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// Go MySQL Driver - A MySQL-Driver for Go's database/sql package
//
// Copyright 2013 The Go-MySQL-Driver Authors. All rights reserved.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.
package mysql
import "io"
const defaultBufSize = 4096
// A buffer which is used for both reading and writing.
// This is possible since communication on each connection is synchronous.
// In other words, we can't write and read simultaneously on the same connection.
// The buffer is similar to bufio.Reader / Writer but zero-copy-ish
// Also highly optimized for this particular use case.
type buffer struct {
buf []byte
rd io.Reader
idx int
length int
}
func newBuffer(rd io.Reader) buffer {
var b [defaultBufSize]byte
return buffer{
buf: b[:],
rd: rd,
}
}
// fill reads into the buffer until at least _need_ bytes are in it
func (b *buffer) fill(need int) error {
n := b.length
// move existing data to the beginning
if n > 0 && b.idx > 0 {
copy(b.buf[0:n], b.buf[b.idx:])
}
// grow buffer if necessary
// TODO: let the buffer shrink again at some point
// Maybe keep the org buf slice and swap back?
if need > len(b.buf) {
// Round up to the next multiple of the default size
newBuf := make([]byte, ((need/defaultBufSize)+1)*defaultBufSize)
copy(newBuf, b.buf)
b.buf = newBuf
}
b.idx = 0
for {
nn, err := b.rd.Read(b.buf[n:])
n += nn
switch err {
case nil:
if n < need {
continue
}
b.length = n
return nil
case io.EOF:
if n >= need {
b.length = n
return nil
}
return io.ErrUnexpectedEOF
default:
return err
}
}
}
// returns next N bytes from buffer.
// The returned slice is only guaranteed to be valid until the next read
func (b *buffer) readNext(need int) ([]byte, error) {
if b.length < need {
// refill
if err := b.fill(need); err != nil {
return nil, err
}
}
offset := b.idx
b.idx += need
b.length -= need
return b.buf[offset:b.idx], nil
}
// returns a buffer with the requested size.
// If possible, a slice from the existing buffer is returned.
// Otherwise a bigger buffer is made.
// Only one buffer (total) can be used at a time.
func (b *buffer) takeBuffer(length int) []byte {
if b.length > 0 {
return nil
}
// test (cheap) general case first
if length <= defaultBufSize || length <= cap(b.buf) {
return b.buf[:length]
}
if length < maxPacketSize {
b.buf = make([]byte, length)
return b.buf
}
return make([]byte, length)
}
// shortcut which can be used if the requested buffer is guaranteed to be
// smaller than defaultBufSize
// Only one buffer (total) can be used at a time.
func (b *buffer) takeSmallBuffer(length int) []byte {
if b.length == 0 {
return b.buf[:length]
}
return nil
}
// takeCompleteBuffer returns the complete existing buffer.
// This can be used if the necessary buffer size is unknown.
// Only one buffer (total) can be used at a time.
func (b *buffer) takeCompleteBuffer() []byte {
if b.length == 0 {
return b.buf
}
return nil
}
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