maptool/docs/architecture.adoc

Architecture

Table of Contents

• Overview
• Directory layout
• Offline maps
  • Offline text labels and color palette
• Weather radar overlay
• GPX tracks and waypoints
• Live GNSS position
• Networking
• Authentication

Overview

MapTool is a Sinatra web application, served locally by Puma and opened in a browser.

Directory layout

Path	Purpose
app.rb, config.ru	Sinatra application and Rack entry point.
config/puma.rb	Puma server configuration (binds to 127.0.0.1 only — the app is local-only, not exposed on the network).
public/, views/	Frontend assets and Sinatra templates. The map view uses MapLibre GL JS, rendering vector tiles.
public/vendor/	Third-party frontend libraries, vendored (not loaded from a CDN) so the app also works with no internet access. See docs/third-party-notices.adoc.
data/	Local, gitignored data files, e.g. offline.pmtiles and uploaded GPX files under data/gpx/.
lib/maptool/	Application code beyond routing: the GPX parser and file store.
docs/	Project documentation, in AsciiDoc.

Offline maps

Map data is vector, not raster: the app ships MapLibre GL JS (vendored, see below) and the map view (public/js/map.js) offers two styles:

• Online — a full hosted vector style, OpenFreeMap "liberty", requires internet access.

• Offline — built at runtime from a local PMTiles archive at data/offline.pmtiles, served as-is (see below) at /tiles/offline.pmtiles, decoded client-side by pmtiles.js registered as a pmtiles:// protocol handler, and styled with base layers from protomaps-themes-base.

GET /api/offline-tiles reports whether data/offline.pmtiles is present ({"available": true|false}); the frontend uses it once, on load, to default to the offline style when local tile data exists — otherwise it defaults to the online style. Either way, the layer toggle in the top-left of the map lets the user switch manually.

PMTiles is a single, self-indexed file, which is why this needs no tile-decoding logic on the server: app.rb’s `/tiles/offline.pmtiles route (send_file, which Sinatra serves with HTTP range-request support) just returns byte ranges of the file; pmtiles.js in the browser reads the archive’s own directory and requests only the bytes it needs for the tiles on screen.

Offline text labels and color palette

Label rendering in MapLibre needs a "glyphs" server serving font PBF ranges (256 Unicode code points each); data/offline.pmtiles’s fields (`name, name:en, script, …​) match what protomaps-themes-base’s `layers(source, theme, { lang: "en" }) expects for its label layers (verified against the actual PMTiles vector layer schema), so passing that option turns labels on. The glyphs themselves are vendored under public/vendor/fonts/ — Noto Sans Regular/Italic/Medium, ranges 0-255 and 256-511 (Basic Latin + Latin-1 Supplement + Latin Extended-A, SIL OFL licensed, from protomaps/basemaps-assets), covering accented Latin place names (Slovak, Czech, Polish, German, …​). Labels in other scripts (Cyrillic, Greek, CJK, …​) won’t render offline, since those glyph ranges aren’t vendored.

public/js/map.js’s `OFFLINE_THEME also nudges a handful of color roles (background, water, wood, buildings, the two road-importance tiers) from `protomaps-themes-base’s stock "light" theme towards the online "liberty" style’s actual palette (sampled from its style JSON), so Online/Offline don’t look like two different apps. This is deliberately partial — most roles (labels, casings, minor terrain fills, …​) are left at their theme defaults — not the kind of full per-layer recolor a previous iteration of this app did (and removed, along with any dependency on OsmAnd’s own tile server, which this app cannot use per OsmAnd’s terms restricting tile use to "personal, non-commercial use within OsmAnd applications and platforms").

No PMTiles file ships with the repository — it is expected to be supplied locally (see docs/development.adoc) and stays gitignored because such extracts are typically large binary files.

Weather radar overlay

public/js/radar.js adds a "Radar" map control that overlays recent precipitation radar from RainViewer's free public API (no API key required). Enabling it:

1. Fetches https://api.rainviewer.com/public/weather-maps.json, which lists RainViewer’s past radar frames (fixed 10-minute cadence, at most 13 covering the last 120 minutes).

2. Takes the most recent 7 (last ~60 minutes — the same default as the Home Assistant weather-radar-card, for a consistent feel with that setup) and adds one MapLibre raster source/layer per frame, all pre-loaded but only the current frame’s raster-opacity non-zero.

3. Animates by toggling that opacity across frames on an interval (play/pause + a scrub slider), rather than swapping tiles in and out — avoids reloading tiles on every step.

Tile URL: {host}{frame.path}/256/{z}/{x}/{y}/2/1_0.png — 2 is RainViewer’s "Universal Blue" color scheme, 1 enables their smoothing, 0 disables the snow overlay. host and each frame’s path come from the API response.

Since map.setStyle() (switching Online/Offline) tears down all custom sources and layers, the control listens for style.load and re-adds the radar layers if the overlay was on.

This is a live, online-only overlay — it always needs internet access and is unrelated to the offline PMTiles basemap above. Per RainViewer’s terms, the API is free for personal/non-commercial use.

GPX tracks and waypoints

The "GPX" map control (public/js/gpx.js) opens a side panel to upload GPX files by dragging them in, organize them into folders (also by dragging), and toggle each one on the map individually.

Storage

Files are stored as-is under data/gpx/, in a folder hierarchy the user manages directly — Maptool::GpxStore (lib/maptool/gpx_store.rb) provides save, create_folder, delete_file, delete_folder and move. Every path coming from the client (a folder to create/upload/move into, a file path in a URL) is resolved with File.expand_path and checked against the store root before touching the filesystem, so ../..-style path traversal can’t escape data/gpx/; delete_folder additionally refuses an empty path or one that resolves to the store root itself, so it can never rm -rf the whole store. GET /api/gpx/tree returns the resulting folder/file tree as JSON, which the panel renders recursively (folders as <details>, files as a checkbox, both with a delete button).

