# mdns-termux

**mDNS + Tailscale hostname resolution for Termux (Android).**

Termux runs on Android's Bionic libc, which does **not** resolve `.local` names
and lacks `getent`. This repo ships small, dependency-light helpers that fix
that — without root, and without a custom system resolver.

Works on any network: LAN via multicast, off-LAN via Tailscale MagicDNS.

---

## What's in here

| Script | Role |
|--------|------|
| `mdns-resolve`    | Resolve `<host>.local` via raw multicast UDP (pure Python, stdlib only). |
| `mdns-publish.py` | Publish this device on the LAN as `movil.local` using `zeroconf`. |
| `ssh-mdns-proxy`  | SSH `ProxyCommand`: mDNS → Tailscale DNS → cached IP. |
| `ssh-fallback`    | SSH `ProxyCommand`: Tailscale → LAN, for flaky Tailscale. |
| `resolve`         | Generic resolver for **any** command (ping, curl, kubectl, nc…). Same order. |

## Install

```bash
git clone https://devops.ingeniumcodex.com/andresgarcia0313/mdns-termux.git
cd mdns-termux
bash install.sh          # or --dry-run first
```

Then follow the printed reminders (append `bashrc.snippet`, set your
`TAILSCALE_DOMAIN`, optionally merge `ssh_config.example`).

## Usage

### Generic resolver — works in any command

```bash
resolve lenovo                       # -> 100.69.236.16
ping   $(resolve hp62a)
curl   "http://$(resolve dell):8080"
kubectl --server="https://$(resolve master):6443" get nodes
```

Environment knobs:

- `TAILSCALE_DOMAIN` — defaults to `tailb0bb74.ts.net`. Set to your own tailnet.
- `MDNS_TIMEOUT` — seconds waiting for multicast (default `1`, keeps off-LAN snappy).

### Shell helpers (from `config/bashrc.snippet`)

```bash
alias r='resolve'
pingr <host>              # ping -c 3 to resolved IP
curlr <host> [flags]      # curl http://<resolved-ip>
sshr  <host> [cmd...]     # ssh via resolved IP with correct HostKeyAlias
```

### SSH by hostname (via `ProxyCommand`)

Drop `config/ssh_config.example` into `~/.ssh/config`. Then:

```bash
ssh lenovo                # resolves via mDNS then Tailscale, connects
ssh lenovo.local          # forces mDNS-first path
```

### Publishing this device as `movil.local`

```bash
python ~/.local/bin/mdns-publish.py                                # foreground
nohup python ~/.local/bin/mdns-publish.py >>~/.cache/mdns.log 2>&1 & disown
```

## Behavior by network

| Scenario           | Path                                       | Typical latency |
|--------------------|--------------------------------------------|-----------------|
| On home LAN        | mDNS multicast (1 s cap) → else Tailscale  | < 100 ms        |
| Mobile data / away | mDNS fails → Tailscale MagicDNS            | < 200 ms        |
| No Tailscale       | Both fail → cached last-known IP           | instant         |

## Gotchas found the hard way

- **`getent` doesn't exist on Termux.** Scripts that shell out to it silently
  fail. This repo uses `python -c "import socket; socket.gethostbyname(...)"`
  as the portable fallback on Bionic.
- **Shebang matters.** `#!/data/data/com.termux/files/usr/bin/bash` is required
  for `declare -A`. A stray backslash (`#\!`) makes the kernel fall through to
  `sh`, which rejects bash-only syntax with `Syntax error: "(" unexpected`.
- **mDNS off-LAN is a no-op.** Multicast (224.0.0.251) does not cross networks.
  Over mobile data, only Tailscale resolves.
- **`zeroconf` is not `pkg`-managed.** After restoring Termux from a `tar`
  backup, re-run `pip install zeroconf` or `mdns-publish.py` will silently die
  with `ModuleNotFoundError`.
- **Silent failures are the enemy.** The `.bashrc` snippet deliberately logs
  to `~/.cache/mdns.log` instead of `/dev/null`. Keep it that way.

## Tailscale on Termux

Tailscale runs as the **Android app**, not as a Termux CLI — `tailscale up`
inside a shell won't work. The app provides MagicDNS for
`*.<your-tailnet>.ts.net`, which Bionic-libc resolves fine (it's just a
regular DNS lookup).

## Related

- [claude-code-termux](https://devops.ingeniumcodex.com/andresgarcia0313/claude-code-termux)
  — Claude Code CLI setup for Termux. Uses this repo for SSH/host resolution.

## License

MIT — see `LICENSE`.