encoding/base32: fix buffer without padding

If unpadded content was passed, in some occassions content was omitted,
because the division result was floored. Ceiling it makes sure all
content is always read.

Fixes golang#65166

Signed-off-by: Niklas Ott <ceriath12@gmail.com>

src/encoding/base32/base32.go

@@ -7,6 +7,7 @@ package base32
 
 import (
 	"io"
+	"math"
 	"slices"
 	"strconv"
 )
@@ -467,7 +468,7 @@ func (d *decoder) Read(p []byte) (n int, err error) {
 	}
 
 	// Read a chunk.
-	nn := len(p) / 5 * 8
+	nn := int(math.Ceil(float64(len(p))/float64(5)) * 8)
 	if nn < 8 {
 		nn = 8
 	}

src/encoding/base32/base32_test.go

@@ -92,6 +92,24 @@ func TestEncoderBuffering(t *testing.T) {
 	}
 }
 
+func TestDecoderBufferingAll(t *testing.T) {
+	for bs := 0; bs <= 12; bs++ {
+		for _, s := range pairs {
+			decoder := NewDecoder(StdEncoding, strings.NewReader(s.encoded))
+			buf := make([]byte, len(s.decoded)+bs)
+
+			var n int
+			var err error
+			n, err = decoder.Read(buf)
+
+			if err != nil && err != io.EOF {
+				t.Errorf("Read from %q at pos %d = %d, unexpected error %v", s.encoded, len(s.decoded), n, err)
+			}
+			testEqual(t,"Decoding/%d of %q = %q, want %q\n", bs, s.encoded, string(buf[:n]), s.decoded)
+		}
+	}
+}
+
 func TestDecode(t *testing.T) {
 	for _, p := range pairs {
 		dbuf := make([]byte, StdEncoding.DecodedLen(len(p.encoded)))