Improve Base62 encoding/decoding performance and robustness

base62/base62.go

@@ -3,56 +3,75 @@ package base62
 import (
 	"fmt"
 	"math"
-	"strings"
 )
 
 const (
-	alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
-	base     = uint32(len(alphabet))
+	alphabet        = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+	base            = uint32(len(alphabet))
+	maxBase62Digits = 6 // max number of digits required to encode MaxUint32
+
 )
 
-// Encode encodes a uint32 value to a base62 string.
-func Encode(num uint32) string {
-	if num == 0 {
-		return string(alphabet[0])
+var (
+	ErrEmptyString = fmt.Errorf("empty string")
+	ErrInvalidChar = fmt.Errorf("invalid character")
+	ErrOverflow    = fmt.Errorf("integer overflow")
+)
+
+// Fixed-size arrays have better performance and lower memory overhead compared to maps for small static sets of data
+var charToIndex [123]int8 // Assuming ASCII from '\0' - 'z'
+
+func init() {
+	for i := range charToIndex {
+		charToIndex[i] = -1
+	}
+	for i, c := range alphabet {
+		charToIndex[c] = int8(i)
 	}
+}
 
-	var encoded strings.Builder
+// Encode encodes a uint32 value to a base62 string.
+// The returned string will be between 1-6 characters long.
+func Encode(n uint32) string {
+	if n < base {
+		return string(alphabet[n])
+	}
+	// avoid dynamic memory usage for small, fixed size data
+	buf := [maxBase62Digits]byte{}
+	idx := len(buf)
 
-	for num > 0 {
-		remainder := num % base
-		encoded.WriteByte(alphabet[remainder])
-		num /= base
+	for n > 0 {
+		idx--
+		buf[idx] = alphabet[n%base]
+		n /= base
 	}
 
-	// Reverse the encoded string
-	encodedString := encoded.String()
-	reversed := reverse(encodedString)
-	return reversed
+	return string(buf[idx:])
 }
 
 // Decode decodes a base62 string to a uint32 value.
+// Returns an error if the input string is empty, contains invalid characters,
+// or would result in integer overflow.
 func Decode(encoded string) (uint32, error) {
+	if len(encoded) == 0 {
+		return 0, ErrEmptyString
+	}
 	var decoded uint32
-	strLen := len(encoded)
-
-	for i, char := range encoded {
-		index := strings.IndexRune(alphabet, char)
+	for _, char := range encoded {
+		index := int8(-1)
+		if int(char) < len(charToIndex) {
+			index = charToIndex[char]
+		}
 		if index < 0 {
-			return 0, fmt.Errorf("invalid character: %c", char)
+			return 0, fmt.Errorf("%w: %c", ErrInvalidChar, char)
+		}
+		// Add overflow check when calculating the decoded value to prevent silent overflow of uint32
+		if decoded > (math.MaxUint32-uint32(index))/base {
+			return 0, fmt.Errorf("%w: %s", ErrOverflow, encoded)
 		}
 
-		decoded += uint32(index) * uint32(math.Pow(float64(base), float64(strLen-i-1)))
+		decoded = decoded*base + uint32(index)
 	}
 
 	return decoded, nil
 }
-
-// Reverse a string.
-func reverse(s string) string {
-	runes := []rune(s)
-	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
-		runes[i], runes[j] = runes[j], runes[i]
-	}
-	return string(runes)
-}

base62/base62_test.go

@@ -1,31 +1,67 @@
 package base62
 
 import (
+	"errors"
+	"math"
 	"testing"
 )
 
 func TestEncodeDecode(t *testing.T) {
-	tests := []struct {
-		num uint32
+	testCases := []struct {
+		input    uint32
+		expected string
 	}{
-		{0},
-		{1},
-		{42},
-		{12345},
-		{99999},
-		{123456789},
+		{0, "0"},
+		{1, "1"},
+		{5, "5"},
+		{9, "9"},
+		{10, "A"},
+		{42, "g"},
+		{61, "z"},
+		{62, "10"},
+		{'0', "m"},
+		{'9', "v"},
+		{'A', "13"},
+		{'Z', "1S"},
+		{'a', "1Z"},
+		{'z', "1y"},
+		{99999, "Q0t"},
+		{12345, "3D7"},
+		{123456789, "8M0kX"},
+		{math.MaxUint32, "4gfFC3"},
 	}
 
-	for _, tt := range tests {
-		encoded := Encode(tt.num)
+	for _, tc := range testCases {
+		encoded := Encode(tc.input)
+		if encoded != tc.expected {
+			t.Errorf("Encode(%d) = %s; want %s", tc.input, encoded, tc.expected)
+		}
 		decoded, err := Decode(encoded)
-
 		if err != nil {
-			t.Errorf("Decode error: %v", err)
+			t.Errorf("Expected error nil, got %v", err)
 		}
 
-		if decoded != tt.num {
-			t.Errorf("Decode(%v) = %v, want %v", encoded, decoded, tt.num)
+		if decoded != tc.input {
+			t.Errorf("Decode(%v) = %v, want %v", encoded, decoded, tc.input)
 		}
 	}
 }
+
+// Decode handles empty string input with appropriate error
+func TestDecodeEmptyString(t *testing.T) {
+	if _, err := Decode(""); !errors.Is(err, ErrEmptyString) {
+		t.Errorf("Expected error %v, got %v", ErrEmptyString, err)
+	}
+}
+
+func TestDecodeOverflow(t *testing.T) {
+	if _, err := Decode("4gfFC4"); !errors.Is(err, ErrOverflow) {
+		t.Errorf("Expected error %v, got %v", ErrOverflow, err)
+	}
+}
+
+func TestDecodeInvalid(t *testing.T) {
+	if _, err := Decode("/"); !errors.Is(err, ErrInvalidChar) {
+		t.Errorf("Expected error %v, got %v", ErrInvalidChar, err)
+	}
+}