exif

package module
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 Go to latest Published: Aug 26, 2023 License: MIT Imports: 20 Imported by: 20

Documentation

Overview

Package exif parses raw EXIF information given a block of raw EXIF data. It can also construct new EXIF information, and provides tools for doing so. This package is not involved with the parsing of particular file-formats.

The EXIF data must first be extracted and then provided to us. Conversely, when constructing new EXIF data, the caller is responsible for packaging this in whichever format they require.

Index

Examples

Constants

View Source 
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)
)
View Source 
const (

	// ThumbnailFqIfdPath is the fully-qualified IFD path that the thumbnail
	// must be found in.
	ThumbnailFqIfdPath = "IFD1"

	// ThumbnailOffsetTagId returns the tag-ID of the thumbnail offset.
	ThumbnailOffsetTagId = 0x0201

	// ThumbnailSizeTagId returns the tag-ID of the thumbnail size.
	ThumbnailSizeTagId = 0x0202
)
View Source 
const (

	// TagGpsVersionId is the ID of the GPS version tag.
	TagGpsVersionId = 0x0000

	// TagLatitudeId is the ID of the GPS latitude tag.
	TagLatitudeId = 0x0002

	// TagLatitudeRefId is the ID of the GPS latitude orientation tag.
	TagLatitudeRefId = 0x0001

	// TagLongitudeId is the ID of the GPS longitude tag.
	TagLongitudeId = 0x0004

	// TagLongitudeRefId is the ID of the GPS longitude-orientation tag.
	TagLongitudeRefId = 0x0003

	// TagTimestampId is the ID of the GPS time tag.
	TagTimestampId = 0x0007

	// TagDatestampId is the ID of the GPS date tag.
	TagDatestampId = 0x001d

	// TagAltitudeId is the ID of the GPS altitude tag.
	TagAltitudeId = 0x0006

	// TagAltitudeRefId is the ID of the GPS altitude-orientation tag.
	TagAltitudeRefId = 0x0005
)
View Source 
const (
	// ExifSignatureLength is the number of bytes in the EXIF signature (which
	// customarily includes the first IFD offset).
	ExifSignatureLength = 8
)
View Source 
const (
	// Tag-ID + Tag-Type + Unit-Count + Value/Offset.
	IfdTagEntrySize = uint32(2 + 2 + 4 + 4)
)

Variables

View Source 
var (
	// ErrTagNotFound indicates that the tag was not found.
	ErrTagNotFound = errors.New("tag not found")

	// ErrTagNotKnown indicates that the tag is not registered with us as a
	// known tag.
	ErrTagNotKnown = errors.New("tag is not known")
)
View Source 
var (
	ExifBigEndianSignature    = [4]byte{'M', 'M', 0x00, 0x2a}
	ExifLittleEndianSignature = [4]byte{'I', 'I', 0x2a, 0x00}
)
View Source 
var (
	ErrNoExif          = errors.New("no exif data")
	ErrExifHeaderError = errors.New("exif header error")
)
View Source 
var (
	ErrTagEntryNotFound = errors.New("tag entry not found")
	ErrChildIbNotFound  = errors.New("child IB not found")
)
View Source 
var (
	// ErrNoThumbnail means that no thumbnail was found.
	ErrNoThumbnail = errors.New("no thumbnail")

	// ErrNoGpsTags means that no GPS info was found.
	ErrNoGpsTags = errors.New("no gps tags")

	// ErrTagTypeNotValid means that the tag-type is not valid.
	ErrTagTypeNotValid = errors.New("tag type invalid")

	// ErrOffsetInvalid means that the file offset is not valid.
	ErrOffsetInvalid = errors.New("file offset invalid")
)
View Source 
var (
	// ErrGpsCoordinatesNotValid means that some part of the geographic data was
	// unparseable.
	ErrGpsCoordinatesNotValid = errors.New("GPS coordinates not valid")
)
View Source 
var (
	// ValidGpsVersions is the list of recognized EXIF GPS versions/signatures.
	ValidGpsVersions = [][4]byte{

		{2, 0, 0, 0},

		{2, 2, 0, 0},

		{2, 3, 0, 0},
	}
)

Functions

func BuildExifHeader 

func BuildExifHeader(byteOrder binary.ByteOrder, firstIfdOffset uint32) (headerBytes []byte, err error)

BuildExifHeader constructs the bytes that go at the front of the stream.

Example 
headerBytes, err := BuildExifHeader(exifcommon.TestDefaultByteOrder, 0x11223344)
log.PanicIf(err)

eh, err := ParseExifHeader(headerBytes)
log.PanicIf(err)

fmt.Printf("%v\n", eh)

Output:

ExifHeader<BYTE-ORDER=[BigEndian] FIRST-IFD-OFFSET=(0x11223344)>

func Collect 

func Collect(ifdMapping *exifcommon.IfdMapping, tagIndex *TagIndex, exifData []byte) (eh ExifHeader, index IfdIndex, err error)

Collect recursively builds a static structure of all IFDs and tags.

func ExifFullTimestampString 

func ExifFullTimestampString(t time.Time) (fullTimestampPhrase string)

ExifFullTimestampString produces a string like "2018:11:30 13:01:49" from a `time.Time` struct. It will attempt to convert to UTC first.

