum: checksum,
    name: [ "ActiveStorage-#{id}-", filename.extension_with_delimiter ], tmpdir: tmpdir, &block

Destroys the blob record and then deletes the file on the service. This is the recommended way to dispose of unwanted blobs. Note, though, that deleting the file off the service will initiate an 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 287
def purge
rescue ActiveRecord::InvalidForeignKey

Enqueues an ActiveStorage::PurgeJob to call purge. This is the recommended way to purge blobs from a transaction, an Active Record callback, or in any other real-time scenario.

# File activestorage/app/models/active_storage/blob.rb, line 295
def purge_later

Returns an instance of service, which can be configured globally or per attachment

# File activestorage/app/models/active_storage/blob.rb, line 300
def service

Returns a Hash of headers for service_url_for_direct_upload requests.

# File activestorage/app/models/active_storage/blob.rb, line 205
def service_headers_for_direct_upload
  service.headers_for_direct_upload key, filename: filename, content_type: content_type, content_length: byte_size, checksum: checksum
service_url(expires_in: ActiveStorage.service_urls_expire_in, disposition: :inline, filename: nil, **options)
Alias for: url
service_url_for_direct_upload(expires_in: ActiveStorage.service_urls_expire_in)

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 200
def service_url_for_direct_upload(expires_in: ActiveStorage.service_urls_expire_in)
  service.url_for_direct_upload key, expires_in: expires_in, content_type: content_type, content_length: byte_size, checksum: checksum
signed_id(purpose: :blob_id)

Returns a signed ID for this blob that's suitable for reference on the client-side without fear of tampering.

# File activestorage/app/models/active_storage/blob.rb, line 146
def signed_id(purpose: :blob_id)

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 182
def text?
upload(io, identify: true)

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. The content type is automatically extracted from the io unless you specify a content_type and pass identify as false.

Normally, you do not have to call this method directly at all. Use the create_and_upload! class method instead. If you do use this method directly, make sure you are using it on a persisted Blob as otherwise another blob's data might get overwritten on the service.

# File activestorage/app/models/active_storage/blob.rb, line 232
def upload(io, identify: true)
  unfurl io, identify: identify
  upload_without_unfurling io
url(expires_in: ActiveStorage.service_urls_expire_in, disposition: :inline, filename: nil, **options)

Returns the URL of the blob on the service. This returns a permanent URL for public files, and returns a short-lived URL for private files. Private files are signed, and not for public use. Instead, the URL should only be exposed as a redirect from a stable, possibly authenticated URL. Hiding the URL behind a redirect also allows you to change services without updating all URLs.

Also aliased as: service_url
# File activestorage/app/models/active_storage/blob.rb, line 190
def url(expires_in: ActiveStorage.service_urls_expire_in, disposition: :inline, filename: nil, **options)
  service.url key, expires_in: expires_in, filename: ActiveStorage::Filename.wrap(filename || self.filename),
    content_type: content_type_for_serving, disposition: forced_disposition_for_serving || disposition, **options

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 177
def video?