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pagebuf.go
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pagebuf.go
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package pagebuf
import (
"io"
"math/bits"
)
const (
DefaultMaxIdlePages = 4
DefaultPageSize = 1024
)
// PageBuffer ...
type PageBuffer struct {
bits int
mask int
maxIdlePages int
pages [][]byte
size int
off struct {
page int
from int
}
}
// NewPageBuffer creates a PageBuffer with default options
func NewPageBuffer() *PageBuffer {
return NewPageBufferSize(DefaultMaxIdlePages, DefaultPageSize)
}
// NewPageBufferSize creates a PageBuffer with specified options
func NewPageBufferSize(maxIdlePages, pageSize int) *PageBuffer {
mask := pageSize - 1
if mask&pageSize != 0 {
panic("pipe: pageSize is not a power of two")
}
if maxIdlePages <= 0 {
maxIdlePages = 2
}
return &PageBuffer{
bits: bits.OnesCount(uint(mask)),
mask: mask,
maxIdlePages: maxIdlePages,
}
}
// Reset clears the buffer
func (p *PageBuffer) Reset() {
p.off.page = 0
p.off.from = 0
p.size = 0
if len(p.pages) > p.maxIdlePages {
pages := make([][]byte, p.maxIdlePages)
copy(pages, p.pages[:p.maxIdlePages])
p.pages = pages
}
}
// Len returns the length of buffer
func (p *PageBuffer) Len() int {
return p.size
}
// PageSize returns size per page
func (p *PageBuffer) PageSize() int {
return p.mask + 1
}
// Format formats the buffer as a string
func (p *PageBuffer) Format() string {
const hex = "0123456789abcdef"
if p.size == 0 {
return "[]"
}
var (
buf = make([]byte, 0, p.size*3+1)
page = p.off.page
from = p.off.from
)
buf = append(buf, '[')
for i := 0; i < p.size; i++ {
b := p.pages[page][from]
if i > 0 {
buf = append(buf, ' ')
}
buf = append(buf, hex[b>>4], hex[b&0xF])
if from == p.mask {
from = 0
page++
} else {
from++
}
}
buf = append(buf, ']')
return string(buf)
}
func (p *PageBuffer) tail() (page, from, size int) {
end := p.off.from + p.size
page = p.off.page + end>>p.bits
from = end & p.mask
size = (len(p.pages)-page)<<p.bits - from
return
}
func (p *PageBuffer) grow(n int) (endPage, endFrom int) {
var remainSize int
endPage, endFrom, remainSize = p.tail()
if remainSize < n {
remainSize += p.off.page << p.bits
if endFrom > 0 {
endPage++
}
if remainSize < n {
// allocate new pages
need := (n - remainSize + p.mask) >> p.bits
if need < (len(p.pages) >> 1) {
need = len(p.pages) >> 1
}
pages := make([][]byte, need+len(p.pages))
for i := range pages {
pages[i] = make([]byte, p.mask+1)
}
copy(pages, p.pages[p.off.page:endPage])
p.pages = pages
} else {
// shift content pages to front
maxIdleSize := p.maxIdlePages << p.bits
numPage := len(p.pages)
if numPage > p.maxIdlePages &&
maxIdleSize > (p.size+n)<<1 &&
maxIdleSize > p.size+p.off.from+n {
pages := make([][]byte, p.maxIdlePages)
if numPage >= p.off.page+p.maxIdlePages {
copy(pages, p.pages[p.off.page:p.off.page+p.maxIdlePages])
} else {
copy(pages, p.pages[p.off.page:])
copy(pages[numPage-p.off.page:], p.pages[:p.maxIdlePages-numPage+p.off.page])
}
p.pages = pages
} else {
copy(p.pages, p.pages[p.off.page:endPage])
}
}
p.off.page = 0
endPage, endFrom, _ = p.tail()
}
return
}
// Write implements io.Writer Write method
func (p *PageBuffer) Write(data []byte) (n int, err error) {
size := len(data)
if size == 0 {
return
}
endPage, endFrom := p.grow(size)
for n < size {
remain := p.mask + 1 - endFrom
if size-n > remain {
copy(p.pages[endPage][endFrom:], data[n:n+remain])
n += remain
endPage++
endFrom = 0
} else {
copy(p.pages[endPage][endFrom:], data[n:])
n = size
}
}
p.size += n
return
}
// Read implements io.Reader Read method
func (p *PageBuffer) Read(data []byte) (n int, err error) {
size := len(data)
for n < size {
if p.size == 0 {
err = io.EOF
return
}
nn := p.mask + 1 - p.off.from
if nn > p.size {
nn = p.size
}
if size-n < nn {
nn = size - n
copy(data[n:], p.pages[p.off.page][p.off.from:p.off.from+nn])
p.off.from += nn
} else {
copy(data[n:], p.pages[p.off.page][p.off.from:])
p.off.page++
p.off.from = 0
}
p.size -= nn
n += nn
}
if p.size == 0 {
p.Reset()
}
return
}