Lead POS Middleware Developer: Hardware Hooks & Print Stream Interception
Location: ["United Kingdom"]
Job Description: We are looking for a Senior Windows Systems Engineer to develop a critical middleware "Bridge" for retail POS systems. This software functions as a silent background service that intercepts hardware signals, processes them locally, and synchronizes the data with a remote API. This is a low-level integration project. You will be responsible for creating a "shim" that sits between legacy retail hardware (scanners, printers) and the Windows OS, ensuring data capture is seamless and invisible to the host POS application. Key Technical Responsibilities: HID Silent Interception (C#): Implement a low-level keyboard hook using SetWindowsHookEx. The service must monitor USB scanner input for specific prefixes, "swallow" the keystrokes to prevent them from reaching the POS UI, and store the data in a volatile RAM buffer. Print Spooler Harvesting (C++): Develop a custom Print Processor or Monitor using the Windows Driver Kit (WDK) to intercept .SPL files. You must implement coordinate-based mapping to scrape specific text and numerical values from the GDI/RAW print stream. Local Data Bundling: Develop the logic to pair the intercepted HID/NFC tokens with the scraped printer data into a single JSON payload. NFC Interface: Interfacing with USB NFC readers using the PC/SC standard to capture encrypted tokens. Resilience Layer: Implementation of a local SQLite-based cache to handle network outages, featuring automated "burst-upload" and exponential backoff retry logic. Deployment: Prepare the suite for silent installation and ensure all binaries are compatible with EV Code Signing requirements. Technical Requirements: Expert-level C# / .NET 8 and C++. Deep experience with Win32 API and Windows Driver Kit (WDK). Proven experience in Low-level Hooks and Print Spooler/Processor internals. Familiarity with PC/SC and HID descriptor protocols. Experience in the retail or POS automation space is highly preferred. Confidentiality: This project involves proprietary retail technology. Detailed documentation and the specific business use case will be provided to the selected candidate under a non-disclosure agreement (NDA).