gotosocial/vendor/github.com/dsoprea/go-exif/ifd_builder_encode.go

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package exif
import (
"bytes"
"fmt"
"strings"
"encoding/binary"
"github.com/dsoprea/go-logging"
)
const (
// Tag-ID + Tag-Type + Unit-Count + Value/Offset.
IfdTagEntrySize = uint32(2 + 2 + 4 + 4)
)
type ByteWriter struct {
b *bytes.Buffer
byteOrder binary.ByteOrder
}
func NewByteWriter(b *bytes.Buffer, byteOrder binary.ByteOrder) (bw *ByteWriter) {
return &ByteWriter{
b: b,
byteOrder: byteOrder,
}
}
func (bw ByteWriter) writeAsBytes(value interface{}) (err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
err = binary.Write(bw.b, bw.byteOrder, value)
log.PanicIf(err)
return nil
}
func (bw ByteWriter) WriteUint32(value uint32) (err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
err = bw.writeAsBytes(value)
log.PanicIf(err)
return nil
}
func (bw ByteWriter) WriteUint16(value uint16) (err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
err = bw.writeAsBytes(value)
log.PanicIf(err)
return nil
}
func (bw ByteWriter) WriteFourBytes(value []byte) (err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
len_ := len(value)
if len_ != 4 {
log.Panicf("value is not four-bytes: (%d)", len_)
}
_, err = bw.b.Write(value)
log.PanicIf(err)
return nil
}
// ifdOffsetIterator keeps track of where the next IFD should be written by
// keeping track of where the offsets start, the data that has been added, and
// bumping the offset *when* the data is added.
type ifdDataAllocator struct {
offset uint32
b bytes.Buffer
}
func newIfdDataAllocator(ifdDataAddressableOffset uint32) *ifdDataAllocator {
return &ifdDataAllocator{
offset: ifdDataAddressableOffset,
}
}
func (ida *ifdDataAllocator) Allocate(value []byte) (offset uint32, err error) {
_, err = ida.b.Write(value)
log.PanicIf(err)
offset = ida.offset
ida.offset += uint32(len(value))
return offset, nil
}
func (ida *ifdDataAllocator) NextOffset() uint32 {
return ida.offset
}
func (ida *ifdDataAllocator) Bytes() []byte {
return ida.b.Bytes()
}
// IfdByteEncoder converts an IB to raw bytes (for writing) while also figuring
// out all of the allocations and indirection that is required for extended
// data.
type IfdByteEncoder struct {
// journal holds a list of actions taken while encoding.
journal [][3]string
}
func NewIfdByteEncoder() (ibe *IfdByteEncoder) {
return &IfdByteEncoder{
journal: make([][3]string, 0),
}
}
func (ibe *IfdByteEncoder) Journal() [][3]string {
return ibe.journal
}
func (ibe *IfdByteEncoder) TableSize(entryCount int) uint32 {
// Tag-Count + (Entry-Size * Entry-Count) + Next-IFD-Offset.
return uint32(2) + (IfdTagEntrySize * uint32(entryCount)) + uint32(4)
}
func (ibe *IfdByteEncoder) pushToJournal(where, direction, format string, args ...interface{}) {
event := [3]string{
direction,
where,
fmt.Sprintf(format, args...),
}
ibe.journal = append(ibe.journal, event)
}
// PrintJournal prints a hierarchical representation of the steps taken during
// encoding.
func (ibe *IfdByteEncoder) PrintJournal() {
maxWhereLength := 0
for _, event := range ibe.journal {
where := event[1]
len_ := len(where)
if len_ > maxWhereLength {
maxWhereLength = len_
}
}
level := 0
for i, event := range ibe.journal {
direction := event[0]
where := event[1]
message := event[2]
if direction != ">" && direction != "<" && direction != "-" {
log.Panicf("journal operation not valid: [%s]", direction)
}
if direction == "<" {
if level <= 0 {
log.Panicf("journal operations unbalanced (too many closes)")
}
level--
}
indent := strings.Repeat(" ", level)
fmt.Printf("%3d %s%s %s: %s\n", i, indent, direction, where, message)
if direction == ">" {
level++
}
}
if level != 0 {
log.Panicf("journal operations unbalanced (too many opens)")
}
}
// encodeTagToBytes encodes the given tag to a byte stream. If
// `nextIfdOffsetToWrite` is more than (0), recurse into child IFDs
// (`nextIfdOffsetToWrite` is required in order for them to know where the its
// IFD data will be written, in order for them to know the offset of where
// their allocated-data block will start, which follows right behind).
