gtsocial-umbx

ifd_builder_encode.go (15437B)

---

 package exif
 
 import (
 	"bytes"
 	"fmt"
 	"strings"
 
 	"encoding/binary"
 
 	"github.com/dsoprea/go-logging"
 
 	"github.com/dsoprea/go-exif/v3/common"
 )
 
 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 == exifcommon.TypeUndefined {
 			effectiveType = exifcommon.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.IfdIdentity().UnindexedString(), bt.value.Ib().IfdIdentity().UnindexedString())
 
 			// 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().IfdIdentity().UnindexedString(), ib.IfdIdentity().UnindexedString())
 
 			// 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().IfdIdentity().UnindexedString())
 
 			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.IfdIdentity().UnindexedString())
 
 		ibe.pushToJournal("encodeAndAttachIfd", ">", "Calculating size: (%d) [%s]", i, thisIb.IfdIdentity().UnindexedString())
 
 		_, tableSize, allocatedDataSize, _, err := ibe.encodeIfdToBytes(thisIb, ifdAddressableOffset, 0, false)
 		log.PanicIf(err)
 
 		ibe.pushToJournal("encodeAndAttachIfd", "<", "Finished calculating size: (%d) [%s]", i, thisIb.IfdIdentity().UnindexedString())
 
 		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.IfdIdentity().UnindexedString(), 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.IfdIdentity().UnindexedString())
 
 		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.IfdIdentity().UnindexedString(), 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
 }