tunnel/README.md

tunnel

A single-node, self-hosted OpenTunnel-compatible server in Go: blind TLS tunnels where the server routes by SNI and never sees plaintext or private keys. It speaks the exact wire protocol from docs/protocol.md, so the official opentunnel CLI and SDK work against it unchanged.

Status: M2 — core data path works end-to-end with the official CLI, and tunnels get publicly trusted certificates through ACME DNS-01 (Let's Encrypt

• Porkbun) with automatic renewal. The built-in local CA remains the default when no DNS provider is configured.

Quick start (local development)

go build -o .local/tunneld ./cmd/tunneld
.local/tunneld -domain localhost
# tls: listening on 127.0.0.1:8443, http: listening on 127.0.0.1:8080 (mode serve)

In another terminal, with the official CLI (npm i -g opentunnel or brew install anomalyco/tap/opentunnel):

python3 -m http.server 4096 &                      # something to expose
export OPENTUNNEL_API=http://localhost:8080
opentunnel route add 4096 --name api
# https://api.<id>.localhost

The tunnel's TLS is terminated by the CLI with a certificate from the server's local CA; the CA certificate is written next to the data file (ca.pem). Test the visitor side with SNI (macOS curl skips SNI on *.localhost names, so use openssl s_client or Homebrew curl):

printf 'GET / HTTP/1.1\r\nHost: api.<id>.localhost\r\nConnection: close\r\n\r\n' \
  | openssl s_client -connect 127.0.0.1:8443 -servername api.<id>.localhost \
      -CAfile ~/.local/share/tunneld/ca.pem -quiet

Configuration

Every flag also reads an environment variable (tunneld -h):

Flag	Env	Default
-domain	OPENTUNNEL_DOMAIN	localhost	API domain; tunnels are <id>.<domain>
-tls-listen	TLS_LISTEN	127.0.0.1:8443	public SNI router
-http-listen	HTTP_LISTEN	127.0.0.1:8080	off disables
-http-mode	HTTP_MODE	serve	serve = plain-HTTP app (dev); redirect = 301 to the domain
-data	TUNNELD_DATA	$XDG_DATA_HOME/tunneld/data.json	tunnel store (0600)
-ca-file	LOCAL_CA_FILE	<data dir>/ca.pem	where the local CA cert is written
-admin-token	ADMIN_TOKEN	(empty)	bearer token for the admin dashboard; empty disables the admin API
-dns-provider	DNS_PROVIDER	(auto)	porkbun or challtestsrv; defaults to Porkbun when its keys are set
-porkbun-api-key	PORKBUN_API_KEY	(empty)	Porkbun API key for DNS-01 records
-porkbun-secret-api-key	PORKBUN_SECRET_API_KEY	(empty)	Porkbun secret API key
-dns-zone	DNS_ZONE	derived from -domain	zone holding the challenge records (tzgyn.dev for tunnel.tzgyn.dev)
-acme-directory	ACME_DIRECTORY_URL	Let's Encrypt production	ACME directory URL (use staging for tests)
-acme-email	ACME_EMAIL	(empty)	contact email registered with the ACME account
-acme-propagation-seconds	ACME_PROPAGATION_TIMEOUT_SECONDS	60	how long to wait for challenge TXT records; 0 skips the check
-acme-ca-bundle	ACME_CA_BUNDLE	(empty)	extra roots for the ACME server itself (Pebble)
-challtestsrv-url	CHALLTESTSRV_URL	http://127.0.0.1:8055	pebble-challtestsrv management URL (dev only)

Certificates

Certificates have two modes, selected at startup:

• Local CA (default): signs instantly and needs no network. Clients must trust <data dir>/ca.pem (--ca-cert / OPENTUNNEL_CA_CERT), and visitors see a certificate warning.
• ACME DNS-01 (Porkbun): when PORKBUN_API_KEY and PORKBUN_SECRET_API_KEY are set (or DNS_PROVIDER=porkbun), tunneld orders a per-tunnel certificate from Let's Encrypt covering <id>.<domain> and, when the CSR asks for it, *.<id>.<domain>. The client keeps its private key: it sends a CSR and tunneld returns the certificate for that key. Issuance is asynchronous — the bind answers issuing, and the client polls until ready or failed (typically 20–60 seconds).

Porkbun setup

1. Porkbun → Account → API Access → create an API key and secret key. Restrict the key to the zone when Porkbun offers it.
2. Domain Management → tzgyn.dev → Details → enable API access for the domain (or turn on Opt In All Domains). Without this, reads fail with API_ACCESS_DISABLED.
3. Set on the server (for example in Coolify's environment variables): PORKBUN_API_KEY, PORKBUN_SECRET_API_KEY.
4. Redeploy. Startup logs show dns: Porkbun zone tzgyn.dev and certificate issuer: ACME https://acme-v02.api.letsencrypt.org/directory.
5. Set DNS_ZONE only if the derived zone is wrong. For -domain tunnel.tzgyn.dev, the derived zone is tzgyn.dev.

