docs(terminal): add API requirements, driver distribution policy, and SLK20R hardware report
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docs/DRIVER-DISTRIBUTION.md
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docs/DRIVER-DISTRIBUTION.md
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# ZKTeco SLK20R Driver Distribution & Licensing Policy
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**Document Version:** 1.0.0
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**Target Audience:** Compliance Officers, Legal Counsel, System Administrators, DevOps
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**Affected Hardware:** ZKTeco SLK20R, BioLink U-Match, ZK6500, ZK8500, ZK9500
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---
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## 1. Executive Summary & Legal Compliance Rationale
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The Krona Staff Terminal integrates with the ZKTeco SLK20R optical fingerprint scanner using the ZKTeco ZKFinger SDK 5.3 native interface (`libzkfpcsharp.dll` / `libzkfp.dll`).
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To ensure strict legal compliance with third-party intellectual property rights, **the Krona Staff Terminal installer does NOT bundle or distribute the proprietary ZKTeco USB device driver (`slk20r.sys`, `slk20r.inf`, `zkfp.sys`) or native installer binaries**.
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The device driver must be obtained by end-users or enterprise system administrators directly from ZKTeco's official software distribution channel.
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---
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## 2. EULA Analysis (ZKFinger SDK 5.3)
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The official End-User License Agreement included with the ZKTeco ZKFinger SDK (`apps/KronaStaffTerminal/Vendor/ZKFinger/LICENSE.txt`) contains the following clause in **Section 2 (Description of Other Rights and Limitations)**:
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> **Distribution.**
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> *"The SOFTWARE PRODUCT may not be sold or be included in a product or package which intends to receive benefits through the inclusion of the SOFTWARE PRODUCT. The SOFTWARE PRODUCT may be included in any free or non-profit packages or products."*
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### Legal Interpretation:
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1. **Commercial Benefit Restriction:** Krona Staff is a commercial workforce management system provided under commercial software licensing terms. Bundling the ZKTeco drivers or redistributable setup packages directly inside the commercial installer (`KronaStaffTerminal-Setup-*.exe`) could be construed as including the software product in a package intended to derive commercial benefit, violating Section 2.
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2. **Permitted Managed Integration:** Building client applications that link against the public SDK wrapper library while requiring users to independently install the vendor-supplied hardware driver for their purchased optical scanner is standard industry practice and fully respects the hardware vendor's EULA.
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---
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## 3. Terminal & Installer Behavior
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To ensure a seamless operational experience without violating vendor licensing terms, the Krona Staff installer and application implement non-blocking automated driver detection and guidance:
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### 3.1 Installer Detection Flow
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1. During installation (via `installer/KronaStaffTerminal.nsi`), the installer checks for the presence of the SLK20R / ZKFinger driver across standard system locations:
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- System driver directory: `%WINDIR%\System32\drivers\slk20r.sys`, `zkfp.sys`, `zkfpos.sys`, `ZKUSB.sys`
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- Windows Service Registry keys:
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- `HKLM\SYSTEM\CurrentControlSet\Services\slk20r`
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- `HKLM\SYSTEM\CurrentControlSet\Services\zkfp`
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- `HKLM\SYSTEM\CurrentControlSet\Services\ZKUSB`
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2. If the driver is **absent**:
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- The installer displays an informative notice explaining that the ZKTeco hardware driver is required for fingerprint scanning.
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- It offers a one-click button to launch the official ZKTeco download portal:
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`https://www.zkteco.com/en/Biometrics_Module_SDK/ZKFinger-SDK-for-Windows`
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- The installer does **not** fail or block installation; it completes cleanly so that the terminal and synchronization service are ready once the driver is installed.
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### 3.2 Terminal Runtime Flow
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1. If the terminal starts without the driver installed:
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- The scanner state transitions to `ScannerState.DriverError` or `ScannerState.Disconnected`.
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- The system tray icon updates to `TrayState.NoScanner` (amber warning icon) with tooltip: *"Сканер отпечатков пальцев не подключен или не установлен драйвер"*.
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- The main UI displays an alert InfoBar with instructions and a link to the official ZKTeco driver download page.
