Print station (for POS backends)¶

Let every device of a shop print to its printers from anywhere — tablets on mobile data, a hosted web POS, another branch — through your POS backend.

The shop computer running the bridge becomes a print station. It keeps one outgoing connection to your server and prints the jobs you queue, so it needs no open ports, fixed IP address or router setup.

sequenceDiagram
  participant D as Any device (web POS)
  participant S as Your POS backend
  participant B as Bridge (print station)
  participant P as Printer
  D->>S: Print bill (receipt blocks)
  S->>S: Queue job for the shop's station
  B->>S: Long-poll: next jobs?
  S-->>B: Job
  B->>P: Print
  B->>S: Result: printed / error
  S-->>D: Printed ✓

The protocol¶

Implement five routes on your server — the full contract, with every field and the rules that keep a bill from printing twice or late, is in the print station protocol (Print station protocol tab; raw spec: print-station.openapi.yaml).

A job carries what to print — a line-by-line receipt ({ "blocks": [...] }, the same as POST /print/receipt), or an html page for A4/A5 printers — plus the printer's API name, copies and a title.

Setup at the shop¶

1. In your POS, the owner opens a Add print station screen that shows your server address and a 6-digit code (valid for 10 minutes).
2. In the bridge, under Connect your POS → With a code, they enter that address, a name for the computer (e.g. Front counter PC) and the code, then click Connect.
3. The station shows up in your POS with its printers. From then on, every device can print to it.

Built so a bill never prints twice or late¶

• Jobs that aren't picked up in time expire, so a bill never prints an hour later when the computer wakes up. Offer the cashier another way to print.
• The bridge remembers the jobs it printed: if the connection drops after printing, a job delivered again is reported, not printed again.
• After sleep, a network change or a server restart, the bridge reconnects by itself.
• The station token is kept in the computer's keychain (Windows DPAPI, macOS Keychain) and never shown. Disconnect in the bridge revokes it.

Previews in your POS¶

The heartbeat reports each receipt printer's columns (32, 42 or 48). Lay the receipt out with the SDK's layoutReceipt at that width and your preview matches the paper exactly.