DNS-01 uses _acme-challenge.<id>.<domain>; the hostname and its wildcard share that name, so an attempt creates up to two TXT values there. Records are deleted when the attempt ends. The ACME account key is persisted in the data file, so restarts reuse the same account.

Certificates are renewed once they have less than 30 days left, checked every 6 hours; a failed renewal keeps the old certificate serving and is retried. Switching a running server from the local CA to ACME re-issues every existing tunnel automatically, keeping the old certificate in service until the new one is ready.

For testing against Let's Encrypt staging (untrusted certificates, separate rate limits), set ACME_DIRECTORY_URL=https://acme-staging-v02.api.letsencrypt.org/directory.

Admin dashboard

With ADMIN_TOKEN set, https://<domain>/ (and /admin) serves the admin dashboard: server uptime and version, CA expiry, tunnels with state/routes/cert expiry, and attached bridges with client version and live connection counts. It is a Svelte 5 + TypeScript app (pure CSS, no component libraries) in web/, built with bun and embedded into the binary; it polls GET /api/admin/overview (Authorization: Bearer <ADMIN_TOKEN>) every 5 seconds and stores the token in localStorage. Without ADMIN_TOKEN the endpoint answers 503 and the page is inert; with a wrong token, 401.

cd web && bun install
bun run build   # writes internal/dashboard/dist (gitignored), embedded by go:embed
bun run check   # svelte-check

The Dockerfile builds the frontend in a bun stage before the Go build.

Deploy on Coolify (or any Docker host)

The repo has a multi-stage Dockerfile producing a static, non-root alpine image. Two topologies work; both need DNS for tunnel.example.com and *.tunnel.example.com pointing at the host.

A. Coolify-managed host (Traefik already owns 443/80). The API domain is served through Traefik (Let's Encrypt); tunnel traffic is passed through untouched by SNI, because visitor TLS is terminated by the clients:

• App from this repo, Dockerfile build pack, private repo → deploy key.
• Domain https://tunnel.example.com; ports_exposes=8080 (Traefik routes HTTPS → the plain-HTTP API port).
• Env: OPENTUNNEL_DOMAIN=tunnel.example.com, HTTP_MODE=serve (the API sits behind Traefik; it must not redirect to HTTPS itself), and, for real certificates, PORKBUN_API_KEY + PORKBUN_SECRET_API_KEY (see Certificates).
• Custom Traefik labels (Coolify stores them base64-encoded): traefik.tcp.routers.tunnel-data.entrypoints=https, ...rule=HostSNIRegexp(^.+.tunnel.example.com$), ...tls.passthrough=true, traefik.tcp.services.tunnel-data.loadbalancer.server.port=8443.
• Persistent volume on /app/data; healthcheck on /health.

B. Plain Docker host. tunneld owns the public ports itself: map host 443 → container 8443 and 80 → container 8080 (HTTP_MODE=redirect serves /health on 80 and 301s the rest), volume on /app/data. No TLS-terminating proxy may sit in front of the tunnel ports.

Without ACME credentials, certificates come from the server's built-in local CA: clients need --ca-cert <data dir>/ca.pem (or OPENTUNNEL_CA_CERT), and visitors must trust that CA. With Porkbun configured, every tunnel gets a publicly trusted Let's Encrypt certificate and no client or visitor trust setup is needed.

What works (M1 + M2)

• The full HTTP API contract (paths, status codes, bodies, key order) as recorded in the reference's worker-contract.json
• Provisioning: tunnel creation, CSR bind with the reference's hostname rules, asynchronous issuance states (issuing/ready/failed), the local CA, and ACME DNS-01 through Porkbun
• Per-tunnel Let's Encrypt certificates (<id>.<domain> + optional wildcard) that keep the client's key, with automatic renewal 30 days before expiry and retries on failure
• The bridge WebSocket: attach/attached, route claiming with conflicts, heartbeats, idle retirement, open/end/reset, 32 KiB data frames
• SNI routing on the TLS listener: the domain is terminated (API), tunnel hostnames are passed through still encrypted
• Admin dashboard at / (bearer ADMIN_TOKEN): tunnels, bridges, cert state/expiry, issuer, CA expiry
• Persistence: JSON store with the CA, ACME account, server certificate, and tunnels
• Graceful shutdown: drain + close to every bridge

Not yet (later milestones)

• Issuance rate limits, CA cool-down, stale-DNS-record sweeps
• Metrics, more admin endpoints
• Multi-region mesh, inbound PROXY protocol on the TLS listener
• 60 s half-close timeout, per-connection flow control, control messages cutting ahead of queued data (single ordered outbound queue today)
• Go client/CLI — for now use the official opentunnel CLI

Development

go build ./...
go test ./...   # includes the shared spec vectors from .reference/opentunnel

The reference implementation lives in .reference/ (untracked); see .reference/opentunnel.md for what we take from it and what we skip.