Printlink

PrintLink

Website: https://najm07.github.io/Printlink/

Peer-to-peer LAN printer sharing for small offices — no Windows printer sharing, no cloud, no accounts. Print from any PC to a printer attached to another PC on the LAN, with per-PC access grants that expire automatically.

How it works

• Every PC runs the PrintLink tray agent.
• On the PC with the printer: share it under a friendly alias.
• On any other PC: add a remote printer by entering that PC’s 9-digit ID. The host gets an accept/refuse dialog. Access lasts 7 days (configurable) and can be revoked anytime. When you add a printer you give it a friendly name (shown as alias @ name, e.g. CANON @ Lina's PC), so the lists stay readable even with many printers — rename or remove entries any time from “Manage remote printers…” (removing also tells the host to revoke your grant).
• Send a document with right-click → “Print with PrintLink” or the tray menu → “Send document…”. A preview dialog lets you pick the target printer and print options before anything leaves your machine.

Your document -> preview dialog (printer, copies, pages, paper, color,
                 duplex, orientation, fit)
   -> sender agent -> AES-GCM over HTTP :9100 -> host agent -> printer

No virtual printer and no port monitor: jobs are delivered directly between agents and handed to the physical printer by format:

Format	Receiver handling
PDF	PyMuPDF page-range subset + SumatraPDF (or printto)
Word (docx/doc)	Word COM automation (copies, page range)
Excel/PPTX	shell printto verb
PNG/JPEG/GIF/BMP/WEBP/TIFF/EMF	GDI+ via PowerShell
Text	spooler TEXT datatype

Jobs travel encrypted (AES-GCM keyed by the pairing token) directly PC-to-PC.

Repository layout

agent/         Python tray agent (all PCs)
installer/     Inno Setup script (agent-only install)
docs/          architecture.md, protocol.md, security.md, debugging-notes.md
tests/         pytest suite

agent/pipe_reader.py is legacy code from the retired port monitor: it is not used by the shipping product. It only activates if the agent is started with LEGACY_PIPE_ENV=1 (see main.py); kept for anyone still running an old port monitor.

Development setup

python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install -r agent/requirements.txt
python agent/main.py

Requires Windows for real use (pywin32, spooler/COM/GDI+ printing). The share/identity logic and HTTP API are platform-independent and covered by tests that run on any OS.

Testing

python -m pytest tests/

Building the installer

1. Bundle the agent:

   python -m PyInstaller --noconfirm PrintLinkAgent.spec
   

   Produces dist\PrintLinkAgent.exe (onefile, windowed, ~52 MB; the spec pins the excludes so the build stays fast and small).

2. Build the installer:

   & "C:\Program Files (x86)\Inno Setup 6\ISCC.exe" installer\printlink.iss
   

   Produces installer\output\PrintLinkSetup-<version>.exe.

The installer registers the tray agent at login, opens firewall rules for TCP 9100 (API) and UDP 5353 (mDNS) on the Private profile, and calls the agent’s --install-verbs to add the right-click verb. On domain networks the firewall rules are per-PC; adjust via GPO.

Since 0.2.3, agent data (printers, grants, tokens, identity) is shared machine-wide in %PROGRAMDATA%\PrintLink so every user account on a PC sees the same printers. This makes tokens readable by any local user — see docs/security.md for the threat model and planned hardening.

Security model

• Host-controlled access: nothing prints without an accepted grant.
• Grants: 7-day expiry by default, hourly enforcement, manual revocation or extension (“Manage grants…” on the host).
• Pairing token (64 hex chars) = auth credential + encryption key.
• Payloads encrypted AES-256-GCM; tampering fails decryption.
• /ping ID verification prevents stale-IP impersonation after DHCP churn.
• POST /revoke-grant lets a remote revoke its own access (token-verified, so nobody can cut someone else’s grant); unsharing a printer revokes all its grants.

See docs/protocol.md for wire formats, docs/architecture.md for design, and docs/security.md for the threat model.

Licensing

PrintLink itself is MIT-licensed (see LICENSE). The preview thumbnails and PDF page-range rendering use PyMuPDF, which is AGPL-3.0 / commercial dual license. Anyone redistributing PrintLink commercially must swap in pypdfium2 or drop the preview (the receiver falls back to printing the whole file). Pillow (thumbnails) and PyInstaller (bundling) are similarly bundled under their respective licenses.

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