Drag & drop

The dropzone at the top of the panel accepts one or more .gpx files (POST /api/gpx, multipart) into the top level, or click it to browse instead. An already-uploaded file (a .gpx-tree__file row, draggable) can be dragged onto a folder to move it there (POST /api/gpx/move), or dropped anywhere else in the tree to move it back to the top level; an OS file can also be dropped directly onto a folder to upload straight into it. Both drag sources land on the same drop targets and are told apart by a custom application/x-gpx-path drag payload type versus the browser’s own "Files" type. If a file that’s currently checked (visible on the map) gets moved, its map layers are re-added under the new path so it stays visible; if it (or its containing folder) gets deleted, its layers are removed instead.

Rendering

Checking a file fetches GET /api/gpx/file/<path> — Maptool::Gpx (lib/maptool/gpx.rb) parses the GPX with REXML and converts it to a GeoJSON FeatureCollection: <wpt> waypoints become Point features (with name, desc and time carried through as properties), each <trk> becomes one MultiLineString feature (one line per <trkseg>). MapLibre’s geometry-type expression treats MultiLineString the same as LineString, so a single GeoJSON source per file with a line layer and a circle layer (each filtered by geometry type) is enough to render both waypoints and tracks. <rte> routes are not handled.

Like the radar overlay, GPX layers are removed by map.setStyle() (switching Online/Offline) and get re-added on style.load for whichever files were checked.

Waypoint popups

Clicking a waypoint circle opens a MapLibre popup with its name, description and time. Click/hover handling is registered once per file (via map.on(type, layerId, handler), a delegated listener that survives setStyle()) rather than on every style.load re-add, which would otherwise stack duplicate handlers and pop up several copies per click. Waypoint text comes straight from an uploaded file — untrusted input — so public/js/gpx.js’s `linkify() turns bare URLs in the description into <a> links by splitting the text on a URL pattern and escaping every piece (including the URL itself, as both href and link text) before assembling any HTML; the URL pattern excludes quote characters, so a matched URL can never break out of the href="…​" attribute. Every other value is HTML-escaped before being handed to Popup#setHTML.

Live GNSS position

A "GNSS" map control (public/js/gnss.js) shows the fix from a local GNSS receiver (a real one, plugged into the machine running the server — distinct from NavigationControl’s browser `navigator.geolocation, which the OS may or may not derive from such a receiver at all).

lib/maptool/gpsd_client.rb is a small client for gpsd's JSON protocol over TCP (port 2947 by default): it watches for TPV — "time-position-velocity", gpsd’s term for a fix — reports and yields each as a plain hash, reconnecting on any I/O error so a receiver that isn’t plugged in yet (or gpsd not running) is not fatal. app.rb runs one of these in a background thread for the whole process and keeps the latest fix in GNSS_LATEST, guarded by a mutex since the HTTP threads read it concurrently.

GET /api/gnss/position, polled by the frontend every 1.5s, is a deliberate choice over a push channel (SSE/WebSocket): gpsd itself only reports at roughly 1Hz, so a push channel buys nothing here, and it sidesteps a real problem — Sinatra’s stream(:keep_open) helper, absent an EventMachine reactor (i.e. under plain threaded Puma, as here), calls its block in a tight loop instead of waiting for external writes. That is fine for a stream that itself blocks between writes, but for a "register once, get pushed to later" connection — which is what a live position feed is — the block returns immediately and gets re-invoked immediately, forever: every iteration re-registers the connection, so held connections and memory grow unbounded. This was caught in testing (the dev server hit ~98% CPU and ~28GB RSS within minutes) before it shipped.

The endpoint reports available: false once the last fix is more than GNSS_STALE_AFTER (10s) old, rather than serving a stale position forever after the receiver loses its fix or gets unplugged.

MapLibre Marker`s (used for the fix) are plain positioned DOM elements, not tied to the style’s sources/layers, so — unlike the radar/GPX layers — the marker survives `map.setStyle() (switching Online/Offline) with no extra re-add handling needed.

Networking

By default (local dev) the Sinatra server only binds to 127.0.0.1 and isn’t reachable from other machines. The deployed instance is an exception — see docs/deployment.adoc for BIND_HOST and how it’s exposed via Docker/nginx as map.priesol.net.

Authentication

The GPX store’s read endpoints (viewing the map, the folder tree, individual files) are public — anyone with the URL can look. Its write endpoints (POST /api/gpx, POST /api/gpx/folder, DELETE /api/gpx/file/, DELETE /api/gpx/folder/, POST /api/gpx/move) require login, guarded by require_login! in app.rb.

Login delegates to the Gitea instance at git.priesol.net via OAuth2 (GET /login redirects to Gitea’s authorize endpoint, GET /auth/callback exchanges the code and fetches /api/v1/user) rather than maintaining a separate local username/password — there’s already an account to reuse, and it keeps credential storage (password hash, resets, …​) out of this app entirely. Successfully authenticating with Gitea is not by itself enough to write, though — the callback also checks the returned login against MAPTOOL_ALLOWED_GITEA_USER, so registering (or already having) any other account on that Gitea instance doesn’t grant access here.

Session state is a signed cookie (Rack::Session::Cookie, secure in production, httponly, same_site: lax) keyed off SESSION_SECRET — see docs/deployment.adoc for where that and the OAuth2 client id/secret live (not committed to the repo).