OpenPrinterPrinter Discovery
Providers, normalization, fingerprints, and stable local identities.
Discovery is provider-based. The initial workspace supports operating-system queues, manually configured raw TCP printers, and virtual printers. Optional platform providers can be compiled when their implementation is available.
Stable identity
No hardware attribute is universal. MAC addresses may be absent, randomized, shared behind a print server, or unrelated to a USB queue. Discovery therefore builds a fingerprint from the metadata a provider can actually observe:
- queue and driver name
- device URI
- host and port
- USB vendor and product IDs
- serial number
- MAC address when available
OPPA assigns its own stable local printer ID and persists the binding between that ID and the best available fingerprint.
Normalization
The discovery manager executes enabled providers independently, normalizes descriptors, and deduplicates likely duplicates while retaining provider metadata. A provider failure is reported in diagnostics and does not crash other discovery work.
Inventory
An inventory entry includes a concrete local ID, display name, connection details, available capabilities, enabled state, and availability state. The integrating platform may attach that ID to its own logical routing model.
Manual network printers
A manually configured printer records a validated host and port. Raw TCP submission normally uses port 9100, but the port is explicit. Discovery does not imply reachability; the spooler applies a bounded connection and write timeout for each submission. The existing manual raw TCP receipt-printer flow is configured for ESC/POS. Port 9100 alone does not prove that a device understands ESC/POS; use this flow only with a compatible printer.
System queues and printing modes
A discovered system queue defaults to System driver mode. OPPA renders a page and asks the installed operating-system printer driver to submit it. On Windows this uses silent GDI printing; on Unix, OPPA gives CUPS a page file so its filters can prepare the device language.
The queue can instead be explicitly configured as ESC/POS direct for a compatible thermal receipt printer. This sends printer-ready ESC/POS bytes to the queue as RAW data. Queue names and port numbers do not identify a printer language, so OPPA does not infer ESC/POS from a generic system queue. Use raw mode only when the printer is known to support ESC/POS.
Driver mode can also interpret a supported ESC/POS command stream and render its receipt on a page. The interpreter covers the subset emitted by OPPA and stops on unknown commands; it does not claim to recognize every vendor's ESC/POS extensions.