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Token Metadata API Features

Blockchain importer​

The BlockchainImporter is a component in the Token metadata API that takes token contracts from the API database. This component is only used on service boot.

It connects to the Stacks Blockchain API database and scans the entire smart_contracts table looking for any contract that conforms to SIP-009, SIP-010 or SIP-013. When it finds a token contract, it creates a ProcessSmartContractJob and adds it to the Job queue, ßso its tokens can be read and processed thereafter.

This process runs only once. If the Token metadata API is ever restarted, though, this component re-scans the API smart_contracts table from the last processed block height. So, it can pick up any newer contracts it might have missed while the service was unavailable.

Smart contract monitor​

The BlockchainSmartContractMonitor component constantly listens to the following Stacks Blockchain API events:

  • Smart contract log events

    If a contract print event conforms to SIP-019, it finds the affected tokens and marks them for metadata refresh.

  • Smart contract deployments

    If the new contract is a token contract, it saves the new token contract and adds the contract to the job queue for token processing.

This process is kept alive throughout the entire service lifetime.

Job queue​

The role of the JobQueue is to perform all the smart contract and token processing in the service.

It is a priority queue that organizes all necessary work for contract ingestion and token metadata processing. Every job this queue processes corresponds to one row in the jobs DB table, which marks its processing status and related objects to be worked on (smart contract or token).

This object essentially runs an infinite loop that follows these steps:

  1. Upon start(), it fetches a set number of job rows that are 'pending' and loads their corresponding Job objects into memory for processing, marking those rows now as 'queued'.
  2. It executes each loaded job to completion concurrently. Depending on success or failure, the job row is marked as either 'done' or 'failed'.
  3. Once all loaded jobs are done (and the queue is now empty), it goes back to step 1.

There are two environment variables that can help you tune how the queue performs:

  • ENV.JOB_QUEUE_SIZE_LIMIT: The in-memory size of the queue, i.e., the number of pending jobs that are loaded from the database while they wait for execution (see step 1 above).
  • ENV.JOB_QUEUE_CONCURRENCY_LIMIT: The number of jobs that will be run simultaneously.

This queue runs continuously and can handle an unlimited number of jobs.

Process smart contract job​

This job makes a contract call to the Stacks node to determine the total number of tokens declared by the given contract. Once determined, it creates and enqueues all of these tokens for metadata ingestion.

Process token job​

This job fetches the metadata JSON object for a single token and other relevant properties depending on the token type (symbol, decimals, etc.). Once fetched, it parses and ingests this data to save it into the local database for API endpoints to return.

Following are the features of Token-Metadata API:

  • Complete SIP-016 metadata ingestion for
  • Automatic metadata refreshes via SIP-019 notifications
  • Metadata localization support
  • Metadata fetching via http:, https:, data: URIs. Also supported via customizable gateways:
    • IPFS
    • Arweave
  • Easy to use REST JSON endpoints with ETag caching.=
  • Prometheus metrics for job queue status, contract and token counts, API performance, etc
  • Image cache/CDN support