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bal-server/docs/03_architecture_and_data_flow.md
svatantrya df8effcc60 refactor: remove bal-pusher-enhanced and update docs/env
- Remove src/bin/bal-pusher-enhanced.rs (synchronous pusher variant)
- Remove bal-pusher.env and bal-pusher.sh from git tracking (now in .gitignore)
- Update all documentation to remove references to bal-pusher-enhanced:
  * 01_project_overview.md
  * 02_glossary_and_bitcoin_domain.md
  * 03_architecture_and_data_flow.md
  * 04_modules_detail.md
  * 05_api_reference.md (remove rawblock ZMQ section, update references)
  * 08_security_audit.md (remove references to bal-pusher-enhanced in DoS and ZMQ sections)
  * 09_references_and_links.md
- Build verified: cargo check passes for bal-pusher and bal-server binaries
2026-07-16 14:32:59 -04:00

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# Architecture and Data Flow
## Quick Reference
- **What this file contains:** high-level architecture, data flow, state machine, and error handling strategy.
- **See also:** [01_project_overview.md](01_project_overview.md), [04_modules_detail.md](04_modules_detail.md), [05_api_reference.md](05_api_reference.md), [06_database_schema.md](06_database_schema.md)
## High-Level Architecture
```
User
|
| HTTP POST (raw hex transactions)
v
+-----------------+
| bal-server | (hyper + tokio, async)
| (src/bin/bal-server.rs) |
+-----------------+
| SQLite insert (db.rs)
v
bal.db
| (transactions with status=0, waiting locktime)
|
| ZMQ (hashblock / rawblock)
v
+-----------------+
+-----------------+
| bal-pusher | (async, ZMQ + RPC + reqwest)
| (src/bin/bal-pusher.rs)
+-----------------+
+-----------------+
| bitcoincore-rpc
| sendrawtransaction
v
Bitcoin Network
```
## Data Flow (Transaction Lifecycle)
1. **Submission**: A client sends one or more raw hex transactions to the `pushtxs` endpoint.
2. **Validation**: The `bal-server` parses each transaction using `bitcoin::Transaction`. It checks for the fee output, extracts inputs/outputs, and validates the locktime.
3. **Storage**: Valid transactions are stored in `tbl_tx` with `status = 0` (waiting). The inputs and outputs are stored in `tbl_inp` and `tbl_out`.
4. **Monitoring**: The `bal-pusher` listens to the ZMQ `hashblock` topic. When a new block is detected, it fetches the `mediantime` via `getblockchaininfo` (or via the block's median time in the enhanced version).
5. **Evaluation**: The pusher queries the database for transactions with `status=0` and compares their locktime to the current blockchain median time.
6. **Broadcast**: If the locktime is satisfied, the pusher sends the transaction via `sendrawtransaction` and updates the status to `1` (sent) or `2` (failed if the RPC returns an error).
7. **Statistics**: The pusher periodically sends statistics to a remote server (`welist`) using a signed POST request. The server also collects stats on its own.
## State Machine
```
[Submitted] -> status=0 (waiting)
|
| locktime satisfied
v
[Push attempt] -> status=1 (sent) or status=2 (failed)
```
The `status` field in `tbl_tx` is an integer:
- `0`: Waiting for locktime.
- `1`: Successfully sent to the network.
- `2`: Failed (e.g., RPC error `-25 bad-txns-inputs-missingorspent`).
## Error Handling Strategy
The codebase is currently inconsistent with error handling. The `bal-server` uses `unwrap()` on many critical paths (e.g., `sqlite::open`, `Regex::new`, body parsing), which causes panics in the async runtime. The `bal-pusher` also panics on RPC connection failures (`panic!("impossible to get client {}", e)`) which crashes the entire ZMQ loop.
## Logging and Monitoring
The project uses `env_logger` and `log`. By default, `RUST_LOG=info` is set. The `bal-pusher` sends signed statistics to a remote server. The server exposes a `stats` endpoint (`/<network>/stats`) if `expose_stats` is enabled.