Example 
originalPhrase := "2018:11:30 13:01:49"

timestamp, err := ParseExifFullTimestamp(originalPhrase)
log.PanicIf(err)

restoredPhrase := ExifFullTimestampString(timestamp)
fmt.Printf("To EXIF timestamp: [%s]\n", restoredPhrase)

Output:

To EXIF timestamp: [2018:11:30 13:01:49]

func GpsDegreesEquals 

func GpsDegreesEquals(gi1, gi2 GpsDegrees) bool

GpsDegreesEquals returns true if the two `GpsDegrees` are identical.

func IsTime 

func IsTime(v interface{}) bool

IsTime returns true if the value is a `time.Time`.

func LoadStandardIfds 

func LoadStandardIfds(im *exifcommon.IfdMapping) (err error)

LoadStandardIfds loads the standard IFDs into the mapping.

func LoadStandardTags 

func LoadStandardTags(ti *TagIndex) (err error)

LoadStandardTags registers the tags that all devices/applications should support.

func NewIfdMapping 

func NewIfdMapping() (ifdMapping *exifcommon.IfdMapping)

NewIfdMapping returns a new IfdMapping struct.

func NewIfdMappingWithStandard 

func NewIfdMappingWithStandard() (ifdMapping *exifcommon.IfdMapping)

NewIfdMappingWithStandard retruns a new IfdMapping struct preloaded with the standard IFDs.

func ParseExifFullTimestamp 

func ParseExifFullTimestamp(fullTimestampPhrase string) (timestamp time.Time, err error)

ParseExifFullTimestamp parses dates like "2018:11:30 13:01:49" into a UTC `time.Time` struct.

Example 
originalPhrase := "2018:11:30 13:01:49"

timestamp, err := ParseExifFullTimestamp(originalPhrase)
log.PanicIf(err)

fmt.Printf("To Go timestamp: [%s]\n", timestamp.Format(time.RFC3339))

Output:

To Go timestamp: [2018-11-30T13:01:49Z]

func SearchAndExtractExif 

func SearchAndExtractExif(data []byte) (rawExif []byte, err error)

SearchAndExtractExif searches for an EXIF blob in the byte-slice.

func SearchAndExtractExifWithReader 

func SearchAndExtractExifWithReader(r io.Reader) (rawExif []byte, err error)

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 SearchFileAndExtractExif 

func SearchFileAndExtractExif(filepath string) (rawExif []byte, err error)

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).

Types

type BuilderTag 

type BuilderTag struct {
	// contains filtered or unexported fields
}

func NewBuilderTag 

func NewBuilderTag(ifdPath string, tagId uint16, typeId exifcommon.TagTypePrimitive, value *IfdBuilderTagValue, byteOrder binary.ByteOrder) *BuilderTag

func NewChildIfdBuilderTag 

func NewChildIfdBuilderTag(ifdPath string, tagId uint16, value *IfdBuilderTagValue) *BuilderTag

func NewStandardBuilderTag 

func NewStandardBuilderTag(ifdPath string, it *IndexedTag, byteOrder binary.ByteOrder, value interface{}) *BuilderTag

NewStandardBuilderTag constructs a `BuilderTag` instance. The type is looked up. `ii` is the type of IFD that owns this tag.

func (*BuilderTag) SetValue 

func (bt *BuilderTag) SetValue(byteOrder binary.ByteOrder, value interface{}) (err error)
Example 
testImageFilepath := getTestImageFilepath()

rawExif, err := SearchFileAndExtractExif(testImageFilepath)
log.PanicIf(err)

im := NewIfdMapping()

err = LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()

_, index, err := Collect(im, ti, rawExif)
log.PanicIf(err)

// Create builder.

rootIb := NewIfdBuilderFromExistingChain(index.RootIfd)

// Find tag to update.

exifBt, err := rootIb.FindTagWithName("ExifTag")
log.PanicIf(err)

ucBt, err := exifBt.value.Ib().FindTagWithName("UserComment")
log.PanicIf(err)

// Update the value. Since this is an "undefined"-type tag, we have to use
// its type-specific struct.

// TODO(dustin): !! Add an example for setting a non-unknown value, too.
uc := exifundefined.Tag9286UserComment{
	EncodingType:  exifundefined.TagUndefinedType_9286_UserComment_Encoding_ASCII,
	EncodingBytes: []byte("TEST COMMENT"),
}

err = ucBt.SetValue(rootIb.byteOrder, uc)
log.PanicIf(err)

// Encode.

ibe := NewIfdByteEncoder()

// This returns the raw bytes that you will be looking for, but there's no
// use for them at this point in the example.
_, err = ibe.EncodeToExif(rootIb)
log.PanicIf(err)

Output:

func (*BuilderTag) String 

func (bt *BuilderTag) String() string

func (*BuilderTag) Value 

func (bt *BuilderTag) Value() (value *IfdBuilderTagValue)

type ByteWriter 

type ByteWriter struct {
	// contains filtered or unexported fields
}

func NewByteWriter 

func NewByteWriter(b *bytes.Buffer, byteOrder binary.ByteOrder) (bw *ByteWriter)

func (ByteWriter) WriteFourBytes 

func (bw ByteWriter) WriteFourBytes(value []byte) (err error)

func (ByteWriter) WriteUint16 

func (bw ByteWriter) WriteUint16(value uint16) (err error)

func (ByteWriter) WriteUint32 

func (bw ByteWriter) WriteUint32(value uint32) (err error)

type ExifHeader 

type ExifHeader struct {
	ByteOrder      binary.ByteOrder
	FirstIfdOffset uint32
}

func ParseExifHeader 

func ParseExifHeader(data []byte) (eh ExifHeader, err error)

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 Visit 

func Visit(rootIfdIdentity *exifcommon.IfdIdentity, ifdMapping *exifcommon.IfdMapping, tagIndex *TagIndex, exifData []byte, visitor TagVisitorFn) (eh ExifHeader, furthestOffset uint32, err error)

Visit recursively invokes a callback for every tag.

func (ExifHeader) String 

func (eh ExifHeader) String() string

type ExifTag 

type ExifTag struct {
	// IfdPath is the fully-qualified IFD path (even though it is not named as
	// such).
	IfdPath string `json:"ifd_path"`

	// TagId is the tag-ID.
	TagId uint16 `json:"id"`

	// TagName is the tag-name. This is never empty.
	TagName string `json:"name"`

	// UnitCount is the recorded number of units constution of the value.
	UnitCount uint32 `json:"unit_count"`

	// TagTypeId is the type-ID.
	TagTypeId exifcommon.TagTypePrimitive `json:"type_id"`

