303 lines
6.7 KiB
Go
303 lines
6.7 KiB
Go
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// This is a derivitive work of Go's bytes.Buffer implementation.
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//
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// Originally copyright 2009 The Go Authors. All rights reserved.
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//
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// Modifications copyright 2018 Steven Allen. All rights reserved.
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//
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// Use of this source code is governed by both a BSD-style and an MIT-style
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// license that can be found in the LICENSE_BSD and LICENSE files.
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package pool
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import (
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"io"
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)
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// Buffer is a buffer like bytes.Buffer that:
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//
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// 1. Uses a buffer pool.
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// 2. Frees memory on read.
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//
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// If you only have a few buffers and read/write at a steady rate, *don't* use
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// this package, it'll be slower.
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//
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// However:
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//
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// 1. If you frequently create/destroy buffers, this implementation will be
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// significantly nicer to the allocator.
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// 2. If you have many buffers with bursty traffic, this implementation will use
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// significantly less memory.
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type Buffer struct {
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// Pool is the buffer pool to use. If nil, this Buffer will use the
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// global buffer pool.
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Pool *BufferPool
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buf []byte
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rOff int
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// Preallocated slice for samll reads/writes.
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// This is *really* important for performance and only costs 8 words.
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bootstrap [64]byte
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}
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// NewBuffer constructs a new buffer initialized to `buf`.
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// Unlike `bytes.Buffer`, we *copy* the buffer but don't reuse it (to ensure
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// that we *only* use buffers from the pool).
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func NewBuffer(buf []byte) *Buffer {
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b := new(Buffer)
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if len(buf) > 0 {
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b.buf = b.getBuf(len(buf))
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copy(b.buf, buf)
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}
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return b
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}
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// NewBufferString is identical to NewBuffer *except* that it allows one to
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// initialize the buffer from a string (without having to allocate an
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// intermediate bytes slice).
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func NewBufferString(buf string) *Buffer {
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b := new(Buffer)
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if len(buf) > 0 {
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b.buf = b.getBuf(len(buf))
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copy(b.buf, buf)
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}
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return b
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}
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func (b *Buffer) grow(n int) int {
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wOff := len(b.buf)
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bCap := cap(b.buf)
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if bCap >= wOff+n {
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b.buf = b.buf[:wOff+n]
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return wOff
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}
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bSize := b.Len()
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minCap := 2*bSize + n
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// Slide if cap >= minCap.
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// Reallocate otherwise.
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if bCap >= minCap {
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copy(b.buf, b.buf[b.rOff:])
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} else {
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// Needs new buffer.
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newBuf := b.getBuf(minCap)
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copy(newBuf, b.buf[b.rOff:])
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b.returnBuf()
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b.buf = newBuf
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}
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b.rOff = 0
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b.buf = b.buf[:bSize+n]
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return bSize
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}
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func (b *Buffer) getPool() *BufferPool {
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if b.Pool == nil {
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return GlobalPool
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}
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return b.Pool
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}
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func (b *Buffer) returnBuf() {
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if cap(b.buf) > len(b.bootstrap) {
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b.getPool().Put(b.buf)
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}
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b.buf = nil
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}
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func (b *Buffer) getBuf(n int) []byte {
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if n <= len(b.bootstrap) {
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return b.bootstrap[:n]
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}
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return b.getPool().Get(n)
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}
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// Len returns the number of bytes that can be read from this buffer.
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func (b *Buffer) Len() int {
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return len(b.buf) - b.rOff
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}
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// Cap returns the current capacity of the buffer.
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//
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// Note: Buffer *may* re-allocate when writing (or growing by) `n` bytes even if
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// `Cap() < Len() + n` to avoid excessive copying.
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func (b *Buffer) Cap() int {
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return cap(b.buf)
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}
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// Bytes returns the slice of bytes currently buffered in the Buffer.
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//
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// The buffer returned by Bytes is valid until the next call grow, truncate,
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// read, or write. Really, just don't touch the Buffer until you're done with
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// the return value of this function.
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func (b *Buffer) Bytes() []byte {
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return b.buf[b.rOff:]
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}
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// String returns the string representation of the buffer.
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//
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// It returns `<nil>` the buffer is a nil pointer.
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func (b *Buffer) String() string {
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if b == nil {
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return "<nil>"
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}
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return string(b.buf[b.rOff:])
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}
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// WriteString writes a string to the buffer.
