use exif-terminator

vendor/github.com/dsoprea/go-exif/v3/exif.go

@@ -0,0 +1,333 @@
+package exif
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+
+	"encoding/binary"
+	"io/ioutil"
+
+	"github.com/dsoprea/go-logging"
+
+	"github.com/dsoprea/go-exif/v3/common"
+)
+
+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)
+)
+
+const (
+	// ExifSignatureLength is the number of bytes in the EXIF signature (which
+	// customarily includes the first IFD offset).
+	ExifSignatureLength = 8
+)
+
+var (
+	exifLogger = log.NewLogger("exif.exif")
+
+	ExifBigEndianSignature    = [4]byte{'M', 'M', 0x00, 0x2a}
+	ExifLittleEndianSignature = [4]byte{'I', 'I', 0x2a, 0x00}
+)
+
+var (
+	ErrNoExif          = errors.New("no exif data")
+	ErrExifHeaderError = errors.New("exif header error")
+)
+
+// SearchAndExtractExif searches for an EXIF blob in the byte-slice.
+func SearchAndExtractExif(data []byte) (rawExif []byte, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	b := bytes.NewBuffer(data)
+
+	rawExif, err = SearchAndExtractExifWithReader(b)
+	if err != nil {
+		if err == ErrNoExif {
+			return nil, err
+		}
+
+		log.Panic(err)
+	}
+
+	return rawExif, nil
+}
+
+// SearchAndExtractExifN searches for an EXIF blob in the byte-slice, but skips
+// the given number of EXIF blocks first. This is a forensics tool that helps
+// identify multiple EXIF blocks in a file.
+func SearchAndExtractExifN(data []byte, n int) (rawExif []byte, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	skips := 0
+	totalDiscarded := 0
+	for {
+		b := bytes.NewBuffer(data)
+
+		var discarded int
+
+		rawExif, discarded, err = searchAndExtractExifWithReaderWithDiscarded(b)
+		if err != nil {
+			if err == ErrNoExif {
+				return nil, err
+			}
+
+			log.Panic(err)
+		}
+
+		exifLogger.Debugf(nil, "Read EXIF block (%d).", skips)
+
+		totalDiscarded += discarded
+
+		if skips >= n {
+			exifLogger.Debugf(nil, "Reached requested EXIF block (%d).", n)
+			break
+		}
+
+		nextOffset := discarded + 1
+		exifLogger.Debugf(nil, "Skipping EXIF block (%d) by seeking to position (%d).", skips, nextOffset)
+
+		data = data[nextOffset:]
+		skips++
+	}
+
+	exifLogger.Debugf(nil, "Found EXIF blob (%d) bytes from initial position.", totalDiscarded)
+	return rawExif, nil
+}
+
+// searchAndExtractExifWithReaderWithDiscarded searches for an EXIF blob using
+// an `io.Reader`. We can't know how much long the EXIF data is without parsing
+// it, so this will likely grab up a lot of the image-data, too.
+//
+// This function returned the count of preceding bytes.
+func searchAndExtractExifWithReaderWithDiscarded(r io.Reader) (rawExif []byte, discarded int, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	// Search for the beginning of the EXIF information. The EXIF is near the
+	// beginning of most JPEGs, so this likely doesn't have a high cost (at
+	// least, again, with JPEGs).
+
+	br := bufio.NewReader(r)
+
+	for {
+		window, err := br.Peek(ExifSignatureLength)
+		if err != nil {
+			if err == io.EOF {
+				return nil, 0, ErrNoExif
+			}
+
+			log.Panic(err)
+		}
+
+		_, err = ParseExifHeader(window)
+		if err != nil {
+			if log.Is(err, ErrNoExif) == true {
+				// No EXIF. Move forward by one byte.
+
+				_, err := br.Discard(1)
+				log.PanicIf(err)
+
+				discarded++
+
+				continue
+			}
+
+			// Some other error.
