go-exif/ifd_tag_entry.go

package exif

import (
	"fmt"
	"reflect"

	"encoding/binary"

	"github.com/dsoprea/go-logging"
)

var (
	iteLogger = log.NewLogger("exif.ifd_tag_entry")
)

type IfdTagEntry struct {
	TagId          uint16
	TagIndex       int
	TagType        TagTypePrimitive
	UnitCount      uint32
	ValueOffset    uint32
	RawValueOffset []byte

	// ChildIfdName is the right most atom in the IFD-path. We need this to
	// construct the fully-qualified IFD-path.
	ChildIfdName string

	// ChildIfdPath is the IFD-path of the child if this tag represents a child
	// IFD.
	ChildIfdPath string

	// ChildFqIfdPath is the IFD-path of the child if this tag represents a
	// child IFD. Includes indices.
	ChildFqIfdPath string

	// TODO(dustin): !! IB's host the child-IBs directly in the tag, but that's not the case here. Refactor to accomodate it for a consistent experience.

	// IfdPath is the IFD that this tag belongs to.
	IfdPath string

	// TODO(dustin): !! We now parse and read the value immediately. Update the rest of the logic to use this and get rid of all of the staggered and different resolution mechanisms.
	value              []byte
	isUnhandledUnknown bool
}

func (ite *IfdTagEntry) String() string {
	return fmt.Sprintf("IfdTagEntry<TAG-IFD-PATH=[%s] TAG-ID=(0x%04x) TAG-TYPE=[%s] UNIT-COUNT=(%d)>", ite.IfdPath, ite.TagId, TypeNames[ite.TagType], ite.UnitCount)
}

// TODO(dustin): TODO(dustin): Stop exporting IfdPath and TagId.
//
// func (ite *IfdTagEntry) IfdPath() string {
// 	return ite.IfdPath
// }

// TODO(dustin): TODO(dustin): Stop exporting IfdPath and TagId.
//
// func (ite *IfdTagEntry) TagId() uint16 {
// 	return ite.TagId
// }

// ValueString renders a string from whatever the value in this tag is.
func (ite *IfdTagEntry) ValueString(addressableData []byte, byteOrder binary.ByteOrder) (value string, err error) {
	defer func() {
		if state := recover(); state != nil {
			err = log.Wrap(state.(error))
		}
	}()

	valueContext :=
		newValueContextFromTag(
			ite,
			addressableData,
			byteOrder)

	if ite.TagType == TypeUndefined {
		valueRaw, err := valueContext.Undefined()
		log.PanicIf(err)

		value = fmt.Sprintf("%v", valueRaw)
	} else {
		value, err = valueContext.Format()
		log.PanicIf(err)
	}

	return value, nil
}

// ValueBytes renders a specific list of bytes from the value in this tag.
func (ite *IfdTagEntry) ValueBytes(addressableData []byte, byteOrder binary.ByteOrder) (value []byte, err error) {
	defer func() {
		if state := recover(); state != nil {
			err = log.Wrap(state.(error))
		}
	}()

	// Return the exact bytes of the unknown-type value. Returning a string
	// (`ValueString`) is easy because we can just pass everything to
	// `Sprintf()`. Returning the raw, typed value (`Value`) is easy
	// (obviously). However, here, in order to produce the list of bytes, we
	// need to coerce whatever `Undefined()` returns.
	if ite.TagType == TypeUndefined {
		valueContext :=
			newValueContextFromTag(
				ite,
				addressableData,
				byteOrder)

		value, err := valueContext.Undefined()
		log.PanicIf(err)

		switch value.(type) {
		case []byte:
			return value.([]byte), nil
		case TagUnknownType_UnknownValue:
			b := []byte(value.(TagUnknownType_UnknownValue))
			return b, nil
		case string:
			return []byte(value.(string)), nil
		case UnknownTagValue:
			valueBytes, err := value.(UnknownTagValue).ValueBytes()
			log.PanicIf(err)

			return valueBytes, nil
		default:
			// TODO(dustin): !! Finish translating the rest of the types (make reusable and replace into other similar implementations?)
			log.Panicf("can not produce bytes for unknown-type tag (0x%04x) (2): [%s]", ite.TagId, reflect.TypeOf(value))
		}
	}

	originalType := NewTagType(ite.TagType, byteOrder)
	byteCount := uint32(originalType.Type().Size()) * ite.UnitCount

	tt := NewTagType(TypeByte, byteOrder)

	if tt.valueIsEmbedded(byteCount) == true {
		iteLogger.Debugf(nil, "Reading BYTE value (ITE; embedded).")

		// In this case, the bytes normally used for the offset are actually
		// data.
		value, err = tt.ParseBytes(ite.RawValueOffset, byteCount)
		log.PanicIf(err)
	} else {
		iteLogger.Debugf(nil, "Reading BYTE value (ITE; at offset).")

		value, err = tt.ParseBytes(addressableData[ite.ValueOffset:], byteCount)
		log.PanicIf(err)
	}

	return value, nil
}

// Value returns the specific, parsed, typed value from the tag.
func (ite *IfdTagEntry) Value(addressableData []byte, byteOrder binary.ByteOrder) (value interface{}, err error) {
	defer func() {
		if state := recover(); state != nil {
			err = log.Wrap(state.(error))
		}
	}()

	valueContext :=
		newValueContextFromTag(
			ite,
			addressableData,
			byteOrder)

	if ite.TagType == TypeUndefined {
		value, err = valueContext.Undefined()
		log.PanicIf(err)
	} else {
		tt := NewTagType(ite.TagType, byteOrder)

		value, err = tt.Resolve(valueContext)
		log.PanicIf(err)
	}

	return value, nil
}

// IfdTagEntryValueResolver instances know how to resolve the values for any
// tag for a particular EXIF block.
type IfdTagEntryValueResolver struct {
	addressableData []byte
	byteOrder       binary.ByteOrder
}

func NewIfdTagEntryValueResolver(exifData []byte, byteOrder binary.ByteOrder) (itevr *IfdTagEntryValueResolver) {
	return &IfdTagEntryValueResolver{
		addressableData: exifData[ExifAddressableAreaStart:],
		byteOrder:       byteOrder,
	}
}

// ValueBytes will resolve embedded or allocated data from the tag and return the raw bytes.
func (itevr *IfdTagEntryValueResolver) ValueBytes(ite *IfdTagEntry) (value []byte, err error) {
	defer func() {
		if state := recover(); state != nil {
			err = log.Wrap(state.(error))
		}
	}()

	// OBSOLETE(dustin): This is now redundant. Use `(*ValueContext).readRawEncoded()` instead of this method.

	valueContext := newValueContextFromTag(
		ite,
		itevr.addressableData,
		itevr.byteOrder)

	rawBytes, err := valueContext.readRawEncoded()
	log.PanicIf(err)

	return rawBytes, nil
}

func (itevr *IfdTagEntryValueResolver) Value(ite *IfdTagEntry) (value interface{}, err error) {
	defer func() {
		if state := recover(); state != nil {
			err = log.Wrap(state.(error))
		}
	}()

	// OBSOLETE(dustin): This is now redundant. Use `(*ValueContext).Values()` instead of this method.

	valueContext := newValueContextFromTag(
		ite,
		itevr.addressableData,
		itevr.byteOrder)

	values, err := valueContext.Values()
	log.PanicIf(err)

	return values, nil
}