go-exif/type_encode.go

package exif

import (
    "reflect"
    "bytes"

    "encoding/binary"

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

var (
    typeEncodeLogger = log.NewLogger("exif.type_encode")
)


// EncodedData encapsulates the compound output of an encoding operation.
type EncodedData struct {
    Type uint16
    Encoded []byte
    UnitCount uint32
}


type ValueEncoder struct {
    byteOrder binary.ByteOrder
}

func NewValueEncoder(byteOrder binary.ByteOrder) *ValueEncoder {
    return &ValueEncoder{
        byteOrder: byteOrder,
    }
}


func (ve *ValueEncoder) encodeBytes(value []uint8) (ed EncodedData, err error) {
    ed.Type = TypeByte
    ed.Encoded = []byte(value)
    ed.UnitCount = uint32(len(value))

    return ed, nil
}

func (ve *ValueEncoder) encodeAscii(value string) (ed EncodedData, err error) {
    ed.Type = TypeAscii

    ed.Encoded = []byte(value)
    ed.Encoded = append(ed.Encoded, 0)

    ed.UnitCount = uint32(len(ed.Encoded))

    return ed, nil
}

// encodeAsciiNoNul returns a string encoded as a byte-string without a trailing
// NUL byte.
//
// Note that:
//
// 1. This type can not be automatically encoded using `Encode()`. The default
//    mode is to encode *with* a trailing NUL byte using `encodeAscii`. Only
//    certain undefined-type tags using an unterminated ASCII string and these
//    are exceptional in nature.
//
// 2. The presence of this method allows us to completely test the complimentary
//    no-nul parser.
//
func (ve *ValueEncoder) encodeAsciiNoNul(value string) (ed EncodedData, err error) {
    ed.Type = TypeAsciiNoNul
    ed.Encoded = []byte(value)
    ed.UnitCount = uint32(len(ed.Encoded))

    return ed, nil
}

func (ve *ValueEncoder) encodeShorts(value []uint16) (ed EncodedData, err error) {
    defer func() {
        if state := recover(); state != nil {
            err = log.Wrap(state.(error))
        }
    }()

    ed.UnitCount = uint32(len(value))
    ed.Encoded = make([]byte, ed.UnitCount * 2)

    for i := uint32(0); i < ed.UnitCount; i++ {
        if ve.byteOrder == binary.BigEndian {
            binary.BigEndian.PutUint16(ed.Encoded[i*2:(i+1)*2], value[i])
        } else {
            binary.LittleEndian.PutUint16(ed.Encoded[i*2:(i+1)*2], value[i])
        }
    }

    ed.Type = TypeShort

    return ed, nil
}

func (ve *ValueEncoder) encodeLongs(value []uint32) (ed EncodedData, err error) {
    defer func() {
        if state := recover(); state != nil {
            err = log.Wrap(state.(error))
        }
    }()

    ed.UnitCount = uint32(len(value))
    ed.Encoded = make([]byte, ed.UnitCount * 4)

    for i := uint32(0); i < ed.UnitCount; i++ {
        if ve.byteOrder == binary.BigEndian {
            binary.BigEndian.PutUint32(ed.Encoded[i*4:(i+1)*4], value[i])
        } else {
            binary.LittleEndian.PutUint32(ed.Encoded[i*4:(i+1)*4], value[i])
        }
    }

    ed.Type = TypeLong

    return ed, nil
}

func (ve *ValueEncoder) encodeRationals(value []Rational) (ed EncodedData, err error) {
    defer func() {
        if state := recover(); state != nil {
            err = log.Wrap(state.(error))
        }
    }()

    ed.UnitCount = uint32(len(value))
    ed.Encoded = make([]byte, ed.UnitCount * 8)

    for i := uint32(0); i < ed.UnitCount; i++ {
        if ve.byteOrder == binary.BigEndian {
            binary.BigEndian.PutUint32(ed.Encoded[i*8+0:i*8+4], value[i].Numerator)
            binary.BigEndian.PutUint32(ed.Encoded[i*8+4:i*8+8], value[i].Denominator)
        } else {
            binary.LittleEndian.PutUint32(ed.Encoded[i*8+0:i*8+4], value[i].Numerator)
            binary.LittleEndian.PutUint32(ed.Encoded[i*8+4:i*8+8], value[i].Denominator)
        }
    }