func (ibe *IfdByteEncoder) encodeTagToBytes(ib *IfdBuilder, bt *BuilderTag, bw *ByteWriter, ida *ifdDataAllocator, nextIfdOffsetToWrite uint32) (childIfdBlock []byte, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
// Write tag-ID.
err = bw.WriteUint16(bt.tagId)
log.PanicIf(err)
// Works for both values and child IFDs (which have an official size of
// LONG).
err = bw.WriteUint16(uint16(bt.typeId))
log.PanicIf(err)
// Write unit-count.
if bt.value.IsBytes() == true {
effectiveType := bt.typeId
if bt.typeId == TypeUndefined {
effectiveType = TypeByte
}
// It's a non-unknown value.Calculate the count of values of
// the type that we're writing and the raw bytes for the whole list.
typeSize := uint32(effectiveType.Size())
valueBytes := bt.value.Bytes()
len_ := len(valueBytes)
unitCount := uint32(len_) / typeSize
if _, found := tagsWithoutAlignment[bt.tagId]; found == false {
remainder := uint32(len_) % typeSize
if remainder > 0 {
log.Panicf("tag (0x%04x) value of (%d) bytes not evenly divisible by type-size (%d)", bt.tagId, len_, typeSize)
}
}
err = bw.WriteUint32(unitCount)
log.PanicIf(err)
// Write four-byte value/offset.
if len_ > 4 {
offset, err := ida.Allocate(valueBytes)
log.PanicIf(err)
err = bw.WriteUint32(offset)
log.PanicIf(err)
} else {
fourBytes := make([]byte, 4)
copy(fourBytes, valueBytes)
err = bw.WriteFourBytes(fourBytes)
log.PanicIf(err)
}
} else {
if bt.value.IsIb() == false {
log.Panicf("tag value is not a byte-slice but also not a child IB: %v", bt)
}
// Write unit-count (one LONG representing one offset).
err = bw.WriteUint32(1)
log.PanicIf(err)
if nextIfdOffsetToWrite > 0 {
var err error
ibe.pushToJournal("encodeTagToBytes", ">", "[%s]->[%s]", ib.ifdPath, bt.value.Ib().ifdPath)
// Create the block of IFD data and everything it requires.
childIfdBlock, err = ibe.encodeAndAttachIfd(bt.value.Ib(), nextIfdOffsetToWrite)
log.PanicIf(err)
ibe.pushToJournal("encodeTagToBytes", "<", "[%s]->[%s]", bt.value.Ib().ifdPath, ib.ifdPath)
// Use the next-IFD offset for it. The IFD will actually get
// attached after we return.
err = bw.WriteUint32(nextIfdOffsetToWrite)
log.PanicIf(err)
} else {
// No child-IFDs are to be allocated. Finish the entry with a NULL
// pointer.
ibe.pushToJournal("encodeTagToBytes", "-", "*Not* descending to child: [%s]", bt.value.Ib().ifdPath)
err = bw.WriteUint32(0)
log.PanicIf(err)
}
}
return childIfdBlock, nil
}
// encodeIfdToBytes encodes the given IB to a byte-slice. We are given the
// offset at which this IFD will be written. This method is used called both to
// pre-determine how big the table is going to be (so that we can calculate the
// address to allocate data at) as well as to write the final table.
