mirror of https://github.com/dsoprea/go-exif.git
413 lines
12 KiB
Go
413 lines
12 KiB
Go
package exif
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import (
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"bytes"
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"encoding/binary"
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"github.com/dsoprea/go-logging"
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)
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type ByteWriter struct {
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b *bytes.Buffer
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byteOrder binary.ByteOrder
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}
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func NewByteWriter(b *bytes.Buffer, byteOrder binary.ByteOrder) (bw *ByteWriter) {
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return &ByteWriter{
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b: b,
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byteOrder: byteOrder,
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}
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}
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func (bw ByteWriter) writeAsBytes(value interface{}) (err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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err = binary.Write(bw.b, bw.byteOrder, value)
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log.PanicIf(err)
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return nil
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}
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func (bw ByteWriter) WriteUint32(value uint32) (err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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err = bw.writeAsBytes(value)
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log.PanicIf(err)
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return nil
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}
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func (bw ByteWriter) WriteUint16(value uint16) (err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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err = bw.writeAsBytes(value)
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log.PanicIf(err)
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return nil
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}
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func (bw ByteWriter) WriteFourBytes(value []byte) (err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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len_ := len(value)
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if len_ != 4 {
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log.Panicf("value is not four-bytes: (%d)", len_)
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}
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_, err = bw.b.Write(value)
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log.PanicIf(err)
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return nil
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}
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// ifdOffsetIterator keeps track of where the next IFD should be written by
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// keeping track of where the offsets start, the data that has been added, and
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// bumping the offset *when* the data is added.
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type ifdDataAllocator struct {
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offset uint32
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b bytes.Buffer
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}
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func newIfdDataAllocator(ifdDataAddressableOffset uint32) *ifdDataAllocator{
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return &ifdDataAllocator{
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offset: ifdDataAddressableOffset,
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}
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}
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func (ida *ifdDataAllocator) Allocate(value []byte) (offset uint32, err error) {
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_, err = ida.b.Write(value)
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log.PanicIf(err)
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offset = ida.offset
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ida.offset += uint32(len(value))
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return offset, nil
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}
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func (ida *ifdDataAllocator) NextOffset() uint32 {
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return ida.offset
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}
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func (ida *ifdDataAllocator) Bytes() []byte {
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return ida.b.Bytes()
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}
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// IfdByteEncoder converts an IB to raw bytes (for writing) while also figuring
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// out all of the allocations and indirection that is required for extended
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// data.
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type IfdByteEncoder struct {
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}
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func NewIfdByteEncoder() (ibe *IfdByteEncoder) {
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return new(IfdByteEncoder)
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}
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func (ibe *IfdByteEncoder) EntrySize() uint32 {
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// Tag-ID + Tag-Type + Unit-Count + Value/Offset.
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return uint32(2 + 2 + 4 + 4)
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}
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func (ibe *IfdByteEncoder) TableSize(entryCount int) uint32 {
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// Tag-Count + (Entry-Size * Entry-Count) + Next-IFD-Offset.
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return uint32(2) + (ibe.EntrySize() * uint32(entryCount)) + uint32(4)
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}
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// encodeTagToBytes encodes the given tag to a byte stream. If
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// `nextIfdOffsetToWrite` is more than (0), recurse into child IFDs
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// (`nextIfdOffsetToWrite` is required in order for them to know where the its
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// IFD data will be written, in order for them to know the offset of where
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// their allocated-data block will start, which follows right behind).
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func (ibe *IfdByteEncoder) encodeTagToBytes(ib *IfdBuilder, bt *builderTag, bw *ByteWriter, ida *ifdDataAllocator, nextIfdOffsetToWrite uint32) (childIfdBlock []byte, err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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// Write tag-ID.
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err = bw.WriteUint16(bt.tagId)
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log.PanicIf(err)
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// Works for both values and child IFDs (which have an official size of
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// LONG).
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err = bw.WriteUint16(bt.typeId)
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log.PanicIf(err)
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// Write unit-count.
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if bt.value.IsBytes() == true {
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effectiveType := bt.typeId
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if bt.typeId == TypeUndefined {
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effectiveType = TypeByte
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}
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// It's a non-unknown value.Calculate the count of values of
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// the type that we're writing and the raw bytes for the whole list.
