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Add ReadByte method, satisfies the io.ByteReader interface #51

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Jun 8, 2021
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Add ReadByte method, satisfies the io.ByteReader interface #51

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83 changes: 53 additions & 30 deletions decode.go
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Original file line number Diff line number Diff line change
Expand Up @@ -118,32 +118,23 @@ func (r *Reader) readFull(p []byte, allowEOF bool) (ok bool) {
return true
}

// Read satisfies the io.Reader interface.
func (r *Reader) Read(p []byte) (int, error) {
if r.err != nil {
return 0, r.err
}
for {
if r.i < r.j {
n := copy(p, r.decoded[r.i:r.j])
r.i += n
return n, nil
}
func (r *Reader) fill() error {
for r.i >= r.j {
if !r.readFull(r.buf[:4], true) {
return 0, r.err
return r.err
}
chunkType := r.buf[0]
if !r.readHeader {
if chunkType != chunkTypeStreamIdentifier {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
r.readHeader = true
}
chunkLen := int(r.buf[1]) | int(r.buf[2])<<8 | int(r.buf[3])<<16
if chunkLen > len(r.buf) {
r.err = ErrUnsupported
return 0, r.err
return r.err
}

// The chunk types are specified at
Expand All @@ -153,31 +144,31 @@ func (r *Reader) Read(p []byte) (int, error) {
// Section 4.2. Compressed data (chunk type 0x00).
if chunkLen < checksumSize {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
buf := r.buf[:chunkLen]
if !r.readFull(buf, false) {
return 0, r.err
return r.err
}
checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
buf = buf[checksumSize:]

n, err := DecodedLen(buf)
if err != nil {
r.err = err
return 0, r.err
return r.err
}
if n > len(r.decoded) {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
if _, err := Decode(r.decoded, buf); err != nil {
r.err = err
return 0, r.err
return r.err
}
if crc(r.decoded[:n]) != checksum {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
r.i, r.j = 0, n
continue
Expand All @@ -186,25 +177,25 @@ func (r *Reader) Read(p []byte) (int, error) {
// Section 4.3. Uncompressed data (chunk type 0x01).
if chunkLen < checksumSize {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
buf := r.buf[:checksumSize]
if !r.readFull(buf, false) {
return 0, r.err
return r.err
}
checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
// Read directly into r.decoded instead of via r.buf.
n := chunkLen - checksumSize
if n > len(r.decoded) {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
if !r.readFull(r.decoded[:n], false) {
return 0, r.err
return r.err
}
if crc(r.decoded[:n]) != checksum {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
r.i, r.j = 0, n
continue
Expand All @@ -213,15 +204,15 @@ func (r *Reader) Read(p []byte) (int, error) {
// Section 4.1. Stream identifier (chunk type 0xff).
if chunkLen != len(magicBody) {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
if !r.readFull(r.buf[:len(magicBody)], false) {
return 0, r.err
return r.err
}
for i := 0; i < len(magicBody); i++ {
if r.buf[i] != magicBody[i] {
r.err = ErrCorrupt
return 0, r.err
return r.err
}
}
continue
Expand All @@ -230,12 +221,44 @@ func (r *Reader) Read(p []byte) (int, error) {
if chunkType <= 0x7f {
// Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f).
r.err = ErrUnsupported
return 0, r.err
return r.err
}
// Section 4.4 Padding (chunk type 0xfe).
// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
if !r.readFull(r.buf[:chunkLen], false) {
return 0, r.err
return r.err
}
}

return nil
}

// Read satisfies the io.Reader interface.
func (r *Reader) Read(p []byte) (int, error) {
if r.err != nil {
return 0, r.err
}

if err := r.fill(); err != nil {
return 0, err
}

n := copy(p, r.decoded[r.i:r.j])
r.i += n
return n, nil
}

// ReadByte satisfies the io.ByteReader interface.
func (r *Reader) ReadByte() (byte, error) {
if r.err != nil {
return 0, r.err
}

if err := r.fill(); err != nil {
return 0, err
}

c := r.decoded[r.i]
r.i++
return c, nil
}
65 changes: 65 additions & 0 deletions snappy_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1032,6 +1032,71 @@ func TestReaderReset(t *testing.T) {
}
}

func TestReaderReadByte(t *testing.T) {
// Test all 32 possible sub-sequences of these 5 input slices prefixed by
// their size encoded as a uvarint.
//
// Their lengths sum to 400,000, which is over 6 times the Writer ibuf
// capacity: 6 * maxBlockSize is 393,216.
inputs := [][]byte{
bytes.Repeat([]byte{'a'}, 40000),
bytes.Repeat([]byte{'b'}, 150000),
bytes.Repeat([]byte{'c'}, 60000),
bytes.Repeat([]byte{'d'}, 120000),
bytes.Repeat([]byte{'e'}, 30000),
}
loop:
for i := 0; i < 1<<uint(len(inputs)); i++ {
var want []int
buf := new(bytes.Buffer)
w := NewBufferedWriter(buf)
p := make([]byte, binary.MaxVarintLen64)
for j, input := range inputs {
if i&(1<<uint(j)) == 0 {
continue
}
n := binary.PutUvarint(p, uint64(len(input)))
if _, err := w.Write(p[:n]); err != nil {
t.Errorf("i=%#02x: j=%d: Write Uvarint: %v", i, j, err)
continue loop
}
if _, err := w.Write(input); err != nil {
t.Errorf("i=%#02x: j=%d: Write: %v", i, j, err)
continue loop
}
want = append(want, j)
}
if err := w.Close(); err != nil {
t.Errorf("i=%#02x: Close: %v", i, err)
continue
}
r := NewReader(buf)
for _, j := range want {
size, err := binary.ReadUvarint(r)
if err != nil {
t.Errorf("i=%#02x: ReadUvarint: %v", i, err)
continue loop
}
if wantedSize := uint64(len(inputs[j])); size != wantedSize {
t.Errorf("i=%#02x: expected size %d, got %d", i, wantedSize, size)
continue loop
}
got := make([]byte, size)
if _, err := io.ReadFull(r, got); err != nil {
t.Errorf("i=%#02x: ReadFull: %v", i, err)
continue loop
}
if err := cmp(got, inputs[j]); err != nil {
t.Errorf("i=%#02x: %v", i, err)
continue
}
}
if _, err := r.ReadByte(); err != io.EOF {
t.Errorf("i=%#02x: expected size EOF, got %v", i, err)
}
}
}

func TestWriterReset(t *testing.T) {
gold := bytes.Repeat([]byte("Not all those who wander are lost;\n"), 10000)
const n = 20
Expand Down