exif: Improve performance

Also, do not return an error when input format isn't supported. Just return `nil` exif.

Using the stream API and avoid creating the Ifd mapping and tag index every time makes it faster:

```
name           old time/op    new time/op    delta
DecodeExif-16    3.42ms ± 0%    0.65ms ± 0%  -81.12%  (p=0.029 n=4+4)

name           old alloc/op   new alloc/op   delta
DecodeExif-16    1.51MB ± 0%    0.59MB ± 0%  -60.77%  (p=0.029 n=4+4)

name           old allocs/op  new allocs/op  delta
DecodeExif-16     12.9k ± 0%      1.9k ± 0%  -85.48%  (p=0.029 n=4+4)
```

It's still slower than what we had, though, but correctness comes at a cost:

```

name           old time/op    new time/op    delta
DecodeExif-16     186µs ± 0%     648µs ± 1%  +249.21%  (p=0.029 n=4+4)

name           old alloc/op   new alloc/op   delta
DecodeExif-16     184kB ± 0%     593kB ± 0%  +222.38%  (p=0.029 n=4+4)

name           old allocs/op  new allocs/op  delta
DecodeExif-16     1.20k ± 0%     1.88k ± 0%   +55.99%  (p=0.029 n=4+4)
```

See #8586

go.mod

@@ -72,3 +72,6 @@ require (
 )
 
 go 1.16
+
+
+replace github.com/dsoprea/go-exif/v3 => /Users/bep/dev/go/dump/go-exif/v3

resources/images/exif/exif.go

@@ -14,9 +14,7 @@
 package exif
 
 import (
-	"fmt"
 	"io"
-	"io/ioutil"
 	"math/big"
 	"regexp"
 	"strings"
@@ -26,7 +24,6 @@ import (
 
 	_exif "github.com/dsoprea/go-exif/v3"
 	exifcommon "github.com/dsoprea/go-exif/v3/common"
-	png "github.com/dsoprea/go-png-image-structure"
 )
 
 const (
@@ -47,6 +44,9 @@ type Decoder struct {
 	excludeFieldsrRe *regexp.Regexp
 	noDate           bool
 	noLatLong        bool
+
+	idfm *exifcommon.IfdMapping
+	ti   *_exif.TagIndex
 }
 
 func IncludeFields(expression string) func(*Decoder) error {
@@ -99,7 +99,12 @@ func compileRegexp(expression string) (*regexp.Regexp, error) {
 }
 
 func NewDecoder(options ...func(*Decoder) error) (*Decoder, error) {
-	d := &Decoder{}
+	im, err := exifcommon.NewIfdMappingWithStandard()
+	if err != nil {
+		return nil, err
+	}
+	ti := _exif.NewTagIndex()
+	d := &Decoder{idfm: im, ti: ti}
 	for _, opt := range options {
 		if err := opt(d); err != nil {
 			return nil, err
@@ -110,28 +115,14 @@ func NewDecoder(options ...func(*Decoder) error) (*Decoder, error) {
 }
 
 func (d *Decoder) Decode(r io.Reader) (*Exif, error) {
-	rawBytes, err := ioutil.ReadAll(r)
-	if err != nil {
-		return nil, err
-	}
-	rawExif, err := _exif.SearchAndExtractExif(rawBytes)
+	rawExif, err := _exif.SearchAndExtractExifWithReader(r)
 
 	if err != nil {
-		parsed := png.NewPngMediaParser()
-		if parsed.LooksLikeFormat(rawBytes) {
-			return nil, fmt.Errorf("type not supported")
-		}
 		// No Exif data
 		return nil, nil
 	}
 
-	im, err := exifcommon.NewIfdMappingWithStandard()
-	if err != nil {
-		return nil, err
-	}
-	ti := _exif.NewTagIndex()
-
-	_, index, err := _exif.Collect(im, ti, rawExif)
+	_, index, err := _exif.Collect(d.idfm, d.ti, rawExif)
 	if err != nil {
 		return nil, err
 	}

resources/images/exif/exif_test.go

@@ -14,13 +14,16 @@
 package exif
 
 import (
+	"context"
 	"encoding/json"
+	"errors"
 	"math/big"
 	"os"
 	"path/filepath"
 	"testing"
 	"time"
 
+	"github.com/gohugoio/hugo/common/para"
 	"github.com/gohugoio/hugo/htesting/hqt"
 	"github.com/google/go-cmp/cmp"
 
@@ -62,6 +65,42 @@ func TestExif(t *testing.T) {
 	c.Assert(x2, eq, x)
 }
 
+func TestExifParallel(t *testing.T) {
+	c := qt.New(t)
+
+	d, err := NewDecoder(IncludeFields("Lens|Date"))
+	c.Assert(err, qt.IsNil)
+
+	p := para.New(4)
+	r, _ := p.Start(context.Background())
+
+	for i := 0; i < 20; i++ {
+		r.Run(func() error {
+			f, err := os.Open(filepath.FromSlash("../../testdata/sunset.jpg"))
+			if err != nil {
+				return err
+			}
+			defer f.Close()
+
+			x, err := d.Decode(f)
+			if err != nil {
+				return err
+			}
+
+			if x.Date.Format("2006-01-02") != "2017-10-27" {
+				return errors.New("invalid date")
+			}
+
+			return nil
+
+		})
+
+	}
+
+	c.Assert(r.Wait(), qt.IsNil)
+
+}
+
 func TestImageWithoutExifData(t *testing.T) {
 	c := qt.New(t)
 	f, err := os.Open(filepath.FromSlash("../../testdata/sunset_without_exif.jpg"))
@@ -143,8 +182,9 @@ func TestExifPNG(t *testing.T) {
 
 	d, err := NewDecoder()
 	c.Assert(err, qt.IsNil)
-	_, err = d.Decode(f)
-	c.Assert(err, qt.Not(qt.IsNil))
+	x, err := d.Decode(f)
+	c.Assert(err, qt.IsNil)
+	c.Assert(x, qt.IsNil)
 }
 
 func TestIssue8079(t *testing.T) {