	// TagTypeName is the type name.
	TagTypeName string `json:"type_name"`

	// Value is the decoded value.
	Value interface{} `json:"value"`

	// ValueBytes is the raw, encoded value.
	ValueBytes []byte `json:"value_bytes"`

	// Formatted is the human representation of the first value (tag values are
	// always an array).
	FormattedFirst string `json:"formatted_first"`

	// Formatted is the human representation of the complete value.
	Formatted string `json:"formatted"`

	// ChildIfdPath is the name of the child IFD this tag represents (if it
	// represents any). Otherwise, this is empty.
	ChildIfdPath string `json:"child_ifd_path"`
}

ExifTag is one simple representation of a tag in a flat list of all of them.

func GetFlatExifData 

func GetFlatExifData(exifData []byte) (exifTags []ExifTag, err error)

GetFlatExifData returns a simple, flat representation of all tags.

func (ExifTag) String 

func (et ExifTag) String() string

String returns a string representation.

type GpsDegrees 

type GpsDegrees struct {
	// Orientation describes the N/E/S/W direction that this position is
	// relative to.
	Orientation byte

	// Degrees is a simple float representing the underlying rational degrees
	// amount.
	Degrees float64

	// Minutes is a simple float representing the underlying rational minutes
	// amount.
	Minutes float64

	// Seconds is a simple float representing the underlying ration seconds
	// amount.
	Seconds float64
}

GpsDegrees is a high-level struct representing geographic data.

func NewGpsDegreesFromRationals 

func NewGpsDegreesFromRationals(refValue string, rawCoordinate []exifcommon.Rational) (gd GpsDegrees, err error)

NewGpsDegreesFromRationals returns a GpsDegrees struct given the EXIF-encoded information. The refValue is the N/E/S/W direction that this position is relative to.

func (GpsDegrees) Decimal 

func (d GpsDegrees) Decimal() float64

Decimal calculates and returns the simplified float representation of the component degrees.

func (GpsDegrees) Raw 

func (d GpsDegrees) Raw() []exifcommon.Rational

Raw returns a Rational struct that can be used to *write* coordinates. In practice, the denominator are typically (1) in the original EXIF data, and, that being the case, this will best preserve precision.

func (GpsDegrees) String 

func (d GpsDegrees) String() string

String provides returns a descriptive string.

type GpsInfo 

type GpsInfo struct {
	Latitude, Longitude GpsDegrees
	Altitude            int
	Timestamp           time.Time
}

GpsInfo encapsulates all of the geographic information in one place.

func (*GpsInfo) S2CellId 

func (gi *GpsInfo) S2CellId() s2.CellID

S2CellId returns the cell-ID of the geographic location on the earth.

func (*GpsInfo) String 

func (gi *GpsInfo) String() string

String returns a descriptive string.

type Ifd 

type Ifd struct {
	ByteOrder binary.ByteOrder

	Id int

	ParentIfd *Ifd

	// ParentTagIndex is our tag position in the parent IFD, if we had a parent
	// (if `ParentIfd` is not nil and we weren't an IFD referenced as a sibling
	// instead of as a child).
	ParentTagIndex int

	Offset uint32

	Entries        []*IfdTagEntry
	EntriesByTagId map[uint16][]*IfdTagEntry

	Children []*Ifd

	ChildIfdIndex map[string]*Ifd

	NextIfdOffset uint32
	NextIfd       *Ifd
	// contains filtered or unexported fields
}

Ifd represents a single, parsed IFD.

func FindIfdFromRootIfd 

func FindIfdFromRootIfd(rootIfd *Ifd, ifdPath string) (ifd *Ifd, err error)

FindIfdFromRootIfd returns the given `Ifd` given the root-IFD and path of the desired IFD.

func (*Ifd) ChildWithIfdPath 

func (ifd *Ifd) ChildWithIfdPath(iiChild *exifcommon.IfdIdentity) (childIfd *Ifd, err error)

ChildWithIfdPath returns an `Ifd` struct for the given child of the current IFD.

func (*Ifd) DumpTags 

func (ifd *Ifd) DumpTags() []*IfdTagEntry

DumpTags prints the IFD hierarchy.

func (*Ifd) DumpTree 

func (ifd *Ifd) DumpTree() []string

DumpTree returns a list of strings describing the IFD hierarchy.

func (*Ifd) EnumerateTagsRecursively 

func (ifd *Ifd) EnumerateTagsRecursively(visitor ParsedTagVisitor) (err error)

EnumerateTagsRecursively calls the given visitor function for every tag and IFD in the current IFD, recursively.

Example 
testImageFilepath := getTestImageFilepath()

rawExif, err := SearchFileAndExtractExif(testImageFilepath)
log.PanicIf(err)

im := NewIfdMapping()

err = LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()

_, index, err := Collect(im, ti, rawExif)
log.PanicIf(err)

cb := func(ifd *Ifd, ite *IfdTagEntry) error {

	// Something useful.

	return nil
}

err = index.RootIfd.EnumerateTagsRecursively(cb)
log.PanicIf(err)

Output:

func (*Ifd) FindTagWithId 

func (ifd *Ifd) FindTagWithId(tagId uint16) (results []*IfdTagEntry, err error)

FindTagWithId returns a list of tags (usually just zero or one) that match the given tag ID. This is efficient.

func (*Ifd) FindTagWithName 

func (ifd *Ifd) FindTagWithName(tagName string) (results []*IfdTagEntry, err error)

FindTagWithName returns a list of tags (usually just zero or one) that match the given tag name. This is not efficient (though the labor is trivial).

Example 
testImageFilepath := getTestImageFilepath()

rawExif, err := SearchFileAndExtractExif(testImageFilepath)
log.PanicIf(err)

im := NewIfdMapping()

err = LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()

_, index, err := Collect(im, ti, rawExif)
log.PanicIf(err)

tagName := "Model"

rootIfd := index.RootIfd

// We know the tag we want is on IFD0 (the first/root IFD).
results, err := rootIfd.FindTagWithName(tagName)
log.PanicIf(err)

// This should never happen.
if len(results) != 1 {
	log.Panicf("there wasn't exactly one result")
}

ite := results[0]

valueRaw, err := ite.Value()
log.PanicIf(err)

value := valueRaw.(string)
fmt.Println(value)

Output:

Canon EOS 5D Mark III

func (*Ifd) GpsInfo 

func (ifd *Ifd) GpsInfo() (gi *GpsInfo, err error)

GpsInfo parses and consolidates the GPS info. This can only be called on the GPS IFD.

