# OSM taxiway bastion (broker mode)

A **self-contained, whitelisted** SSH box for an OSM taxiway export pipeline. It lets a
backend fetch/generate airport ground-layout GeoJSON without handing it a shell or root:
the bastion only ever runs **three** commands, validated whole-line against a regex
allowlist and exec'd **shell-free** (no `sh -c`, so nothing an ICAO argument contains can
become a shell operator or a path).

```
ssh agent@<osm-host>
  └─ bastion-broker           (key auth; matches request vs allowed-commands.list)
       ├─ taxiways-list            → ls *-taxiways.geojson in /osm-maps
       ├─ taxiways-export <ICAO>   → export-icao-geojson.sh <ICAO>   (osmium/ogr2ogr/jq)
       └─ taxiways-cat <ICAO>      → base64 <ICAO>-taxiways.geojson   (ssh-safe tunnel)
```

The OSM toolchain (`osmium`, `ogr2ogr`, `jq`) is baked into the image (see `Dockerfile`),
so the export runs **inside** this container against the mounted `osm-maps` directory
(which holds a region PBF + `export-icao-geojson.sh`). No docker socket, no second
container — the only host data reachable is that one directory.

## Files

| file | purpose |
|------|---------|
| `Dockerfile` | Debian base (Alpine has no `osmium-tool`) + `osmium-tool`/`gdal-bin`/`jq` + openssh + the wrappers |
| `bastion-broker` | the allowlist gate, verbatim from `docker-bastion/scripts` (whole-line ERE match → shell-free exec) |
| `entrypoint` | broker-only sshd: key-only, single non-root user, every session forced through the broker |
| `bin/taxiways-{list,export,cat}` | the only executables the allowlist lets a client run |
| `allowed-commands.list` | the regex allowlist (`taxiways-export [A-Z]{4}`, …) — the security boundary |
| `docker-compose.yml` | broker-mode service, osm-maps + allowlist + keys mounts, port 6770 |

> This flavor is **Debian standalone** (not `FROM blaxsoftware/bastion`) because the export needs
> `osmium`, which Alpine doesn't package. It reuses the base repo's `bastion-broker` unchanged; only
> the sshd bootstrap is a compact broker-only `entrypoint` instead of the Alpine `start-container`.

## Deploy (on the host holding your osm-maps dir)

```bash
# 1) Authorize the backend's agent key
mkdir -p docker-data/bastion/users.d
cp /path/to/agent.pub docker-data/bastion/users.d/backend.pub

# 2) Let the bastion's `agent` user write into osm-maps (export writes files + work/)
AGENT_UID=$(docker run --rm blaxsoftware/bastion:latest id -u agent)
chown -R "$AGENT_UID" /srv/osm-maps          # point at your actual osm-maps dir

# 3) Confirm the osm-maps dir has the script + PBF
ls /srv/osm-maps/export-icao-geojson.sh /srv/osm-maps/*.osm.pbf

# 4) Build + run
docker compose up -d --build
```

To publish the image for reuse:

```bash
docker build --platform linux/amd64 -t blaxsoftware/bastion-osm-taxiways:latest .
docker push blaxsoftware/bastion-osm-taxiways:latest
```

## Test

```bash
ssh -p 6770 agent@<osm-host> taxiways-list                 # → list (maybe empty)
ssh -p 6770 agent@<osm-host> taxiways-export EDDF          # → runs the export (minutes)
ssh -p 6770 agent@<osm-host> taxiways-cat EDDF | base64 -d | head   # → GeoJSON
ssh -p 6770 agent@<osm-host> 'rm -rf /'                    # → "command not permitted", exit 126
ssh -p 6770 agent@<osm-host> taxiways-export eddf          # → refused (lowercase ≠ [A-Z]{4})
```

## Backend wiring

The backend stores the private key whose `*.pub` you dropped in `users.d/`, and connects
as `agent@<osm-host>:6770`, sending one of the three commands per connection. `taxiways-cat`
returns base64 that the backend decodes into its own storage; `taxiways-export` runs the
(minutes-long) OSM export. A pure-PHP SSH client (e.g. phpseclib) works fine — no `ssh`
binary is required on the backend side.