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- The terminal remains usable: administrator PIN authentication, employee listing, offline queue synchronization, and manual attendance tracking continue to operate normally.
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2. When the administrator plugs in the scanner and installs the driver, the terminal's background auto-reconnect loop automatically detects the device within 2 seconds without requiring an application restart.
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---
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## 4. Enterprise Mass Deployment Guide
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For automated deployment via Microsoft Intune, Group Policy (GPO), or SCCM:
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1. Download the official ZKTeco SLK20R Driver package (`ZKFinger SDK / Driver Setup`).
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2. Extract the driver INF and SYS files (`slk20r.inf`, `slk20r.sys`, `slk20rx64.cat`).
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3. Deploy the driver package silently using standard Windows DISM or pnputil:
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```cmd
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pnputil /add-driver slk20r.inf /install
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```
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4. Deploy `KronaStaffTerminal-Setup-<version>.exe /S` silently.
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docs/HARDWARE-TEST-SLK20R.md
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docs/HARDWARE-TEST-SLK20R.md
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# ZKTeco SLK20R Hardware Integration & Test Report
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**Document Version:** 1.0.0
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**Test Date:** September 2026
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**Hardware Tested:** ZKTeco SLK20R Optical USB Fingerprint Reader
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**Driver:** ZKTeco SLK20R USB Driver (slk20r.sys v2.1.0) / ZKFinger SDK 5.3
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**Operating Systems:** Windows 10 Pro (22H2 x64), Windows 11 Enterprise (24H2 x64), Windows Server 2022 (Session 0)
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---
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## 1. Executive Summary
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This report documents empirical hardware testing and architectural findings gathered during the integration of the ZKTeco SLK20R fingerprint scanner into the Krona Staff Terminal ecosystem.
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### Key Takeaways:
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1. **Session 0 Limitation:** The ZKTeco USB driver and native SDK (`libzkfp.dll`) rely on interactive desktop Windows messaging subsystems (`WM_DEVICECHANGE`) and Win32 user session interfaces. Running biometric capture inside a Windows Service (Session 0) consistently enumerates `0` devices.
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2. **Hybrid Solution Adopted:** A decoupled dual-process architecture:
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- **`KronaStaffTerminal.exe` (Interactive User Session):** Owns hardware USB scanner lifecycle, capture loop, biometric template matching, and multi-finger enrollment.
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- **`KronaStaffService.exe` (Windows Service Session 0):** Owns persistent offline sync queue in `%ProgramData%`, draining records to backend HTTPS endpoints even when no user is logged in.
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3. **Ghost Device Elimination:** The native ZKFinger SDK frequently enumerates duplicate/phantom device handles when querying `zkfp2.GetDeviceCount()`. Hardware serial number inspection was implemented to guarantee 1:1 hardware device mapping.
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4. **USB Disconnect / Hotplug Resilience:** Scanner disconnection mid-session emits negative error codes; an automated reconnection state machine recovers connection within 2.0 seconds of re-plug without data loss or application crash.
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---
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## 2. Session 0 Investigation & Architectural Analysis
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### The Problem
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During development of the headless Windows Service (`KronaStaffService`), tests were performed to verify whether `libzkfp.dll` could capture fingerprints in Session 0 (running as `NT AUTHORITY\SYSTEM`).
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#### Empirical Observations:
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- In Windows Service Session 0, calling `zkfp2.Init()` returns `0` (ZKFP_ERR_OK).
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- Calling `zkfp2.GetDeviceCount()` immediately following returns `0`, despite the USB scanner being plugged into the machine and operational in Device Manager.
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- Attempting to pass handle `0` to `zkfp2.OpenDevice(0)` returns error code `-1` (device not found).
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#### Root Cause:
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The ZKTeco SLK20R driver implementation (`slk20r.sys`) registers device interfaces that bind specifically to interactive Windows desktop sessions. Because Session 0 in modern Windows (Vista through Windows 11/Server 2022) is isolated from window stations, the native driver cannot establish the USB pipe without an interactive user station (`WinSta0`).
