Postscript Printer Emulator

This project exposes a local API to send PostScript-formatted data to a printer connected via a COM port (e.g., COM3), from a web application (such as Angular).

It includes two implementations:

• Node.js (print-service-node)
• .NET 6 (WebAPI) (print-service-dotnet)

It also includes:

• Python printer emulator (emulator/postscript_com3_emulator.py) for testing without physical hardware
• Scripts to install the service as a Windows service using NSSM
• Inno Setup script to generate an .exe installer

Project Structure

print-service-node/                 --> Local Node.js service
print-service-dotnet/               --> Local .NET 6 WebAPI service
emulator/postscript_com3_emulator.py  --> Printer emulator on COM3

Requirements

Node.js

• Node.js
• pkg (npm install -g pkg)
• NSSM installed at: C:\Program Files\nssm\nssm.exe

.NET

• .NET 6 SDK
• NSSM
• (Optional) Inno Setup to create .exe installer

For testing without a physical printer

• com0com (virtual COM port pair)
  • Install
  • Create pair: COM3 <-> COM4
  • Use COM3 in the service and COM4 in the emulator, or vice versa

Installation

Node.js

cd print-service-node
npm install
pkg .

To install as a service:

install_service.bat

.NET

cd print-service-dotnet
dotnet build

Then:

install_service.bat

Printer Emulator (Python)

File: emulator/postscript_com3_emulator.py

This script simulates a PostScript printer connected to COM3. Each time it receives a data block (detecting \n or \x0C as end), it saves the content to a .txt file inside a prints folder.

How it works

• Opens port COM3
• Continuously listens for incoming data
• When it detects end of job, saves the received content as:

  impresiones/impresion_YYYYMMDD_HHMMSS.txt

Usage

pip install pyserial
python emulator/postscript_com3_emulator.py

Sequence Diagrams

Node.js (print-service-node/server.js)

sequenceDiagram
    participant Browser
    participant server.js
    participant COM3

    Browser->>server.js: POST /print (PostScript content)
    server.js->>COM3: Send data to port
    COM3-->>server.js: Confirmation (optional)
    server.js-->>Browser: HTTP Response (OK / Error)

.NET (print-service-dotnet/Controllers/PrintController.cs)

sequenceDiagram
    participant Browser
    participant PrintController.cs
    participant COM3

    Browser->>PrintController.cs: POST /api/print (PostScript content)
    PrintController.cs->>COM3: Write to serial port
    COM3-->>PrintController.cs: Confirmation (optional)
    PrintController.cs-->>Browser: HTTP Response (OK / Error)

Create .exe Installer with Inno Setup (.NET)

1. Install Inno Setup
2. Open PrintServiceInstaller.iss in Inno
3. Compile

Uninstall

Both versions have their own uninstall_service.bat to stop and remove the service.

License

MIT