Storage Drivers

This document defines the interface that storage driver implementations must adhere to.

Overview

The abstract driver base class for storage drivers is \local_archiving\driver\archvingstore.

classDiagram
    direction TB

    class archivingstore {
        <<abstract>>

        +get_storage_tier()$ storage_tier
        +supports_retrieve()$ bool
        +is_available() bool
        +get_free_bytes() int|null
        +store(jobid: int, file: stored_file, path: string) file_handle
        +retrieve(handle: file_handle, fileinfo: stdClass) stored_file
        +delete(handle: file_handle, strict: bool) void
    }

    class base {
        <<abstract>>
        +ALLOWED_PLUGIN_TYPES: const string[]

        +get_frankenstyle_name() stdClass
        +get_plugin_type() string
        +get_plugin_name() string
        +is_ready()$ bool
        +is_enabled() bool
    }

    class archivingstore_localdir {
    }

    class archivingstore_moodle {
    }

    class archivingstore_other {
    }

    class storage_tier {
        <<enumeration>>
        LOCAL
        REMOTE_FAST
        REMOTE_SLOW
    }

    class file_handle {
        +id: int
        +jobid: int
        +archivingstorename: string 
        +deleted: bool
        +filename: string
        +filepath: string
        +filesize: int
        +sha256sum: string
        +mimetype: string
        +timecreated: int
        +timemodified: int
        +filekey: string

        +create()$ file_handle
        +destroy(removefile: bool) void
    }

    %% Relationships
    base  <|--  archivingstore
    archivingstore <|-- archivingstore_localdir
    archivingstore <|-- archivingstore_moodle
    archivingstore <|-- archivingstore_other
    storage_tier -- archivingstore
    file_handle -- archivingstore

    %% style
    style storage_tier fill:#dedede,stroke:#666666
    style file_handle fill:#dedede,stroke:#666666

Implementation

Each storage driver must implement the \local_archiving\driver\archivingstore interface with a class, placed at the following location: /local/archiving/driver/store/<pluginname>/classes/archivingstore.php, where <pluginname> is the name of the storage driver (e.g., localdir, moodle, ...).

Storage is classified into different tiers (\local_archiving\type\storage_tier), which differentiate between local storage that is directly accessible and remote storage that is either fast or slow. If a storage type does only support writing data but not retrieving it, a storage driver can indicate this via the supports_retrieve() method.

Once a storage driver is initiated, it reports whether it is currently available for use via the is_available() method. If supported, the number of free bytes within the storage are reported by the get_free_bytes() method.

Storing a new file via the store() method, requires the source file to be present within the Moodledata storage as an instance of \stored_file. For every file, a \local_archiving\file_handle object is created that holds all relevant metadata to identify the referenced file in the target storage system. To retrieve a previously stored file, the retrieve() method takes the information from the file_handle and tries to load a copy of the referenced file into the Moodledata storage, according to the given $fileinfo record. This standard Moodledata file record will be generated by the archiving manager and simply passed to the storage driver. Never must a storage driver generate its own file record.

If supported, existing files can be remove from the storage system via the delete() method. If working with previously stored files, make sure to also destroy the corresponding file_handle object. It is recommended to access referenced conveniently via the file_handle API instead of interfacing the underlaying storage driver directly.