encoding/base32: handle NoPadding in NewDecoder

This change adds functionality to properly handle NoPadding in NewDecoder.

Removes the following expectations when using NoPadding:

* the input message length is a multiple of 8
* the input message length is 0, or longer than 7 characters

Fixes #25332

src/encoding/base32/base32.go

@@ -404,7 +404,7 @@ type decoder struct {
 	outbuf [1024 / 8 * 5]byte
 }
 
-func readEncodedData(r io.Reader, buf []byte, min int) (n int, err error) {
+func readEncodedData(r io.Reader, buf []byte, min int, expectsPadding bool) (n int, err error) {
 	for n < min && err == nil {
 		var nn int
 		nn, err = r.Read(buf[n:])
@@ -415,7 +415,9 @@ func readEncodedData(r io.Reader, buf []byte, min int) (n int, err error) {
 		err = io.ErrUnexpectedEOF
 	}
 	// no data was read, the buffer already contains some data
-	if min < 8 && n == 0 && err == io.EOF {
+	// when padding is disabled this is not an error, as the message can be of
+	// any length
+	if expectsPadding && min < 8 && n == 0 && err == io.EOF {
 		err = io.ErrUnexpectedEOF
 	}
 	return
@@ -445,15 +447,32 @@ func (d *decoder) Read(p []byte) (n int, err error) {
 		nn = len(d.buf)
 	}
 
-	nn, d.err = readEncodedData(d.r, d.buf[d.nbuf:nn], 8-d.nbuf)
+	// Minimum amount of bytes that needs to be read each cycle
+	var min int
+	var expectsPadding bool
+	if d.enc.padChar == NoPadding {
+		min = 1
+		expectsPadding = false
+	} else {
+		min = 8 - d.nbuf
+		expectsPadding = true
+	}
+
+	nn, d.err = readEncodedData(d.r, d.buf[d.nbuf:nn], min, expectsPadding)
 	d.nbuf += nn
-	if d.nbuf < 8 {
+	if d.nbuf < min {
 		return 0, d.err
 	}
 
 	// Decode chunk into p, or d.out and then p if p is too small.
-	nr := d.nbuf / 8 * 8
-	nw := d.nbuf / 8 * 5
+	var nr int
+	if d.enc.padChar == NoPadding {
+		nr = d.nbuf
+	} else {
+		nr = d.nbuf / 8 * 8
+	}
+	nw := d.enc.DecodedLen(d.nbuf)
+
 	if nw > len(p) {
 		nw, d.end, err = d.enc.decode(d.outbuf[0:], d.buf[0:nr])
 		d.out = d.outbuf[0:nw]

src/encoding/base32/base32_test.go

@@ -686,3 +686,66 @@ func TestWithoutPaddingClose(t *testing.T) {
 		}
 	}
 }
+
+func TestDecodeReadAll(t *testing.T) {
+	encodings := []*Encoding{
+		StdEncoding,
+		StdEncoding.WithPadding(NoPadding),
+	}
+
+	for _, pair := range pairs {
+		for encIndex, encoding := range encodings {
+			encoded := pair.encoded
+			if encoding.padChar == NoPadding {
+				encoded = strings.Replace(encoded, "=", "", -1)
+			}
+
+			decReader, err := ioutil.ReadAll(NewDecoder(encoding, strings.NewReader(encoded)))
+			if err != nil {
+				t.Errorf("NewDecoder error: %v", err)
+			}
+
+			if pair.decoded != string(decReader) {
+				t.Errorf("Expected %s got %s; Encoding %d", pair.decoded, decReader, encIndex)
+			}
+		}
+	}
+}
+
+func TestDecodeSmallBuffer(t *testing.T) {
+	encodings := []*Encoding{
+		StdEncoding,
+		StdEncoding.WithPadding(NoPadding),
+	}
+
+	for bufferSize := 1; bufferSize < 200; bufferSize++ {
+		for _, pair := range pairs {
+			for encIndex, encoding := range encodings {
+				encoded := pair.encoded
+				if encoding.padChar == NoPadding {
+					encoded = strings.Replace(encoded, "=", "", -1)
+				}
+
+				decoder := NewDecoder(encoding, strings.NewReader(encoded))
+
+				var allRead []byte
+
+				for {
+					buf := make([]byte, bufferSize)
+					n, err := decoder.Read(buf)
+					allRead = append(allRead, buf[0:n]...)
+					if err == io.EOF {
+						break
+					}
+					if err != nil {
+						t.Error(err)
+					}
+				}
+
+				if pair.decoded != string(allRead) {
+					t.Errorf("Expected %s got %s; Encoding %d; bufferSize %d", pair.decoded, allRead, encIndex, bufferSize)
+				}
+			}
+		}
+	}
+}