diff options
Diffstat (limited to '')
-rw-r--r-- | dependencies/pkg/mod/github.com/go-sql-driver/mysql@v1.6.0/buffer.go | 182 |
1 files changed, 182 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/github.com/go-sql-driver/mysql@v1.6.0/buffer.go b/dependencies/pkg/mod/github.com/go-sql-driver/mysql@v1.6.0/buffer.go new file mode 100644 index 0000000..0774c5c --- /dev/null +++ b/dependencies/pkg/mod/github.com/go-sql-driver/mysql@v1.6.0/buffer.go @@ -0,0 +1,182 @@ +// 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" + "net" + "time" +) + +const defaultBufSize = 4096 +const maxCachedBufSize = 256 * 1024 + +// 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. +// This buffer is backed by two byte slices in a double-buffering scheme +type buffer struct { + buf []byte // buf is a byte buffer who's length and capacity are equal. + nc net.Conn + idx int + length int + timeout time.Duration + dbuf [2][]byte // dbuf is an array with the two byte slices that back this buffer + flipcnt uint // flipccnt is the current buffer counter for double-buffering +} + +// newBuffer allocates and returns a new buffer. +func newBuffer(nc net.Conn) buffer { + fg := make([]byte, defaultBufSize) + return buffer{ + buf: fg, + nc: nc, + dbuf: [2][]byte{fg, nil}, + } +} + +// flip replaces the active buffer with the background buffer +// this is a delayed flip that simply increases the buffer counter; +// the actual flip will be performed the next time we call `buffer.fill` +func (b *buffer) flip() { + b.flipcnt += 1 +} + +// fill reads into the buffer until at least _need_ bytes are in it +func (b *buffer) fill(need int) error { + n := b.length + // fill data into its double-buffering target: if we've called + // flip on this buffer, we'll be copying to the background buffer, + // and then filling it with network data; otherwise we'll just move + // the contents of the current buffer to the front before filling it + dest := b.dbuf[b.flipcnt&1] + + // grow buffer if necessary to fit the whole packet. + if need > len(dest) { + // Round up to the next multiple of the default size + dest = make([]byte, ((need/defaultBufSize)+1)*defaultBufSize) + + // if the allocated buffer is not too large, move it to backing storage + // to prevent extra allocations on applications that perform large reads + if len(dest) <= maxCachedBufSize { + b.dbuf[b.flipcnt&1] = dest + } + } + + // if we're filling the fg buffer, move the existing data to the start of it. + // if we're filling the bg buffer, copy over the data + if n > 0 { + copy(dest[:n], b.buf[b.idx:]) + } + + b.buf = dest + b.idx = 0 + + for { + if b.timeout > 0 { + if err := b.nc.SetReadDeadline(time.Now().Add(b.timeout)); err != nil { + return err + } + } + + nn, err := b.nc.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 +} + +// takeBuffer 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, error) { + if b.length > 0 { + return nil, ErrBusyBuffer + } + + // test (cheap) general case first + if length <= cap(b.buf) { + return b.buf[:length], nil + } + + if length < maxPacketSize { + b.buf = make([]byte, length) + return b.buf, nil + } + + // buffer is larger than we want to store. + return make([]byte, length), nil +} + +// takeSmallBuffer is shortcut which can be used if length is +// known to be smaller than defaultBufSize. +// Only one buffer (total) can be used at a time. +func (b *buffer) takeSmallBuffer(length int) ([]byte, error) { + if b.length > 0 { + return nil, ErrBusyBuffer + } + return b.buf[:length], nil +} + +// takeCompleteBuffer returns the complete existing buffer. +// This can be used if the necessary buffer size is unknown. +// cap and len of the returned buffer will be equal. +// Only one buffer (total) can be used at a time. +func (b *buffer) takeCompleteBuffer() ([]byte, error) { + if b.length > 0 { + return nil, ErrBusyBuffer + } + return b.buf, nil +} + +// store stores buf, an updated buffer, if its suitable to do so. +func (b *buffer) store(buf []byte) error { + if b.length > 0 { + return ErrBusyBuffer + } else if cap(buf) <= maxPacketSize && cap(buf) > cap(b.buf) { + b.buf = buf[:cap(buf)] + } + return nil +} |