mirror of https://github.com/dsoprea/go-exif.git
529 lines
14 KiB
Go
529 lines
14 KiB
Go
package exif
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import (
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"bytes"
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"fmt"
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"strings"
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"encoding/binary"
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"github.com/dsoprea/go-logging"
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)
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var (
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ifdEnumerateLogger = log.NewLogger("exifjpeg.ifd")
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)
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// IfdTagEnumerator knows how to decode an IFD and all of the tags it
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// describes. Note that the IFDs and the actual values floating throughout the
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// whole EXIF block, but the IFD itself has just a minor header and a set of
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// repeating, statically-sized records. So, the tags (though not their values)
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// are fairly simple to enumerate.
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type IfdTagEnumerator struct {
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byteOrder binary.ByteOrder
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addressableData []byte
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ifdOffset uint32
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buffer *bytes.Buffer
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}
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func NewIfdTagEnumerator(addressableData []byte, byteOrder binary.ByteOrder, ifdOffset uint32) (ite *IfdTagEnumerator) {
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ite = &IfdTagEnumerator{
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addressableData: addressableData,
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byteOrder: byteOrder,
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buffer: bytes.NewBuffer(addressableData[ifdOffset:]),
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}
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return ite
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}
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// getUint16 reads a uint16 and advances both our current and our current
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// accumulator (which allows us to know how far to seek to the beginning of the
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// next IFD when it's time to jump).
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func (ife *IfdTagEnumerator) getUint16() (value uint16, raw []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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raw = make([]byte, 2)
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_, err = ife.buffer.Read(raw)
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log.PanicIf(err)
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if ife.byteOrder == binary.BigEndian {
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value = binary.BigEndian.Uint16(raw)
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} else {
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value = binary.LittleEndian.Uint16(raw)
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}
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return value, raw, nil
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}
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// getUint32 reads a uint32 and advances both our current and our current
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// accumulator (which allows us to know how far to seek to the beginning of the
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// next IFD when it's time to jump).
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func (ife *IfdTagEnumerator) getUint32() (value uint32, raw []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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raw = make([]byte, 4)
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_, err = ife.buffer.Read(raw)
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log.PanicIf(err)
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if ife.byteOrder == binary.BigEndian {
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value = binary.BigEndian.Uint32(raw)
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} else {
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value = binary.LittleEndian.Uint32(raw)
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}
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return value, raw, nil
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}
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type IfdEnumerate struct {
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exifData []byte
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buffer *bytes.Buffer
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byteOrder binary.ByteOrder
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currentOffset uint32
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}
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func NewIfdEnumerate(exifData []byte, byteOrder binary.ByteOrder) *IfdEnumerate {
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// Make it obvious what data we expect and when we don't get it.
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if IsExif(exifData) == false {
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log.Panicf("not exif data")
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}
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return &IfdEnumerate{
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exifData: exifData,
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buffer: bytes.NewBuffer(exifData),
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byteOrder: byteOrder,
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}
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}
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// ValueContext describes all of the parameters required to find and extract
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// the actual tag value.
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type ValueContext struct {
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UnitCount uint32
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ValueOffset uint32
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RawValueOffset []byte
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AddressableData []byte
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}
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func (ie *IfdEnumerate) getTagEnumerator(ifdOffset uint32) (ite *IfdTagEnumerator) {
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ite = NewIfdTagEnumerator(
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ie.exifData[ExifAddressableAreaStart:],
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ie.byteOrder,
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ifdOffset)
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return ite
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}
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// TagVisitor is an optional callback that can get hit for every tag we parse
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// through. `addressableData` is the byte array startign after the EXIF header
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// (where the offsets of all IFDs and values are calculated from).
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type TagVisitor func(indexedIfdName string, tagId uint16, tagType TagType, valueContext ValueContext) (err error)
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type IfdTagEntry struct {
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TagId uint16
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TagIndex int
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TagType uint16
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UnitCount uint32
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ValueOffset uint32
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RawValueOffset []byte
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// ChildIfdName is a name if this tag represents a child IFD.
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ChildIfdName string
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// IfdName is the IFD that this tag belongs to.
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IfdName string
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}
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func (ite IfdTagEntry) String() string {
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return fmt.Sprintf("IfdTagEntry<TAG-IFD=[%s] TAG-ID=(0x%02x) TAG-TYPE=[%s] UNIT-COUNT=(%d)>", ite.ChildIfdName, ite.TagId, TypeNames[ite.TagType], ite.UnitCount)
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}
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func (ite IfdTagEntry) ValueBytes(addressableData []byte, byteOrder binary.ByteOrder) (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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if ite.TagType == TypeUndefined {
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valueContext := ValueContext{
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UnitCount: ite.UnitCount,
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ValueOffset: ite.ValueOffset,
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RawValueOffset: ite.RawValueOffset,
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AddressableData: addressableData,
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}
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value, err := UndefinedValue(ite.IfdName, ite.TagId, valueContext, byteOrder)
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log.PanicIf(err)
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switch value.(type) {
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case []byte:
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return value.([]byte), nil
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case string:
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return []byte(value.(string)), nil
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default:
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// TODO(dustin): !! Finish translating the rest of the types (make reusable and replace into other similar implementations?)