+			log.Panic(err)
+		}
+
+		break
+	}
+
+	exifLogger.Debugf(nil, "Found EXIF blob (%d) bytes from initial position.", discarded)
+
+	rawExif, err = ioutil.ReadAll(br)
+	log.PanicIf(err)
+
+	return rawExif, discarded, nil
+}
+
+// RELEASE(dustin): We should replace the implementation of SearchAndExtractExifWithReader with searchAndExtractExifWithReaderWithDiscarded and drop the latter.
+
+// SearchAndExtractExifWithReader searches for an EXIF blob using an
+// `io.Reader`. We can't know how much long the EXIF data is without parsing it,
+// so this will likely grab up a lot of the image-data, too.
+func SearchAndExtractExifWithReader(r io.Reader) (rawExif []byte, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	rawExif, _, err = searchAndExtractExifWithReaderWithDiscarded(r)
+	if err != nil {
+		if err == ErrNoExif {
+			return nil, err
+		}
+
+		log.Panic(err)
+	}
+
+	return rawExif, 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))
+		}
+	}()
+
+	// Open the file.
+
+	f, err := os.Open(filepath)
+	log.PanicIf(err)
+
+	defer f.Close()
+
+	rawExif, err = SearchAndExtractExifWithReader(f)
+	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) < ExifSignatureLength {
+		exifLogger.Warningf(nil, "Not enough data for EXIF header: (%d)", len(data))
+		return eh, ErrNoExif
+	}
+
+	if bytes.Equal(data[:4], ExifBigEndianSignature[:]) == true {
+		exifLogger.Debugf(nil, "Byte-order is big-endian.")
+		eh.ByteOrder = binary.BigEndian
+	} else if bytes.Equal(data[:4], ExifLittleEndianSignature[:]) == true {
+		eh.ByteOrder = binary.LittleEndian
+		exifLogger.Debugf(nil, "Byte-order is little-endian.")
+	} else {
+		return eh, ErrNoExif
+	}
+
+	eh.FirstIfdOffset = eh.ByteOrder.Uint32(data[4:8])
+
+	return eh, nil
+}
+
+// Visit recursively invokes a callback for every tag.
+func Visit(rootIfdIdentity *exifcommon.IfdIdentity, ifdMapping *exifcommon.IfdMapping, tagIndex *TagIndex, exifData []byte, visitor TagVisitorFn, so *ScanOptions) (eh ExifHeader, furthestOffset uint32, err error) {
+	defer func() {
+		if state := recover(); state != nil {
+			err = log.Wrap(state.(error))
+		}
+	}()
+
+	eh, err = ParseExifHeader(exifData)
+	log.PanicIf(err)
+
+	ebs := NewExifReadSeekerWithBytes(exifData)
+	ie := NewIfdEnumerate(ifdMapping, tagIndex, ebs, eh.ByteOrder)
+
+	_, err = ie.Scan(rootIfdIdentity, eh.FirstIfdOffset, visitor, so)
+	log.PanicIf(err)
+
+	furthestOffset = ie.FurthestOffset()
+
+	return eh, furthestOffset, nil
+}
+
+// Collect recursively builds a static structure of all IFDs and tags.
+func Collect(ifdMapping *exifcommon.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)
+
+	ebs := NewExifReadSeekerWithBytes(exifData)
+	ie := NewIfdEnumerate(ifdMapping, tagIndex, ebs, eh.ByteOrder)
+
+	index, err = ie.Collect(eh.FirstIfdOffset)
+	log.PanicIf(err)
+
+	return eh, index, nil
+}
+
+// BuildExifHeader constructs the bytes that go at the front of the stream.
+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)
+
+	var signatureBytes []byte
+	if byteOrder == binary.BigEndian {
+		signatureBytes = ExifBigEndianSignature[:]
+	} else {
+		signatureBytes = ExifLittleEndianSignature[:]
+	}
+
+	_, err = b.Write(signatureBytes)
+	log.PanicIf(err)
+
+	err = binary.Write(b, byteOrder, firstIfdOffset)
+	log.PanicIf(err)
+
+	return b.Bytes(), nil
+}