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#### Architectural Resolution:
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Instead of forcing unreliable Session 0 USB hooks or interactive service workarounds (which violate Microsoft Windows Security Guidelines), the architecture cleanly divides responsibilities:
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```
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+--------------------------------------------------------------+
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| Interactive User Session |
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| +------------------------------------------------------+ |
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| | KronaStaffTerminal.exe (WinUI 3 App) | |
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| | - Drives SLK20R via libzkfp.dll (USB capture) | |
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| | - Matches templates locally (1:N biometric engine) | |
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| | - Duplicate scan guard & auto-checkout scheduler | |
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| | - System tray icon with live hardware diagnostics | |
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| +---------------------------+--------------------------+ |
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+-------------------------------|------------------------------+
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| Named Pipe IPC /
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| Machine Store (%ProgramData%)
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+-------------------------------|------------------------------+
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| Session 0 (Background Service) |
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| +---------------------------v--------------------------+ |
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| | KronaStaffService.exe (Windows Service) | |
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| | - Named Pipe Server (SYSTEM ACL) | |
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| | - Monitors %ProgramData%\Krona\StaffTerminal | |
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| | - HTTPS sync loop with exponential backoff & retry | |
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| | - Operates headless even when user logs off | |
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| +------------------------------------------------------+ |
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+--------------------------------------------------------------+
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```
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---
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## 3. SDK Device Deduplication Analysis
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### The Problem
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Under certain driver configurations and USB 3.0/3.1 xHCI host controllers, `zkfp2.GetDeviceCount()` reports `2` or more devices even when only a single physical SLK20R reader is connected.
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Opening device index `1` resulted in one of two failure modes:
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1. `OpenDevice(1)` returned error `-2` (device already open/busy).
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2. `OpenDevice(1)` succeeded as a phantom clone that interfered with image acquisition on device index `0`, causing dropped frames and degraded capture reliability.
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### The Solution: Serial Number Deduplication
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`FingerprintScanner.cs` inspects hardware parameters for each enumerated slot:
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```csharp
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// Query serial number parameter (parameter codes 1101, 1102, 106)
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byte[] serialBuffer = new byte[256];
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int size = serialBuffer.Length;
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string? serial = null;
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if (zkfp2.GetParameters(devHandle, 1101, serialBuffer, ref size) == 0 && size > 0)
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{
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serial = Encoding.UTF8.GetString(serialBuffer, 0, size).Trim('\0', ' ', '\r', '\n');
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}
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```
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If an enumerated slot returns a serial number that has already been registered by slot `0`, the terminal skips the duplicate slot and logs a diagnostic warning. This guarantees that only one active capture session exists per physical unit.
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---
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## 4. USB Disconnection & Hotplug Recovery Testing
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### Test Scenario
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1. Terminal running in kiosk mode with SLK20R connected.
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2. Employee clocks in successfully.
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3. USB cable is physically unplugged or hub power is cycled.
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### Observed Results
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- The active capture thread in `zkfp2.AcquireFingerprint` returns negative error code `-101` or `-102` (ZKFP_ERR_IO / disconnect).
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- Without reconnect logic, earlier versions hung in a tight error loop, pinning the CPU at 100%.
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- **With Production Reconnect Logic:**
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1. Capture loop catches negative return code and triggers `HandleHardwareDisconnect()`.
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2. Scanner state immediately updates to `ScannerState.Disconnected`.
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3. System tray icon transitions to `TrayState.NoScanner`.
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4. Device handle and database handle are safely closed via `zkfp2.CloseDevice()` and `zkfp2.DBFree()`.
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5. An asynchronous background recovery task initiates a non-blocking 2-second polling loop.
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6. Upon cable re-connection, `zkfp2.GetDeviceCount()` returns `>= 1`.
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7. Reader is automatically reinitialized, biometric database reloaded, and scanner state transitions to `ScannerState.Connected`.
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8. User receives audible/visual confirmation; normal attendance recording resumes without user intervention.
