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

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package exif
import (
"bytes"
"errors"
"fmt"
"os"
"encoding/binary"
"io/ioutil"
"github.com/dsoprea/go-logging"
)
const (
// ExifAddressableAreaStart is the absolute offset in the file that all
// offsets are relative to.
ExifAddressableAreaStart = uint32(0x0)
// ExifDefaultFirstIfdOffset is essentially the number of bytes in addition
// to `ExifAddressableAreaStart` that you have to move in order to escape
// the rest of the header and get to the earliest point where we can put
// stuff (which has to be the first IFD). This is the size of the header
// sequence containing the two-character byte-order, two-character fixed-
// bytes, and the four bytes describing the first-IFD offset.
ExifDefaultFirstIfdOffset = uint32(2 + 2 + 4)
)
var (
exifLogger = log.NewLogger("exif.exif")
// EncodeDefaultByteOrder is the default byte-order for encoding operations.
EncodeDefaultByteOrder = binary.BigEndian
// Default byte order for tests.
TestDefaultByteOrder = binary.BigEndian
BigEndianBoBytes = [2]byte{'M', 'M'}
LittleEndianBoBytes = [2]byte{'I', 'I'}
ByteOrderLookup = map[[2]byte]binary.ByteOrder{
BigEndianBoBytes: binary.BigEndian,
LittleEndianBoBytes: binary.LittleEndian,
}
ByteOrderLookupR = map[binary.ByteOrder][2]byte{
binary.BigEndian: BigEndianBoBytes,
binary.LittleEndian: LittleEndianBoBytes,
}
ExifFixedBytesLookup = map[binary.ByteOrder][2]byte{
binary.LittleEndian: {0x2a, 0x00},
binary.BigEndian: {0x00, 0x2a},
}
)
var (
ErrNoExif = errors.New("no exif data")
ErrExifHeaderError = errors.New("exif header error")
)
// SearchAndExtractExif returns a slice from the beginning of the EXIF data to
// end of the file (it's not practical to try and calculate where the data
// actually ends; it needs to be formally parsed).
func SearchAndExtractExif(data []byte) (rawExif []byte, err error) {
defer func() {
if state := recover(); state != nil {
err := log.Wrap(state.(error))
log.Panic(err)
}
}()
// Search for the beginning of the EXIF information. The EXIF is near the
// beginning of our/most JPEGs, so this has a very low cost.
foundAt := -1
for i := 0; i < len(data); i++ {
if _, err := ParseExifHeader(data[i:]); err == nil {
foundAt = i
break
} else if log.Is(err, ErrNoExif) == false {
return nil, err
}
}
if foundAt == -1 {
return nil, ErrNoExif
}
return data[foundAt:], nil
}
// SearchFileAndExtractExif returns a slice from the beginning of the EXIF data
// to the end of the file (it's not practical to try and calculate where the
// data actually ends).
func SearchFileAndExtractExif(filepath string) (rawExif []byte, err error) {
defer func() {
if state := recover(); state != nil {
err := log.Wrap(state.(error))
log.Panic(err)
}
}()
// Open the file.
f, err := os.Open(filepath)
log.PanicIf(err)
defer f.Close()
data, err := ioutil.ReadAll(f)
log.PanicIf(err)
rawExif, err = SearchAndExtractExif(data)
log.PanicIf(err)
return rawExif, nil
}
type ExifHeader struct {
ByteOrder binary.ByteOrder
FirstIfdOffset uint32
}
func (eh ExifHeader) String() string {
return fmt.Sprintf("ExifHeader<BYTE-ORDER=[%v] FIRST-IFD-OFFSET=(0x%02x)>", eh.ByteOrder, eh.FirstIfdOffset)
}
// ParseExifHeader parses the bytes at the very top of the header.
//
// This will panic with ErrNoExif on any data errors so that we can double as
// an EXIF-detection routine.
func ParseExifHeader(data []byte) (eh ExifHeader, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
// Good reference:
//
// CIPA DC-008-2016; JEITA CP-3451D
// -> http://www.cipa.jp/std/documents/e/DC-008-Translation-2016-E.pdf
if len(data) < 2 {
exifLogger.Warningf(nil, "Not enough data for EXIF header (1): (%d)", len(data))
return eh, ErrNoExif
}
byteOrderBytes := [2]byte{data[0], data[1]}
byteOrder, found := ByteOrderLookup[byteOrderBytes]
if found == false {
// exifLogger.Warningf(nil, "EXIF byte-order not recognized: [%v]", byteOrderBytes)
return eh, ErrNoExif
}
if len(data) < 4 {
exifLogger.Warningf(nil, "Not enough data for EXIF header (2): (%d)", len(data))
return eh, ErrNoExif
}
fixedBytes := [2]byte{data[2], data[3]}
expectedFixedBytes := ExifFixedBytesLookup[byteOrder]
if fixedBytes != expectedFixedBytes {
// exifLogger.Warningf(nil, "EXIF header fixed-bytes should be [%v] but are: [%v]", expectedFixedBytes, fixedBytes)
return eh, ErrNoExif
}
if len(data) < 2 {
exifLogger.Warningf(nil, "Not enough data for EXIF header (3): (%d)", len(data))
return eh, ErrNoExif
}
firstIfdOffset := byteOrder.Uint32(data[4:8])
eh = ExifHeader{
ByteOrder: byteOrder,
FirstIfdOffset: firstIfdOffset,
}
return eh, nil
}
// Visit recursively invokes a callback for every tag.
func Visit(rootIfdName string, ifdMapping *IfdMapping, tagIndex *TagIndex, exifData []byte, visitor RawTagVisitor) (eh ExifHeader, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
eh, err = ParseExifHeader(exifData)
log.PanicIf(err)
ie := NewIfdEnumerate(ifdMapping, tagIndex, exifData, eh.ByteOrder)
err = ie.Scan(rootIfdName, eh.FirstIfdOffset, visitor, true)
log.PanicIf(err)
return eh, nil
}
// Collect recursively builds a static structure of all IFDs and tags.
func Collect(ifdMapping *IfdMapping, tagIndex *TagIndex, exifData []byte) (eh ExifHeader, index IfdIndex, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
eh, err = ParseExifHeader(exifData)
log.PanicIf(err)
ie := NewIfdEnumerate(ifdMapping, tagIndex, exifData, eh.ByteOrder)
index, err = ie.Collect(eh.FirstIfdOffset, true)
log.PanicIf(err)
return eh, index, nil
}
// BuildExifHeader constructs the bytes that go in the very beginning.
func BuildExifHeader(byteOrder binary.ByteOrder, firstIfdOffset uint32) (headerBytes []byte, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
b := new(bytes.Buffer)
// This is the point in the data that all offsets are relative to.
boBytes := ByteOrderLookupR[byteOrder]
_, err = b.WriteString(string(boBytes[:]))
log.PanicIf(err)
fixedBytes := ExifFixedBytesLookup[byteOrder]
_, err = b.Write(fixedBytes[:])
log.PanicIf(err)
err = binary.Write(b, byteOrder, firstIfdOffset)
log.PanicIf(err)
return b.Bytes(), nil
}