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writer.go
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275 lines (255 loc) · 6.29 KB
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package bufio
import (
"solod.dev/so/io"
"solod.dev/so/mem"
"solod.dev/so/unicode/utf8"
)
// Writer implements buffering for an [io.Writer] object.
// If an error occurs writing to a [Writer], no more data will be
// accepted and all subsequent writes, and [Writer.Flush], will return the error.
// After all data has been written, the client should call the
// [Writer.Flush] method to guarantee all data has been forwarded to
// the underlying [io.Writer].
//
// The caller is responsible for freeing the writer's resources
// with [Writer.Free] when done using it.
type Writer struct {
a mem.Allocator
err error
buf []byte
n int
wr io.Writer
}
// NewWriterSize returns a new [Writer] whose buffer has at least the specified
// size. If the argument io.Writer is already a [Writer] with large enough
// size, it returns the underlying [Writer].
func NewWriterSize(a mem.Allocator, w io.Writer, size int) Writer {
// Is it already a Writer?
_, ok := w.(*Writer)
if ok {
b := w.(*Writer)
if len(b.buf) >= size {
return *b
}
}
if size <= 0 {
size = defaultBufSize
}
wr := Writer{a: a}
wr.buf = mem.AllocSlice[byte](a, size, size)
wr.wr = w
return wr
}
// NewWriter returns a new [Writer] whose buffer has the default size.
// If the argument io.Writer is already a [Writer] with large enough buffer size,
// it returns the underlying [Writer].
func NewWriter(a mem.Allocator, w io.Writer) Writer {
return NewWriterSize(a, w, defaultBufSize)
}
// Size returns the size of the underlying buffer in bytes.
func (b *Writer) Size() int { return len(b.buf) }
// Reset discards any unflushed buffered data, clears any error, and
// resets b to write its output to w.
// Calling Reset on the zero value of [Writer] initializes the internal buffer
// to the default size.
// Calling w.Reset(w) (that is, resetting a [Writer] to itself) does nothing.
func (b *Writer) Reset(w io.Writer) {
// Avoid no-op reset to self.
_, ok := w.(*Writer)
if ok && b == w.(*Writer) {
return
}
if b.buf == nil {
b.buf = mem.AllocSlice[byte](b.a, defaultBufSize, defaultBufSize)
}
b.err = nil
b.n = 0
b.wr = w
}
// Free releases the internal buffer memory.
// The writer must not be used after calling Free.
func (b *Writer) Free() {
mem.FreeSlice(b.a, b.buf)
b.buf = nil
}
// Flush writes any buffered data to the underlying [io.Writer].
func (b *Writer) Flush() error {
if b.err != nil {
return b.err
}
if b.n == 0 {
return nil
}
n, err := b.wr.Write(b.buf[0:b.n])
if n < b.n && err == nil {
err = io.ErrShortWrite
}
if err != nil {
if n > 0 && n < b.n {
copy(b.buf[0:b.n-n], b.buf[n:b.n])
}
b.n -= n
b.err = err
return err
}
b.n = 0
return nil
}
// Available returns how many bytes are unused in the buffer.
func (b *Writer) Available() int { return len(b.buf) - b.n }
// AvailableBuffer returns an empty buffer with b.Available() capacity.
// This buffer is intended to be appended to and
// passed to an immediately succeeding [Writer.Write] call.
// The buffer is only valid until the next write operation on b.
func (b *Writer) AvailableBuffer() []byte {
return b.buf[b.n:][:0]
}
// Buffered returns the number of bytes that have been written into the current buffer.
func (b *Writer) Buffered() int { return b.n }
// Write writes the contents of p into the buffer.
// It returns the number of bytes written.
// If nn < len(p), it also returns an error explaining
// why the write is short.
func (b *Writer) Write(p []byte) (int, error) {
nn := 0
for len(p) > b.Available() && b.err == nil {
var n int
if b.Buffered() == 0 {
// Large write, empty buffer.
// Write directly from p to avoid copy.
n, b.err = b.wr.Write(p)
} else {
n = copy(b.buf[b.n:], p)
b.n += n
b.Flush()
}
nn += n
p = p[n:]
}
if b.err != nil {
return nn, b.err
}
n := copy(b.buf[b.n:], p)
b.n += n
nn += n
return nn, nil
}
// WriteByte writes a single byte.
func (b *Writer) WriteByte(c byte) error {
if b.err != nil {
return b.err
}
if b.Available() <= 0 && b.Flush() != nil {
return b.err
}
b.buf[b.n] = c
b.n++
return nil
}
// WriteRune writes a single Unicode code point, returning
// the number of bytes written and any error.
func (b *Writer) WriteRune(r rune) (int, error) {
// Compare as uint32 to correctly handle negative runes.
if uint32(r) < utf8.RuneSelf {
err := b.WriteByte(byte(r))
if err != nil {
return 0, err
}
return 1, nil
}
if b.err != nil {
return 0, b.err
}
n := b.Available()
if n < utf8.UTFMax {
if b.Flush(); b.err != nil {
return 0, b.err
}
n = b.Available()
if n < utf8.UTFMax {
// Can only happen if buffer is silly small.
return b.WriteString(string(r))
}
}
size := utf8.EncodeRune(b.buf[b.n:], r)
b.n += size
return size, nil
}
// WriteString writes a string.
// It returns the number of bytes written.
// If the count is less than len(s), it also returns an error explaining
// why the write is short.
func (b *Writer) WriteString(s string) (int, error) {
nn := 0
for len(s) > b.Available() && b.err == nil {
n := copy(b.buf[b.n:], s)
b.n += n
b.Flush()
nn += n
s = s[n:]
}
if b.err != nil {
return nn, b.err
}
n := copy(b.buf[b.n:], s)
b.n += n
nn += n
return nn, nil
}
// ReadFrom implements [io.ReaderFrom].
func (b *Writer) ReadFrom(r io.Reader) (int64, error) {
if b.err != nil {
return 0, b.err
}
n := int64(0)
var m int
var err error
for {
if b.Available() == 0 {
if err1 := b.Flush(); err1 != nil {
return n, err1
}
}
nr := 0
for nr < maxConsecutiveEmptyReads {
m, err = r.Read(b.buf[b.n:])
if m != 0 || err != nil {
break
}
nr++
}
if nr == maxConsecutiveEmptyReads {
return n, io.ErrNoProgress
}
b.n += m
n += int64(m)
if err != nil {
break
}
}
if err == io.EOF {
// If we filled the buffer exactly, flush preemptively.
if b.Available() == 0 {
err = b.Flush()
} else {
err = nil
}
}
return n, err
}
// ReadWriter stores pointers to a [Reader] and a [Writer].
// It implements [io.ReadWriter].
type ReadWriter struct {
r *Reader
w *Writer
}
// NewReadWriter allocates a new [ReadWriter] that dispatches to r and w.
func NewReadWriter(r *Reader, w *Writer) ReadWriter {
return ReadWriter{r: r, w: w}
}
func (rw *ReadWriter) Read(p []byte) (int, error) {
return rw.r.Read(p)
}
func (rw *ReadWriter) Write(p []byte) (int, error) {
return rw.w.Write(p)
}