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:
Ahead of the file being uploaded server-side to the service, via
create_and_upload!. A rewindable
iowith the file contents must be available at the server for this operation.
Ahead of the file being directly uploaded client-side to the service, via
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.
- MODULE ActiveStorage::Blob::Analyzable
- MODULE ActiveStorage::Blob::Identifiable
- MODULE ActiveStorage::Blob::Representable
Class Public methods
compose(blobs, filename:, content_type: nil, metadata: nil) Link
Concatenate multiple blobs into a single “composed” blob.
# File activestorage/app/models/active_storage/blob.rb, line 138 def compose(blobs, filename:, content_type: nil, metadata: nil) raise ActiveRecord::RecordNotSaved, "All blobs must be persisted." if blobs.any?(&:new_record?) content_type ||= blobs.pluck(:content_type).compact.first new(filename: filename, content_type: content_type, metadata: metadata, byte_size: blobs.sum(&:byte_size)).tap do |combined_blob| combined_blob.compose(blobs.pluck(:key)) combined_blob.save! end end
create_and_upload!(key: nil, io:, filename:, content_type: nil, metadata: nil, service_name: nil, identify: true, record: nil) Link
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.
# File activestorage/app/models/active_storage/blob.rb, line 92 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| blob.upload_without_unfurling(io) end end
create_before_direct_upload!(key: nil, filename:, byte_size:, checksum:, content_type: nil, metadata: nil, service_name: nil, record: nil) Link
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 103 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 end
find_signed(id, record: nil, purpose: :blob_id) Link
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.
find_signed!(id, record: nil, purpose: :blob_id) Link
find_signed, but will raise an
ActiveSupport::MessageVerifier::InvalidSignature exception if the
signed_id has either expired, has a purpose mismatch, is for another record, or has been tampered with. It will also raise an
ActiveRecord::RecordNotFound exception if the valid signed id can’t find a record.
generate_unique_secure_token(length: MINIMUM_TOKEN_LENGTH) Link
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
Instance Public methods
Returns true if the content_type of this blob is in the audio range, like audio/mpeg.
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_later methods in most circumstances.
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.
Downloads a part of the file associated with this blob.
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.
Returns true if the content_type of this blob is in the image range, like image/png.
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.
open(tmpdir: nil, &block) Link
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
tmpdir: to create it in a different directory:
blob.open(tmpdir: "/path/to/tmp") do |file| # ... end
The tempfile is automatically closed and unlinked after the given block is executed.
ActiveStorage::IntegrityError if the downloaded data does not match the blob’s checksum.
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
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.
Returns an instance of service, which can be configured globally or per attachment
Hash of headers for
service_url_for_direct_upload(expires_in: ActiveStorage.service_urls_expire_in) Link
# File activestorage/app/models/active_storage/blob.rb, line 210 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, custom_metadata: custom_metadata end
signed_id(purpose: :blob_id, expires_in: nil) Link
Returns a signed ID for this blob that’s suitable for reference on the client-side without fear of tampering.
Returns true if the content_type of this blob is in the text range, like text/plain.
upload(io, identify: true) Link
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.
url(expires_in: ActiveStorage.service_urls_expire_in, disposition: :inline, filename: nil, **options) Link
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.
# File activestorage/app/models/active_storage/blob.rb, line 203 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 end