ducoterra
269b64bace
`main()` rewrites a bare invocation into `serve`, which is what makes `mirror --port 8055` work at all — but it did that for every argument that starts with a dash, so `mirror --version` became `mirror serve --version`, the subparser has no such flag, and the command exited with "unrecognized arguments". Found by pulling the image CI published and asking it what it was. The rewrite rule is now `with_serve()`, extracted so the eight interesting inputs are asserted directly — including `--port 9999` still becoming a serve and `serve --version` staying as typed. `serve` also grew its own --version, because typing it there is just as reasonable and argparse does not inherit flags from a parent parser. The extraction is not cosmetic: the first version of this test monkeypatched `cmd_serve` to prove the rewrite, which did nothing, because argparse binds `func` at parse time — the test would have started a real uvicorn on 9999 and hung the suite. Asserting the pure function is both correct and safe. 187 tests pass, 2 skipped; ruff and pyright clean. LLM-Generated: true
mirror
Device-agnostic screen mirroring that lives entirely in the browser.
mirror runs a small HTTP server on your machine. Open it from any device on
your network:
| Page | URL | What it does |
|---|---|---|
| Share | /mirror |
Picks a window, screen, or tab via the OS-native picker and mirrors it. |
| Watch | /watch |
Shows every screen currently being mirrored; click a tile to take the stage. |
| Index | / |
Signpost + live count of mirrors. |
Any number of people can mirror at the same time and any number of people can
watch. There are no accounts and no passwords — this is built for a trusted
local network, and that assumption is deliberate and documented in
SECURITY.md. What does decide who gets in is the source address:
by default any address is welcome, and --allow-cidr / MIRROR_ALLOW_CIDRS
narrows that to the networks you name.
Quickstart
uv sync --extra dev
uv run mirror serve # http://0.0.0.0:8055
Then, from another machine on the LAN:
http://<this-machine>:8055/mirror # to share
http://<this-machine>:8055/watch # to watch
Linux is the primary target. On Linux the native picker is X11/Wayland's own
(Chromium uses xdg-desktop-portal on Wayland/GNOME/KDE, and its built-in X11
picker on Xorg), so nothing has to be installed on the client side.
How it works
Media never touches the server. Each mirror is a WebRTC peer connection established directly between the sharer's browser and each watcher's browser (a "mesh" fan-out). The server is a signaling relay and roster only: it tracks who is publishing what, forwards SDP/ICE between peers, and pushes roster deltas to viewers.
sharer browser ──ws──► ┌──────────────────────┐ ◄──ws── watcher browser
│ │ FastAPI │ ▲
│ offer/ICE ───►│ /ws (signalling) │◄─── offer/ICE │
│ │ registry (in-mem) │ │
└────── WebRTC (SRTP, LAN, p2p) ─────────┴─────────────────┘
Configuration
Environment variables (all optional; a .env file is loaded if present):
| Variable | Default | Meaning |
|---|---|---|
MIRROR_HOST |
0.0.0.0 |
Bind address for mirror serve. |
MIRROR_PORT |
8055 |
Bind port. |
MIRROR_ICE_SERVERS |
[] |
JSON array of RTCIceServer objects, if peers cannot reach each other directly. |
MIRROR_MAX_MIRRORS |
0 |
Cap on concurrent mirrors (0 = unlimited). |
MIRROR_ALLOW_CIDRS |
(unset) | Comma-separated source networks allowed to connect, e.g. 10.2.0.0/22,fd00::/64. Unset means unrestricted. |
MIRROR_TRUSTED_PROXIES |
127.0.0.0/8, ::1/128 |
Which peers may speak for a client via X-Forwarded-For. Only a proxy that overwrites the header belongs here. |
DEBUGPY |
0 |
1 opens a debugpy listener on DEBUGPY_PORT. |
DEBUGPY_PORT |
5678 |
debugpy port. |
Platform notes
Screen capture needs a secure context. http://localhost is one; a plain
http://192.168.x.x opened from another device is not, and the browser hides
getDisplayMedia() completely. The /mirror page detects this and prints the
three ways forward (share from localhost, serve HTTPS, or mark that one origin as
secure on the sharing device). Watching never needs permission.
This is why the fleet deployment terminates TLS in nginx rather than exposing
mirror serve directly — over https://, every device on the network can share
and none of this applies. A bare mirror serve is for the machine it runs on and
for testing.
Linux. On X11/Xorg Chromium uses its native capturer — the picker appears and
that is the end of it. On Wayland (GNOME/KDE) Chromium goes through
xdg-desktop-portal, so the compositor shows its own permission dialog for
each share, which mirror neither controls nor tries to bypass. Chrome's picker
offers whole screens and individual windows; on Wayland what the portal will
agree to depends on the compositor.
Deployment
The internal deployment is https://mirror.reeseapps.com, described and automated
in the deployments repo under mirror/ (app/ quadlet, nginx/ edge, certbot/,
route53/, and a README with the VM SOP). Three things about it are worth knowing
from this side:
- TLS ends at nginx on the service VM, not in this process, so there is no
--httpsflag here. That is what makesgetDisplayMedia()available on every device, and it means anUpgradeheader and a long idle timeout on/wsare load-bearing. - The address list is enforced twice — nginx
allow/deny, andMIRROR_ALLOW_CIDRSin the container for the path that bypasses nginx. Change both in one commit. - The container has no internet egress. Media goes browser-to-browser and the
server only relays JSON, so it dials nothing;
Internal=trueis what makes that a fact rather than an intention.
Development
uv run pytest # unit + API + browser E2E (~20s)
uv run pytest -m "not e2e" # everything except the browser (~0.5s)
uv run ruff check . && uv run ruff format --check . && uv run pyright
The browser suite drives real capture: Chromium's fake media device yields a moving 1280×720 monitor stream, so the assertions are on decoded, changing pixels at the watcher — not on log lines.
There is a second, opt-in rung that exercises Chromium's real X11 capture backend on a private Xvfb display, isolated from your own session so it can never prompt you or mirror your desktop:
MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay
See AGENTS.md for the operating rules, .agents/PLAN.md for the locked architectural decisions, and SECURITY.md for why there is no login.