//
// It is necessary to fully realize the table in order to predetermine its size
// because it is not enough to know the size of the table: If there are child
// IFDs, we will not be able to allocate them without first knowing how much
// data we need to allocate for the current IFD.
func (ibe *IfdByteEncoder) encodeIfdToBytes(ib *IfdBuilder, ifdAddressableOffset uint32, nextIfdOffsetToWrite uint32, setNextIb bool) (data []byte, tableSize uint32, dataSize uint32, childIfdSizes []uint32, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
ibe.pushToJournal("encodeIfdToBytes", ">", "%s", ib)
tableSize = ibe.TableSize(len(ib.tags))
b := new(bytes.Buffer)
bw := NewByteWriter(b, ib.byteOrder)
// Write tag count.
err = bw.WriteUint16(uint16(len(ib.tags)))
log.PanicIf(err)
ida := newIfdDataAllocator(ifdAddressableOffset)
childIfdBlocks := make([][]byte, 0)
// Write raw bytes for each tag entry. Allocate larger data to be referred
// to in the follow-up data-block as required. Any "unknown"-byte tags that
// we can't parse will not be present here (using AddTagsFromExisting(), at
// least).
for _, bt := range ib.tags {
childIfdBlock, err := ibe.encodeTagToBytes(ib, bt, bw, ida, nextIfdOffsetToWrite)
log.PanicIf(err)
if childIfdBlock != nil {
// We aren't allowed to have non-nil child IFDs if we're just
// sizing things up.
if nextIfdOffsetToWrite == 0 {
log.Panicf("no IFD offset provided for child-IFDs; no new child-IFDs permitted")
}
nextIfdOffsetToWrite += uint32(len(childIfdBlock))
childIfdBlocks = append(childIfdBlocks, childIfdBlock)
}
}
dataBytes := ida.Bytes()
dataSize = uint32(len(dataBytes))
childIfdSizes = make([]uint32, len(childIfdBlocks))
childIfdsTotalSize := uint32(0)
for i, childIfdBlock := range childIfdBlocks {
len_ := uint32(len(childIfdBlock))
childIfdSizes[i] = len_
childIfdsTotalSize += len_
}
// N the link from this IFD to the next IFD that will be written in the
// next cycle.
if setNextIb == true {
// Write address of next IFD in chain. This will be the original
// allocation offset plus the size of everything we have allocated for
// this IFD and its child-IFDs.
//
// It is critical that this number is stepped properly. We experienced
// an issue whereby it first looked like we were duplicating the IFD and
// then that we were duplicating the tags in the wrong IFD, and then
// finally we determined that the next-IFD offset for the first IFD was
// accidentally pointing back to the EXIF IFD, so we were visiting it
// twice when visiting through the tags after decoding. It was an
// expensive bug to find.
ibe.pushToJournal("encodeIfdToBytes", "-", "Setting 'next' IFD to (0x%08x).", nextIfdOffsetToWrite)
err := bw.WriteUint32(nextIfdOffsetToWrite)
log.PanicIf(err)
} else {
err := bw.WriteUint32(0)
log.PanicIf(err)
}
_, err = b.Write(dataBytes)
log.PanicIf(err)
// Append any child IFD blocks after our table and data blocks. These IFDs
// were equipped with the appropriate offset information so it's expected
// that all offsets referred to by these will be correct.
//
// Note that child-IFDs are append after the current IFD and before the
// next IFD, as opposed to the root IFDs, which are chained together but
// will be interrupted by these child-IFDs (which is expected, per the
// standard).
for _, childIfdBlock := range childIfdBlocks {
_, err = b.Write(childIfdBlock)
log.PanicIf(err)
}
ibe.pushToJournal("encodeIfdToBytes", "<", "%s", ib)
return b.Bytes(), tableSize, dataSize, childIfdSizes, nil
}
// encodeAndAttachIfd is a reentrant function that processes the IFD chain.
func (ibe *IfdByteEncoder) encodeAndAttachIfd(ib *IfdBuilder, ifdAddressableOffset uint32) (data []byte, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
ibe.pushToJournal("encodeAndAttachIfd", ">", "%s", ib)
b := new(bytes.Buffer)
i := 0
for thisIb := ib; thisIb != nil; thisIb = thisIb.nextIb {
// Do a dry-run in order to pre-determine its size requirement.
