Open PDFs externally in Chrome

A minimal manifest v3 extension that opens PDF/DjVu links in Zathura via a native messaging host.

Originally it used a custom wza: URL protocol, but Chromium M130 (the StandardCompliantNonSpecialSchemeURLParsing change) broke forwarding custom schemes from JS to the OS, so it now talks to the host directly instead.

How it works

• The service worker watches for main-frame navigations to .pdf/.djvu URLs (chrome.webNavigation).
• On match it sends the URL to the native host (wza_host) via chrome.runtime.sendNativeMessage.
• wza_host pipes the URL through curl | zathura -.

Files

File	Purpose
manifest.json	Extension manifest (nativeMessaging + webNavigation permissions, service worker)
background.js	Detects PDF/DjVu navigation and forwards the URL to the host
wza_host	Native messaging host (Python): reads the URL, runs curl | zathura
wza.json	Native host manifest (template; see CHANGE_ME below)

Setup

1. Load the unpacked extension from this directory in chrome://extensions.
2. Note the extension's ID (shown on the extension card).
3. Copy wza.json to ~/.config/chromium/NativeMessagingHosts/ (or ~/.config/google-chrome/NativeMessagingHosts/ for Chrome), replacing CHANGE_ME with the extension ID, and run chmod +x wza_host:

   mkdir -p ~/.config/chromium/NativeMessagingHosts
   sed "s/CHANGE_ME/<extension-id>/" wza.json > ~/.config/chromium/NativeMessagingHosts/wza.json
   chmod +x wza_host

4. Reload the extension.

The extension ID is derived from the unpacked directory path, so it stays stable across reloads (only changes if you move the folder).