Poster: Thermal Printer Driver & ESC/POS Utility

A professional, production-ready Go library and command-line utility for controlling ESC/POS thermal printers. Designed for high-reliability retail and POS environments, it features a robust JSON-based document protocol, native Windows Spooler integration, an advanced graphics engine, and a visual emulator for testing without physical hardware.

🚀 Key Features

• JSON Document Protocol: Define print jobs using a clean, versioned JSON schema (v1.0). Decouples business logic from hardware commands with full schema validation.
• Native Windows Integration: Prints directly via the Windows Print Spooler API (winspool.drv), supporting USB, Serial, and Network printers installed in Windows.
• Advanced Graphics Engine:
  • High-quality image printing with Atkinson Dithering.
  • Automatic scaling with bilinear interpolation.
  • Supports PNG, JPG, BMP formats.
• Smart QR & Barcodes: Automatically chooses between native printer firmware commands (fastest) or software rendering (maximum compatibility) based on the printer profile.
• Dynamic Table Layout: Built-in engine for generating perfectly aligned receipts with word wrapping, multi-column support, configurable spacing, automatic overflow detection, and smart column auto-reduction that preserves small columns while shrinking larger ones to fit paper width.
• Visual Emulator: Render print jobs as PNG images for preview and testing without physical hardware.
• Hardware Agnostic: Includes profiles for standard 80mm (Epson-compatible), 58mm (generic), PT-210, GP-58N, and EC-PM-80250 printers.
• Smart Printer Discovery: Auto-detects thermal/POS printers from installed Windows devices, filtering virtual printers and matching common hardware patterns.
• 11 Command Types: text, image, barcode, qr, table, separator, feed, cut, raw, pulse, beep.
• Raw Command Support: Send raw ESC/POS bytes when full control is needed.

🏗️ Architecture

The project follows a layered architecture to ensure modularity and testability:

graph TD
    JSON["JSON Document<br/>(v1.0 Schema)"] --> Parser["Parser & Validator<br/>(pkg/document/schema)"]
    Parser --> Builder["Command Builder<br/>(pkg/document/builder)"]
    Builder --> Executor["Command Executor<br/>(pkg/document/executor)"]
    Executor --> Service["Printer Service<br/>(pkg/service)"]

    subgraph "Core Logic"
        Service --> Protocol["ESC/POS Composer<br/>(pkg/composer)"]
        Service --> Profile["Device Profile<br/>(pkg/profile)"]
        Service --> Graphics["Graphics Engine<br/>(pkg/graphics)"]
        Service --> Tables["Table Engine<br/>(pkg/tables)"]
    end

    subgraph "Command Modules (pkg/commands)"
        Protocol --> Barcode["Barcode"]
        Protocol --> BitImage["Bit Image"]
        Protocol --> Character["Character"]
        Protocol --> LineSpacing["Line Spacing"]
        Protocol --> MechControl["Mechanism Control"]
        Protocol --> PrintCmd["Print"]
        Protocol --> PrintPos["Print Position"]
        Protocol --> QRCode["QR Code"]
    end

    Service --> Connector["Connection Interface<br/>(pkg/connection)"]

    subgraph "Output Layer"
        Connector --> WinAPI["Windows Spooler API<br/>(winspool.drv)"]
        Connector --> Network["Network<br/>(TCP/9100)"]
        Connector --> Serial["Serial<br/>(COM Port)"]
        Connector --> FileOut["File<br/>(Debug Output)"]
        Connector --> Emulator["Visual Emulator<br/>(pkg/emulator)"]
        WinAPI --> Device["Physical Printer"]
        Emulator --> PNG["PNG Image"]
    end

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Package Structure

Package	Description
pkg/commands	ESC/POS command implementations (barcode, bitimage, character, linespacing, mechanismcontrol, print, printposition, qrcode)
pkg/composer	ESC/POS byte sequence generation and protocol composition
pkg/connection	Connection interfaces — Windows Spooler, Network, Serial, File
pkg/constants	Shared constants, unit conversions, and default values
pkg/document	Document parsing, building, and execution (schema, builder, executor)
pkg/emulator	Visual emulator for rendering print jobs as PNG images
pkg/graphics	Image processing pipeline — dithering, scaling, bitmap handling
pkg/profile	Printer profiles and character encoding tables
pkg/service	High-level printer service facade (PrinterActions interface)
pkg/tables	Table engine — column alignment, word wrapping, header styling, auto-reduction

📦 Installation

Prerequisites

• Go 1.24 or higher
• Windows OS (for native spooler support; cross-platform for library/emulator use)

As a Go Module

go get github.com/adcondev/poster@latest

Build from Source

# Clone the repository
git clone https://github.com/adcondev/poster.git
cd poster

# Build the binary
go build -o poster.exe ./cmd/poster

# Or use Taskfile
task build

📖 Usage

Command Line Interface (CLI)

The poster utility takes a JSON document and sends it to a specified printer.