ibe.pushToJournal("encodeAndAttachIfd", ">", "Beginning encoding process: (%d) [%s]", i, thisIb.ifdPath)
ibe.pushToJournal("encodeAndAttachIfd", ">", "Calculating size: (%d) [%s]", i, thisIb.ifdPath)
_, tableSize, allocatedDataSize, _, err := ibe.encodeIfdToBytes(thisIb, ifdAddressableOffset, 0, false)
log.PanicIf(err)
ibe.pushToJournal("encodeAndAttachIfd", "<", "Finished calculating size: (%d) [%s]", i, thisIb.ifdPath)
ifdAddressableOffset += tableSize
nextIfdOffsetToWrite := ifdAddressableOffset + allocatedDataSize
ibe.pushToJournal("encodeAndAttachIfd", ">", "Next IFD will be written at offset (0x%08x)", nextIfdOffsetToWrite)
// Write our IFD as well as any child-IFDs (now that we know the offset
// where new IFDs and their data will be allocated).
setNextIb := thisIb.nextIb != nil
ibe.pushToJournal("encodeAndAttachIfd", ">", "Encoding starting: (%d) [%s] NEXT-IFD-OFFSET-TO-WRITE=(0x%08x)", i, thisIb.ifdPath, nextIfdOffsetToWrite)
tableAndAllocated, effectiveTableSize, effectiveAllocatedDataSize, childIfdSizes, err :=
ibe.encodeIfdToBytes(thisIb, ifdAddressableOffset, nextIfdOffsetToWrite, setNextIb)
log.PanicIf(err)
if effectiveTableSize != tableSize {
log.Panicf("written table size does not match the pre-calculated table size: (%d) != (%d) %s", effectiveTableSize, tableSize, ib)
} else if effectiveAllocatedDataSize != allocatedDataSize {
log.Panicf("written allocated-data size does not match the pre-calculated allocated-data size: (%d) != (%d) %s", effectiveAllocatedDataSize, allocatedDataSize, ib)
}
ibe.pushToJournal("encodeAndAttachIfd", "<", "Encoding done: (%d) [%s]", i, thisIb.ifdPath)
totalChildIfdSize := uint32(0)
for _, childIfdSize := range childIfdSizes {
totalChildIfdSize += childIfdSize
}
if len(tableAndAllocated) != int(tableSize+allocatedDataSize+totalChildIfdSize) {
log.Panicf("IFD table and data is not a consistent size: (%d) != (%d)", len(tableAndAllocated), tableSize+allocatedDataSize+totalChildIfdSize)
}
// TODO(dustin): We might want to verify the original tableAndAllocated length, too.
_, err = b.Write(tableAndAllocated)
log.PanicIf(err)
// Advance past what we've allocated, thus far.
ifdAddressableOffset += allocatedDataSize + totalChildIfdSize
ibe.pushToJournal("encodeAndAttachIfd", "<", "Finishing encoding process: (%d) [%s] [FINAL:] NEXT-IFD-OFFSET-TO-WRITE=(0x%08x)", i, ib.ifdPath, nextIfdOffsetToWrite)
i++
}
ibe.pushToJournal("encodeAndAttachIfd", "<", "%s", ib)
return b.Bytes(), nil
}
// EncodeToExifPayload is the base encoding step that transcribes the entire IB
// structure to its on-disk layout.
func (ibe *IfdByteEncoder) EncodeToExifPayload(ib *IfdBuilder) (data []byte, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
data, err = ibe.encodeAndAttachIfd(ib, ExifDefaultFirstIfdOffset)
log.PanicIf(err)
return data, nil
}
// EncodeToExif calls EncodeToExifPayload and then packages the result into a
// complete EXIF block.
func (ibe *IfdByteEncoder) EncodeToExif(ib *IfdBuilder) (data []byte, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
encodedIfds, err := ibe.EncodeToExifPayload(ib)
log.PanicIf(err)
// Wrap the IFD in a formal EXIF block.
b := new(bytes.Buffer)
headerBytes, err := BuildExifHeader(ib.byteOrder, ExifDefaultFirstIfdOffset)
log.PanicIf(err)
_, err = b.Write(headerBytes)
log.PanicIf(err)
_, err = b.Write(encodedIfds)
log.PanicIf(err)
return b.Bytes(), nil
}