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log.Panicf("can not produce bytes for unknown-type tag (0x%02x)", ite.TagId)
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}
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}
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originalType := NewTagType(ite.TagType, byteOrder)
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byteCount := uint32(originalType.Size()) * ite.UnitCount
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tt := NewTagType(TypeByte, byteOrder)
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if tt.ValueIsEmbedded(byteCount) == true {
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typeDecodeLogger.Debugf(nil, "Reading BYTE value (ITE; embedded).")
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// In this case, the bytes normally used for the offset are actually
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// data.
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value, err = tt.ParseBytes(ite.RawValueOffset, byteCount)
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log.PanicIf(err)
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} else {
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typeDecodeLogger.Debugf(nil, "Reading BYTE value (ITE; at offset).")
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value, err = tt.ParseBytes(addressableData[ite.ValueOffset:], byteCount)
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log.PanicIf(err)
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}
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return value, nil
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}
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type IfdTagEntryValueResolver struct {
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addressableData []byte
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byteOrder binary.ByteOrder
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}
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func NewIfdTagEntryValueResolver(exifData []byte, byteOrder binary.ByteOrder) (itevr *IfdTagEntryValueResolver) {
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// Make it obvious what data we expect and when we don't get it.
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if IsExif(exifData) == false {
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log.Panicf("not exif data")
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}
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return &IfdTagEntryValueResolver{
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addressableData: exifData[ExifAddressableAreaStart:],
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byteOrder: byteOrder,
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}
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}
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func (itevr *IfdTagEntryValueResolver) ValueBytes(ite *IfdTagEntry) (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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value, err = ite.ValueBytes(itevr.addressableData, itevr.byteOrder)
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return value, err
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}
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// ParseIfd decodes the IFD block that we're currently sitting on the first
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// byte of.
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func (ie *IfdEnumerate) ParseIfd(ifdName string, ifdIndex int, ifdOffset uint32, visitor TagVisitor, doDescend bool) (nextIfdOffset uint32, entries []IfdTagEntry, 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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ifdEnumerateLogger.Debugf(nil, "Parsing IFD [%s] (%d) at offset (%04x).", ifdName, ifdIndex, ifdOffset)
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// Return the name of the IFD as its known in our tag-index. We should skip
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// over the current IFD if this is empty (which means we don't recognize/
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// understand the IFD and, therefore, don't know the tags that are valid for
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// it). Note that we could leave ignoring the tags as a responsibility for
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// the visitor, but then it'd be easy for people to integrate that logic and
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// not realize that they needed to specially handle an empty IFD name until
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// they happened upon some obscure media one day and suddenly have issue if
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// they unwittingly write something that breaks in that situation.
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indexedIfdName := IfdName(ifdName, ifdIndex)
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if indexedIfdName == "" {
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ifdEnumerateLogger.Debugf(nil, "IFD not known and will not be visited: [%s] (%d)", ifdName, ifdIndex)
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}
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ite := ie.getTagEnumerator(ifdOffset)
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tagCount, _, err := ite.getUint16()
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log.PanicIf(err)
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ifdEnumerateLogger.Debugf(nil, "Current IFD tag-count: (%d)", tagCount)
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entries = make([]IfdTagEntry, tagCount)
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for i := uint16(0); i < tagCount; i++ {
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tagId, _, err := ite.getUint16()
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log.PanicIf(err)
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tagType, _, err := ite.getUint16()
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log.PanicIf(err)
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unitCount, _, err := ite.getUint32()
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log.PanicIf(err)
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valueOffset, rawValueOffset, err := ite.getUint32()
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log.PanicIf(err)
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if visitor != nil && indexedIfdName != "" {
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tt := NewTagType(tagType, ie.byteOrder)
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vc := ValueContext{
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UnitCount: unitCount,
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ValueOffset: valueOffset,
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RawValueOffset: rawValueOffset,
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AddressableData: ie.exifData[ExifAddressableAreaStart:],
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}
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err := visitor(indexedIfdName, tagId, tt, vc)
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log.PanicIf(err)
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}
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tag := IfdTagEntry{
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IfdName: ifdName,
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TagId: tagId,
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TagIndex: int(i),
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TagType: tagType,
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UnitCount: unitCount,
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ValueOffset: valueOffset,
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RawValueOffset: rawValueOffset,
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}
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childIfdName, isIfd := IsIfdTag(tagId)
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if isIfd == true {
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tag.ChildIfdName = childIfdName
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if doDescend == true {
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ifdEnumerateLogger.Debugf(nil, "Descending to IFD [%s].", childIfdName)
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err := ie.Scan(childIfdName, valueOffset, visitor)
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log.PanicIf(err)
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}
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}
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entries[i] = tag
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}
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nextIfdOffset, _, err = ite.getUint32()
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log.PanicIf(err)
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ifdEnumerateLogger.Debugf(nil, "Next IFD at offset: (%08x)", nextIfdOffset)
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return nextIfdOffset, entries, nil
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}
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// Scan enumerates the different EXIF blocks (called IFDs).