Example 
filepath := getTestGpsImageFilepath()

rawExif, err := SearchFileAndExtractExif(filepath)
log.PanicIf(err)

im := NewIfdMapping()

err = LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()

_, index, err := Collect(im, ti, rawExif)
log.PanicIf(err)

ifd, err := index.RootIfd.ChildWithIfdPath(exifcommon.IfdGpsInfoStandardIfdIdentity)
log.PanicIf(err)

gi, err := ifd.GpsInfo()
log.PanicIf(err)

fmt.Printf("%s\n", gi)

Output:

GpsInfo<LAT=(26.58667) LON=(-80.05361) ALT=(0) TIME=[2018-04-29 01:22:57 +0000 UTC]>

func (*Ifd) IfdIdentity 

func (ifd *Ifd) IfdIdentity() *exifcommon.IfdIdentity

IfdIdentity returns IFD identity that this struct represents.

func (*Ifd) PrintIfdTree 

func (ifd *Ifd) PrintIfdTree()

PrintIfdTree prints the IFD hierarchy.

func (*Ifd) PrintTagTree 

func (ifd *Ifd) PrintTagTree(populateValues bool)

PrintTagTree prints the IFD hierarchy.

func (*Ifd) String 

func (ifd *Ifd) String() string

String returns a description string.

func (*Ifd) Thumbnail 

func (ifd *Ifd) Thumbnail() (data []byte, err error)

Thumbnail returns the raw thumbnail bytes. This is typically directly readable by any standard image viewer.

Example 
testImageFilepath := getTestImageFilepath()

rawExif, err := SearchFileAndExtractExif(testImageFilepath)
log.PanicIf(err)

im := NewIfdMapping()

err = LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()

_, index, err := Collect(im, ti, rawExif)
log.PanicIf(err)

// This returns the raw bytes that you will be looking for, but there's no
// use for them at this point in the example.
_, err = index.RootIfd.NextIfd.Thumbnail()
log.PanicIf(err)

Output:

type IfdBuilder 

type IfdBuilder struct {
	// contains filtered or unexported fields
}

func GetOrCreateIbFromRootIb 

func GetOrCreateIbFromRootIb(rootIb *IfdBuilder, fqIfdPath string) (ib *IfdBuilder, err error)

GetOrCreateIbFromRootIb returns an IB representing the requested IFD, even if an IB doesn't already exist for it. This function may call itself recursively.

func NewIfdBuilder 

func NewIfdBuilder(ifdMapping *exifcommon.IfdMapping, tagIndex *TagIndex, ii *exifcommon.IfdIdentity, byteOrder binary.ByteOrder) (ib *IfdBuilder)

func NewIfdBuilderFromExistingChain 

func NewIfdBuilderFromExistingChain(rootIfd *Ifd) (firstIb *IfdBuilder)

NewIfdBuilderFromExistingChain creates a chain of IB instances from an IFD chain generated from real data.

func NewIfdBuilderWithExistingIfd 

func NewIfdBuilderWithExistingIfd(ifd *Ifd) (ib *IfdBuilder)

NewIfdBuilderWithExistingIfd creates a new IB using the same header type information as the given IFD.

func (*IfdBuilder) Add 

func (ib *IfdBuilder) Add(bt *BuilderTag) (err error)

func (*IfdBuilder) AddChildIb 

func (ib *IfdBuilder) AddChildIb(childIb *IfdBuilder) (err error)

AddChildIb adds a tag that branches to a new IFD.

func (*IfdBuilder) AddStandard 

func (ib *IfdBuilder) AddStandard(tagId uint16, value interface{}) (err error)

AddStandard quickly and easily composes and adds the tag using the information already known about a tag. Only works with standard tags.

func (*IfdBuilder) AddStandardWithName 

func (ib *IfdBuilder) AddStandardWithName(tagName string, value interface{}) (err error)

AddStandardWithName quickly and easily composes and adds the tag using the information already known about a tag (using the name). Only works with standard tags.

func (*IfdBuilder) AddTagsFromExisting 

func (ib *IfdBuilder) AddTagsFromExisting(ifd *Ifd, includeTagIds []uint16, excludeTagIds []uint16) (err error)

AddTagsFromExisting does a verbatim copy of the entries in `ifd` to this builder. It excludes child IFDs. These must be added explicitly via `AddChildIb()`.

func (*IfdBuilder) ChildWithTagId 

func (ib *IfdBuilder) ChildWithTagId(childIfdTagId uint16) (childIb *IfdBuilder, err error)

func (*IfdBuilder) DeleteAll 

func (ib *IfdBuilder) DeleteAll(tagId uint16) (n int, err error)

func (*IfdBuilder) DeleteFirst 

func (ib *IfdBuilder) DeleteFirst(tagId uint16) (err error)

func (*IfdBuilder) DeleteN 

func (ib *IfdBuilder) DeleteN(tagId uint16, n int) (err error)

func (*IfdBuilder) DumpToStrings 

func (ib *IfdBuilder) DumpToStrings() (lines []string)

func (*IfdBuilder) Find 

func (ib *IfdBuilder) Find(tagId uint16) (position int, err error)

func (*IfdBuilder) FindN 

func (ib *IfdBuilder) FindN(tagId uint16, maxFound int) (found []int, err error)

func (*IfdBuilder) FindTag 

func (ib *IfdBuilder) FindTag(tagId uint16) (bt *BuilderTag, err error)

func (*IfdBuilder) FindTagWithName 

func (ib *IfdBuilder) FindTagWithName(tagName string) (bt *BuilderTag, err error)

