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Diffstat (limited to 'activestorage/app/models/active_storage/blob.rb')
| -rw-r--r-- | activestorage/app/models/active_storage/blob.rb | 195 |
1 files changed, 195 insertions, 0 deletions
diff --git a/activestorage/app/models/active_storage/blob.rb b/activestorage/app/models/active_storage/blob.rb new file mode 100644 index 0000000000..debc62bd41 --- /dev/null +++ b/activestorage/app/models/active_storage/blob.rb @@ -0,0 +1,195 @@ +# 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. +class ActiveStorage::Blob < ActiveRecord::Base + self.table_name = "active_storage_blobs" + + has_secure_token :key + store :metadata, coder: JSON + + class_attribute :service + + class << self + # 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. + def find_signed(id) + find ActiveStorage.verifier.verify(id, purpose: :blob_id) + end + + # Returns a new, unsaved blob instance after the `io` has been uploaded to the service. + 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 doing to avoid opening a transaction and talking to + # the service during that (which is a bad idea and leads to deadlocks). + 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. + 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 + 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. + def signed_id + ActiveStorage.verifier.generate(id, purpose: :blob_id) + 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 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. + 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 + + # Returns a `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. + 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. + def image? + content_type =~ /^image/ + end + + # Returns true if the content_type of this blob is in the audio range, like audio/mpeg. + def audio? + content_type =~ /^audio/ + end + + # Returns true if the content_type of this blob is in the video range, like video/mp4. + def video? + content_type =~ /^video/ + end + + # Returns true if the content_type of this blob is in the text range, like text/plain. + def text? + content_type =~ /^text/ + end + + # Returns a `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. + def variant(transformations) + ActiveStorage::Variant.new(self, ActiveStorage::Variation.new(transformations)) + 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. + def service_url(expires_in: 5.minutes, disposition: :inline) + service.url key, expires_in: expires_in, disposition: disposition, 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. + 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 Hash of headers for `service_url_for_direct_upload` requests. + 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 + + # 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!`. + def upload(io) + self.checksum = compute_checksum_in_chunks(io) + self.byte_size = io.size + + service.upload(key, io, checksum: checksum) + 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. + def download(&block) + service.download key, &block + 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. + def delete + service.delete key + 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. + def purge + delete + destroy + end + + # Enqueues a `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. + def purge_later + ActiveStorage::PurgeJob.perform_later(self) + end + + private + 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 +end |