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