    ed.Type = TypeRational

    return ed, nil
}

func (ve *ValueEncoder) encodeSignedLongs(value []int32) (ed EncodedData, err error) {
    defer func() {
        if state := recover(); state != nil {
            err = log.Wrap(state.(error))
        }
    }()

    ed.UnitCount = uint32(len(value))

    b := bytes.NewBuffer(make([]byte, 0, 8 * ed.UnitCount))

    for i := uint32(0); i < ed.UnitCount; i++ {
        if ve.byteOrder == binary.BigEndian {
            err := binary.Write(b, binary.BigEndian, value[i])
            log.PanicIf(err)
        } else {
            err := binary.Write(b, binary.LittleEndian, value[i])
            log.PanicIf(err)
        }
    }

    ed.Type = TypeSignedLong
    ed.Encoded = b.Bytes()

    return ed, nil
}

func (ve *ValueEncoder) encodeSignedRationals(value []SignedRational) (ed EncodedData, err error) {
    defer func() {
        if state := recover(); state != nil {
            err = log.Wrap(state.(error))
        }
    }()

    ed.UnitCount = uint32(len(value))

    b := bytes.NewBuffer(make([]byte, 0, 8 * ed.UnitCount))

    for i := uint32(0); i < ed.UnitCount; i++ {
        if ve.byteOrder == binary.BigEndian {
            err := binary.Write(b, binary.BigEndian, value[i].Numerator)
            log.PanicIf(err)

            err = binary.Write(b, binary.BigEndian, value[i].Denominator)
            log.PanicIf(err)
        } else {
            err := binary.Write(b, binary.LittleEndian, value[i].Numerator)
            log.PanicIf(err)

            err = binary.Write(b, binary.LittleEndian, value[i].Denominator)
            log.PanicIf(err)
        }
    }

    ed.Type = TypeSignedRational
    ed.Encoded = b.Bytes()

    return ed, nil
}

func (ve *ValueEncoder) Encode(value interface{}) (ed EncodedData, err error) {
    defer func() {
        if state := recover(); state != nil {
            err = log.Wrap(state.(error))
        }
    }()

    switch value.(type) {
    case []byte:
        ed, err = ve.encodeBytes(value.([]byte))
        log.PanicIf(err)
    case string:
        ed, err = ve.encodeAscii(value.(string))
        log.PanicIf(err)
    case []uint16:
        ed, err = ve.encodeShorts(value.([]uint16))
        log.PanicIf(err)
    case []uint32:
        ed, err = ve.encodeLongs(value.([]uint32))
        log.PanicIf(err)
    case []Rational:
        ed, err = ve.encodeRationals(value.([]Rational))
        log.PanicIf(err)
    case []int32:
        ed, err = ve.encodeSignedLongs(value.([]int32))
        log.PanicIf(err)
    case []SignedRational:
        ed, err = ve.encodeSignedRationals(value.([]SignedRational))
        log.PanicIf(err)
    default:
        log.Panicf("value not encodable: [%s] [%v]", reflect.TypeOf(value), value)
    }

    return ed, nil
}

func (ve *ValueEncoder) EncodeWithType(tt TagType, value interface{}) (ed EncodedData, err error) {
    defer func() {
        if state := recover(); state != nil {
            err = log.Wrap(state.(error))
        }
    }()

    switch tt.Type() {
    case TypeByte:
        ed, err = ve.encodeBytes(value.([]byte))
        log.PanicIf(err)
    case TypeAscii:
        ed, err = ve.encodeAscii(value.(string))
        log.PanicIf(err)
    case TypeShort:
        ed, err = ve.encodeShorts(value.([]uint16))
        log.PanicIf(err)
    case TypeLong:
        ed, err = ve.encodeLongs(value.([]uint32))
        log.PanicIf(err)
    case TypeRational:
        ed, err = ve.encodeRationals(value.([]Rational))
        log.PanicIf(err)
    case TypeSignedLong:
        ed, err = ve.encodeSignedLongs(value.([]int32))
        log.PanicIf(err)
    case TypeSignedRational:
        ed, err = ve.encodeSignedRationals(value.([]SignedRational))
        log.PanicIf(err)
    default:
        log.Panicf("value not encodable (with type): %v [%v]", tt, value)
    }

    return ed, nil
}