imagehash: Add new serialization API dump/load. (#24)

Create a new APIs for serializing purpose which can use
standard io.Reader/io.Writer APIs.

ToString() API will be remain for debugging purpose and
ExtImageHashFromString, ImageHashFromString will be removed after next
version.

- New APIs are added: LoadExtImageHash, LoadImageHash, xxxHash.Dump
- These APIs are deprecated: ExtImageHashFromString, ImageHashFromString

README.md

@@ -45,8 +45,8 @@ func main() {
 ## Release Note
 
 ### v0.4.0(TBA)
-- **IMPORTANT** goimagehash does not have compatible with the before version
-when it comes to the serialization based on string. bit set order is changed.
+- **IMPORTANT** goimagehash v0.0.4 does not have compatible with the before
+version when it comes to the serialization.
 
 ### v0.3.0
 - Support DifferenceHashExtend.

_examples/load_and_dump.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"github.com/corona10/goimagehash"
+	"image/jpeg"
+	"os"
+)
+
+func main() {
+	file1, _ := os.Open("sample1.jpg")
+	file2, _ := os.Open("sample2.jpg")
+	defer file1.Close()
+	defer file2.Close()
+	var b bytes.Buffer
+	foo := bufio.NewWriter(&b)
+	img1, _ := jpeg.Decode(file1)
+	img2, _ := jpeg.Decode(file2)
+	hash1, _ := goimagehash.AverageHashExtend(img1, 15)
+	hash2, _ := goimagehash.AverageHashExtend(img2, 15)
+	distance, _ := hash1.Distance(hash2)
+	fmt.Printf("Distance between images: %v\n", distance)
+
+	err := hash1.Dump(foo)
+	if err != nil {
+		fmt.Println(err)
+	}
+	foo.Flush()
+	bar := bufio.NewReader(&b)
+	hash3, err := goimagehash.LoadImageHashExtend(bar)
+	if err != nil {
+		fmt.Println(err)
+	}
+	distance, _ = hash1.Distance(hash3)
+	fmt.Printf("Distance between hash1 and hash3: %v\n", distance)
+	distance, _ = hash2.Distance(hash3)
+	fmt.Printf("Distance between hash2 and hash3: %v\n", distance)
+	fmt.Println(hash1.ToString())
+	fmt.Println(hash2.ToString())
+	fmt.Println(hash3.ToString())
+}

imagehash.go

@@ -6,9 +6,11 @@ package goimagehash
 
 import (
 	"encoding/binary"
+	"encoding/gob"
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"io"
 )
 
 // Kind describes the kinds of hash.
@@ -73,7 +75,38 @@ func (h *ImageHash) leftShiftSet(idx int) {
 
 const strFmt = "%1s:%016x"
 
+// Dump method writes a binary serialization into w io.Writer.
+func (h *ImageHash) Dump(w io.Writer) error {
+	type D struct {
+		Hash uint64
+		Kind Kind
+	}
+	enc := gob.NewEncoder(w)
+	err := enc.Encode(D{Hash: h.hash, Kind: h.kind})
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// LoadImageHash method loads a ExtImageHash from io.Reader.
+func LoadImageHash(b io.Reader) (*ImageHash, error) {
+	type E struct {
+		Hash uint64
+		Kind Kind
+	}
+	var e E
+	dec := gob.NewDecoder(b)
+	err := dec.Decode(&e)
+	if err != nil {
+		return nil, err
+	}
+	return &ImageHash{hash: e.Hash, kind: e.Kind}, nil
+}
+
 // ImageHashFromString returns an image hash from a hex representation
+//
+// Deprecated: Use goimagehash.LoadImageHash instead.
 func ImageHashFromString(s string) (*ImageHash, error) {
 	var kindStr string
 	var hash uint64
@@ -148,9 +181,40 @@ func (h *ExtImageHash) GetKind() Kind {
 	return h.kind
 }
 
+// Dump method writes a binary serialization into w io.Writer.
+func (h *ExtImageHash) Dump(w io.Writer) error {
+	type D struct {
+		Hash []uint64
+		Kind Kind
+	}
+	enc := gob.NewEncoder(w)
+	err := enc.Encode(D{Hash: h.hash, Kind: h.kind})
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// LoadImageHashExtend method loads a ExtImageHash from io.Reader.
+func LoadImageHashExtend(b io.Reader) (*ExtImageHash, error) {
+	type E struct {
+		Hash []uint64
+		Kind Kind
+	}
+	var e E
+	dec := gob.NewDecoder(b)
+	err := dec.Decode(&e)
+	if err != nil {
+		return nil, err
+	}
+	return &ExtImageHash{hash: e.Hash, kind: e.Kind}, nil
+}
+
 const extStrFmt = "%1s:%s"
 
 // ExtImageHashFromString returns a big hash from a hex representation
+//
+// Deprecated: Use goimagehash.LoadImageHashExtend instead.
 func ExtImageHashFromString(s string) (*ExtImageHash, error) {
 	var kindStr string
 	var hashStr string

imagehash_test.go

@@ -5,6 +5,8 @@
 package goimagehash
 
 import (
+	"bufio"
+	"bytes"
 	"errors"
 	"image"
 	_ "image/jpeg"
@@ -124,3 +126,76 @@ func TestSerialization(t *testing.T) {
 		}
 	}
 }
+
+func TestDumpAndLoad(t *testing.T) {
+	checkErr := func(err error) {
+		if err != nil {
+			t.Errorf("%v", err)
+		}
+	}
+
+	methods := []func(img image.Image) (*ImageHash, error){
+		AverageHash, PerceptionHash, DifferenceHash,
+	}
+	examples := []string{
+		"_examples/sample1.jpg", "_examples/sample2.jpg", "_examples/sample3.jpg", "_examples/sample4.jpg",
+	}
+
+	for _, ex := range examples {
+		file, err := os.Open(ex)
+		checkErr(err)
+
+		defer file.Close()
+
+		img, _, err := image.Decode(file)
+		checkErr(err)
+
+		for _, method := range methods {
+			hash, err := method(img)
+			checkErr(err)
+			var b bytes.Buffer
+			foo := bufio.NewWriter(&b)
+			err = hash.Dump(foo)
+			checkErr(err)
+			foo.Flush()
+			bar := bufio.NewReader(&b)
+			reHash, err := LoadImageHash(bar)
+			checkErr(err)
+
+			distance, err := hash.Distance(reHash)
+			checkErr(err)
+
+			if distance != 0 {
+				t.Errorf("Original and unserialized objects should be identical, got distance=%v", distance)
+			}
+		}
+
+		// test for ExtIExtImageHash
+		extMethods := []func(img image.Image, hashSize int) (*ExtImageHash, error){
+			AverageHashExtend, PerceptionHashExtend, DifferenceHashExtend,
+		}
+
+		hashSizeList := []int{8, 16}
+		for _, hashSize := range hashSizeList {
+			for _, method := range extMethods {
+				hash, err := method(img, hashSize)
+				checkErr(err)
+				var b bytes.Buffer
+				foo := bufio.NewWriter(&b)
+				err = hash.Dump(foo)
+				checkErr(err)
+				foo.Flush()
+				bar := bufio.NewReader(&b)
+				reHash, err := LoadImageHashExtend(bar)
+				checkErr(err)
+
+				distance, err := hash.Distance(reHash)
+				checkErr(err)
+
+				if distance != 0 {
+					t.Errorf("Original and unserialized objects should be identical, got distance=%v", distance)
+				}
+			}
+		}
+	}
+}