julian
b2a0471b08
Add the rongta PrinterDevice driver (ESC/POS over raw TCP 9100) and the device-agnostic pieces around it: - Roles + failover: each printer declares a role (entry-dispenser/booth- receipt) and failoverRank; printer-routing.ts picks the best healthy printer and falls back outside->booth for entry tickets (never the reverse). - Live status: MonitorableDevice.readStatus()/PrinterStatus capability. The Rongta driver scrapes the device's own /prn_stat.htm (Cover/Cutter/Paper End/Near End/Off-Line) rather than hand-decoding DLE EOT, whose reply bytes on this clone don't match the canonical ESC/POS bit layout (verified on hardware) -- avoids a false-healthy. Maps to ready/degraded/offline, fail safe on an unreachable or unexpected page. - Server PrinterMonitor polls enabled printers (PRINTER_POLL_MS, default 5s), caches latest, emits "printer-status" on change. Exposed via GET /api/printers/status and an SSE stream for the booth UI. Verified against 10.0.10.6: ready when healthy, offline when unreachable (no throw), bus emits on change and suppresses unchanged reads. Wiki: new rongta-printer entity, printer-roles-failover and printer-status-monitoring concepts; BOM/index/log updated.
54 lines
2.4 KiB
Markdown
54 lines
2.4 KiB
Markdown
---
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type: concept
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tags: [parking, printer, device, reliability]
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sources: []
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updated: 2026-06-14
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---
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# Printer roles & failover
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A lane runs **more than one printer**, and the system knows each one's job so it can fail over
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automatically. This is a reliability decision, not a threat-model one: an entry ticket must
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still print when the outside dispenser jams or drops off the network.
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## Roles
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Each printer instance (a `lane_devices` row, category `printer`) declares a **role** in its
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config:
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- **`entry-dispenser`** — outside, at the lane. Prints the entry ticket the driver takes.
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- **`booth-receipt`** — inside the booth. Prints receipts at exit/payment, AND serves as the
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**backup** for entry tickets.
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It also declares a **`failoverRank`** (higher = preferred within a role) to order multiple
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printers of the same role deterministically (ties broken by id).
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## Failover rule (asymmetric, on purpose)
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For an **entry ticket** (`wantRole = entry-dispenser`): try the entry dispensers (best rank
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first), then fall back to the **booth printer**. So a driver still gets a ticket when the
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outside unit is offline — the operator hands it over from the booth.
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The reverse is **deliberately not** done: a **receipt** never prints on the outside dispenser.
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Receipts are a booth-only job; an entry dispenser falling back to print receipts makes no
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physical sense.
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## Where the logic lives
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- The driver (`rongta`) is **role-agnostic** — role/rank are just config; the transport doesn't
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care. Keeps [[device-adapter-pattern|adapters]] swappable.
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- Selection is pure logic in `packages/devices/printer-routing.ts`: `orderForRole()` ranks
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candidates; `printWithFailover()` attempts the print down the list and throws
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`NoPrinterAvailableError` only when every candidate fails.
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- It **attempts the print directly** rather than racing a `healthCheck` first — the print is
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the real reachability test, and a health probe that passes can still be followed by a failed
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print.
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## Open: the all-printers-down policy
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When `printWithFailover` exhausts every candidate, what should entry do — raise the barrier
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with no paper ticket (the plate/[[lpr-camera]] is the independent record), or hold? That policy
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belongs to the **entry flow** ([[device-input-flow]], [[fail-state-safety]]), not the printer
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layer, and is **not yet decided**. The signed event ([[append-only-event-chain]]) is created
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regardless of whether paper prints.
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