GoHTML Server

A self-hosted HTML → PDF conversion server, fully compatible with the [gohtml client library].
This project serves as a drop-in replacement for UniDoc’s commercial UniHTML server.

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✨ Features

• Convert HTML files to PDF
• Convert HTML directories (with CSS, JS, images) to PDF
• Convert web URLs to PDF
• Customizable page size (A4, Letter, custom dimensions)
• Configurable margins and orientation
• Support for dynamic content rendering (JavaScript)
• Wait for specific selectors (ready/visible)
• Pixel-perfect output via Chrome/Chromium rendering engine
• Docker support for easy deployment

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🏗 Architecture

This project includes two main components:

1. Server (server/main.go) – HTTP server that converts HTML to PDF using [chromedp].
2. Client – the [gohtml] library that communicates with the server.

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📦 Prerequisites

Option 1: Docker (recommended)

• Docker installed on your system

Option 2: Local development

• Go 1.21+
• Chrome/Chromium (will be auto-downloaded by chromedp if missing)

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🚀 Quick Start with Docker

Build image

docker build -t gohtml-server:latest .

Run server

docker run -p 8080:8080 gohtml-server:latest

Run in background

docker run -d -p 8080:8080 --name gohtml-server gohtml-server:latest

[gohtml]: https://github.com/unitechio/gohtml
[chromedp]: https://github.com/chromedp/chromedp

Docker Compose

# Start server
docker-compose up -d

# View logs
docker-compose logs -f

# Stop server
docker-compose down

Local Development

Install Dependencies

cd server
go mod download

Run Server

go run ./server/main.go

Server will start on http://localhost:8080

API Endpoints

Health Check

curl http://localhost:8080/health

Convert HTML to PDF

POST http://localhost:8080/v1/pdf
Content-Type: application/json

{
  "content": "base64_encoded_html_or_raw_bytes",
  "contentType": "text/html",
  "method": "html",
  "PageParameters": {
    "paperWidth": "210mm",
    "paperHeight": "297mm",
    "orientation": "portrait",
    "marginTop": "10mm",
    "marginBottom": "10mm",
    "marginLeft": "10mm",
    "marginRight": "10mm"
  },
  "RenderParameters": {
    "waitTime": 1000
  }
}

Response: PDF binary data with status 201 Created

Using with gohtml Client

Install Client Library

go get github.com/unitechio/gohtml
go get github.com/unitechio/gopdf

Example Code

package main

import (
    "fmt"
    "os"
    
    "github.com/unitechio/gohtml"
    "github.com/unitechio/gopdf/creator"
    "github.com/unitechio/gopdf/common"
)

func main() {
    if len(os.Args) != 3 {
        fmt.Println("Usage: program <server-url> <input-path>")
        os.Exit(1)
    }

    // Connect to server
    if err := gohtml.Connect(os.Args[1]); err != nil {
        fmt.Printf("Connect failed: %v\n", err)
        os.Exit(1)
    }

    // Create PDF creator
    c := creator.New()

    // Load HTML document
    doc, err := gohtml.NewDocument(os.Args[2])
    if err != nil {
        fmt.Printf("NewDocument failed: %v\n", err)
        os.Exit(1)
    }

    // Convert to PDF
    if err = c.Draw(doc); err != nil {
        fmt.Printf("Draw failed: %v\n", err)
        os.Exit(1)
    }

    // Write output
    if err = c.WriteToFile("output.pdf"); err != nil {
        fmt.Printf("WriteToFile failed: %v\n", err)
        os.Exit(1)
    }

    fmt.Println("Success: output.pdf created")
}

Run Client

# Convert HTML file
go run main.go http://localhost:8080 input.html

# Convert web page
go run main.go http://localhost:8080 https://example.com

# Convert directory
go run main.go http://localhost:8080 ./html-folder

Configuration

Page Sizes

Supported page sizes:

• A4 (210mm × 297mm)
• Letter (8.5in × 11in)
• Custom dimensions (e.g., paperWidth: "200mm", paperHeight: "300mm")

Margins

Default margins: 10mm on all sides

doc.SetMargins(left, right, top, bottom) // in points

Orientation

doc.SetLandscapeOrientation() // Default is portrait

Wait for Content

// Wait for time
doc.WaitTime(2 * time.Second)

// Wait for selector to be ready
doc.WaitReady(".content", selector.ByCSS)

// Wait for selector to be visible
doc.WaitVisible("#main", selector.ByID)

Environment Variables

Variable	Description	Default
PORT	Server port	8080
TZ	Timezone	UTC

Performance

• Typical conversion time: 2-5 seconds per page
• Memory usage: ~200MB per Chrome instance
• Concurrent requests: Limited by available RAM

Troubleshooting

Chrome fails to start

Problem: chromedp run: chrome failed to start

Solution:

• Use Docker (recommended) - Chrome is pre-installed
• Or let chromedp auto-download Chromium (~150MB)

Out of memory

Problem: Server crashes under load

Solution:

# Limit concurrent conversions
# Add connection pooling
# Increase Docker memory limit
docker run --memory=2g -p 8080:8080 gohtml-server

Timeout errors

Problem: Conversion takes too long

Solution:

doc.SetTimeoutDuration(60 * time.Second) // Increase timeout

Project Structure

.
├── server/
│   └── main.go           # Server implementation
├── Dockerfile            # Docker build configuration
├── docker-compose.yml    # Docker Compose setup
├── go.mod               # Go dependencies
├── go.sum
└── README.md

Technology Stack

• Language: Go 1.21+
• PDF Engine: chromedp (Chrome DevTools Protocol)
• HTTP Server: net/http (stdlib)
• Container: Docker + chromedp/headless-shell

License

This is a fork of UniDoc's UniHTML with license restrictions removed. Use at your own discretion.

Credits

• Original UniHTML: UniDoc.io
• chromedp: github.com/chromedp/chromedp
• gohtml fork: github.com/unitechio/gohtml

Support

For issues and questions, please open an issue on GitHub.

Alternatives

• wkhtmltopdf: Faster but outdated WebKit engine
• Puppeteer: Node.js alternative with similar features
• WeasyPrint: Python-based, CSS-focused
• UniHTML Cloud: Official commercial service