README.md
# Shrine::Plugins::ContentAddressable
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Generate content addressable locations for shrine uploads.
## Installation
Add this line to your application's Gemfile:
```ruby
gem 'shrine-content_addressable'
```
And then execute:
$ bundle
Or install it yourself as:
$ gem install shrine-content_addressable
## Usage
This plugin depends on the `signature` plugin:
```Ruby
require 'shrine/plugins/content_addressable'
require 'shrine/plugins/signature'
class MyUploader < Shrine
plugin :signature
plugin :content_addressable, hash: :sha256, prefix: '/'
end
```
Currently you can enter `:md5`, `:sha`, `:sha256` and `:sha512` for `hash:`. If you have a different algorithm that is
correctly supported by the `signature` plugin, and has a `multihash` code, add the multihash code mapping:
```Ruby
# Let's say the signature plugin starts supporting blake 2b as :blake2_b,
# the multihash code is 'blake2b'
plugin :content_addressable, hash: :blake2_b, multihash: 'blake2b'
```
Your uploaded files will be extended with some multihash capability:
```Ruby
uploader = Uploader.new(:cache)
uploaded_file = uploader.upload(my_file)
uploaded_file.content_addressable # => the content addressable hash, regardless of location
uploaded_file.decode # => the decoded multihash
uploaded_file.digest # => the decoded digest (in bytes. Use .unpack('H*') to turn into hex)
uploaded_file.digest_function # => the digest function used to create the multihash
uploaded_file.to_content_addressable! # => ContentAddressableFile, and auto registers the storage
```
### ContentAddressable IO
Since a content-addressable stored file is the same across whichever storage, it *MUST* not matter what storage the file
is accessed from when it comes to reading. A wrapper is provided so files can be looked up by their content-addressable
id / hash, instead of a data hash (default for Shrine).
```Ruby
require 'content_addressable_file'
# You currently need to register the storages, unless you use uploaded_file.to_content_addressable!
ContentAddressableFile.register_storage(lookup, lookup, lookup)
# You can disallow deletion
ContentAddressableFile.register_read_only_storage(lookup, lookup, lookup)
file = ContentAddressableFile.new(content_addressable_hash)
# Shares the interface with UploadedFile
# => file methods like open, rewind, read, close and eof? are available
# => file.url gives the first url that exists
# => file.exists? is true if it exists in any storage
# => file.delete attempts to delete it from ALL storages
```
To reset known storages use:
```Ruby
ContentAddressableFile.reset
```
Registration is only automatic when using `#to_content_addressable!`. Do not rely on that behaviour
if you're not always uploading files, but trying to retrieve them.
A lookup storage needs to respond to:
```Ruby
lookup = Shrine::Storage::Memory.new
content_addressable = content_addressable_hash
lookup.open(content_addressable) # IO.open
lookup.exists?(content_addressable) # true if storage has it (and can open)
# optional
lookup.url(content_addressable) # url to the io (only if storage has it)
lookup.delete(content_addressable) # delete from storage
lookup.download(content_addressable) # download the io
```
Note that you input the hash, and not some arbitrary path.
## Development
After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test` to run the tests. You can
also run `bin/console` for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the
version number in `shrine-configurable_storage.gemspec.rb`, and then run `bundle exec rake release`, which will create
a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
## Contributing
Bug reports and pull requests are welcome on GitHub at [SleeplessByte/shrine-configurable_storage](https://github.com/SleeplessByte/shrine-configurable_storage).
This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to
the [Contributor Covenant](http://contributor-covenant.org) code of conduct.
## License
The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).
## Code of Conduct
Everyone interacting in the `Shrine::Plugins::ContentAddressable` project’s codebases, issue trackers, chat rooms and
mailing lists is expected to follow the [code of conduct](https://github.com/SleeplessByte/shrine-configurable_storage/blob/master/CODE_OF_CONDUCT.md).