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func (ie *IfdEnumerate) Scan(ifdName string, ifdOffset uint32, visitor TagVisitor) (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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for ifdIndex := 0;; ifdIndex++ {
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nextIfdOffset, _, err := ie.ParseIfd(ifdName, ifdIndex, ifdOffset, visitor, true)
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log.PanicIf(err)
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if nextIfdOffset == 0 {
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break
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}
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ifdOffset = nextIfdOffset
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}
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return nil
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}
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type Ifd struct {
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Id int
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ParentIfd *Ifd
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Name string
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Index int
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Offset uint32
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// TODO(dustin): !! Add a find method.
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Entries []IfdTagEntry
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Children []*Ifd
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NextIfdOffset uint32
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NextIfd *Ifd
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}
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func (ifd Ifd) String() string {
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parentOffset := uint32(0)
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if ifd.ParentIfd != nil {
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parentOffset = ifd.ParentIfd.Offset
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}
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return fmt.Sprintf("IFD<ID=(%d) N=[%s] IDX=(%d) OFF=(0x%04x) COUNT=(%d) CHILDREN=(%d) PARENT=(0x%04x) NEXT-IFD=(0x%04x)", ifd.Id, ifd.Name, ifd.Index, ifd.Offset, len(ifd.Entries), len(ifd.Children), parentOffset, ifd.NextIfdOffset)
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}
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func (ifd Ifd) printNode(level int, nextLink bool) {
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indent := strings.Repeat(" ", level * 2)
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prefix := " "
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if nextLink {
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prefix = ">"
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}
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fmt.Printf("%s%s%s\n", indent, prefix, ifd)
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for _, childIfd := range ifd.Children {
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childIfd.printNode(level + 1, false)
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}
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if ifd.NextIfd != nil {
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ifd.NextIfd.printNode(level, true)
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}
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}
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func (ifd Ifd) PrintTree() {
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ifd.printNode(0, false)
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}
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type QueuedIfd struct {
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Name string
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Index int
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Offset uint32
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Parent *Ifd
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}
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type IfdIndex struct {
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RootIfd *Ifd
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Ifds []*Ifd
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Tree map[int]*Ifd
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Lookup map[string][]*Ifd
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}
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// Scan enumerates the different EXIF blocks (called IFDs).
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func (ie *IfdEnumerate) Collect(rootIfdOffset uint32) (index IfdIndex, 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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tree := make(map[int]*Ifd)
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ifds := make([]*Ifd, 0)
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lookup := make(map[string][]*Ifd)
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queue := []QueuedIfd {
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{
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Name: IfdStandard,
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Index: 0,
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Offset: rootIfdOffset,
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},
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}
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edges := make(map[uint32]*Ifd)
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for {
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if len(queue) == 0 {
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break
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}
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name := queue[0].Name
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index := queue[0].Index
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offset := queue[0].Offset
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parentIfd := queue[0].Parent
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queue = queue[1:]
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nextIfdOffset, entries, err := ie.ParseIfd(name, index, offset, nil, false)
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log.PanicIf(err)
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id := len(ifds)
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ifd := Ifd{
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Id: id,
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ParentIfd: parentIfd,
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Name: name,
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Index: index,
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Offset: offset,
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Entries: entries,
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Children: make([]*Ifd, 0),
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NextIfdOffset: nextIfdOffset,
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}
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// Add ourselves to a big list of IFDs.
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ifds = append(ifds, &ifd)
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// Install ourselves into a by-id lookup table (keys are unique).
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tree[id] = &ifd
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// Install into by-name buckets.
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if list_, found := lookup[name]; found == true {
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lookup[name] = append(list_, &ifd)
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} else {
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list_ = make([]*Ifd, 1)
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list_[0] = &ifd
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lookup[name] = list_
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}
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// Add a link from the previous IFD in the chain to us.
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if previousIfd, found := edges[offset]; found == true {
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previousIfd.NextIfd = &ifd
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}
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// Attach as a child to our parent (where we appeared as a tag in
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// that IFD).
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if parentIfd != nil {
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parentIfd.Children = append(parentIfd.Children, &ifd)
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}
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// Determine if any of our entries is a child IFD and queue it.
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for _, entry := range entries {
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if entry.ChildIfdName == "" {
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continue
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}
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qi := QueuedIfd {
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Name: entry.ChildIfdName,
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Index: 0,
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Offset: entry.ValueOffset,
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Parent: &ifd,
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}
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queue = append(queue, qi)
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}
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// If there's another IFD in the chain.
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if nextIfdOffset != 0 {
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// Allow the next link to know what the previous link was.
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edges[nextIfdOffset] = &ifd
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qi := QueuedIfd {
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Name: IfdStandard,
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Index: index + 1,
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Offset: nextIfdOffset,
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}
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queue = append(queue, qi)
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}
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}
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index.RootIfd = tree[0]
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index.Ifds = ifds
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index.Tree = tree
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index.Lookup = lookup
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return index, nil
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}
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