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|
package blockcodecs
import (
"encoding/binary"
"errors"
"fmt"
"io"
)
type encoder struct {
w io.Writer
codec Codec
closed bool
header [10]byte
buf []byte
pos int
scratch []byte
}
const (
// defaultBufferSize is 32KB, same as size of buffer used in io.Copy.
defaultBufferSize = 32 << 10
)
var (
_ io.WriteCloser = (*encoder)(nil)
)
func (e *encoder) Write(p []byte) (int, error) {
if e.closed {
return 0, errors.New("blockcodecs: encoder is closed")
}
n := len(p)
// Complete current block
if e.pos != 0 {
m := copy(e.buf[e.pos:], p)
p = p[m:]
e.pos += m
if e.pos == len(e.buf) {
e.pos = 0
if err := e.doFlush(e.buf); err != nil {
return 0, err
}
}
}
// Copy huge input directly to output
for len(p) >= len(e.buf) {
if e.pos != 0 {
panic("broken invariant")
}
var chunk []byte
if len(p) > len(e.buf) {
chunk = p[:len(e.buf)]
p = p[len(e.buf):]
} else {
chunk = p
p = nil
}
if err := e.doFlush(chunk); err != nil {
return 0, err
}
}
// Store suffix in buffer
m := copy(e.buf, p)
e.pos += m
if m != len(p) {
panic("broken invariant")
}
return n, nil
}
func (e *encoder) Close() error {
if e.closed {
return nil
}
if err := e.Flush(); err != nil {
return err
}
e.closed = true
return e.doFlush(nil)
}
func (e *encoder) doFlush(block []byte) error {
var err error
e.scratch, err = e.codec.Encode(e.scratch, block)
if err != nil {
return fmt.Errorf("blockcodecs: block compression error: %w", err)
}
binary.LittleEndian.PutUint16(e.header[:2], uint16(e.codec.ID()))
binary.LittleEndian.PutUint64(e.header[2:], uint64(len(e.scratch)))
if _, err := e.w.Write(e.header[:]); err != nil {
return err
}
if _, err := e.w.Write(e.scratch); err != nil {
return err
}
return nil
}
func (e *encoder) Flush() error {
if e.closed {
return errors.New("blockcodecs: flushing closed encoder")
}
if e.pos == 0 {
return nil
}
err := e.doFlush(e.buf[:e.pos])
e.pos = 0
return err
}
func NewEncoder(w io.Writer, codec Codec) io.WriteCloser {
return NewEncoderBuffer(w, codec, defaultBufferSize)
}
func NewEncoderBuffer(w io.Writer, codec Codec, bufferSize int) io.WriteCloser {
return &encoder{w: w, codec: codec, buf: make([]byte, bufferSize)}
}
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