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Poster — ESC/POS Thermal Printer Driver & Utility

Project Overview

Poster is a production-ready Go library and CLI utility that provides a full abstraction layer for ESC/POS thermal printers. It decouples business logic from hardware specifics through a versioned JSON document protocol, enabling developers to define complex print jobs (text, images, barcodes, QR codes, tables) without writing raw byte sequences. The system includes native Windows Print Spooler integration, a custom graphics pipeline with Atkinson dithering, a dynamic table layout engine, and a visual emulator for testing without physical hardware.

Tech Stack & Infrastructure

Category Technologies
Language Go 1.24 (primary), Node.js (release tooling)
Platform Windows (primary, winspool.drv via syscall/unsafe), Linux/macOS (cross-platform test targets)
Protocol ESC/POS binary protocol (Epson standard)
API / Schema JSON Schema v1.0, versioned document format
CI/CD GitHub Actions — 11 workflows (CI, Release, CodeQL, Dependabot Automerge, Stale, Tag Protection)
Security Trivy vulnerability scanner, GitHub CodeQL static analysis
Testing Multi-OS matrix (Ubuntu, Windows, macOS), race detection, Codecov coverage, performance benchmarks
Linting golangci-lint (exhaustive config: gofmt, govet, errcheck, staticcheck, gosec, etc.)
Release Mgmt Conventional Commits, standard-version, automated semantic versioning via GitHub App tokens
Quality Gates Pre-commit hooks, commit linting (@commitlint), semantic PR title validation
Task Runner Taskfile v3 with modular per-package task includes
Dependencies Dependabot (Go modules + GitHub Actions), auto-merge for patch/minor updates

Notable Libraries

Library Purpose
golang.org/x/image High-quality image scaling (bilinear interpolation) and advanced draw.Scaler interface for resizing
golang.org/x/text Character encoding conversion for international code tables (CP437, CP850, WPC1252)
github.com/yeqown/go-qrcode QR code generation with error correction levels (L/M/Q/H), embedded logos, and circular block shapes
github.com/fogleman/gg 2D graphics context (transitive dependency via go-qrcode) for rendering QR codes as images
github.com/stretchr/testify Test assertions, mocking (testify/mock), and table-driven test patterns across ~50 test files

CV-Ready Achievements

  • Architected a layered, modular Go library following SOLID principles (Facade, Strategy, Command, Registry patterns) with 12+ packages organized by domain responsibility, enabling clean separation between protocol generation, device profiles, connection strategies, and document execution.

  • Engineered a custom image processing pipeline featuring Atkinson dithering, bilinear interpolation scaling, and monochrome bitmap generation optimized for 1-bit thermal printer output, delivering high-fidelity rendering of photos and logos on hardware limited to black-and-white.

  • Developed a comprehensive ESC/POS binary protocol implementation supporting 11 command types (text, image, barcode, QR, table, separator, feed, cut, raw, pulse, beep) with full text formatting (bold, underline, inverse, 8 size multipliers, Font A/B) and 8 barcode symbologies.

  • Implemented native Windows Print Spooler integration using syscall and unsafe packages to interact directly with winspool.drv, mapping C-style structs (DOC_INFO_1, PRINTER_INFO_2) for print job management and printer enumeration via EnumPrintersW — including smart auto-detection that filters thermal/POS printers from virtual ones and supports proper job tracking in production POS environments.

  • Designed a hardware-aware dynamic table engine with automatic column width reduction ("reduce longest first" algorithm), word wrapping, configurable spacing, and overflow protection — validating Σ(columns) + (n-1) × spacing ≤ maxChars before rendering to prevent print failures on 58mm/80mm thermal paper.

  • Built a visual emulator (pkg/emulator) that renders ESC/POS documents as PNG images using a canvas-based system with TTF font management (JetBrains Mono), state machine tracking, and bitmap fallback — enabling development and automated testing without physical printer hardware.

  • Established a production-grade CI/CD pipeline with 11 GitHub Actions workflows including multi-OS test matrix with race detection, automated semantic versioning with changelog generation, CodeQL and Trivy security scanning, PR automation with benchmark comparison, Dependabot auto-merge, and Codecov coverage reporting.

  • Implemented a secure JSON document parsing layer with file path traversal protection, document schema validation ( version format, paper width, DPI constraints), and a multi-strategy printer resolution system that resolves printer names from CLI flags → JSON profile → auto-detection with thermal-pattern matching.

Skills Demonstrated

Go (Golang), Systems Programming, Windows API Integration (syscall/unsafe), ESC/POS Protocol Engineering, Binary Protocol Implementation, Image Processing (Dithering, Scaling, Monochrome Conversion), JSON Schema Design & Validation, Interface-Driven Architecture, Design Patterns (Facade, Strategy, Command, Builder, Registry), Table-Driven Testing, CI/CD Pipeline Design (GitHub Actions), Static Analysis & Security Scanning (CodeQL, Trivy, golangci-lint), Automated Semantic Versioning, Cross-Platform Development, Hardware Abstraction, Conventional Commits