Architecture

System context

flowchart TB
  subgraph node [BCH_full_node]
    RPC[JSON-RPC]
    ZMQ[ZMQ_rawtx_rawblock]
  end

  subgraph indexer [psf_memo_indexer]
    BI[Block_indexer_process]
    TI[TX_indexer_process]
    BI -->|GET_tx-start| TI
  end

  subgraph db [psf_memo_db]
    Koa[Koa_REST]
    LDB[(LevelDB_instances)]
    Koa --> LDB
  end

  RPC --> BI
  RPC --> TI
  ZMQ --> BI
  ZMQ --> TI
  BI -->|axios_level_CRUD| Koa
  TI -->|axios_level_CRUD| Koa

Two-process indexer design

The indexer splits work the same way as psf-slp-indexer-g2:

Process	Responsibility	Why separate
Block indexer	Historical catch-up (IBD) and confirmed blocks via ZMQ	Heavy, sequential block work; must finish before mempool indexing is trustworthy for “at tip”
TX indexer	Unconfirmed transactions via ZMQ	High volume, duplicate ZMQ events; isolated so IBD memory/CPU does not contend with mempool flood

Coordination is deliberately minimal: after IBD, the block indexer issues GET http://{TX_REST_API_IP}:{TX_REST_API_PORT}/tx-start. The TX indexer polls that flag every two seconds until set, then subscribes to ZMQ.

Tradeoff: No shared memory or message queue between processes—only HTTP and the database. Simplicity and operational parity with SLP outweigh lower latency startup.

Clean Architecture (indexer)

Both repos follow Clean Architecture: dependencies point inward; framework and I/O live at the edges.

psf-memo-indexer layers

Entry points (framework)
  psf-memo-block-indexer.js
  psf-memo-tx-indexer.js
        │
        ▼
Controllers
  keyboard.js          — graceful stop (q key)
  tx-rest-api.js       — Express /tx-start
        │
        ▼
Use cases
  index-blocks.js      — processBlock, processMemoTx
  filter-block.js      — filterMemoTxs (parallel pre-check)
  state.js             — synced block height
  action-types/*.js    — per Memo action handlers
  utils.js
        │
        ▼
Adapters
  rpc.js               — full node JSON-RPC
  zmq.js               — @psf/bitcoincash-zmq-decoder
  transaction.js       — fetch tx + memo detection cache
  status-db.js, *-db   — axios → psf-memo-db
  tx-indexer.js        — start signal to TX process
  backup-db.js         — POST /level/backup
        │
        ▼
Libraries
  memo-parser.js       — OP_RETURN pushdata, signer address
  memo-codes.js        — action prefixes and limits

Rule: Use cases contain business rules (valid pushdata counts, reply parent links, like tips). Adapters only move bytes on the network or disk API.

psf-memo-db layers

index.js → bin/server.js (Koa)
        │
        ▼
Controllers
  rest-api/index.js
  rest-api/level/*     — CRUD handlers
  rest-api/health/
        │
        ▼
Use cases
  index.js             — minimal stub (parity with psf-slp-db)
        │
        ▼
Adapters
  level-db.js          — open/close LevelDB instances
  db-backup.js         — zip / restore

Level CRUD bypasses use cases intentionally—same as psf-slp-db’s /level controller calling adapters.level.*Db.put directly. The DB service is a thin persistence plane, not a domain model server.

Repository layout (indexer)

Path	Purpose
`config/index.js`	Environment-driven settings
`src/lib/`	Pure protocol parsing (no I/O)
`src/adapters/`	External systems
`src/use-cases/`	Indexing orchestration and handlers
`src/controllers/`	HTTP and keyboard
`production/docker/`	Docker Compose, per-service Dockerfile and `.env`
`test/unit/`	Mocha + c8

Repository layout (database)

Path	Purpose
`bin/server.js`	Koa bootstrap (mirrors psf-slp-db)
`config/env/`	`SVC_ENV` profiles
`src/adapters/level-db.js`	Twelve LevelDB stores under `leveldb/current/`
`src/controllers/rest-api/level/`	Generic CRUD + status + backup routes
`leveldb/current/{name}/`	Runtime data (gitignored)
`leveldb/zips/`	Epoch backups

LevelDB schema (summary)

Each store is a separate LevelDB with JSON values. Keys are txids, addresses, or composite strings depending on entity. Full detail: psf-memo-db.md.

Store	Typical key	Value role
`status`	`status`	`syncedBlockHeight`, `chainBlockHeight`, `startBlockHeight`
`posts`	txid	Author address, text, timestamp
`postParents`	child txid	Parent txid (reply)
`postChildren`	parent txid	Reverse index for replies
`likes`	like txid	Post txid, liker, optional tip
`names`	address	Display name + provenance txid
`profiles`	address	Profile text
`profilePics`	address	Avatar URL
`follows`	`follower:followeePkHash`	Follow/unfollow event
`rooms`	composite	Topic posts and topic follows
`processErrors`	txid	Validation / parse failures
`ptxs`	txid	Idempotency marker (already processed)

External dependencies

Package	Used by	Role
`@psf/bch-js`	Indexer	Script decompile for signer address; optional REST
`@psf/bitcoincash-zmq-decoder`	Indexer	Decode `rawtx` / `rawblock` ZMQ messages
`zeromq`	Indexer	Subscribe to full node
`@chris.troutner/retry-queue`	Indexer	Retry RPC on transient failure
`axios`	Indexer	psf-memo-db REST client
`p-queue` / `p-retry`	Indexer	Parallel block filter with retries
`express`	Indexer	TX indexer control API
`level`	psf-memo-db	Embedded JSON LevelDB
`koa` + `koa-router`	psf-memo-db	REST server

Not used: slp-parser, Lokad ID checks, DAG sorting, token UTXO graphs.

Deployment topology

production/docker/
├── docker-compose.yml
├── memo-db/          → build context: ../../psf-memo-db
├── block-indexer/    → build context: indexer repo root
└── tx-indexer/

Volumes mount .env and start scripts per service, matching the SLP production pattern. LevelDB data can persist under production/data/leveldb.

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