func (*IfdBuilder) IfdIdentity 

func (ib *IfdBuilder) IfdIdentity() *exifcommon.IfdIdentity

func (*IfdBuilder) NewBuilderTagFromBuilder 

func (ib *IfdBuilder) NewBuilderTagFromBuilder(childIb *IfdBuilder) (bt *BuilderTag)

func (*IfdBuilder) NextIb 

func (ib *IfdBuilder) NextIb() (nextIb *IfdBuilder, err error)

func (*IfdBuilder) PrintIfdTree 

func (ib *IfdBuilder) PrintIfdTree()

func (*IfdBuilder) PrintTagTree 

func (ib *IfdBuilder) PrintTagTree()

func (*IfdBuilder) Replace 

func (ib *IfdBuilder) Replace(tagId uint16, bt *BuilderTag) (err error)

func (*IfdBuilder) ReplaceAt 

func (ib *IfdBuilder) ReplaceAt(position int, bt *BuilderTag) (err error)

func (*IfdBuilder) Set 

func (ib *IfdBuilder) Set(bt *BuilderTag) (err error)

Set will add a new entry or update an existing entry.

func (*IfdBuilder) SetNextIb 

func (ib *IfdBuilder) SetNextIb(nextIb *IfdBuilder) (err error)

func (*IfdBuilder) SetStandard 

func (ib *IfdBuilder) SetStandard(tagId uint16, value interface{}) (err error)

SetStandard quickly and easily composes and adds or replaces the tag using the information already known about a tag. Only works with standard tags.

func (*IfdBuilder) SetStandardWithName 

func (ib *IfdBuilder) SetStandardWithName(tagName string, value interface{}) (err error)

SetStandardWithName quickly and easily composes and adds or replaces the tag using the information already known about a tag (using the name). Only works with standard tags.

Example

ExampleIfdBuilder_SetStandardWithName establishes a chain of `IfdBuilder` structs from an existing chain of `Ifd` structs, navigates to the IB representing IFD0, updates the ProcessingSoftware tag to a different value, encodes down to a new EXIF block, reparses, and validates that the value for that tag is what we set it to. 

testImageFilepath := getTestImageFilepath()

rawExif, err := SearchFileAndExtractExif(testImageFilepath)
log.PanicIf(err)

// Boilerplate.

im := NewIfdMapping()

err = LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()

// Load current IFDs.

_, index, err := Collect(im, ti, rawExif)
log.PanicIf(err)

ib := NewIfdBuilderFromExistingChain(index.RootIfd)

// Read the IFD whose tag we want to change.

// Standard:
// - "IFD0"
// - "IFD0/Exif0"
// - "IFD0/Exif0/Iop0"
// - "IFD0/GPSInfo0"
//
// If the numeric indices are not included, (0) is the default. Note that
// this isn't strictly necessary in our case since IFD0 is the first IFD anyway, but we're putting it here to show usage.
ifdPath := "IFD0"

childIb, err := GetOrCreateIbFromRootIb(ib, ifdPath)
log.PanicIf(err)

// There are a few functions that allow you to surgically change the tags in an
// IFD, but we're just gonna overwrite a tag that has an ASCII value.

tagName := "ProcessingSoftware"

err = childIb.SetStandardWithName(tagName, "alternative software")
log.PanicIf(err)

// Encode the in-memory representation back down to bytes.

ibe := NewIfdByteEncoder()

updatedRawExif, err := ibe.EncodeToExif(ib)
log.PanicIf(err)

// Reparse the EXIF to confirm that our value is there.

_, index, err = Collect(im, ti, updatedRawExif)
log.PanicIf(err)

// This isn't strictly necessary for the same reason as above, but it's here
// for documentation.
childIfd, err := FindIfdFromRootIfd(index.RootIfd, ifdPath)
log.PanicIf(err)

results, err := childIfd.FindTagWithName(tagName)
log.PanicIf(err)

for _, ite := range results {
	valueRaw, err := ite.Value()
	log.PanicIf(err)

	stringValue := valueRaw.(string)
	fmt.Println(stringValue)
}

Output:

alternative software
Example (Timestamp) 
// Check initial value.

filepath := getTestGpsImageFilepath()

rawExif, err := SearchFileAndExtractExif(filepath)
log.PanicIf(err)

im := NewIfdMapping()

err = LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()

_, index, err := Collect(im, ti, rawExif)
log.PanicIf(err)

rootIfd := index.RootIfd

// Update the value.

rootIb := NewIfdBuilderFromExistingChain(rootIfd)

exifIb, err := rootIb.ChildWithTagId(exifcommon.IfdExifStandardIfdIdentity.TagId())
log.PanicIf(err)

t := time.Date(2020, 06, 7, 1, 30, 0, 0, time.UTC)

err = exifIb.SetStandardWithName("DateTimeDigitized", t)
log.PanicIf(err)

// Encode to bytes.

ibe := NewIfdByteEncoder()

updatedRawExif, err := ibe.EncodeToExif(rootIb)
log.PanicIf(err)

// Decode from bytes.

_, updatedIndex, err := Collect(im, ti, updatedRawExif)
log.PanicIf(err)

updatedRootIfd := updatedIndex.RootIfd

// Test.

updatedExifIfd, err := updatedRootIfd.ChildWithIfdPath(exifcommon.IfdExifStandardIfdIdentity)
log.PanicIf(err)

results, err := updatedExifIfd.FindTagWithName("DateTimeDigitized")
log.PanicIf(err)

ite := results[0]

phrase, err := ite.FormatFirst()
log.PanicIf(err)

fmt.Printf("%s\n", phrase)

Output:

2020:06:07 01:30:00
Example (UpdateGps) 
// Check initial value.

filepath := getTestGpsImageFilepath()

rawExif, err := SearchFileAndExtractExif(filepath)
log.PanicIf(err)

im := NewIfdMapping()

err = LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()

_, index, err := Collect(im, ti, rawExif)
log.PanicIf(err)

rootIfd := index.RootIfd

gpsIfd, err := rootIfd.ChildWithIfdPath(exifcommon.IfdGpsInfoStandardIfdIdentity)
log.PanicIf(err)

initialGi, err := gpsIfd.GpsInfo()
log.PanicIf(err)

fmt.Printf("Original:\n%s\n\n", initialGi.Latitude.String())

// Update the value.

rootIb := NewIfdBuilderFromExistingChain(rootIfd)

gpsIb, err := rootIb.ChildWithTagId(exifcommon.IfdGpsInfoStandardIfdIdentity.TagId())
log.PanicIf(err)

updatedGi := GpsDegrees{
	Degrees: 11,
	Minutes: 22,
	Seconds: 33,
}

raw := updatedGi.Raw()

err = gpsIb.SetStandardWithName("GPSLatitude", raw)
log.PanicIf(err)

// Encode to bytes.

ibe := NewIfdByteEncoder()

updatedRawExif, err := ibe.EncodeToExif(rootIb)
log.PanicIf(err)

// Decode from bytes.

