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Learning & Achievements - Scale Daemon

Project Overview

Scale Daemon is a production-grade Windows Service written in Go that bridges industrial weighing scales ( RS232/Serial) with modern web applications. It reads weight data in real-time from serial-connected hardware and broadcasts it to multiple clients simultaneously via a low-latency WebSocket server, serving as persistent middleware for retail and logistics environments.

Tech Stack & Infrastructure

  • Language: Go (Golang) 1.24+
  • Platform: Windows (System Services via SCM)
  • Communication Protocols:
    • Serial (RS232): 9600 baud, hardware scale communication with configurable timeouts
    • WebSocket: Real-time bidirectional streaming (hybrid JSON/string protocol)
    • HTTP: REST endpoints for health checks, diagnostics, and dashboard serving
  • Frontend: Embedded HTML/CSS/JS dashboard served via Go's embed package
  • Authentication: bcrypt password hashing (via golang.org/x/crypto), session-based auth with HttpOnly cookies
  • Build & Automation: Taskfile (Task v3), Go Modules, ldflags injection for secrets and metadata
  • CI/CD: GitHub Actions (test, lint, build, benchmark, PR automation, PR status dashboard)
  • Security Scanning: GitHub CodeQL (weekly + on PR), golangci-lint with gosec enabled
  • Code Coverage: Codecov integration with race detection
  • API Specification: JSON Schema (Draft-07) for WebSocket protocol

Notable Libraries

  • go.bug.st/serial: Cross-platform serial port communication. Solved configuring baud rates, read timeouts, and handling raw bytes from industrial hardware.
  • github.com/coder/websocket: Minimal, idiomatic WebSocket library with context.Context support. Used for real-time broadcast server and JSON message handling via wsjson.
  • github.com/judwhite/go-svc: Abstraction for Windows Service Control Manager (SCM). Handles OS signals (SIGINT, SIGTERM) and service lifecycle (Init, Start, Stop) cleanly in Go.
  • golang.org/x/crypto/bcrypt: Industry-standard password hashing. Used to validate dashboard login credentials without storing plaintext passwords in the binary.

CV-Ready Achievements

  • Architected a concurrent, event-driven Windows Service in Go that interfaces with RS232 industrial scales, using a Producer–Consumer pattern with goroutines and channels to decouple hardware I/O from WebSocket fan-out broadcasting to multiple clients simultaneously.
  • Engineered a layered security system featuring bcrypt password authentication, cryptographically random session tokens (HttpOnly/SameSite cookies), per-IP brute-force lockout (5 attempts → 5-minute ban), and per-client WebSocket rate limiting (15 config changes/min) — all with comprehensive [AUDIT] logging.
  • Developed a real-time embedded web dashboard using Go's embed package and HTML templates, with server-side token injection to solve the "static file authentication paradox" for WebSocket config authorization.
  • Implemented a hybrid WebSocket API protocol (JSON objects for control messages, raw JSON strings for weight streaming) validated by a JSON Schema specification, minimizing overhead and latency for high-frequency weight data broadcasting.
  • Optimized service reliability with automatic serial port reconnection, configurable log rotation (5 MB threshold with last-1000-line preservation), verbose/non-verbose log filtering, and graceful multi-component shutdown with context cancellation and sync.WaitGroup coordination.
  • Built a comprehensive CI/CD pipeline using GitHub Actions with 5 workflows: automated testing with race detection, Codecov coverage reporting, golangci-lint with 15+ linters (including gosec), GitHub CodeQL security analysis ( weekly + on PR), performance benchmarking with base/PR comparison, semantic PR title validation, auto-labeling, and a weekly PR status dashboard.
  • Designed a hot-swappable runtime configuration system allowing serial port, scale brand, and test mode changes via authenticated WebSocket messages without service restarts, using sync.RWMutex for thread-safe config snapshots.

Skills Demonstrated

Go Concurrent Programming, Windows Service Development, Serial Port Communication (RS232), WebSocket Real-Time Streaming, REST API Design, Authentication & Session Management, bcrypt Password Hashing, Brute-Force Protection, Rate Limiting, Embedded File Systems (go:embed), CI/CD Pipeline Design (GitHub Actions), Static Analysis & Security Scanning (golangci-lint, CodeQL, gosec), Performance Benchmarking, JSON Schema API Specification, Log Rotation & Filtering, Graceful Shutdown Patterns, Producer–Consumer Architecture, Build-Time Secret Injection (ldflags)