Quersi (QRC) - Quantus Remote Config

Minimal Axum service that serves wallet feature flags, USD exchange rates, and Ethereum address risk reports over HTTP.

Design

Feature flags are intentionally public to read. There is no write/admin HTTP API — updates are done by replacing the JSON file on disk (hot-reloaded).

Signing config files does not help against a compromised host: anyone who can replace the service binary (or its config) can serve arbitrary responses anyway. Trust is host/deploy integrity, not a signature on the JSON.

Operator/CI --> wallet_config.json --> VPS mount
                                    |
                          remote-config (load / hot-reload)
                                    |
                          GET /api/configs/wallet

ExchangeRate-API v6  -->  in-memory cache  -->  GET /api/exchange-rates

Infura (ENS) + Etherscan  -->  GET /api/risk-checker/{address_or_ens}

API

Method	Path	Auth	Response
GET	/api/configs/wallet	none	{ "data": { ...flags } }
GET	/api/exchange-rates	none	{ "data": { "conversion_rates": { ... }, "time_next_update_unix": … } }
GET	/api/risk-checker/{address_or_ens}	none	{ "data": { "address", "ensName", "balance", … } }
GET	/health	none	{ "healthy": true, "service": "RemoteConfig", "version": "…" }

Example wallet payload:

{
  "data": {
    "enableTestButtons": false,
    "enableKeystoneHardwareWallet": false,
    "enableHighSecurity": true,
    "enableRemoteNotifications": true,
    "enableSwap": true
  }
}

Payload is opaque JSON: add or change keys by updating the file — no service redeploy required. Only invalid JSON is rejected.

Exchange rates are fetched from ExchangeRate-API (v6, USD base) and cached in memory until time_next_update_unix.

Risk reports resolve an Ethereum address or .eth ENS name (via Infura) and fetch balance / transaction / contract data from Etherscan. Invalid input returns 400; unresolved ENS or missing address data returns 404; upstream rate limits return 429.

CORS is off by default (cors_allowed_origins = []). Set origins in TOML when browser clients need cross-origin access.

Quick start

wallet_config.json is gitignored (host-managed). Copy the example first:

cp wallet_config.example.json wallet_config.json
cargo run -- --config config/default.toml
# GET http://127.0.0.1:6767/api/configs/wallet
# GET http://127.0.0.1:6767/api/exchange-rates
# GET http://127.0.0.1:6767/api/risk-checker/0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045
# GET http://127.0.0.1:6767/health

Hot reload

Every ~250ms the service re-reads the JSON file:

• Valid update → memory updated
• Invalid JSON → last known good kept (warn log)

Startup fails hard if the initial file is missing or invalid.

Configuration

File	Purpose
config/default.toml	Local defaults (127.0.0.1:6767)
config/docker.toml.example	Container template (0.0.0.0:6767)

Paths in TOML that are relative are resolved against the TOML file’s directory.

config/docker.toml and wallet_config.json are gitignored — create them on the host (or in CI) and bind-mount them. For containers:

cp config/docker.toml.example config/docker.toml

Environment overrides use the REMOTE_CONFIG prefix and __ separator, e.g.:

REMOTE_CONFIG__SERVER__PORT=9090
REMOTE_CONFIG__REMOTE_CONFIGS__WALLET_CONFIGS_FILE=/path/to/flags.json
REMOTE_CONFIG__EXCHANGE_RATE__API_KEY=your-key
REMOTE_CONFIG__RISK_CHECKER__ETHERSCAN_API_KEY=your-etherscan-key
REMOTE_CONFIG__RISK_CHECKER__INFURA_API_KEY=your-infura-key

Docker

The image ships the binary only. Mount host-managed TOML and JSON at runtime (same pattern IAC should use).

cp config/docker.toml.example config/docker.toml
cp wallet_config.example.json wallet_config.json

docker build -t remote-config .
docker run --rm -p 6767:6767 \
  -e REMOTE_CONFIG__EXCHANGE_RATE__API_KEY=your-key \
  -e REMOTE_CONFIG__RISK_CHECKER__ETHERSCAN_API_KEY=your-etherscan-key \
  -e REMOTE_CONFIG__RISK_CHECKER__INFURA_API_KEY=your-infura-key \
  -v "$(pwd)/wallet_config.json:/app/wallet_config.json:ro" \
  -v "$(pwd)/config/docker.toml:/app/config/docker.toml:ro" \
  remote-config

• Default command: --config config/docker.toml (expects that path to be mounted; listens on 0.0.0.0:6767)
• Mount wallet_config.json at /app/wallet_config.json (path from the TOML)
• Mount configs read-only; the image runs as uid 10001
• If host files are mode 0640, run the container as the file owner (IAC pattern: set user: to the admin UID) so the process can read them
• Set REMOTE_CONFIG__EXCHANGE_RATE__API_KEY and risk-checker keys (or put them in the mounted TOML)

Development

cargo fmt --all
cargo clippy --all-targets --all-features -- -D warnings
cargo test