# Print a document to a specific printer
poster.exe -file receipt.json -printer "EPSON TM-T88V"

# Dry-run (validate JSON without printing)
poster.exe -file receipt.json --dry-run

# List all installed printers (Windows only)
poster.exe --list

# List thermal/POS printers only
poster.exe --list-thermal

# List physical printers only (exclude virtual)
poster.exe --list-physical

# Output printer list as JSON
poster.exe --list --json

# Show version
poster.exe -v

JSON Document Example

Create a file named ticket.json:

{
  "version": "1.0",
  "profile": {
    "model": "Generic 80mm",
    "paper_width": 80,
    "dpi": 203,
    "has_qr": true
  },
  "commands": [
    {
      "type": "text",
      "data": {
        "content": {
          "text": "STORE NAME",
          "content_style": {
            "bold": true,
            "size": "2x2",
            "align": "center"
          }
        }
      }
    },
    {
      "type": "separator",
      "data": {
        "char": "-"
      }
    },
    {
      "type": "table",
      "data": {
        "definition": {
          "columns": [
            { "header": "Item", "width": 20, "align":  "left" },
            { "header":  "Price", "width": 10, "align": "right" }
          ]
        },
        "show_headers": true,
        "rows": [
          ["Coffee", "$3.50"],
          ["Sandwich", "$8.00"]
        ],
        "options": {
          "header_bold": true,
          "word_wrap": true,
          "column_spacing": 1,
          "auto_reduce": true
        }
      }
    },
    {
      "type": "qr",
      "data": {
        "data": "https://example.com",
        "align": "center",
        "pixel_width": 150
      }
    },
    {
      "type": "cut",
      "data": {
        "feed": 3
      }
    }
  ]
}

Library Usage (Go)

You can also use the packages directly in your Go application:

package main

import (
	"github.com/adcondev/poster/pkg/composer"
	"github.com/adcondev/poster/pkg/connection"
	"github.com/adcondev/poster/pkg/profile"
	"github.com/adcondev/poster/pkg/service"
)

func main() {
	// 1. Configure Profile
	prof := profile.CreateProfile80mm()

	// 2. Connect to Printer
	conn, _ := connection.NewWindowsPrintConnector("POS-80")
	defer conn.Close()

	// 3. Initialize Service
	proto := composer.NewEscpos()
	printer, _ := service.NewPrinter(proto, prof, conn)
	defer printer.Close()

	// 4. Print
	printer.Initialize()
	printer.PrintLine("Hello World!")
	printer.FullFeedAndCut(2)
}

📋 Supported Commands

Command	Description
text	Print formatted text with styles (bold, underline, inverse, sizing)
image	Print images with dithering and scaling options
barcode	Generate barcodes (CODE128, EAN13, UPC-A, CODE39, etc.)
qr	Generate QR codes with optional logos and human-readable text
table	Create formatted tables with column alignment and word wrapping
separator	Print separator lines
feed	Advance paper by specified lines
cut	Perform full or partial paper cut
raw	Send raw ESC/POS bytes directly
pulse	Send electrical pulse to open cash drawer
beep	Emit buzzer alert sound

For complete documentation, see api/v1/DOCUMENT_V1.md.

⚙️ Configuration

Connection Types

Type	Status	Description
windows	✅ Implemented	Windows Print Spooler (default). USB/Network printers installed in Windows.
network	🔜 Planned	Direct network connection via Raw TCP/9100
serial	🔜 Planned	Serial/USB direct connection (COM ports)
file	🔜 Planned	Output to file for debugging or emulator testing

Printer Profiles

The library includes built-in profiles for common hardware:

Profile	Description
CreateProfile80mm()	Standard ESC/POS 80mm (Epson TM-T88, etc.)
CreateProfile58mm()	Generic 58mm thermal printers
CreatePt210()	PT-210 portable printer with QR support
CreateGP58N()	GP-58N 58mm thermal printer
CreateECPM80250()	EC-PM-80250 80mm thermal printer

🎨 Visual Emulator

The pkg/emulator package provides a visual emulator that renders print jobs as PNG images:

import (
	"github.com/adcondev/poster/pkg/emulator"
)

// Create emulator with configuration
emu, _ := emulator.NewEngine(emulator.DefaultConfig())

// Render text
emu.SetBold(true)
emu.SetSize(2, 2)
emu.AlignCenter()
emu.PrintLine("STORE NAME")

// Render and save as PNG
img := emu.Render()

📊 Code Coverage

📈 Coverage Trends

🤝 Contributing

Contributions are welcome! Please read CONTRIBUTING.md for guidelines on how to submit pull requests. This project uses Conventional Commits and enforces semantic PR titles.

📄 License

This project is licensed under the MIT License — see the LICENSE file for details.