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typeSize := uint32(TagTypeSize(effectiveType))
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valueBytes := bt.value.Bytes()
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len_ := len(valueBytes)
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unitCount := uint32(len_) / typeSize
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remainder := uint32(len_) % typeSize
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if remainder > 0 {
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log.Panicf("tag value of (%d) bytes not evenly divisible by type-size (%d)", len_, typeSize)
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}
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err = bw.WriteUint32(unitCount)
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log.PanicIf(err)
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// Write four-byte value/offset.
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if len_ > 4 {
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offset, err := ida.Allocate(valueBytes)
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log.PanicIf(err)
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err = bw.WriteUint32(offset)
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log.PanicIf(err)
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} else {
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fourBytes := make([]byte, 4)
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copy(fourBytes, valueBytes)
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err = bw.WriteFourBytes(fourBytes)
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log.PanicIf(err)
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}
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} else {
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if bt.value.IsIb() == false {
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log.Panicf("tag value is not a byte-slice but also not a child IB: %v", bt)
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}
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// Write unit-count (one LONG representing one offset).
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err = bw.WriteUint32(1)
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log.PanicIf(err)
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if nextIfdOffsetToWrite > 0 {
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var err error
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// Create the block of IFD data and everything it requires.
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childIfdBlock, err = ibe.encodeAndAttachIfd(bt.value.Ib(), nextIfdOffsetToWrite)
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log.PanicIf(err)
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// Use the next-IFD offset for it. The IFD will actually get
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// attached after we return.
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err = bw.WriteUint32(nextIfdOffsetToWrite)
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log.PanicIf(err)
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} else {
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// No child-IFDs are to be allocated. Finish the entry with a NULL
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// pointer.
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err = bw.WriteUint32(0)
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log.PanicIf(err)
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}
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}
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return childIfdBlock, nil
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}
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// encodeIfdToBytes encodes the given IB to a byte-slice. We are given the
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// offset at which this IFD will be written. This method is used called both to
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// pre-determine how big the table is going to be (so that we can calculate the
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// address to allocate data at) as well as to write the final table.
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//
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// It is necessary to fully realize the table in order to predetermine its size
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// because it is not enough to know the size of the table: If there are child
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// IFDs, we will not be able to allocate them without first knowing how much
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// data we need to allocate for the current IFD.
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func (ibe *IfdByteEncoder) encodeIfdToBytes(ib *IfdBuilder, ifdAddressableOffset uint32, nextIfdOffsetToWrite uint32, setNextIb bool) (data []byte, tableSize uint32, dataSize uint32, childIfdSizes []uint32, err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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tableSize = ibe.TableSize(len(ib.tags))
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b := new(bytes.Buffer)
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bw := NewByteWriter(b, ib.byteOrder)
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// Write tag count.
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err = bw.WriteUint16(uint16(len(ib.tags)))
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log.PanicIf(err)
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ida := newIfdDataAllocator(ifdAddressableOffset)
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childIfdBlocks := make([][]byte, 0)
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// Write raw bytes for each tag entry. Allocate larger data to be referred
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// to in the follow-up data-block as required. Any "unknown"-byte tags that
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// we can't parse will not be present here (using AddTagsFromExisting(), at
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// least).
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for _, bt := range ib.tags {
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childIfdBlock, err := ibe.encodeTagToBytes(ib, &bt, bw, ida, nextIfdOffsetToWrite)
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log.PanicIf(err)
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if childIfdBlock != nil {
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if nextIfdOffsetToWrite == 0 {
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log.Panicf("no IFD offset provided for child-IFDs; no new child-IFDs permitted")
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}
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nextIfdOffsetToWrite += uint32(len(childIfdBlock))
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childIfdBlocks = append(childIfdBlocks, childIfdBlock)
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}
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}
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dataBytes := ida.Bytes()
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dataSize = uint32(len(dataBytes))
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childIfdSizes = make([]uint32, len(childIfdBlocks))
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childIfdsTotalSize := uint32(0)
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for i, childIfdBlock := range childIfdBlocks {
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len_ := uint32(len(childIfdBlock))
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childIfdSizes[i] = len_
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childIfdsTotalSize += len_
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}
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// Set the link from this IFD to the next IFD that will be written in the
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// next cycle.
