echolot/server

echolot-server

The probe server (spec). Pure Go, stdlib only, GPL-3.0-or-later.

Skeleton status: control plane (enroll / profile / sessions with the spec's HKDF key schedule), UDP data plane (ECHO with observation block, TIMESYNC, HMAC gate, anti-replay, anti-amplification — wire format covered by tests). Not yet: TCP/TLS echo, STUN, canary DNS, actions, observations API, admin UI beyond token minting.

Run in Docker (config via env)

docker compose up -d          # see compose.yaml — network_mode: host is required

Host networking is not negotiable: behind Docker NAT the server would observe the proxy's source addresses and TTLs instead of the client's — falsifying exactly what it measures. Container mode is autodetected (/.dockerenv etc.); --docker / ECHOLOT_DOCKER=1 forces it. In this mode systemd install and self-update are refused — update by pulling a new image tag.

Run native (systemd)

go build -o /usr/local/bin/echolot-server ./cmd/echolot-server
sudo /usr/local/bin/echolot-server --install-systemd     # writes unit, enables, starts
sudo /usr/local/bin/echolot-server --uninstall-systemd

Config precedence: flags > ECHOLOT_* env > defaults. Every flag has an env twin (--udp-listen ↔ ECHOLOT_UDP_LISTEN).

Self-update (opt-in, native only)

echolot-server --self-update \
  --self-update-api https://git.example.net/api/v1/repos/owner/repo

Fetches the newest server-v* release asset for this OS/arch and atomically replaces the binary; systemd's Restart= brings up the new version. Run it from a systemd timer for unattended updates. TODO before enabling anywhere untrusted: signature verification of the downloaded asset.

First contact

# 1. mint an enrollment token (admin listener is loopback-only)
curl -s -X POST 'http://127.0.0.1:8444/admin/enroll-tokens?note=phone'
# 2. device enrolls with it (normally via the echolot:// QR code)
curl -sk -X POST https://<host>:8443/v1/enroll -H 'Authorization: Bearer <token>'
# 3. device fetches its profile
curl -sk https://<host>:8443/v1/profile -H 'Authorization: Bearer <credential>'

The SPKI pin clients must verify is logged at startup (pin-sha256).

Development

go test ./...   # includes wire-format tests for the UDP data plane
go vet ./...

CI (.gitea/workflows/build-server.yml): tests on every push touching server/; tagging server-v1.2.3 builds + pushes the container image to the Gitea registry and attaches static linux amd64/arm64 binaries (+ SHA256SUMS) to a release — the same artifacts --self-update consumes.