fillpdf.go

package main

import (
	"bufio"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"path/filepath"
)

// Form represents the PDF form.
// This is a key value map.
type Form map[string]interface{}

// Fill a PDF form with the specified form values and create a final filled PDF file.
// One variadic boolean specifies, whenever to overwrite the destination file if it exists.
func Fill(form Form, formPDFFile, destPDFFile string, overwrite ...bool) (err error) {
	// Get the absolute paths.
	formPDFFile, err = filepath.Abs(formPDFFile)
	if err != nil {
		return fmt.Errorf("failed to create the absolute path: %v", err)
	}
	destPDFFile, err = filepath.Abs(destPDFFile)
	if err != nil {
		return fmt.Errorf("failed to create the absolute path: %v", err)
	}

	// Check if the form file exists.
	e, err := exists(formPDFFile)
	if err != nil {
		return fmt.Errorf("failed to check if form PDF file exists: %v", err)
	} else if !e {
		return fmt.Errorf("form PDF file does not exists: '%s'", formPDFFile)
	}

	// Check if the pdftk utility exists.
	_, err = exec.LookPath("pdftk")
	if err != nil {
		return fmt.Errorf("pdftk utility is not installed!")
	}

	// Create a temporary directory.
	tmpDir, err := ioutil.TempDir("", "fillpdf-")
	if err != nil {
		return fmt.Errorf("failed to create temporary directory: %v", err)
	}

	// Remove the temporary directory on defer again.
	defer func() {
		errD := os.RemoveAll(tmpDir)
		// Log the error only.
		if errD != nil {
			log.Printf("fillpdf: failed to remove temporary directory '%s' again: %v", tmpDir, errD)
		}
	}()

	// Create the temporary output file path.
	outputFile := filepath.Clean(tmpDir + "/output.pdf")

	// Create the fdf data file.
	fdfFile := filepath.Clean(tmpDir + "/data.xfdf")
	err = createXFdfFile(form, fdfFile)

	if err != nil {
		return fmt.Errorf("failed to create fdf form data file: %v", err)
	}

	// Create the pdftk command line arguments.
	args := []string{
		formPDFFile,
		"fill_form", fdfFile,
		"output", outputFile,
		"flatten",
	}

	// Run the pdftk utility.
	err = runCommandInPath(tmpDir, "pdftk", args...)
	if err != nil {
		return fmt.Errorf("pdftk error: %v", err)
	}

	// Check if the destination file exists.
	e, err = exists(destPDFFile)
	if err != nil {
		return fmt.Errorf("failed to check if destination PDF file exists: %v", err)
	} else if e {
		if len(overwrite) == 0 || !overwrite[0] {
			return fmt.Errorf("destination PDF file already exists: '%s'", destPDFFile)
		}

		err = os.Remove(destPDFFile)
		if err != nil {
			return fmt.Errorf("failed to remove destination PDF file: %v", err)
		}
	}

	// On success, copy the output file to the final destination.
	err = copyFile(outputFile, destPDFFile)
	if err != nil {
		return fmt.Errorf("failed to copy created output PDF to final destination: %v", err)
	}

	return nil
}

func createXFdfFile(form Form, path string) error {
	// Create the file.
	file, err := os.Create(path)
	if err != nil {
		return err
	}
	defer file.Close()

	// Create a new writer.
	w := bufio.NewWriter(file)

	// Write the fdf header.
	fmt.Fprintln(w, fdfHeader)

	// Write the form data.
	for key, value := range form {
		fmt.Fprintf(w, `<field name="%s"><value>%v</value></field>\n`, key, value)
	}

	// Write the fdf footer.
	fmt.Fprintln(w, fdfFooter)

	// Flush everything.
	return w.Flush()
}

const fdfHeader = `<?xml version="1.0" encoding="UTF-8"?>
<xfdf xmlns="http://ns.adobe.com/xfdf/" xml:space="preserve">
<fields>`

const fdfFooter = `</fields>
</xfdf>
 %%EOF`