Split xref table and stream code and tests
This commit is contained in:
Paul van Brouwershaven
272
sign/pdfxref.go
272
sign/pdfxref.go
@@ -2,26 +2,18 @@ package sign
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import (
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"bytes"
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"compress/zlib"
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"encoding/binary"
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"encoding/hex"
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"errors"
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"fmt"
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"io"
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)
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type xrefEntry struct {
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ID uint32
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Offset int64
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ID uint32
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Offset int64
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Generation int
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Free bool
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}
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const (
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xrefStreamColumns = 6 // Column width (1+4+1)
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xrefStreamPredictor = 12
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defaultPredictor = 1 // No prediction (the default value)
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pngSubPredictor = 11 // PNG prediction (on encoding, PNG Sub on all rows)
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pngUpPredictor = 12 // PNG prediction (on encoding, PNG Up on all rows)
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objectFooter = "\nendobj\n"
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objectFooter = "\nendobj\n"
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)
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func (context *SignContext) addObject(object []byte) (uint32, error) {
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@@ -117,257 +109,3 @@ func (context *SignContext) getLastObjectIDFromXref() (uint32, error) {
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return maxID + 1, nil
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}
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// writeIncrXrefTable writes the incremental cross-reference table to the output buffer.
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func (context *SignContext) writeIncrXrefTable() error {
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// Write xref header
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if _, err := context.OutputBuffer.Write([]byte("xref\n")); err != nil {
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return fmt.Errorf("failed to write incremental xref header: %w", err)
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}
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// Write updated entries
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for _, entry := range context.updatedXrefEntries {
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pageXrefObj := fmt.Sprintf("%d %d\n", entry.ID, 1)
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if _, err := context.OutputBuffer.Write([]byte(pageXrefObj)); err != nil {
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return fmt.Errorf("failed to write updated xref object: %w", err)
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}
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xrefLine := fmt.Sprintf("%010d 00000 n\r\n", entry.Offset)
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if _, err := context.OutputBuffer.Write([]byte(xrefLine)); err != nil {
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return fmt.Errorf("failed to write updated incremental xref entry: %w", err)
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}
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}
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// Write xref subsection header
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startXrefObj := fmt.Sprintf("%d %d\n", context.lastXrefID+1, len(context.newXrefEntries))
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if _, err := context.OutputBuffer.Write([]byte(startXrefObj)); err != nil {
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return fmt.Errorf("failed to write starting xref object: %w", err)
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}
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// Write new entries
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for _, entry := range context.newXrefEntries {
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xrefLine := fmt.Sprintf("%010d 00000 n\r\n", entry.Offset)
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if _, err := context.OutputBuffer.Write([]byte(xrefLine)); err != nil {
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return fmt.Errorf("failed to write incremental xref entry: %w", err)
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}
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}
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return nil
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}
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// writeXrefStream writes the cross-reference stream to the output buffer.
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func (context *SignContext) writeXrefStream() error {
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var buffer bytes.Buffer
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predictor := context.PDFReader.Trailer().Key("DecodeParms").Key("Predictor").Int64()
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if predictor == 0 {
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predictor = xrefStreamPredictor
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}
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if err := writeXrefStreamEntries(&buffer, context); err != nil {
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return fmt.Errorf("failed to write xref stream entries: %w", err)
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}
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streamBytes, err := encodeXrefStream(buffer.Bytes(), predictor)
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if err != nil {
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return fmt.Errorf("failed to encode xref stream: %w", err)
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}
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var xrefStreamObject bytes.Buffer
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if err := writeXrefStreamHeader(&xrefStreamObject, context, len(streamBytes)); err != nil {
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return fmt.Errorf("failed to write xref stream header: %w", err)
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}
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if err := writeXrefStreamContent(&xrefStreamObject, streamBytes); err != nil {
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return fmt.Errorf("failed to write xref stream content: %w", err)
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}
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_, err = context.addObject(xrefStreamObject.Bytes())
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if err != nil {
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return fmt.Errorf("failed to add xref stream object: %w", err)
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}
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return nil
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}
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// writeXrefStreamEntries writes the individual entries for the xref stream.
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func writeXrefStreamEntries(buffer *bytes.Buffer, context *SignContext) error {
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// Write updated entries first
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for _, entry := range context.updatedXrefEntries {
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writeXrefStreamLine(buffer, 1, int(entry.Offset), 0)
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}
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// Write new entries
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for _, entry := range context.newXrefEntries {
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writeXrefStreamLine(buffer, 1, int(entry.Offset), 0)
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}
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return nil
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}
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// encodeXrefStream applies the appropriate encoding to the xref stream.
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func encodeXrefStream(data []byte, predictor int64) ([]byte, error) {
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// Use FlateDecode without prediction for xref streams
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var b bytes.Buffer
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w := zlib.NewWriter(&b)
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if _, err := w.Write(data); err != nil {
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return nil, err
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}
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w.Close()
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return b.Bytes(), nil
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}
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// writeXrefStreamHeader writes the header for the xref stream.