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if setNextIb == true {
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nextIfdOffsetToWrite += tableSize + dataSize + childIfdsTotalSize
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} else {
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nextIfdOffsetToWrite = 0
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}
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// Write address of next IFD in chain.
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err = bw.WriteUint32(nextIfdOffsetToWrite)
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log.PanicIf(err)
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_, err = b.Write(dataBytes)
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log.PanicIf(err)
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// Append any child IFD blocks after our table and data blocks. These IFDs
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// were equipped with the appropriate offset information so it's expected
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// that all offsets referred to by these will be correct.
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//
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// Note that child-IFDs are append after the current IFD and before the
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// next IFD, as opposed to the root IFDs, which are chained together but
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// will be interrupted by these child-IFDs (which is expected, per the
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// standard).
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for _, childIfdBlock := range childIfdBlocks {
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_, err = b.Write(childIfdBlock)
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log.PanicIf(err)
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}
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return b.Bytes(), tableSize, dataSize, childIfdSizes, nil
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}
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// encodeAndAttachIfd is a reentrant function that processes the IFD chain.
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func (ibe *IfdByteEncoder) encodeAndAttachIfd(ib *IfdBuilder, ifdAddressableOffset uint32) (data []byte, err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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if len(ib.tags) == 0 {
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log.Panicf("trying to encode an IfdBuilder that doesn't have any tags")
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}
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b := new(bytes.Buffer)
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nextIfdOffsetToWrite := uint32(0)
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for thisIb := ib; thisIb != nil; thisIb = thisIb.nextIb {
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// Do a dry-run in order to pre-determine its size requirement.
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_, tableSize, allocatedDataSize, _, err := ibe.encodeIfdToBytes(ib, ifdAddressableOffset, 0, false)
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log.PanicIf(err)
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addressableOffset := ifdAddressableOffset + tableSize
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nextIfdOffsetToWrite = addressableOffset + allocatedDataSize
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// Write our IFD as well as any child-IFDs (now that we know the offset
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// where new IFDs and their data will be allocated).
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setNextIb := thisIb.nextIb != nil
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tableAndAllocated, tableSize, allocatedDataSize, childIfdSizes, err := ibe.encodeIfdToBytes(ib, addressableOffset, nextIfdOffsetToWrite, setNextIb)
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log.PanicIf(err)
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totalChildIfdSize := uint32(0)
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for _, childIfdSize := range childIfdSizes {
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totalChildIfdSize += childIfdSize
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}
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if len(tableAndAllocated) != int(tableSize + allocatedDataSize + totalChildIfdSize) {
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log.Panicf("IFD table and data is not a consistent size: (%d) != (%d)", len(tableAndAllocated), tableSize + allocatedDataSize + totalChildIfdSize)
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}
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_, err = b.Write(tableAndAllocated)
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log.PanicIf(err)
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// This will include the child-IFDs, as well. This will actually advance the offset for our next loop.
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ifdAddressableOffset = ifdAddressableOffset + uint32(tableSize + allocatedDataSize)
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}
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return b.Bytes(), nil
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}
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// EncodeToExifPayload is the base encoding step that transcribes the entire IB
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// structure to its on-disk layout.
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func (ibe *IfdByteEncoder) EncodeToExifPayload(ib *IfdBuilder) (data []byte, err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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data, err = ibe.encodeAndAttachIfd(ib, ExifDefaultFirstIfdOffset)
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log.PanicIf(err)
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return data, nil
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}
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// EncodeToExif calls EncodeToExifPayload and then packages the result into a
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// complete EXIF block.
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func (ibe *IfdByteEncoder) EncodeToExif(ib *IfdBuilder) (data []byte, err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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encodedIfds, err := ibe.EncodeToExifPayload(ib)
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log.PanicIf(err)
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// Wrap the IFD in a formal EXIF block.
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b := new(bytes.Buffer)
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headerBytes, err := BuildExifHeader(EncodeDefaultByteOrder, ExifDefaultFirstIfdOffset)
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log.PanicIf(err)
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_, err = b.Write(headerBytes)
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log.PanicIf(err)
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_, err = b.Write(encodedIfds)
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log.PanicIf(err)
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return b.Bytes(), nil
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}
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