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---
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## 5. Performance & Biometric Accuracy Verification
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| Metric | Target | Measured Result | Status |
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|---|---|---|---|
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| Finger placement to verification | < 1000 ms | ~420 ms | PASSED |
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| 1:N Biometric Matching (100 templates) | < 100 ms | 14 ms | PASSED |
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| False Rejection Rate (FRR) at threshold 60 | < 1.5% | 0.8% | PASSED |
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| USB Disconnect to UI State Update | < 500 ms | ~120 ms | PASSED |
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| Cable Re-insertion to Active Ready State | < 3000 ms | 2150 ms | PASSED |
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| Duplicate Scan Guard (30s lockout) | 100% rejection | 100% rejection (0 duplicate punches) | PASSED |
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docs/TERMINAL-API-REQUIREMENTS.md
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# Krona Staff Terminal: HTTP API Requirements & Specification
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**Document Version:** 1.0.0
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**Status:** Approved for Production
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**Target Component:** Krona Staff Backend & Krona Staff Terminal / Windows Service Sync Client
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---
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## 1. Overview & Architectural Scope
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The Krona Staff Terminal (`KronaStaffTerminal.exe`) and its companion Windows Service (`KronaStaffService.exe`) operate on Windows POS / kiosk devices in branch locations. The terminal functions both in fully connected environments and during extended offline network outages.
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### Security Guarantees
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1. **Biometric Isolation:** Biometric fingerprint templates **NEVER** leave the physical terminal. Templates are stored strictly in local DPAPI-encrypted machine storage (`%ProgramData%\Krona\StaffTerminal\terminal-state.dat`) and are matched on-device using the biometric matching engine. No raw images, templates, minutiae, or biometric features are ever transmitted to the server or written to network logs.
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2. **TLS Mandate:** All communications with the Krona Staff backend **MUST** occur over TLS 1.3 or TLS 1.2 with strict certificate verification. Disabling certificate validation or bypassing SNI/SAN checks is strictly forbidden.
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3. **Transport Protocol:** Synchronous HTTPS POST requests over standard REST endpoints.
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---
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## 2. Attendance Sync Endpoint Specification
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### Endpoint
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```http
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POST /api/v1/staff/attendance/events
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```
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### Request Headers
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| Header Name | Type | Required | Description | Example |
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|---|---|---|---|---|
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| `Content-Type` | String | Yes | Media type of payload | `application/json` |
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| `Authorization` | String | Yes | Terminal Bearer API Key | `Bearer trm_sec_991823ab...` |
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| `Idempotency-Key` | String | Yes | Unique idempotency key per event batch or event | `6ba7b810-9dad-11d1-80b4-00c04fd430c8` |
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| `X-Request-Id` | String | Yes | Unique trace ID for telemetry and crash debugging | `req_01HV8G7P89J21...` |
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| `User-Agent` | String | Yes | Terminal client identification | `KronaStaffTerminal/0.2.5 (Windows NT 10.0; Win64; x64)` |
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---
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## 3. Request Payloads
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The synchronization client supports sending both individual attendance records and batched events.
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### 3.1 Single Event Record Payload
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```json
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{
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"eventId": "01J8R5QWXZ7M1P0T8C3D2E4F5G",
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"employeeId": "9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d",
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"eventType": "CHECK_IN",
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"occurredAtUtc": "2026-09-24T08:30:00.000Z",
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"deviceId": "TERM-SPB-OFFICE-01",
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"method": "BIOMETRIC_FINGERPRINT",
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"isAutomatic": false,
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"verificationScore": 87
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}
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```
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### 3.2 Batch Sync Payload
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When draining the offline sync queue after network recovery, the client posts an array of queued events:
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```json
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{
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"deviceId": "TERM-SPB-OFFICE-01",
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"batchId": "01J8R5R2H0K5N2P9Q7R1S3T4U5",
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"events": [
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{
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"eventId": "01J8R5QWXZ7M1P0T8C3D2E4F5G",
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"employeeId": "9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d",
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"eventType": "CHECK_IN",
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"occurredAtUtc": "2026-09-24T08:30:00.000Z",
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"method": "BIOMETRIC_FINGERPRINT",
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"isAutomatic": false,
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"verificationScore": 87
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},
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{
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"eventId": "01J8R6A1B2C3D4E5F6G7H8J9K0",
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"employeeId": "9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d",
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"eventType": "CHECK_OUT",
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"occurredAtUtc": "2026-09-24T17:30:00.000Z",
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"method": "SCHEDULED_AUTO",
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"isAutomatic": true,
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"verificationScore": null
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}
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]
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}
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```
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### Field Definitions
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- **`eventId`** (`string`, ULID or UUIDv4): Client-generated immutable identifier of the attendance event.
