130 tests, ~20s, 94% coverage. Four rungs, each proving something the one
below it cannot:
registry admission, fan-out, signal authorization and teardown, no I/O
wire camelCase round-trip, malformed frames, WebSocket lifecycle
e2e real capture -> encode -> SRTP -> decode -> painted frames
realdisplay the actual X11 capture backend on a private Xvfb display
The e2e rung drives Chromium's fake media device, which produces a genuine
moving 1280x720 monitor stream, so the assertion is that a watcher's <video>
has a size and that its pixels change over time -- a frozen or never-started
peer connection fails the suite, which a "signal arrived" assertion would
not have caught.
Findings encoded as flags and comments, because each cost a debugging cycle:
the headless shell has no media stack at all (use channel="chromium");
mediaDevices is undefined off a secure context (serve over 127.0.0.1); and
--use-fake-ui-for-media-stream breaks real X11 capture by approving the
request without ever selecting a source, so the realdisplay suite selects
the source explicitly instead.
The realdisplay fixture strips WAYLAND_DISPLAY and DBUS_SESSION_BUS_ADDRESS
from the browser environment. Without that, a headed Chromium reaches
xdg-desktop-portal, mirrors the developer's actual desktop and raises a
permission dialog on their real screen -- which is exactly what happened
before this was isolated. Skipped unless MIRROR_REALDISPLAY=1.
Also guards the frontend's structure: scripts must parse as ES modules,
every id a script looks up must exist in its page, ids must not collide
across pages that share one stylesheet, and nothing may load from a CDN.
LLM-Generated: true
A FastAPI server with two pages and one WebSocket. /mirror captures a
window, screen or tab through the OS-native getDisplayMedia picker; /watch
shows every live mirror as a wall and takes one fullscreen on click. Any
number of sharers and watchers, at the same time.
Media never touches the server: each watcher gets its own RTCPeerConnection
to the sharer, and the Python process only relays JSON. The roster lives in
registry.py, which is transport-free by design -- every operation returns
the envelopes to deliver, so admission, fan-out and teardown policy are all
unit-testable without a socket.
Registry rules worth stating: a signal frame is relayed only along an
existing subscription in either direction; viewer-to-peer traffic is
refused; and teardown is broadcast to every viewer rather than only the
subscribers, because a tile is drawn on stream_added and a viewer that has
not yet subscribed still has a stale tile to clear.
Frontend is hand-written ES modules with no build step and no external
asset. Chromium scales a monitor capture to the capturing window and
requires a secure context, so /mirror detects an insecure origin and prints
the three ways out rather than failing on a button click.
LLM-Generated: true
ducoterra