src/log/slog/internal/buffer/buffer.go

// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package buffer provides a pool-allocated byte buffer.
package buffer

import "sync"

// buffer adapted from go/src/fmt/print.go
type Buffer []byte

// Having an initial size gives a dramatic speedup.
var bufPool = sync.Pool{
	New: func() any {
		b := make([]byte, 0, 1024)
		return (*Buffer)(&b)
	},
}

func New() *Buffer {
	return bufPool.Get().(*Buffer)
}

func (b *Buffer) Free() {
	// To reduce peak allocation, return only smaller buffers to the pool.
	const maxBufferSize = 16 << 10
	if cap(*b) <= maxBufferSize {
		*b = (*b)[:0]
		bufPool.Put(b)
	}
}

func (b *Buffer) Reset() {
	*b = (*b)[:0]
}

func (b *Buffer) Write(p []byte) (int, error) {
	*b = append(*b, p...)
	return len(p), nil
}

func (b *Buffer) WriteString(s string) (int, error) {
	*b = append(*b, s...)
	return len(s), nil
}

func (b *Buffer) WriteByte(c byte) error {
	*b = append(*b, c)
	return nil
}

func (b *Buffer) WritePosInt(i int) {
	b.WritePosIntWidth(i, 0)
}

// WritePosIntWidth writes non-negative integer i to the buffer, padded on the left
// by zeroes to the given width. Use a width of 0 to omit padding.
func (b *Buffer) WritePosIntWidth(i, width int) {
	// Cheap integer to fixed-width decimal ASCII.
	// Copied from log/log.go.

	if i < 0 {
		panic("negative int")
	}

	// Assemble decimal in reverse order.
	var bb [20]byte
	bp := len(bb) - 1
	for i >= 10 || width > 1 {
		width--
		q := i / 10
		bb[bp] = byte('0' + i - q*10)
		bp--
		i = q
	}
	// i < 10
	bb[bp] = byte('0' + i)
	b.Write(bb[bp:])
}

func (b *Buffer) String() string {
	return string(*b)
}