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//
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// This function is identical to Write except that it allows one to write a
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// string directly without allocating an intermediate byte slice.
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func (b *Buffer) WriteString(buf string) (int, error) {
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wOff := b.grow(len(buf))
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return copy(b.buf[wOff:], buf), nil
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}
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// Truncate truncates the Buffer.
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//
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// Panics if `n > b.Len()`.
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//
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// This function may free memory by shrinking the internal buffer.
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func (b *Buffer) Truncate(n int) {
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if n < 0 || n > b.Len() {
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panic("truncation out of range")
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}
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b.buf = b.buf[:b.rOff+n]
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b.shrink()
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}
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// Reset is equivalent to Truncate(0).
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func (b *Buffer) Reset() {
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b.returnBuf()
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b.rOff = 0
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}
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// ReadByte reads a single byte from the Buffer.
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func (b *Buffer) ReadByte() (byte, error) {
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if b.rOff >= len(b.buf) {
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return 0, io.EOF
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}
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c := b.buf[b.rOff]
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b.rOff++
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return c, nil
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}
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// WriteByte writes a single byte to the Buffer.
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func (b *Buffer) WriteByte(c byte) error {
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wOff := b.grow(1)
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b.buf[wOff] = c
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return nil
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}
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// Grow grows the internal buffer such that `n` bytes can be written without
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// reallocating.
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func (b *Buffer) Grow(n int) {
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wOff := b.grow(n)
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b.buf = b.buf[:wOff]
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}
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// Next is an alternative to `Read` that returns a byte slice instead of taking
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// one.
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//
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// The returned byte slice is valid until the next read, write, grow, or
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// truncate.
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func (b *Buffer) Next(n int) []byte {
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m := b.Len()
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if m < n {
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n = m
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}
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data := b.buf[b.rOff : b.rOff+n]
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b.rOff += n
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return data
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}
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// Write writes the byte slice to the buffer.
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func (b *Buffer) Write(buf []byte) (int, error) {
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wOff := b.grow(len(buf))
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return copy(b.buf[wOff:], buf), nil
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}
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// WriteTo copies from the buffer into the given writer until the buffer is
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// empty.
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func (b *Buffer) WriteTo(w io.Writer) (int64, error) {
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if b.rOff < len(b.buf) {
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n, err := w.Write(b.buf[b.rOff:])
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b.rOff += n
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if b.rOff > len(b.buf) {
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panic("invalid write count")
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}
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b.shrink()
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return int64(n), err
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}
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return 0, nil
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}
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// MinRead is the minimum slice size passed to a Read call by
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// Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond
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// what is required to hold the contents of r, ReadFrom will not grow the
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// underlying buffer.
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const MinRead = 512
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// ReadFrom reads from the given reader into the buffer.
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func (b *Buffer) ReadFrom(r io.Reader) (int64, error) {
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n := int64(0)
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for {
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wOff := b.grow(MinRead)
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// Use *entire* buffer.
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b.buf = b.buf[:cap(b.buf)]
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read, err := r.Read(b.buf[wOff:])
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b.buf = b.buf[:wOff+read]
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n += int64(read)
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switch err {
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case nil:
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case io.EOF:
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err = nil
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fallthrough
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default:
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b.shrink()
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return n, err
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}
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}
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}
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// Read reads at most `len(buf)` bytes from the internal buffer into the given
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// buffer.
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func (b *Buffer) Read(buf []byte) (int, error) {
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if len(buf) == 0 {
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return 0, nil
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}
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if b.rOff >= len(b.buf) {
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return 0, io.EOF
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}
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n := copy(buf, b.buf[b.rOff:])
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b.rOff += n
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b.shrink()
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return n, nil
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}
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func (b *Buffer) shrink() {
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c := b.Cap()
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// Either nil or bootstrap.
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if c <= len(b.bootstrap) {
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return
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}
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l := b.Len()
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if l == 0 {
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// Shortcut if empty.
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b.returnBuf()
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b.rOff = 0
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} else if l*8 < c {
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// Only shrink when capacity > 8x length. Avoids shrinking too aggressively.
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newBuf := b.getBuf(l)
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copy(newBuf, b.buf[b.rOff:])
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b.returnBuf()
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b.rOff = 0
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b.buf = newBuf[:l]
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}
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}
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