Server

Detailed documentation of the ALS Image Server module
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Overview

The Server utility module exposes ALS processing results through a lightweight HTTP and WebSocket service.

It is responsible for:

  • Publishing the latest stacked image and session metrics in the configured web folder
  • Serving the viewer web application (index.html, JavaScript and icons)
  • Streaming live new-image notifications to connected browsers over WebSockets
  • Providing a QR-code friendly URL so that tablets or phones can join the session quickly

The module runs in its own asyncio event loop and accepts concurrent browser clients. It never alters the processing pipeline; it only serves the web image written by the Save module.

Configuration

Setting Source Data Type Required Default Value
Web Folder Preferences: Output Tab Path to a folder Yes Work folder alias
Dedicated Web Folder Preferences: Output Tab Boolean No Disabled
Port Number Preferences: Output Tab Integer (1024–65535) Yes 8000

Control

Source Type Response
Main controls Command: START Prepare web assets and launch the server thread
Main controls Command: STOP Gracefully notify clients and shut the server down. Keep web assets available; QR code hidden by UI

Outputs

Once started, the module maintains the following artefacts inside the web folder:

Artefact Description
index.html The embedded viewer that displays the live stacked image
favicon.ico & icons/*.png Viewer assets copied from the ALS resources bundle
data.json Session metrics (STACK_SIZE, EXPO) refreshed after each stack update
web_image.jpg Latest processed frame saved in JPEG for browser consumption
openseadragon.min.js Deep-zoom viewer script used by the web interface

Behavior

Startup sequence

  1. Validate availability — the module resolves the current host IP and ensures the configured port is free. A PortInUseError is raised if another process already listens on the port.
  2. Publish static assets — index.html, icons, and the waiting image are written (or refreshed) in the web folder so that first-time clients load instantly.
  3. Expose session metrics — data.json is generated with the current stack size and cumulative exposure time.
  4. Run the server loop — an asyncio loop starts in a dedicated thread, serving HTTP on http://<host>:<port> and accepting WebSocket connections on /ws.
  5. Advertise availability — the UI updates its status and QR code, broadcasting the final URL to the session log.

If ALS can only bind to 127.0.0.1, the module keeps running but reports Web server access is limited so that you can adjust your network settings.

Live updates

  • After each processed image, the latest JPEG and data.json are overwritten in the web folder.
  • notify_browsers_about_new_image() pushes { "type": "new_image" } to all WebSocket clients so that browsers reload the image without polling.
  • The same infrastructure is used to deliver { "type": "disconnect" } right before shutdown, allowing clients to display an appropriate message.

Shutdown

When the STOP command is triggered:

  1. All connected clients receive a disconnect message.
  2. The module waits briefly (2 seconds) for browsers to close the socket.
  3. The asyncio runner is cleaned up and the dedicated thread stops.
  4. UI status and QR code are reset; the static files remain on disk for the next session.

WebSocket reference

Message Payload Trigger
new_image { "type": "new_image" } A freshly processed frame becomes available
disconnect { "type": "disconnect" } Server is shutting down
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