PDF Unlocker with Go

A simple HTTP service built in Go that removes password protection from PDF files using the pdfcpu library.

Features

• HTTP API for unlocking password-protected PDFs
• Support for user password decryption
• File validation to ensure only PDF files are processed
• Simple REST API interface
• Lightweight and fast processing

Prerequisites

• Go 1.19 or higher
• Git

Installation

1. Clone the repository:

git clone <repository-url>
cd go-pdf-unlock

2. Initialize Go module and install dependencies:

go mod init go-pdf-unlock
go mod tidy

3. Run the service:

go run main.go

The service will start on port 8080.

Usage

API Endpoint

POST /unlock

Unlocks a password-protected PDF file.

Request

• Content-Type: multipart/form-data
• Parameters:
  • file: The password-protected PDF file (required)
  • password: The password for the PDF file (required)

Response

• Success (200): Returns the unlocked PDF file
  • Content-Type: application/pdf
  • Content-Disposition: attachment; filename="unlocked.pdf"
• Error (4xx/5xx): Returns error message in plain text

Example using curl

curl -X POST \
  -F "[email protected]" \
  -F "password=mypassword" \
  -o unlocked.pdf \
  http://localhost:8080/unlock

Example using JavaScript (fetch)

const formData = new FormData();
formData.append("file", pdfFile); // File object from input
formData.append("password", "mypassword");

fetch("http://localhost:8080/unlock", {
  method: "POST",
  body: formData,
})
  .then((response) => {
    if (response.ok) {
      return response.blob();
    }
    throw new Error("Failed to unlock PDF");
  })
  .then((blob) => {
    // Handle the unlocked PDF blob
    const url = URL.createObjectURL(blob);
    const a = document.createElement("a");
    a.href = url;
    a.download = "unlocked.pdf";
    a.click();
  });

Error Handling

The API returns appropriate HTTP status codes and error messages:

• 400 Bad Request:
  • Invalid request method (not POST)
  • No file provided
  • Uploaded file is not a PDF
  • Password not provided
• 405 Method Not Allowed: Request method other than POST
• 500 Internal Server Error:
  • Failed to read file content
  • Failed to unlock PDF (incorrect password or corrupted file)

Dependencies

• pdfcpu - PDF processing library

Building for Production

To build a binary for production:

go build -o pdf-unlock-service main.go
./pdf-unlock-service

Docker Support

Create a Dockerfile:

FROM golang:1.19-alpine AS builder
WORKDIR /app
COPY . .
RUN go mod download
RUN go build -o pdf-unlock-service main.go

FROM alpine:latest
RUN apk --no-cache add ca-certificates
WORKDIR /root/
COPY --from=builder /app/pdf-unlock-service .
EXPOSE 8080
CMD ["./pdf-unlock-service"]

Build and run with Docker:

docker build -t pdf-unlock-service .
docker run -p 8080:8080 pdf-unlock-service

Security Considerations

• This service processes uploaded files in memory
• Passwords are transmitted in form data (consider HTTPS in production)
• No authentication or rate limiting is implemented
• Files are not persisted on the server

License

MIT License