Tryanks/pdfsign
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Refactor object handling

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This commit is contained in:
Paul van Brouwershaven
2024-12-11 16:24:26 +01:00
parent 21dd78d75e
commit e5cdb61bea
11 changed files with 311 additions and 327 deletions
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69
sign/pdfsignature.go
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@@ -21,23 +21,20 @@ import (
const signatureByteRangePlaceholder = "/ByteRange[0 ********** ********** **********]"
func (context *SignContext) createSignaturePlaceholder() (dssd string, byte_range_start_byte int64, signature_contents_start_byte int64) {
func (context *SignContext) createSignaturePlaceholder() []byte {
// Using a buffer because it's way faster than concatenating.
var signature_buffer bytes.Buffer
signature_buffer.WriteString(strconv.Itoa(int(context.SignData.ObjectId)) + " 0 obj\n")
signature_buffer.WriteString("<< /Type /Sig\n")
signature_buffer.WriteString("<<\n")
signature_buffer.WriteString(" /Type /Sig\n")
signature_buffer.WriteString(" /Filter /Adobe.PPKLite\n")
signature_buffer.WriteString(" /SubFilter /adbe.pkcs7.detached\n")
signature_buffer.WriteString(context.createPropBuild())
byte_range_start_byte = int64(signature_buffer.Len()) + 1
// Create a placeholder for the byte range string, we will replace it later.
signature_buffer.WriteString(" " + signatureByteRangePlaceholder)
signature_contents_start_byte = int64(signature_buffer.Len()) + 11
// Create a placeholder for the actual signature content, we will replace it later.
signature_buffer.WriteString(" /Contents<")
signature_buffer.Write(bytes.Repeat([]byte("0"), int(context.SignatureMaxLength)))
@@ -168,40 +165,47 @@ func (context *SignContext) createSignaturePlaceholder() (dssd string, byte_rang
signature_buffer.WriteString(pdfString(context.SignData.Signature.Info.ContactInfo))
signature_buffer.WriteString("\n")
}
signature_buffer.WriteString(" /M ")
signature_buffer.WriteString(pdfDateTime(context.SignData.Signature.Info.Date))
signature_buffer.WriteString("\n")
signature_buffer.WriteString(" >>\n")
signature_buffer.WriteString("endobj\n")
// (Optional) The time of signing. Depending on the signature handler, this may
// be a normal unverified computer time or a time generated in a verifiable way
// from a secure time server.
//
// This value should be used only when the time of signing is not available in the
// signature. If SubFilter is ETSI.RFC3161, this entry should not be used and
// should be ignored by a PDF processor.
//
// A timestamp can be embedded in a CMS binary data object (see 12.8.3.3, "CMS
// (PKCS #7) signatures").
if context.SignData.TSA.URL == "" {
signature_buffer.WriteString(" /M ")
signature_buffer.WriteString(pdfDateTime(context.SignData.Signature.Info.Date))
signature_buffer.WriteString("\n")
}
return signature_buffer.String(), byte_range_start_byte, signature_contents_start_byte
signature_buffer.WriteString(">>\n")
return signature_buffer.Bytes()
}
func (context *SignContext) createTimestampPlaceholder() (dssd string, byte_range_start_byte int64, signature_contents_start_byte int64) {
func (context *SignContext) createTimestampPlaceholder() []byte {
var timestamp_buffer bytes.Buffer
timestamp_buffer.WriteString(strconv.Itoa(int(context.SignData.ObjectId)) + " 0 obj\n")
timestamp_buffer.WriteString("<< /Type /DocTimeStamp\n")
timestamp_buffer.WriteString("<<\n")
timestamp_buffer.WriteString(" /Type /DocTimeStamp\n")
timestamp_buffer.WriteString(" /Filter /Adobe.PPKLite\n")
timestamp_buffer.WriteString(" /SubFilter /ETSI.RFC3161\n")
timestamp_buffer.WriteString(context.createPropBuild())
byte_range_start_byte = int64(timestamp_buffer.Len()) + 1
// Create a placeholder for the byte range string, we will replace it later.
timestamp_buffer.WriteString(" " + signatureByteRangePlaceholder)
signature_contents_start_byte = int64(timestamp_buffer.Len()) + 11
timestamp_buffer.WriteString(" /Contents<")
timestamp_buffer.Write(bytes.Repeat([]byte("0"), int(context.SignatureMaxLength)))
timestamp_buffer.WriteString(">\n")
timestamp_buffer.WriteString(">>\n")
timestamp_buffer.WriteString("endobj\n")
return timestamp_buffer.String(), byte_range_start_byte, signature_contents_start_byte
return timestamp_buffer.Bytes()
}
func (context *SignContext) fetchRevocationData() error {
@@ -446,16 +450,31 @@ func (context *SignContext) replaceSignature() error {
}
file_content := context.OutputBuffer.Buff.Bytes()
if _, err := context.OutputBuffer.Write(file_content[:(context.ByteRangeValues[0] + context.ByteRangeValues[1] + 1)]); err != nil {
// Write the file content up to the signature
if _, err := context.OutputBuffer.Write(file_content[context.ByteRangeValues[0]:context.ByteRangeValues[1]]); err != nil {
return err
}
// Write new signature
if _, err := context.OutputBuffer.Write([]byte("<")); err != nil {
return err
}
// Write new ByteRange.
if _, err := context.OutputBuffer.Write([]byte(dst)); err != nil {
return err
}
if _, err := context.OutputBuffer.Write(file_content[(context.ByteRangeValues[0]+context.ByteRangeValues[1]+1)+int64(len(dst)):]); err != nil {
// Write 0s to ensure the signature remains the same size
zeroPadding := bytes.Repeat([]byte("0"), int(context.SignatureMaxLength)-len(dst))
if _, err := context.OutputBuffer.Write(zeroPadding); err != nil {
return err
}
if _, err := context.OutputBuffer.Write([]byte(">")); err != nil {
return err
}
if _, err := context.OutputBuffer.Write(file_content[context.ByteRangeValues[2] : context.ByteRangeValues[2]+context.ByteRangeValues[3]]); err != nil {
return err
}