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Signature

The signature plugin provides the ability to calculate a hash from file content. This hash can be used as a checksum or just as a unique signature for the uploaded file.

Shrine.plugin :signature

API

The plugin adds a #calculate_signature instance and class method to the uploader. The method accepts an IO object and a hashing algorithm, and returns the calculated hash.

Shrine.calculate_signature(io, :md5) #=> "9a0364b9e99bb480dd25e1f0284c8555" 
# or just 
Shrine.signature(io, :md5) #=> "9a0364b9e99bb480dd25e1f0284c8555" 

The following hashing algorithms are supported: SHA1, SHA256, SHA384, SHA512, MD5, and CRC32.

You can also choose which format will the calculated hash be encoded in:

Shrine.calculate_signature(io, :sha256, format: :base64)

The supported encoding formats are hex (default), base64, and none.

Adding metadata

You can then use the add_metadata plugin to add a new metadata field with the calculated hash.

plugin :add_metadata
 
add_metadata :md5 do |io|
  calculate_signature(io, :md5)
end

This will generate a hash for each uploaded file, but if you want to generate one only for the original file, you can add a conditional:

add_metadata :md5 do |io, action: nil, **|
  calculate_signature(io, :md5) if action == :cache
end

Rewinding

If you want to calculate signature from a non-rewindable IO object, you can tell Shrine to skip rewinding:

Shrine.calculate_signature(io, :md5, rewind: false)

Instrumentation

If the instrumentation plugin has been loaded, the signature plugin adds instrumentation around signature calculation.

# instrumentation plugin needs to be loaded *before* signature 
plugin :instrumentation
plugin :signature

Calculating signature will trigger a signature.shrine event with the following payload:

Key	Description
:io	The IO object
:uploader	The uploader class that sent the event

A default log subscriber is added as well which logs these events:

MIME Type (33ms) – {:io=>StringIO, :uploader=>Shrine}

You can also use your own log subscriber:

plugin :signature, log_subscriber: -> (event) { 
  Shrine.logger.info JSON.generate(name: event.name, duration: event.duration, **event.payload)
}

{"name":"signature","duration":24,"io":"#","uploader":"Shrine"}

Or disable logging altogether:

plugin :signature, log_subscriber: nil