Merge pull request #46 from dolmen-go/fix-EncodeHex

Fix EncodeHex/DecodeHex

hashids.go

@@ -10,7 +10,6 @@ import (
 	"errors"
 	"fmt"
 	"math"
-	"strconv"
 	"strings"
 )
 
@@ -224,16 +223,26 @@ func (h *HashID) EncodeInt64(numbers []int64) (string, error) {
 // EncodeHex hashes a hexadecimal string to a string containing at least MinLength characters taken from the Alphabet.
 // A hexadecimal string should not contain the 0x prefix.
 // Use DecodeHex using the same Alphabet and Salt to get back the hexadecimal string.
+//
+// Each hex nibble is encoded as an integer in range [16, 31].
 func (h *HashID) EncodeHex(hex string) (string, error) {
-	chars := []rune(hex)
-	nums := []int{}
-
-	for _, s := range chars {
-		n, err := strconv.ParseInt(fmt.Sprintf("1%s", string(s)), 16, 64)
-		if err != nil {
-			return "", err
+	nums := make([]int, len(hex))
+
+	for i := 0; i < len(hex); i++ {
+		b := hex[i]
+		switch {
+		case (b >= '0') && (b <= '9'):
+			b -= '0'
+		case (b >= 'a') && (b <= 'f'):
+			b -= 'a' - 'A'
+			fallthrough
+		case (b >= 'A') && (b <= 'F'):
+			b -= ('A' - 0xA)
+		default:
+			return "", errors.New("invalid hex digit")
 		}
-		nums = append(nums, int(n))
+		// Each int is in range [16, 31]
+		nums[i] = 0x10 + int(b)
 	}
 
 	return h.Encode(nums)
@@ -322,19 +331,23 @@ func (h *HashID) DecodeInt64WithError(hash string) ([]int64, error) {
 
 // DecodeHex unhashes the string passed to a hexadecimal string.
 // It is symmetric with EncodeHex if the Alphabet and Salt are the same ones which were used to hash.
+//
+// Each hex nibble is decoded from an integer in range [16, 31].
 func (h *HashID) DecodeHex(hash string) (string, error) {
 	numbers, err := h.DecodeInt64WithError(hash)
 	if err != nil {
 		return "", err
 	}
 
-	ret := ""
-	for _, n := range numbers {
-		nHex := fmt.Sprintf("%X", n)
-		ret = strings.ToLower(fmt.Sprintf("%s%s", ret, nHex[1:len(nHex)]))
+	const hex = "0123456789abcdef"
+	b := make([]byte, len(numbers))
+	for i, n := range numbers {
+		if n < 0x10 || n > 0x1f {
+			return "", errors.New("invalid number")
+		}
+		b[i] = hex[n-0x10]
 	}
-
-	return ret, nil
+	return string(b), nil
 }
 
 func splitRunes(input, seps []rune) [][]rune {

hashids_test.go

@@ -61,6 +61,11 @@ func TestEncodeDecodeHex(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	const expected = "qmTqfesOIqHrsoCYf9UkFZixSKuBT4umuruXuMiDsVsbSrfV"
+	if hash != expected {
+		t.Fatalf("got %q, expected %q", hash, expected)
+	}
+
 	dec, err := hid.DecodeHex(hash)
 	if err != nil {
 		t.Fatal(err)