_, updatedIndex, err := Collect(im, ti, updatedRawExif)
log.PanicIf(err)

updatedRootIfd := updatedIndex.RootIfd

// Test.

updatedGpsIfd, err := updatedRootIfd.ChildWithIfdPath(exifcommon.IfdGpsInfoStandardIfdIdentity)
log.PanicIf(err)

recoveredUpdatedGi, err := updatedGpsIfd.GpsInfo()
log.PanicIf(err)

fmt.Printf("Updated, written, and re-read:\n%s\n", recoveredUpdatedGi.Latitude.String())

Output:

Original:
Degrees<O=[N] D=(26) M=(35) S=(12)>

Updated, written, and re-read:
Degrees<O=[N] D=(11) M=(22) S=(33)>

func (*IfdBuilder) SetThumbnail 

func (ib *IfdBuilder) SetThumbnail(data []byte) (err error)

SetThumbnail sets thumbnail data.

NOTES:

  • We don't manage any facet of the thumbnail data. This is the responsibility of the user/developer.
  • This method will fail unless the thumbnail is set on a the root IFD. However, in order to be valid, it must be set on the second one, linked to by the first, as per the EXIF/TIFF specification.
  • We set the offset to (0) now but will allocate the data and properly assign the offset when the IB is encoded (later).

func (*IfdBuilder) String 

func (ib *IfdBuilder) String() string

func (*IfdBuilder) Tags 

func (ib *IfdBuilder) Tags() (tags []*BuilderTag)

func (*IfdBuilder) Thumbnail 

func (ib *IfdBuilder) Thumbnail() []byte

type IfdBuilderTagValue 

type IfdBuilderTagValue struct {
	// contains filtered or unexported fields
}

func NewIfdBuilderTagValueFromBytes 

func NewIfdBuilderTagValueFromBytes(valueBytes []byte) *IfdBuilderTagValue

func NewIfdBuilderTagValueFromIfdBuilder 

func NewIfdBuilderTagValueFromIfdBuilder(ib *IfdBuilder) *IfdBuilderTagValue

func (IfdBuilderTagValue) Bytes 

func (ibtv IfdBuilderTagValue) Bytes() []byte

func (IfdBuilderTagValue) Ib 

func (ibtv IfdBuilderTagValue) Ib() *IfdBuilder

func (IfdBuilderTagValue) IsBytes 

func (ibtv IfdBuilderTagValue) IsBytes() bool

IsBytes returns true if the bytes are populated. This is always the case when we're loaded from a tag in an existing IFD.

func (IfdBuilderTagValue) IsIb 

func (ibtv IfdBuilderTagValue) IsIb() bool

func (IfdBuilderTagValue) String 

func (ibtv IfdBuilderTagValue) String() string

type IfdByteEncoder 

type IfdByteEncoder struct {
	// contains filtered or unexported fields
}

IfdByteEncoder converts an IB to raw bytes (for writing) while also figuring out all of the allocations and indirection that is required for extended data.

func NewIfdByteEncoder 

func NewIfdByteEncoder() (ibe *IfdByteEncoder)

func (*IfdByteEncoder) EncodeToExif 

func (ibe *IfdByteEncoder) EncodeToExif(ib *IfdBuilder) (data []byte, err error)

EncodeToExif calls EncodeToExifPayload and then packages the result into a complete EXIF block.

Example 
// Construct an IFD.

im := NewIfdMapping()

err := LoadStandardIfds(im)
log.PanicIf(err)

ti := NewTagIndex()
ib := NewIfdBuilder(im, ti, exifcommon.IfdStandardIfdIdentity, exifcommon.TestDefaultByteOrder)

err = ib.AddStandardWithName("ProcessingSoftware", "asciivalue")
log.PanicIf(err)

err = ib.AddStandardWithName("DotRange", []uint8{0x11})
log.PanicIf(err)

err = ib.AddStandardWithName("SubfileType", []uint16{0x2233})
log.PanicIf(err)

err = ib.AddStandardWithName("ImageWidth", []uint32{0x44556677})
log.PanicIf(err)

err = ib.AddStandardWithName("WhitePoint", []exifcommon.Rational{{Numerator: 0x11112222, Denominator: 0x33334444}})
log.PanicIf(err)

err = ib.AddStandardWithName("ShutterSpeedValue", []exifcommon.SignedRational{{Numerator: 0x11112222, Denominator: 0x33334444}})
log.PanicIf(err)

// Encode it.

ibe := NewIfdByteEncoder()

exifData, err := ibe.EncodeToExif(ib)
log.PanicIf(err)

// Parse it so we can see it.

