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item.go
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item.go
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// Copyright (c) 2016 Couchbase, Inc.
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
// except in compliance with the License. You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software distributed under the
// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
// either express or implied. See the License for the specific language governing permissions
// and limitations under the License.
package nitro
import (
"encoding/binary"
"io"
"reflect"
"unsafe"
)
var itemHeaderSize = unsafe.Sizeof(Item{})
// Item represents nitro item header
// The item data is followed by the header.
// Item data is a block of bytes. The user can store key and value into a
// block of bytes and provide custom key comparator.
type Item struct {
bornSn uint32
deadSn uint32
dataLen uint32
}
func (m *Nitro) newItem(data []byte, useMM bool) (itm *Item) {
l := len(data)
itm = m.allocItem(l, useMM)
copy(itm.Bytes(), data)
return itm
}
func (m *Nitro) freeItem(itm *Item) {
if m.useMemoryMgmt {
m.freeFun(unsafe.Pointer(itm))
}
}
func (m *Nitro) allocItem(l int, useMM bool) (itm *Item) {
blockSize := itemHeaderSize + uintptr(l)
if useMM {
itm = (*Item)(m.mallocFun(int(blockSize)))
itm.deadSn = 0
itm.bornSn = 0
} else {
block := make([]byte, blockSize)
itm = (*Item)(unsafe.Pointer(&block[0]))
}
itm.dataLen = uint32(l)
return
}
// EncodeItem encodes in [2 byte len][item_bytes] format.
func (m *Nitro) EncodeItem(itm *Item, buf []byte, w io.Writer) error {
l := 2
if len(buf) < l {
return errNotEnoughSpace
}
binary.BigEndian.PutUint16(buf[0:2], uint16(itm.dataLen))
if _, err := w.Write(buf[0:2]); err != nil {
return err
}
if _, err := w.Write(itm.Bytes()); err != nil {
return err
}
return nil
}
// DecodeItem decodes encoded [2 byte len][item_bytes] format.
func (m *Nitro) DecodeItem(buf []byte, r io.Reader) (*Item, error) {
if _, err := io.ReadFull(r, buf[0:2]); err != nil {
return nil, err
}
l := binary.BigEndian.Uint16(buf[0:2])
if l > 0 {
itm := m.allocItem(int(l), m.useMemoryMgmt)
data := itm.Bytes()
_, err := io.ReadFull(r, data)
return itm, err
}
return nil, nil
}
// Bytes return item data bytes
func (itm *Item) Bytes() (bs []byte) {
if itm == nil {
return
}
l := itm.dataLen
dataOffset := uintptr(unsafe.Pointer(itm)) + itemHeaderSize
hdr := (*reflect.SliceHeader)(unsafe.Pointer(&bs))
hdr.Data = dataOffset
hdr.Len = int(l)
hdr.Cap = hdr.Len
return
}
// ItemSize returns total bytes consumed by item representation
func ItemSize(p unsafe.Pointer) int {
itm := (*Item)(p)
return int(itemHeaderSize + uintptr(itm.dataLen))
}