joystream/testnets/rome/specification/runtime/data-object-storage-registry-module.md

Data Object Storage Registry Module

Table Of Contents

• Name
• Dependencies
• Design
• Future TODOs
• State
• Events
• Dispatchable Methods

Name

DataObjectStorageRegistry

Dependencies

• Data Directory: A storage sub-module which lists all DataObjects on the network.

Design

Motivation

The Data Object Storage Registry is where storage providers commit to storing any given DataObject.

When any storage provider has accepted and stored content - whether it is the Liaison or a mirror - it will create a StorageRelationship entry in the registry to indicate that it can be contacted to serve the content.

For an available DataObject, there is thus at least one, possibly many StorageRelationship entries in the runtime:

• DataObject describes content that should exist on the network, and links to a Liaison which must have it available.
• StorageRelationships indicate that content exists in a particular location.

StorageRelationship contains an available flag, which shows whether the relationship is currently fulfillable by the storage provider. This permits indicating an intent to fulfil on the runtime by providing an inactive relationship, then synchronizing content, and finally updating the relationship when content can be served.

State

• StorageRelationships: a map of ContentId to a vector of StorageRelationship. An empty vector means there is no relationship, i.e. the content is not stored.

However, there still need to be available relationships in the vector. Merely finding a relationship is not sufficient to determine whether the content is stored somewhere on the network.

Events

• StorageRelationshipAdded: a storage provider has committed to serve a particular content.

The event payload consists of the ContentId of the content added, and the AccountId of the storage provider adding it. Note that merely adding a storage relationship does not mean that the content is available to be served.

• StorageRelationshipAvailabilityChanged: the given storage relationship's availability changed.

The event payload consists of the ContentId, the storage provider's AccountId, and the storage relationship's available flag value.

Dispatchable Methods

add_storage_relationship

Payload

• The storage provider origin.
• content_id: The ContentId to add a storage relationship for.

Description

When a storage provider intends to store content, it calls this function to register this intent on the chain. The StorageRelationship created by this function is set to not be available initially.

Errors

• The origin is not a storage provider.
• The ContentId does not exist in the Data Directory.
• There is already a StorageRelationship for this ContentId and storage provider AccountId.

Side effect(s)

A new, not-available StorageRelationship for the ContentId and storage provider AccountId is added to the StorageRelationships state.

Event(s)

• StorageRelationshipAdded

set_storage_relationship_availability

Payload

• The storage provider origin.
• content_id: The ContentId to modify the StorageRelationship for.
• available: a boolean flag indicating the new availability.

Description

When a storage provider has finished synchronizing content identified by the ContentId, it can register itself as having the content available for download. The function only modifies state if new value of the available flag differs from the stored value.

Errors

• The origin is not a storage provider.
• The ContentId does not exist in the Data Directory.
• There is no StorageRelationship for this ContentId and storage provider AccountId.

Side effect(s)

The StorageRelationship identified by the storage provider and ContentId has its available flag set to the passed value.

Event(s)

• StorageRelationshipAvailabilityChanged