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package fwd
import "io"
const (
// DefaultWriterSize is the
// default write buffer size.
DefaultWriterSize = 2048
minWriterSize = minReaderSize
)
// Writer is a buffered writer
type Writer struct {
w io.Writer // writer
buf []byte // 0:len(buf) is bufered data
}
// NewWriter returns a new writer
// that writes to 'w' and has a buffer
// that is `DefaultWriterSize` bytes.
func NewWriter(w io.Writer) *Writer {
if wr, ok := w.(*Writer); ok {
return wr
}
return &Writer{
w: w,
buf: make([]byte, 0, DefaultWriterSize),
}
}
// NewWriterSize returns a new writer
// that writes to 'w' and has a buffer
// that is 'size' bytes.
func NewWriterSize(w io.Writer, size int) *Writer {
if wr, ok := w.(*Writer); ok && cap(wr.buf) >= size {
return wr
}
return &Writer{
w: w,
buf: make([]byte, 0, max(size, minWriterSize)),
}
}
// Buffered returns the number of buffered bytes
// in the reader.
func (w *Writer) Buffered() int { return len(w.buf) }
// BufferSize returns the maximum size of the buffer.
func (w *Writer) BufferSize() int { return cap(w.buf) }
// Flush flushes any buffered bytes
// to the underlying writer.
func (w *Writer) Flush() error {
l := len(w.buf)
if l > 0 {
n, err := w.w.Write(w.buf)
// if we didn't write the whole
// thing, copy the unwritten
// bytes to the beginnning of the
// buffer.
if n < l && n > 0 {
w.pushback(n)
if err == nil {
err = io.ErrShortWrite
}
}
if err != nil {
return err
}
w.buf = w.buf[:0]
return nil
}
return nil
}
// Write implements `io.Writer`
func (w *Writer) Write(p []byte) (int, error) {
c, l, ln := cap(w.buf), len(w.buf), len(p)
avail := c - l
// requires flush
if avail < ln {
if err := w.Flush(); err != nil {
return 0, err
}
l = len(w.buf)
}
// too big to fit in buffer;
// write directly to w.w
if c < ln {
return w.w.Write(p)
}
// grow buf slice; copy; return
w.buf = w.buf[:l+ln]
return copy(w.buf[l:], p), nil
}
// WriteString is analogous to Write, but it takes a string.
func (w *Writer) WriteString(s string) (int, error) {
c, l, ln := cap(w.buf), len(w.buf), len(s)
avail := c - l
// requires flush
if avail < ln {
if err := w.Flush(); err != nil {
return 0, err
}
l = len(w.buf)
}
// too big to fit in buffer;
// write directly to w.w
//
// yes, this is unsafe. *but*
// io.Writer is not allowed
// to mutate its input or
// maintain a reference to it,
// per the spec in package io.
//
// plus, if the string is really
// too big to fit in the buffer, then
// creating a copy to write it is
// expensive (and, strictly speaking,
// unnecessary)
if c < ln {
return w.w.Write(unsafestr(s))
}
// grow buf slice; copy; return
w.buf = w.buf[:l+ln]
return copy(w.buf[l:], s), nil
}
// WriteByte implements `io.ByteWriter`
func (w *Writer) WriteByte(b byte) error {
if len(w.buf) == cap(w.buf) {
if err := w.Flush(); err != nil {
return err
}
}
w.buf = append(w.buf, b)
return nil
}
// Next returns the next 'n' free bytes
// in the write buffer, flushing the writer
// as necessary. Next will return `io.ErrShortBuffer`
// if 'n' is greater than the size of the write buffer.
// Calls to 'next' increment the write position by
// the size of the returned buffer.
func (w *Writer) Next(n int) ([]byte, error) {
c, l := cap(w.buf), len(w.buf)
if n > c {
return nil, io.ErrShortBuffer
}
avail := c - l
if avail < n {
if err := w.Flush(); err != nil {
return nil, err
}
l = len(w.buf)
}
w.buf = w.buf[:l+n]
return w.buf[l:], nil
}
// take the bytes from w.buf[n:len(w.buf)]
// and put them at the beginning of w.buf,
// and resize to the length of the copied segment.
func (w *Writer) pushback(n int) {
w.buf = w.buf[:copy(w.buf, w.buf[n:])]
}
// ReadFrom implements `io.ReaderFrom`
func (w *Writer) ReadFrom(r io.Reader) (int64, error) {
// anticipatory flush
if err := w.Flush(); err != nil {
return 0, err
}
w.buf = w.buf[0:cap(w.buf)] // expand buffer
var nn int64 // written
var err error // error
var x int // read
// 1:1 reads and writes
for err == nil {
x, err = r.Read(w.buf)
if x > 0 {
n, werr := w.w.Write(w.buf[:x])
nn += int64(n)
if err != nil {
if n < x && n > 0 {
w.pushback(n - x)
}
return nn, werr
}
if n < x {
w.pushback(n - x)
return nn, io.ErrShortWrite
}
} else if err == nil {
err = io.ErrNoProgress
break
}
}
if err != io.EOF {
return nn, err
}
// we only clear here
// because we are sure
// the writes have
// succeeded. otherwise,
// we retain the data in case
// future writes succeed.
w.buf = w.buf[0:0]
return nn, nil
}
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