sunmi_external_cloud_printer

A Flutter plugin for Sunmi external cloud printers — NT21x, NT31x, and NT32x series — over USB, LAN, and Bluetooth. Android only.

Features

Scan for nearby Sunmi cloud printers (USB, LAN, Bluetooth)
Connect and disconnect by printer ID
Query printer status (isReady, description)
Build and commit rich print jobs with a fluent PrintJob API:
- Text alignment (left / center / right)
- Character size multiplier (width × height, 1–4)
- Bold text
- Line feeds
- Full or partial paper cut
- QR code printing (size 1–16, four error-correction levels)

Getting started

Prerequisites

Android only (iOS is not supported by Sunmi hardware)
Flutter >=3.3.0, Dart SDK >=3.8.1
A physical Sunmi NT21x, NT31x, or NT32x device

Add the dependency

dependencies:
  sunmi_external_cloud_printer: ^0.2.0

Then run:

flutter pub get

No additional Android permissions are required beyond those already declared by the plugin.

Usage

1 — Scan for printers

import 'package:sunmi_external_cloud_printer/sunmi_external_cloud_printer.dart';

final printer = SunmiExternalCloudPrinter();

final printers = await printer.scan(timeoutSeconds: 5);
for (final p in printers) {
  print('${p.name} [${p.connectionType}] — ${p.id}');
}

2 — Connect

final connected = await printer.connect(printers.first.id);
if (!connected) {
  print('Connection failed');
  return;
}

3 — Build and commit a print job

final result = await printer.commit(
  PrintJob()
    ..initStyle()
    ..setAlignment(SunmiPrintAlignment.center)
    ..setCharacterSize(2, 2)
    ..appendText('RECEIPT\n')
    ..setCharacterSize(1, 1)
    ..setAlignment(SunmiPrintAlignment.left)
    ..appendText('Item 1 ............... 10.00\n')
    ..appendText('Item 2 ............... 25.00\n')
    ..setBold(enabled: true)
    ..appendText('Total ................ 35.00\n')
    ..setBold(enabled: false)
    ..printQrCode('https://example.com/order/123', size: 6)
    ..lineFeed(3)
    ..cutPaper(),
);

if (result.success) {
  print('Printed: ${result.message}');
} else {
  print('Error: ${result.message}');
}

4 — Check status and disconnect

final status = await printer.getStatus();
print('Ready: ${status.isReady} — ${status.description}');

await printer.disconnect();

A full working example is available in the /example folder.

Connection types

The plugin supports three physical connection modes. When scan() is called, all three are probed simultaneously. Each discovered printer exposes its type via SunmiDiscoveredPrinter.connectionType ("USB", "LAN", or "Bluetooth").

USB

Plug the printer into the Android device's USB-A or USB-C (OTG) port.
No pairing or network configuration is required.
SunmiDiscoveredPrinter.vid and .pid hold the USB vendor ID and product ID respectively (useful for filtering specific hardware).
The plugin holds a USB device claim for the duration of the connection; call disconnect() to release it before the app goes to the background if you need to share the port.
Priority: USB connections are preferred when auto-selecting (USB → LAN → Bluetooth).

LAN (Local Area Network)

Printer and device must be on the same Wi-Fi or Ethernet segment.
SunmiDiscoveredPrinter.address contains the printer's IPv4 address and .port contains the TCP port (default 9100).
Static IP assignment on the printer is recommended for production deployments to avoid address changes between scans.
Discovery uses UDP broadcast; ensure the network does not block broadcast traffic between subnets.
The connection is a persistent TCP socket; if the socket drops (e.g. DHCP lease renewal), call disconnect() then connect() again.

Bluetooth

Supports Bluetooth Classic (SPP profile). Bluetooth LE is not supported.
Pair the printer with the Android device via Settings → Bluetooth before scanning — the plugin does not handle the pairing handshake.
SunmiDiscoveredPrinter.mac holds the Bluetooth MAC address (e.g. "AA:BB:CC:DD:EE:FF").
Bluetooth range is typically 5–10 m; signal drops will cause the connection to time out. Add retry logic in production apps.
Android 12+ requires the BLUETOOTH_CONNECT and BLUETOOTH_SCAN runtime permissions. Declare and request them in your app before calling scan().

API reference