hydrant#

hydrant is an AT Protocol indexer built on the fjall database. it's meant to be a flexible indexer, supporting both full-network indexing and filtered indexing (e.g., by DID), also allowing querying with XRPC's like com.atproto.sync.getRepo, com.atproto.repo.listRecords, and so on, which should allow many more usecases compared to just providing an event stream.

configuration#

hydrant is configured via environment variables. all variables are prefixed with HYDRANT_.

api#

management#

• POST /repo/add: register a DID, start backfilling, and subscribe to updates.
  • body: { "dids": ["did:plc:..."] }
• POST /repo/remove: unregister a DID and delete all associated data.
  • body: { "dids": ["did:plc:..."] }

data access (xrpc)#

hydrant implements some AT Protocol XRPC endpoints for reading data:

• com.atproto.repo.getRecord: retrieve a single record by collection and rkey.
• com.atproto.repo.listRecords: list records in a collection, with pagination.
• systems.gaze.hydrant.countRecords: count records in a collection.

event stream#

• GET /stream: subscribe to the event stream.
  • query parameters:
    • cursor (optional): start streaming from a specific event ID.

stats#

• GET /stats: get aggregate counts of repos, records, events, and errors.

vs tap#

while tap is designed primarily as a firehose consumer and relay, hydrant is flexible, it allows you to directly query the database for records, and it also provides an ordered view of events, allowing the use of a cursor to fetch events from a specific point in time.

stream behavior#

the WS /stream (hydrant) and WS /channel (tap) endpoints have different designs: