sign_bug_repro.go

package main

import (
	"bytes"
	"crypto"
	"crypto/x509"
	pdfRead "github.com/digitorus/pdf"
	pdfSign "github.com/digitorus/pdfsign/sign"
	"github.com/signintech/gopdf"
	"os"
	"time"
)

func createPdfWithLink() []byte {
	pdfEngine := &gopdf.GoPdf{}
	pdfEngine.Start(gopdf.Config{PageSize: *gopdf.PageSizeA4})
	pdfEngine.AddTTFFont("default", "./regular.ttf")
	pdfEngine.SetFont("default", "", 16)
	pdfEngine.AddPage()
	pdfEngine.Text("Hello, world!")
	pdfEngine.AddExternalLink("https://google.com", 0, 0, 32, 32)
	return pdfEngine.GetBytesPdf()
}

func createPdfWithoutLink() []byte {
	pdfEngine := &gopdf.GoPdf{}
	pdfEngine.Start(gopdf.Config{PageSize: *gopdf.PageSizeA4})
	pdfEngine.AddTTFFont("default", "./regular.ttf")
	pdfEngine.SetFont("default", "", 16)
	pdfEngine.AddPage()
	pdfEngine.Text("Hello, world!")
	return pdfEngine.GetBytesPdf()
}

func signPdf(pdf []byte, certs CertificateStore) []byte {
	pdfLen := int64(len(pdf))
	pdfReader, err := pdfRead.NewReader(bytes.NewReader(pdf), pdfLen)
	if err != nil {
		panic(err)
	}

	pdfWriter := bytes.NewBuffer(make([]byte, 0, pdfLen))
	err = pdfSign.Sign(bytes.NewReader(pdf), pdfWriter, pdfReader, pdfLen, pdfSign.SignData{
		Signature: pdfSign.SignDataSignature{
			CertType:   pdfSign.CertificationSignature,
			DocMDPPerm: pdfSign.AllowFillingExistingFormFieldsAndSignaturesAndCRUDAnnotationsPerms,
			Info: pdfSign.SignDataSignatureInfo{
				Name:        "Test Signing",
				Reason:      "Demonstrating signing failures",
				Location:    "The Internet",
				ContactInfo: "Twometer",
				Date:        time.Now(),
			},
		},

		DigestAlgorithm:   crypto.SHA384,
		Signer:            certs.key,
		Certificate:       certs.cert,
		CertificateChains: [][]*x509.Certificate{certs.chain},
	})
	if err != nil {
		panic(err)
	}

	return pdfWriter.Bytes()
}

func main() {
	// This is just some internal code for loading PFX files
	certs, err := CertificateStoreFromFile("./test_certs.pfx", "test")
	if err != nil {
		panic(err)
	}

	workingPdf := signPdf(createPdfWithoutLink(), certs)
	failingPdf := signPdf(createPdfWithLink(), certs)

	os.WriteFile("./working.pdf", workingPdf, 0744)
	os.WriteFile("./failing.pdf", failingPdf, 0744)
}