_, index, err := Collect(im, ti, exifData)
log.PanicIf(err)

for i, ite := range index.RootIfd.Entries {
	value, err := ite.Value()
	log.PanicIf(err)

	fmt.Printf("%d: %s [%v]\n", i, ite, value)
}

Output:


0: IfdTagEntry<TAG-IFD-PATH=[IFD] TAG-ID=(0x000b) TAG-TYPE=[ASCII] UNIT-COUNT=(11)> [asciivalue]
1: IfdTagEntry<TAG-IFD-PATH=[IFD] TAG-ID=(0x0150) TAG-TYPE=[BYTE] UNIT-COUNT=(1)> [[17]]
2: IfdTagEntry<TAG-IFD-PATH=[IFD] TAG-ID=(0x00ff) TAG-TYPE=[SHORT] UNIT-COUNT=(1)> [[8755]]
3: IfdTagEntry<TAG-IFD-PATH=[IFD] TAG-ID=(0x0100) TAG-TYPE=[LONG] UNIT-COUNT=(1)> [[1146447479]]
4: IfdTagEntry<TAG-IFD-PATH=[IFD] TAG-ID=(0x013e) TAG-TYPE=[RATIONAL] UNIT-COUNT=(1)> [[{286335522 858997828}]]
5: IfdTagEntry<TAG-IFD-PATH=[IFD] TAG-ID=(0x9201) TAG-TYPE=[SRATIONAL] UNIT-COUNT=(1)> [[{286335522 858997828}]]

func (*IfdByteEncoder) EncodeToExifPayload 

func (ibe *IfdByteEncoder) EncodeToExifPayload(ib *IfdBuilder) (data []byte, err error)

EncodeToExifPayload is the base encoding step that transcribes the entire IB structure to its on-disk layout.

func (*IfdByteEncoder) Journal 

func (ibe *IfdByteEncoder) Journal() [][3]string

func (*IfdByteEncoder) PrintJournal 

func (ibe *IfdByteEncoder) PrintJournal()

PrintJournal prints a hierarchical representation of the steps taken during encoding.

func (*IfdByteEncoder) TableSize 

func (ibe *IfdByteEncoder) TableSize(entryCount int) uint32

type IfdEnumerate 

type IfdEnumerate struct {
	// contains filtered or unexported fields
}

IfdEnumerate is the main enumeration type. It knows how to parse the IFD containers in the EXIF blob.

func NewIfdEnumerate 

func NewIfdEnumerate(ifdMapping *exifcommon.IfdMapping, tagIndex *TagIndex, exifData []byte, byteOrder binary.ByteOrder) *IfdEnumerate

NewIfdEnumerate returns a new instance of IfdEnumerate.

func (*IfdEnumerate) Collect 

func (ie *IfdEnumerate) Collect(rootIfdOffset uint32) (index IfdIndex, err error)

Collect enumerates the different EXIF blocks (called IFDs) and builds out an index struct for referencing all of the parsed data.

func (*IfdEnumerate) FurthestOffset 

func (ie *IfdEnumerate) FurthestOffset() uint32

FurthestOffset returns the furthest offset visited in the EXIF blob. This *does not* account for the locations of any undefined tags since we always evaluate the furthest offset, whether or not the user wants to know it.

We are not willing to incur the cost of actually parsing those tags just to know their length when there are still undefined tags that are out there that we still won't have any idea how to parse, thus making this an approximation regardless of how clever we get.

func (*IfdEnumerate) Scan 

func (ie *IfdEnumerate) Scan(iiRoot *exifcommon.IfdIdentity, ifdOffset uint32, visitor TagVisitorFn) (med *MiscellaneousExifData, err error)

Scan enumerates the different EXIF blocks (called IFDs). `rootIfdName` will be "IFD" in the TIFF standard.

type IfdIndex 

type IfdIndex struct {
	RootIfd *Ifd
	Ifds    []*Ifd
	Tree    map[int]*Ifd
	Lookup  map[string]*Ifd
}

IfdIndex collects a bunch of IFD and tag information stored in several different ways in order to provide convenient lookups.

type IfdTagEntry 

type IfdTagEntry struct {
	// contains filtered or unexported fields
}

IfdTagEntry refers to a tag in the loaded EXIF block.

func ParseOneIfd 

func ParseOneIfd(ifdMapping *exifcommon.IfdMapping, tagIndex *TagIndex, ii *exifcommon.IfdIdentity, byteOrder binary.ByteOrder, ifdBlock []byte, visitor TagVisitorFn) (nextIfdOffset uint32, entries []*IfdTagEntry, err error)

ParseOneIfd is a hack to use an IE to parse a raw IFD block. Can be used for testing. The fqIfdPath ("fully-qualified IFD path") will be less qualified in that the numeric index will always be zero (the zeroth child) rather than the proper number (if its actually a sibling to the first child, for instance).

func ParseOneTag 

func ParseOneTag(ifdMapping *exifcommon.IfdMapping, tagIndex *TagIndex, ii *exifcommon.IfdIdentity, byteOrder binary.ByteOrder, tagBlock []byte) (ite *IfdTagEntry, err error)

ParseOneTag is a hack to use an IE to parse a raw tag block.

func (*IfdTagEntry) ChildFqIfdPath 

func (ite *IfdTagEntry) ChildFqIfdPath() string

ChildFqIfdPath returns the complete path of the child IFD along with the numeric suffixes differentiating sibling occurrences of the same type. "0" indices are omitted.

func (*IfdTagEntry) ChildIfdName 

func (ite *IfdTagEntry) ChildIfdName() string

ChildIfdName returns the name of the child IFD

func (*IfdTagEntry) ChildIfdPath 

func (ite *IfdTagEntry) ChildIfdPath() string

ChildIfdPath returns the path of the child IFD.

func (*IfdTagEntry) Format 

func (ite *IfdTagEntry) Format() (phrase string, err error)

Format returns the tag's value as a string.

func (*IfdTagEntry) FormatFirst 

func (ite *IfdTagEntry) FormatFirst() (phrase string, err error)

FormatFirst returns the same as Format() but only the first item.

func (*IfdTagEntry) GetRawBytes 

func (ite *IfdTagEntry) GetRawBytes() (rawBytes []byte, err error)

GetRawBytes renders a specific list of bytes from the value in this tag.

func (*IfdTagEntry) IfdIdentity 

func (ite *IfdTagEntry) IfdIdentity() *exifcommon.IfdIdentity

IfdIdentity returns the IfdIdentity associated with this tag.

