Checkpoints

Since blockchain data is immutable (can’t be changed) attempts to rewrite its contents are dismissed by the network. To circumvent this we implemented a file-based checkpoint mechanism to version the contents of the Algorand assets/contracts.

Scripts produce various information about assets/contracts and it has to be preserved. This deployment information (transaction IDs, asset indexes, etc.) is persisted into checkpoint files for later use (in future scripts).

The checkpoint files are saved in artifacts/scripts/ in a human-readable YAML format. Editing is possible but duplicate asset names are not allowed (since it prevents to know which script defined which asset).

Please refer to the Checkpoints Spec for more details.

Usage

To retrieve checkpoint data in a script user can call deployer’s functions (script parameter). Overwriting of checkpoint data from scripts is only allowed when --force is used.

Some of its functions provide way to check whether a future checkpoint already deployed an asset with a name: deployer.isDefined("asset name").

Other deployer’s methods can provide more information about currently visible assets (scripts are prevented to view checkpoints of other scripts that are going to be run in the future (by name)). These fields provide a way to view ASA and ASC1 information that was saved in the currently visible checkpoints:

deployer.asa
deployer.asc

They return JS Maps where asset name (string) points to asset information (see Checkpoint type in types.ts). These maps shouldn’t be edited by the script itself. Other deployer functions do that.

Checkpoint supports additional user’s metadata persistence by calling deployer.addCheckpointKV (adds key and value to the current checkpoint) in deploy mode (algob deploy). User can read that metadata in any script (also in run mode or REPL) using deployer.getCheckpointKV.

deployer.addCheckpointKV(key: string, value: string)
deployer.getCheckpointKV(key: string)

All deployment related functions from deployer will automatically add transaction related information to metadata. However, if a deployment script doesn’t use deployer deployment functions (for example if we have a deployment script which funds basic accounts), then a checkpoint will be empty and won’t be stored. So, consecutive run of algob deploy will re-execute that script. If we want to assure script checkpoints (and script re-execution) then a user MUST call deployer.addCheckpointKV in each script where he doesn’t call deployer deployment functions explicitly.

The checkpoint files are only saved after a successful deploy task. The data is not saved if an error happens. There is one checkpoint per deployment script.

When reading metadata (deployer.getCheckpointKV) we browses all checkpoints from all files.

YAML file structure

As it’s possible to work on multiple networks (--network switch) it’s possible to have distinct chain states in their respective networks. Every checkpoint file is defined as a network name pointing into an object of checkpoint object values.

These checkpoint values should contain timestamp, metadata, asa and asc (or more).

metadata, asa and asc are maps which point to their own specific objects. The keys of these maps are strings which should be unique per network inside of all checkpoints.

Editing them by hand is not encouraged (but if it’s needed their names must not match any asset in the same network). Currently it’s possible to edit these files by hand but it may be decided to disallow this in the future.

Note: Checkpoints will not be created or modified when script is running in run mode.

Parameters

For more details on checkpoint parameters and their specific types please refer to Checkpoint type in types.ts. Make sure that your local algob version matches the version from the link.

Checkpoint storage structure for Stateful Smart Contracts(SSC)

We can update App on algorand blockchain, therefore we store checkpoints for App in a nested form. structure for the same is: program-name-key -> timestamp -> AppInfo. Consider a case when App is updated with same programs, this is the case where we append to checkpoint with different timestamp, txConfirmation but same program-name-key.

While retreiving AppInfo from checkpoints only the lastest timestamp AppInfo is used.

Checkpoint storage for logic signature(Lsig)

  • For logic signature in contract mode: You may use addLsigCheckpoint function to store lsigInfo in checkpoint.
  • To load logic signature in contract mode: You may use getContractLsig function.
  • Ex:
    // store checkpoint
    deployer.mkContractLsig(contractName);
    // load checkpoint
    deployer.getContractLsig(contractName);
    
  • For delegated logic signature algob stores checkpoints automatically.
  • To load delegated logic signature you may use getDelegatedLsig function.
  • Ex:
    // store checkpoint
    deployer.mkDelegatedLsig(contractName);
    // load checkpoint
    deployer.getDelegatedLsig(contractName);
    

Checkpoint storage delete boolean

  • Checkpoint structure has an additional flag deleted - if it’s true, that means the respective asa/App is deleted from network. If this is the case, then the deployer will throw an error when trying to use that in any operation other than optOut.