Attention Service

The problem

I procrastinate. Browser extensions and focus apps never worked for me, because closing them takes two clicks. I wanted a blocker that was genuinely annoying to get around — so it had to live below the level where I’d normally go to turn things off.

How it works

Attention Service runs as a Windows Service: it starts in the background, has no window to close, and runs with enough privileges to change system files. A small GUI lets you pick what to block and for how long, then hands over to the service.

Blocking websites

Windows checks the hosts file before it ever asks a DNS server where a domain lives. When a block starts, the service backs up the existing hosts file, then writes the original contents back out with a marked section of extra entries:

#Start of entries inserted by Attention Service
0.0.0.0 youtube.com
0.0.0.0 reddit.com
#End of entries inserted by Attention Service

Pointing a domain at 0.0.0.0 means every browser on the machine fails to reach it. When the timer runs out, the backup is copied back over the hosts file.

Blocking programs

For the length of the block, the service repeatedly takes a snapshot of every running process with CreateToolhelp32Snapshot, walks the list, and compares each executable name against the blocklist. Anything that matches is opened with PROCESS_TERMINATE rights and closed.

Locking it down

A blocker is useless if you can just kill it. So alongside whatever the user adds, a fixed set of tools is always on the blocklist while a session is running: taskmgr.exe, cmd.exe, powershell.exe, mmc.exe (the Services console) and regedit.exe. Every obvious way to stop the service gets closed the moment it opens.

What I learned

• How Windows services work — the service control manager, running without a desktop, and installing and removing a service with sc.
• Wide strings and encodings. The blocklist is stored as UTF-16 (wchar_t), but the hosts file wants plain UTF-8, so every entry goes through WideCharToMultiByte on its way in.
• Failure modes matter more when you have admin rights. If the service is killed mid-block, the entries stay in the hosts file. That’s documented in the README for now; making restore crash-safe is the next thing I want to fix.

What’s next

• Restore the hosts file on startup if a previous session didn’t end cleanly.
• Replace the busy polling loop with process-creation events, so it isn’t burning CPU while it waits.