func (*IfdTagEntry) IfdPath 

func (ite *IfdTagEntry) IfdPath() string

IfdPath returns the fully-qualified path of the IFD that owns this tag.

func (*IfdTagEntry) IsThumbnailOffset 

func (ite *IfdTagEntry) IsThumbnailOffset() bool

IsThumbnailOffset returns true if the tag has the IFD and tag-ID of a thumbnail offset.

func (*IfdTagEntry) IsThumbnailSize 

func (ite *IfdTagEntry) IsThumbnailSize() bool

IsThumbnailSize returns true if the tag has the IFD and tag-ID of a thumbnail size.

func (*IfdTagEntry) SetChildIfd 

func (ite *IfdTagEntry) SetChildIfd(ii *exifcommon.IfdIdentity)

SetChildIfd sets child-IFD information (if we represent a child IFD).

func (*IfdTagEntry) String 

func (ite *IfdTagEntry) String() string

String returns a stringified representation of the struct.

func (*IfdTagEntry) TagId 

func (ite *IfdTagEntry) TagId() uint16

TagId returns the ID of the tag that we represent. The combination of (IfdPath(), TagId()) is unique.

func (*IfdTagEntry) TagName 

func (ite *IfdTagEntry) TagName() string

TagName returns the name of the tag. This is determined else and set after the parse (since it's not actually stored in the stream). If it's empty, it is because it is an unknown tag (nonstandard or otherwise unavailable in the tag-index).

func (*IfdTagEntry) TagType 

func (ite *IfdTagEntry) TagType() exifcommon.TagTypePrimitive

TagType is the type of value for this tag.

func (*IfdTagEntry) UnitCount 

func (ite *IfdTagEntry) UnitCount() uint32

UnitCount returns the unit-count of the tag's value.

func (*IfdTagEntry) Value 

func (ite *IfdTagEntry) Value() (value interface{}, err error)

Value returns the specific, parsed, typed value from the tag.

type IndexedTag 

type IndexedTag struct {
	// Id is the tag-ID.
	Id uint16

	// Name is the tag name.
	Name string

	// IfdPath is the proper IFD path of this tag. This is not fully-qualified.
	IfdPath string

	// SupportedTypes is an unsorted list of allowed tag-types.
	SupportedTypes []exifcommon.TagTypePrimitive
}

IndexedTag describes one index lookup result.

func (*IndexedTag) DoesSupportType 

func (it *IndexedTag) DoesSupportType(tagType exifcommon.TagTypePrimitive) bool

DoesSupportType returns true if this tag can be found/decoded with this type.

func (*IndexedTag) GetEncodingType 

func (it *IndexedTag) GetEncodingType(value interface{}) exifcommon.TagTypePrimitive

GetEncodingType returns the largest type that this tag's value can occupy.

func (*IndexedTag) Is 

func (it *IndexedTag) Is(ifdPath string, id uint16) bool

Is returns true if this tag matched the given tag ID.

func (*IndexedTag) IsName 

func (it *IndexedTag) IsName(ifdPath, name string) bool

IsName returns true if this tag matches the given tag name.

func (*IndexedTag) String 

func (it *IndexedTag) String() string

String returns a descriptive string.

type MiscellaneousExifData 

type MiscellaneousExifData struct {
	// contains filtered or unexported fields
}

MiscellaneousExifData is reports additional data collected during the parse.

func (*MiscellaneousExifData) UnknownTags 

func (med *MiscellaneousExifData) UnknownTags() map[exifcommon.BasicTag]exifcommon.BasicTag

UnknownTags returns the unknown tags encountered during the scan.

type ParsedTagVisitor 

type ParsedTagVisitor func(*Ifd, *IfdTagEntry) error

ParsedTagVisitor is a callback used if wanting to visit through all tags and child IFDs from the current IFD and going down.

type QueuedIfd 

type QueuedIfd struct {
	IfdIdentity *exifcommon.IfdIdentity

	Offset uint32
	Parent *Ifd

	// ParentTagIndex is our tag position in the parent IFD, if we had a parent
	// (if `ParentIfd` is not nil and we weren't an IFD referenced as a sibling
	// instead of as a child).
	ParentTagIndex int
}

QueuedIfd is one IFD that has been identified but yet to be processed.

type TagIndex 

type TagIndex struct {
	// contains filtered or unexported fields
}

TagIndex is a tag-lookup facility.

func NewTagIndex 

func NewTagIndex() *TagIndex

NewTagIndex returns a new TagIndex struct.

func (*TagIndex) Add 

func (ti *TagIndex) Add(it *IndexedTag) (err error)

Add registers a new tag to be recognized during the parse.

func (*TagIndex) FindFirst 

func (ti *TagIndex) FindFirst(id uint16, typeId exifcommon.TagTypePrimitive, ifdIdentities []*exifcommon.IfdIdentity) (it *IndexedTag, err error)

FindFirst looks for the given tag-ID in each of the given IFDs in the given order. If `fqIfdPaths` is `nil` then use a default search order. This defies the standard, which requires each tag to exist in certain IFDs. This is a contingency to make recommendations for malformed data.

Things *can* end badly here, in that the same tag-ID in different IFDs might describe different data and different ata-types, and our decode might then produce binary and non-printable data.

func (*TagIndex) Get 

func (ti *TagIndex) Get(ii *exifcommon.IfdIdentity, id uint16) (it *IndexedTag, err error)

Get returns information about the non-IFD tag given a tag ID. `ifdPath` must not be fully-qualified.

func (*TagIndex) GetWithName 

func (ti *TagIndex) GetWithName(ii *exifcommon.IfdIdentity, name string) (it *IndexedTag, err error)

GetWithName returns information about the non-IFD tag given a tag name.

type TagVisitorFn 

type TagVisitorFn func(fqIfdPath string, ifdIndex int, ite *IfdTagEntry) (err error)

TagVisitorFn is called for each tag when enumerating through the EXIF.

Source Files

View all Source files

Directories

Path Synopsis
This tool dumps EXIF information from images.
 This tool dumps EXIF information from images.

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