encoding/base32: reduce the overflow risk when computing encode/decode length

src/encoding/base32/base32.go

@@ -271,7 +271,7 @@ func NewEncoder(enc *Encoding, w io.Writer) io.WriteCloser {
 // of an input buffer of length n.
 func (enc *Encoding) EncodedLen(n int) int {
 	if enc.padChar == NoPadding {
-		return (n*8 + 4) / 5
+		return n/5*8 + (n%5*8+4)/5
 	}
 	return (n + 4) / 5 * 8
 }
@@ -545,8 +545,7 @@ func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
 // corresponding to n bytes of base32-encoded data.
 func (enc *Encoding) DecodedLen(n int) int {
 	if enc.padChar == NoPadding {
-		return n * 5 / 8
+		return n/8*5 + n%8*5/8
 	}
-
 	return n / 8 * 5
 }

src/encoding/base32/base32_test.go

@@ -8,6 +8,8 @@ import (
 	"bytes"
 	"errors"
 	"io"
+	"math"
+	"strconv"
 	"strings"
 	"testing"
 )
@@ -679,52 +681,86 @@ func TestBufferedDecodingPadding(t *testing.T) {
 	}
 }
 
-func TestEncodedDecodedLen(t *testing.T) {
+func TestEncodedLen(t *testing.T) {
+	var rawStdEncoding = StdEncoding.WithPadding(NoPadding)
 	type test struct {
-		in      int
-		wantEnc int
-		wantDec int
-	}
-	data := bytes.Repeat([]byte("x"), 100)
-	for _, test := range []struct {
-		name  string
 		enc  *Encoding
-		cases []test
+		n    int
-	}{
+		want int64
-		{"StdEncoding", StdEncoding, []test{
-			{0, 0, 0},
-			{1, 8, 5},
-			{5, 8, 5},
-			{6, 16, 10},
-			{10, 16, 10},
-		}},
-		{"NoPadding", StdEncoding.WithPadding(NoPadding), []test{
-			{0, 0, 0},
-			{1, 2, 1},
-			{2, 4, 2},
-			{5, 8, 5},
-			{6, 10, 6},
-			{7, 12, 7},
-			{10, 16, 10},
-			{11, 18, 11},
-		}},
-	} {
-		t.Run(test.name, func(t *testing.T) {
-			for _, tc := range test.cases {
-				encLen := test.enc.EncodedLen(tc.in)
-				decLen := test.enc.DecodedLen(encLen)
-				enc := test.enc.EncodeToString(data[:tc.in])
-				if len(enc) != encLen {
-					t.Fatalf("EncodedLen(%d) = %d but encoded to %q (%d)", tc.in, encLen, enc, len(enc))
 	}
-				if encLen != tc.wantEnc {
+	tests := []test{
-					t.Fatalf("EncodedLen(%d) = %d; want %d", tc.in, encLen, tc.wantEnc)
+		{StdEncoding, 0, 0},
+		{StdEncoding, 1, 8},
+		{StdEncoding, 2, 8},
+		{StdEncoding, 3, 8},
+		{StdEncoding, 4, 8},
+		{StdEncoding, 5, 8},
+		{StdEncoding, 6, 16},
+		{StdEncoding, 10, 16},
+		{StdEncoding, 11, 24},
+		{rawStdEncoding, 0, 0},
+		{rawStdEncoding, 1, 2},
+		{rawStdEncoding, 2, 4},
+		{rawStdEncoding, 3, 5},
+		{rawStdEncoding, 4, 7},
+		{rawStdEncoding, 5, 8},
+		{rawStdEncoding, 6, 10},
+		{rawStdEncoding, 7, 12},
+		{rawStdEncoding, 10, 16},
+		{rawStdEncoding, 11, 18},
 	}
-				if decLen != tc.wantDec {
+	// check overflow
-					t.Fatalf("DecodedLen(%d) = %d; want %d", encLen, decLen, tc.wantDec)
+	switch strconv.IntSize {
+	case 32:
+		tests = append(tests, test{rawStdEncoding, (math.MaxInt-4)/8 + 1, 429496730})
+		tests = append(tests, test{rawStdEncoding, math.MaxInt/8*5 + 4, math.MaxInt})
+	case 64:
+		tests = append(tests, test{rawStdEncoding, (math.MaxInt-4)/8 + 1, 1844674407370955162})
+		tests = append(tests, test{rawStdEncoding, math.MaxInt/8*5 + 4, math.MaxInt})
+	}
+	for _, tt := range tests {
+		if got := tt.enc.EncodedLen(tt.n); int64(got) != tt.want {
+			t.Errorf("EncodedLen(%d): got %d, want %d", tt.n, got, tt.want)
 		}
 	}
-		})
+}
+
+func TestDecodedLen(t *testing.T) {
+	var rawStdEncoding = StdEncoding.WithPadding(NoPadding)
+	type test struct {
+		enc  *Encoding
+		n    int
+		want int64
+	}
+	tests := []test{
+		{StdEncoding, 0, 0},
+		{StdEncoding, 8, 5},
+		{StdEncoding, 16, 10},
+		{StdEncoding, 24, 15},
+		{rawStdEncoding, 0, 0},
+		{rawStdEncoding, 2, 1},
+		{rawStdEncoding, 4, 2},
+		{rawStdEncoding, 5, 3},
+		{rawStdEncoding, 7, 4},
+		{rawStdEncoding, 8, 5},
+		{rawStdEncoding, 10, 6},
+		{rawStdEncoding, 12, 7},
+		{rawStdEncoding, 16, 10},
+		{rawStdEncoding, 18, 11},
+	}
+	// check overflow
+	switch strconv.IntSize {
+	case 32:
+		tests = append(tests, test{rawStdEncoding, math.MaxInt/5 + 1, 268435456})
+		tests = append(tests, test{rawStdEncoding, math.MaxInt, 1342177279})
+	case 64:
+		tests = append(tests, test{rawStdEncoding, math.MaxInt/5 + 1, 1152921504606846976})
+		tests = append(tests, test{rawStdEncoding, math.MaxInt, 5764607523034234879})
+	}
+	for _, tt := range tests {
+		if got := tt.enc.DecodedLen(tt.n); int64(got) != tt.want {
+			t.Errorf("DecodedLen(%d): got %d, want %d", tt.n, got, tt.want)
+		}
 	}
 }