XPost: alt.comp.software.firefox, alt.comp.os.windows-10   
   From: Hank@nospam.invalid   
      
   Maria Sophia wrote on 2/24/2026 4:51 PM:   
   > Maria Sophia wrote:   
   >> As far as I've been able to ascertain by testing, no GUI program will   
   >> ever   
   >> appear on a Windows desktop when launched from a Firefox native host on   
   >> Windows, but, it should still work on Linux.   
   >   
   > Voila!   
   > Success at last!   
   >   
   > The native host runs inside a restricted, non-interactive Windows session.   
   > Unfortunately, we've learned that Windows-GUI programs apparently cannot   
   > appear from that session, but file I/O works perfectly.   
   >   
   > So the example file-based-change-detector below is a natural fit.   
   >   
   > Once I stopped fighting that one immovable Windows-GUI wall, a whole   
   > landscape of genuinely useful, practical, even elegant but non-GUI   
   > possibilities open up for our first working Firefox extension.   
   > Let's write a simple webpage-change detector instead. It will tell us if   
   > a web page has Changed or NotChanged.   
   >   
   > Overview:   
   > a. We'll keep everything in the Firefox home directory, as before   
   >     C:\app\browser\firefox\openwithgvim\*.{js,bat,json,py,log,reg}   
   > b. And create a subdirectory to watch if web pages have been changed.   
   >     C:\app\browser\firefox\openwithgvim\pagewatch\{report.txt,last.html}   
   > c. Inside pagewatch, the Python host will maintain:   
   >     i. last.html, the last version of the page   
   >     ii. report.txt, the human-readable "changed / not changed" result   
   >     iii. (optional) snapshots/, if we ever want to archive versions   
   > This keeps everything tidy and avoids clutter   
   >   
   > The logic will be simple because this is to be an example extension.   
   > A. If last.html does not exist:   
   >     Write the new HTML to last.html   
   >     Write a report saying: FIRST RUN - baseline saved   
   >     Return { ok: true, changed: true }   
   > B. If last.html does exist:   
   >     Read it   
   >     Compare it to the new HTML (simple string comparison)   
   > C. If identical:   
   >     Write: NO CHANGE   
   >     Return { ok: true, changed: false }   
   > D. If different:   
   >     Write:   
   >      CHANGED   
   >      Old length: ####   
   >      New length: ####   
   >      Timestamp: ...   
   >     Overwrite last.html with the new HTML   
   >     Return { ok: true, changed: true }   
   > E. In testing, I had to add code to overcome file locks gracefully.   
   >   
   > Here is every step of the test procedure:   
   > 1. Start Firefox   
   > 2. Click your bookmark for about:debugging#/runtime/this-firefox   
   > 3. Click "Load Temporary Add-on..."   
   > 4. Select C:\app\browser\firefox\openwithgvim\manifest.json   
   > 5. Open a local file file:///C:/data/amazon/vine/vine.htm   
   > 6. Rightclick in white space on that local file   
   > 7. Select "Open page source in gVim" (we never changed it)   
   > 8. Check the pagewatch report file for status   
   >    C:\> type C:\app\browser\firefox\openwithgvim\pagewatch\report.txt   
   >         NO CHANGE   
   >         URL: file:///C:/data/amazon/vine/vine.htm   
   >         Timestamp: 2026-02-24 16:34:02   
   >         Length: 53565 bytes   
   > 9. Edit the source (Control+U or rightclick > View page source   
   >    Change something & refresh the page   Note that ViewPageSource is an   
   > edit due to these settings:   
   >     about:config > view_source.editor   
   >     view_source.editor.external = true   
   >     view_source.editor.path = C:\app\editor\txt\vi\gvim.exe   
   > 10. Check the pagewatch report file for status   
   >     C:\> type C:\app\browser\firefox\openwithgvim\pagewatch\report.txt   
   >          CHANGED   
   >          URL: file:///C:/data/sys/apppath/vistuff/vine.htm   
   >          Timestamp: 2026-02-24 16:39:30   
   >          Old length: 53565 bytes   
   >          New length: 53541 bytes   
   >   
   > The only file that changed was the python native messaging host script.   
   > =====< cut below for gvim_host.py >=====   
   > import sys   
   > import struct   
   > import json   
   > import os   
   > from datetime import datetime   
   >   
   > # Base directory for everything   
   > BASE_DIR = r"C:\app\browser\firefox\openwithgvim"   
   > WATCH_DIR = os.path.join(BASE_DIR, "pagewatch")   
   >   
   > LAST_FILE = os.path.join(WATCH_DIR, "last.html")   
   > REPORT_FILE = os.path.join(WATCH_DIR, "report.txt")   
   >   
   > DEBUG_LOG = os.path.join(BASE_DIR, "host_debug.log")   
   > ERR_LOG = os.path.join(BASE_DIR, "host_stderr.log")   
   >   
   >   
   > def log(msg):   
   >      """Write debug messages to stderr log, but never crash if the file   
   > is locked."""   
   >      try:   
   >          with open(ERR_LOG, "a", encoding="utf-8") as f:   
   >              f.write(str(msg) + "\n")   
   >      except Exception:   
   >          # Windows sometimes locks files; logging must never kill the   
   host   
   >          pass   
   >   
   >   
   > def ensure_directories():   
   >      """Create the pagewatch directory if missing."""   
   >      if not os.path.exists(WATCH_DIR):   
   >          os.makedirs(WATCH_DIR, exist_ok=True)   
   >   
   >   
   > def read_message():   
   >      """Read a native message from Firefox."""   
   >      raw_length = sys.stdin.buffer.read(4)   
   >      if not raw_length:   
   >          log("No length header, stdin closed")   
   >          return None   
   >   
   >      length = struct.unpack("      data = sys.stdin.buffer.read(length).decode("utf-8")   
   >      return json.loads(data)   
   >   
   >   
   > def send_message(msg):   
   >      """Send a native message back to Firefox."""   
   >      encoded = json.dumps(msg).encode("utf-8")   
   >      sys.stdout.buffer.write(struct.pack("      sys.stdout.buffer.write(encoded)   
   >      sys.stdout.buffer.flush()   
   >   
   >   
   > def write_report(text):   
   >      """Write a human-readable report."""   
   >      try:   
   >          with open(REPORT_FILE, "w", encoding="utf-8") as f:   
   >              f.write(text)   
   >      except Exception as e:   
   >          log(f"Failed to write report: {e}")   
   >   
   >   
   > def main():   
   >      ensure_directories()   
   >   
   >      while True:   
   >          msg = read_message()   
   >          if msg is None:   
   >              break   
   >   
   >          html = msg.get("html", "")   
   >          url = msg.get("url", "")   
   >   
   >          timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")   
   >   
   >          # FIRST RUN - no last.html exists   
   >          if not os.path.exists(LAST_FILE):   
   >              try:   
   >                  with open(LAST_FILE, "w", encoding="utf-8")   
   as f:   
   >                      f.write(html)   
   >              except Exception as e:   
      
   [continued in next message]   
      
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