Add sign functionality

sign/sign.go

@@ -0,0 +1,149 @@
+package sign
+
+import (
+	"crypto"
+	"crypto/x509"
+	"os"
+	"time"
+
+	"bitbucket.org/digitorus/pdf"
+)
+
+type CatalogData struct {
+	ObjectId   uint32
+	Length     int64
+	RootString string
+}
+
+type SignData struct {
+	ObjectId         uint32
+	Signature        SignDataSignature
+	Signer           crypto.Signer
+	Certificate      *x509.Certificate
+	CertificateChain []*x509.Certificate
+}
+
+type SignDataSignature struct {
+	Approval bool
+	CertType uint32
+	Info     SignDataSignatureInfo
+}
+
+type SignDataSignatureInfo struct {
+	Name        string
+	Location    string
+	Reason      string
+	ContactInfo string
+	Date        time.Time
+}
+
+type SignContext struct {
+	InputFile                  *os.File
+	OutputFile                 *os.File
+	SignData                   SignData
+	CatalogData                CatalogData
+	PDFReader                  *pdf.Reader
+	NewXrefStart               int64
+	ByteRangeStartByte         int64
+	SignatureContentsStartByte int64
+	ByteRangeValues            []int64
+}
+
+func SignFile(input string, output string, sign_data SignData) error {
+	input_file, err := os.Open(input)
+	if err != nil {
+		return err
+	}
+	defer input_file.Close()
+
+	output_file, err := os.Create(output)
+	if err != nil {
+		return err
+	}
+	defer output_file.Close()
+
+	finfo, err := input_file.Stat()
+	if err != nil {
+		return err
+	}
+	size := finfo.Size()
+
+	rdr, err := pdf.NewReader(input_file, size)
+	if err != nil {
+		return err
+	}
+
+	sign_data.ObjectId = uint32(rdr.XrefInformation.ItemCount) + 1
+
+	context := SignContext{
+		PDFReader:  rdr,
+		InputFile:  input_file,
+		OutputFile: output_file,
+		CatalogData: CatalogData{
+			ObjectId: uint32(rdr.XrefInformation.ItemCount),
+		},
+		SignData: sign_data,
+	}
+
+	err = context.SignPDF()
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (context *SignContext) SignPDF() error {
+	// Write the PDF file to the output up til the xref.
+	if err := writePartFromSourceFileToTargetFile(context.InputFile, context.OutputFile, 0, context.PDFReader.XrefInformation.StartPos); err != nil {
+		return err
+	}
+
+	catalog, err := context.createCatalog()
+	if err != nil {
+		return err
+	}
+
+	context.CatalogData.Length = int64(len(catalog))
+
+	// Write the new catalog object.
+	if _, err := context.OutputFile.Write([]byte(catalog)); err != nil {
+		return err
+	}
+
+	// Create the signature object
+	signature_object, byte_range_start_byte, signature_contents_start_byte := context.createSignaturePlaceholder()
+
+	// Positions are relative to old start position of xref table.
+	byte_range_start_byte += context.PDFReader.XrefInformation.StartPos + int64(len(catalog))
+	signature_contents_start_byte += context.PDFReader.XrefInformation.StartPos + int64(len(catalog))
+
+	context.ByteRangeStartByte = byte_range_start_byte
+	context.SignatureContentsStartByte = signature_contents_start_byte
+
+	// Write the new signature object.
+	if _, err := context.OutputFile.Write([]byte(signature_object)); err != nil {
+		return err
+	}
+
+	// Calculate the new start position of the xref table.
+	context.NewXrefStart = context.PDFReader.XrefInformation.StartPos + int64(len(signature_object)) + int64(len(catalog))
+
+	if err := context.writeXref(); err != nil {
+		return err
+	}
+
+	if err := context.writeTrailer(); err != nil {
+		return err
+	}
+
+	if err := context.updateByteRange(); err != nil {
+		return err
+	}
+
+	if err := context.replaceSignature(); err != nil {
+		return err
+	}
+
+	return nil
+}