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func writeXrefStreamHeader(buffer *bytes.Buffer, context *SignContext, streamLength int) error {
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id := context.PDFReader.Trailer().Key("ID")
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// Calculate total entries and create index array
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totalEntries := uint32(context.PDFReader.XrefInformation.ItemCount)
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var indexArray []uint32
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// Add existing entries section
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if len(context.updatedXrefEntries) > 0 {
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for _, entry := range context.updatedXrefEntries {
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indexArray = append(indexArray, entry.ID, 1)
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}
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}
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// Add new entries section
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if len(context.newXrefEntries) > 0 {
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indexArray = append(indexArray, context.lastXrefID+1, uint32(len(context.newXrefEntries)))
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totalEntries += uint32(len(context.newXrefEntries))
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}
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buffer.WriteString("<< /Type /XRef\n")
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buffer.WriteString(fmt.Sprintf(" /Length %d\n", streamLength))
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buffer.WriteString(" /Filter /FlateDecode\n")
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// Change W array to [1 4 1] to accommodate larger offsets
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buffer.WriteString(" /W [ 1 4 1 ]\n")
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buffer.WriteString(fmt.Sprintf(" /Prev %d\n", context.PDFReader.XrefInformation.StartPos))
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buffer.WriteString(fmt.Sprintf(" /Size %d\n", totalEntries+1))
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// Write index array if we have entries
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if len(indexArray) > 0 {
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buffer.WriteString(" /Index [")
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for _, idx := range indexArray {
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buffer.WriteString(fmt.Sprintf(" %d", idx))
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}
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buffer.WriteString(" ]\n")
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}
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buffer.WriteString(fmt.Sprintf(" /Root %d 0 R\n", context.CatalogData.ObjectId))
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if !id.IsNull() {
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id0 := hex.EncodeToString([]byte(id.Index(0).RawString()))
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id1 := hex.EncodeToString([]byte(id.Index(1).RawString()))
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buffer.WriteString(fmt.Sprintf(" /ID [<%s><%s>]\n", id0, id1))
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}
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buffer.WriteString(">>\n")
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return nil
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}
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// writeXrefStreamContent writes the content of the xref stream.
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func writeXrefStreamContent(buffer *bytes.Buffer, streamBytes []byte) error {
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if _, err := io.WriteString(buffer, "stream\n"); err != nil {
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return err
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}
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if _, err := buffer.Write(streamBytes); err != nil {
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return err
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}
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if _, err := io.WriteString(buffer, "\nendstream\n"); err != nil {
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return err
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}
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return nil
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}
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// writeXrefStreamLine writes a single line in the xref stream.
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func writeXrefStreamLine(b *bytes.Buffer, xreftype byte, offset int, gen byte) {
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// Write type (1 byte)
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b.WriteByte(xreftype)
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// Write offset (4 bytes)
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offsetBytes := make([]byte, 4)
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binary.BigEndian.PutUint32(offsetBytes, uint32(offset))
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b.Write(offsetBytes)
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// Write generation (1 byte)
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b.WriteByte(gen)
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}
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// EncodePNGSUBBytes encodes data using PNG SUB filter.
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func EncodePNGSUBBytes(columns int, data []byte) ([]byte, error) {
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rowCount := len(data) / columns
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if len(data)%columns != 0 {
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return nil, errors.New("invalid row/column length")
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}
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buffer := bytes.NewBuffer(nil)
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tmpRowData := make([]byte, columns)
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for i := 0; i < rowCount; i++ {
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rowData := data[columns*i : columns*(i+1)]
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tmpRowData[0] = rowData[0]
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for j := 1; j < columns; j++ {
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tmpRowData[j] = byte(int(rowData[j]-rowData[j-1]) % 256)
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}
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buffer.WriteByte(1)
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buffer.Write(tmpRowData)
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}
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data = buffer.Bytes()
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var b bytes.Buffer
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w := zlib.NewWriter(&b)
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if _, err := w.Write(data); err != nil {
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return nil, err
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}
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w.Close()
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return b.Bytes(), nil
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}
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// EncodePNGUPBytes encodes data using PNG UP filter.
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func EncodePNGUPBytes(columns int, data []byte) ([]byte, error) {
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rowCount := len(data) / columns
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if len(data)%columns != 0 {
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return nil, errors.New("invalid row/column length")
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}
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prevRowData := make([]byte, columns)
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// Initially all previous data is zero.
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for i := 0; i < columns; i++ {
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prevRowData[i] = 0
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}
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buffer := bytes.NewBuffer(nil)
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tmpRowData := make([]byte, columns)
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for i := 0; i < rowCount; i++ {
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rowData := data[columns*i : columns*(i+1)]
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for j := 0; j < columns; j++ {
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tmpRowData[j] = byte(int(rowData[j]-prevRowData[j]) % 256)
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}
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// Save the previous row for prediction.
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copy(prevRowData, rowData)
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buffer.WriteByte(2)
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buffer.Write(tmpRowData)
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}
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data = buffer.Bytes()
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var b bytes.Buffer
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w := zlib.NewWriter(&b)
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if _, err := w.Write(data); err != nil {
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return nil, err
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}
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w.Close()
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return b.Bytes(), nil
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}
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