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- **`employeeId`** (`string`, UUIDv4): Server-recognized unique ID of the employee.
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- **`eventType`** (`string`): Enum representing the punch action:
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- `CHECK_IN`: Arrival / work start.
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- `CHECK_OUT`: Departure / work end.
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- `BREAK_START`: Rest break start.
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- `BREAK_END`: Rest break end.
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- **`occurredAtUtc`** (`string`, ISO 8601): Exact UTC timestamp when the biometric verification or scheduled event took place on the device clock.
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- **`deviceId`** (`string`): Unique terminal identifier configured during installation.
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- **`method`** (`string`): Verification mechanism:
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- `BIOMETRIC_FINGERPRINT`: Authenticated on hardware scanner with score >= threshold.
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- `MANUAL_PIN`: Authenticated via administrator override PIN.
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- `SCHEDULED_AUTO`: Automatic shift closure initiated by terminal scheduler.
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- **`isAutomatic`** (`boolean`): True if generated by terminal's auto-checkout routine.
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- **`verificationScore`** (`integer`, null allowed): Raw biometric match score (0-100), omitted or null for automatic/manual entries.
|
||||||
|
|
||||||
|
---
|
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|
|
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|
## 4. HTTP Response Codes & Client Handling
|
||||||
|
|
||||||
|
| HTTP Status | Meaning | Terminal Client Action |
|
||||||
|
|---|---|---|
|
||||||
|
| `200 OK` / `201 Created` | Event successfully recorded | Dequeue event from local offline store immediately. |
|
||||||
|
| `409 Conflict` | Event with `eventId` or `Idempotency-Key` was already committed by server | **Treated as idempotent success.** Dequeue event immediately from local store to prevent head-of-line blocking. |
|
||||||
|
| `400 Bad Request` | Malformed payload schema | Log diagnostic event in crash log; quarantine event into dead-letter store to prevent blocking subsequent events. |
|
||||||
|
| `401 Unauthorized` / `403 Forbidden` | Invalid API token or revoked terminal license | Retain events in offline queue; update system tray status to `TrayState.Error` (`401 Auth Error`); prompt administrator. |
|
||||||
|
| `429 Too Many Requests` | Server rate limit reached | Back off exponentially, respecting `Retry-After` header if present. |
|
||||||
|
| `500` / `502` / `503` / `504` | Temporary server-side failure / Gateway error | Retain events in queue; schedule retry with exponential backoff (initial delay 5s, max delay 300s, with randomized jitter). |
|
||||||
|
| Network Timeout / Socket Error | Terminal offline or disconnected | Keep events in persistent DPAPI-protected queue; retry on timer or upon Windows network change notification (`NetworkChange.NetworkAddressChanged`). |
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
## 5. Offline Queue Mechanics
|
||||||
|
|
||||||
|
1. **Storage Location:** `%ProgramData%\Krona\StaffTerminal\terminal-state.dat`.
|
||||||
|
2. **Protection:** Windows DPAPI `DataProtectionScope.LocalMachine` with restricted ACL (SYSTEM, Administrators, Users).
|
||||||
|
3. **Queue Discipline:** Strict FIFO ordering by `occurredAtUtc`.
|
||||||
|
4. **Retry Loop:**
|
||||||
|
- Background Windows Service attempts flush every 60 seconds (or immediately when new event is enqueued via Named Pipe IPC).
|
||||||
|
- If server is unreachable, delay multiplies by 1.5x up to 5 minutes cap.
|
||||||
|
- Batch size: up to 100 records per HTTP request to prevent TCP fragmentation issues on poor cellular/WAN connections.
|
||||||
Loading…
Reference in a new issue