14Label Print Service (Background Service)

The Label Print Service is a standalone background program independent from the main designer. Think of it as a "print server" — it runs 24/7, waiting to receive print jobs.

14.1 Starting and Stopping

14.2 Three Receiving Channels

The Print Service offers 3 ways to receive print jobs:

① TCP Channel (Port 8888)

The most direct method. Any program or device can send ZPL commands via TCP to port 8888.

Use cases:

• LAN scanning devices sending print commands directly
• Production line terminals sending label data
• Low-latency, high-efficiency printing needed

② HTTP REST API (Port 5000)

The most common method. Send print jobs via standard HTTP requests — callable from any language (C#, Java, Python, PHP, etc.).

Management dashboard: Open http://localhost:5000 in a browser to see the service status page.

Available API endpoints:

Python example:

import requests, json

zpl_data = "^XA^FO50,50^ADN,36,20^FDHello World^FS^XZ"
task = {
    "zpl": zpl_data,
    "copies": 2,
    "printer": "ZDesigner ZD421",
    "priority": 0
}

resp = requests.post("http://localhost:5000/print", json=task)
print(resp.json())  # {"success": true, "taskId": "..."}

curl test:

curl -X POST http://localhost:5000/print ^
  -H "Content-Type: application/json" ^
  -d "{\"zpl\":\"^XA^FO50,50^ADN,36,20^FDHello^FS^XZ\",\"copies\":1}"

③ Directory Monitoring

The service watches a specified folder. When .zpl or .iba files arrive, it automatically queues them for printing.

• Success: file moves to .processed subfolder
• Failure: file moves to .failed subfolder
• Great for integration — other systems just drop ZPL files in the folder

14.3 Print Queue Management

When multiple jobs arrive simultaneously, the service queues them:

• FIFO: Default first-in-first-out ordering
• Priority: Set priority (0=highest, higher number = lower priority)
• Auto retry: Automatic retry on failure (default 3 retries, 5 seconds apart)
• Throttling: Set minimum interval between jobs (prevents printer overload)
• Pause/Resume: Temporarily pause the queue (e.g. for ribbon change)
• Persistence: Queue persists to disk — no job loss after service restart

14.4 Settings Management

Right-click the tray printer icon → "Settings":

14.5 Conditional Rules (Advanced)

Rules can intelligently process print jobs based on their content.

Rule examples:

• Content-based routing: "Shanghai" orders → Warehouse A printer; "Beijing" orders → Warehouse B printer
• Source-based routing: HTTP jobs use fast lane, directory jobs use batch lane
• Filtering: Discard certain labels without printing
• Content modification: Prepend fixed header/footer to ZPL commands
• Quantity modification: Auto-print an extra copy for certain label types

Rule structure:

• Condition: When to match (field value match / ZPL content match / source match)
• Action: What to do on match (route printer / block printing / modify content / modify copies)

Rules are evaluated top-to-bottom; the first match stops evaluation.

14.6 System Tray Operations

Find the printer icon near the clock:

• Double-click left: Open management dashboard in browser (http://localhost:5000)
• Right-click menu:
  ┣ Open Dashboard
  ┣ Show Window (service control window)
  ┣ Pause/Resume Printing
  ┣ Settings
  ┣ About
  ┗ Exit

14.7 COM Component Support (Legacy Compatibility)

If your organization still uses VB6, VBA (Excel macros), or other legacy technologies, you can call the print service via COM:

Dim service As Object
Set service = CreateObject("PrintServiceComServer")
service.PrintZPL "^XA...^XZ", "ZDesigner ZD421", 1