Transport Support

KmpPrinter exposes one API across platforms, but transport support depends on OS APIs, permissions, printer firmware, drivers, browser capabilities, and whether the device supports readback status bytes.

Transport	Android	iOS	JVM/Desktop	Web/JS	Notes
Network TCP `9100`	Supported	Supported	Supported	Best-effort	Most reliable ESC/POS transport when the printer exposes raw TCP. Status readback depends on firmware.
USB raw printer	Supported	Not supported	Supported / best-effort	Best-effort	Android requires USB host permission. JVM may need libusb, WinUSB, udev rules, or fallback to serial/print queue. Browser USB requires secure context and user gesture.
Bluetooth Classic SPP	Supported	Not supported	Best-effort	Browser dependent	Android can connect to paired SPP devices. JVM uses OS serial ports, rfcomm, or print queues, not always direct MAC access.
BLE	Supported / best-effort	Supported / best-effort	Best-effort with helper/backends	Browser dependent	BLE printers vary heavily by service UUID, characteristic properties, MTU, and write-with-response support.
Serial	JVM/Desktop	Not supported	Supported	Browser dependent	Useful for USB-serial adapters, Linux rfcomm bindings, and OS-created Bluetooth serial ports.
OS print queue	Not primary	Not primary	Best-effort	Not supported	Print queues can send bytes, but often cannot return ESC/POS status.
Virtual	Supported	Supported	Supported	Supported	Intended for tests, previews, and demos.

Status Readback

queryStatus() and monitorStatus() use ESC/POS status requests where possible. They should be treated as optional capabilities:

Network, serial, and raw USB are the best candidates for status readback.
BLE status requires readable or notifiable characteristics.
OS print queues and many browser transports are usually write-only.
Some printers accept print bytes but ignore DLE EOT status commands.

Always handle PrinterStatus.isStatusSupported == false and continue with a print-only flow when status is unavailable.

Recommended Defaults

Prefer Network TCP for fixed-location printers.
Prefer USB on Android when the printer is physically attached to the device.
Prefer typed configs or PrinterConnection instead of raw string connection types in new code.
Prefer PrinterProfile.MM58 or PrinterProfile.MM80 instead of manually repeating paper width values.
Use printQuality(PrintQuality.Dark) as a best-effort helper when output is too gray, then verify the printer power supply, thermal paper, and head condition.
Reduce sendChunkSize and increase sendChunkDelayMs for cheap BLE or Bluetooth Classic printers that drop bytes.
Use diagnoseUsb, diagnoseBle, and troubleshootingHint before asking users to change OS drivers or permissions.

Print Quality Commands

Density and heat commands are best-effort. KmpPrinter sends common ESC/POS-compatible command sequences, but many printers ignore them or use vendor-specific alternatives.

printer.print(config) {
    printQuality(PrintQuality.Dark)
    line("Darkness test")
    cut()
}

If output remains gray after PrintQuality.Dark, check the power adapter rating, thermal paper quality, printer head cleanliness, and hardware density settings.