/
readwrite.go
262 lines (252 loc) · 6.17 KB
/
readwrite.go
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package lsmtree
import (
"encoding/binary"
"io"
)
// readIndex reads and decodes the provided entry index from r
func readIndex(r io.Reader) (*Index, error) {
// make buffer
buf := make([]byte, 18)
// read index header
_, err := r.Read(buf)
if err != nil {
return nil, err
}
// decode key length
klen := binary.LittleEndian.Uint64(buf[0:8])
// decode data offset
off, _ := binary.Varint(buf[8:18])
// make entry index
i := &Index{
Key: make([]byte, klen),
Offset: off,
}
// read key from data into entry key
_, err = r.Read(i.Key)
if err != nil {
return nil, err
}
// return index
return i, nil
}
// readIndexAt decodes the index at the provided offset using the provided reader
func readIndexAt(r io.ReaderAt, offset int64) (*Index, error) {
// make buffer
buf := make([]byte, 18)
// read index header
n, err := r.ReadAt(buf, offset)
if err != nil {
return nil, err
}
// update offset
offset += int64(n)
// decode key length
klen := binary.LittleEndian.Uint64(buf[0:8])
// decode data offset
off, _ := binary.Varint(buf[8:18])
// make entry index
e := &Index{
Key: make([]byte, klen),
Offset: off,
}
// read key from data into entry key
n, err = r.ReadAt(e.Key, offset)
if err != nil {
return nil, err
}
// update offset
offset += int64(n)
// return entry
return e, nil
}
// writeIndex encodes and writes the provided entry index to w
func writeIndex(w io.WriteSeeker, i *Index) (int64, error) {
// error check
if i == nil {
return -1, ErrNilIndex
}
// get the file pointer offset for the entry
offset, err := w.Seek(0, io.SeekCurrent)
if err != nil {
return -1, err
}
// make buffer
buf := make([]byte, 18)
// encode and write index key length
binary.LittleEndian.PutUint64(buf[0:8], uint64(len(i.Key)))
_, err = w.Write(buf[0:8])
if err != nil {
return -1, err
}
// encode and write index data offset
binary.PutVarint(buf[8:18], i.Offset)
_, err = w.Write(buf[8:18])
if err != nil {
return -1, err
}
// write index key
_, err = w.Write(i.Key)
if err != nil {
return -1, err
}
return offset, nil
}
func readEntryHeader(r io.Reader, hdr *EntryHeader) (int, error) {
// make header buffer to read data into
buf := make([]byte, 16)
// read the header from the underlying reader into the buffer
n, err := r.Read(buf)
if err != nil {
return n, err
}
// decode key length
hdr.klen = binary.LittleEndian.Uint32(buf[0:4])
// decode value length
hdr.vlen = binary.LittleEndian.Uint32(buf[4:8])
// decode crc32 value
hdr.crc = binary.LittleEndian.Uint32(buf[8:12])
// skip the last 4 bytes (reserved for future use)
//
return n, nil
}
// readEntry reads the entry from the provided io.Reader
// and returns the entry or nil and an error
func readEntry(r io.Reader) (*Entry, error) {
// make entry header
hdr := new(EntryHeader)
// reader entry header from r into EntryHeader
_, err := readEntryHeader(r, hdr)
if err != nil {
return nil, err
}
// make entry to read key and value into
e := &Entry{
Key: make([]byte, hdr.klen),
Value: make([]byte, hdr.vlen),
CRC: hdr.crc,
}
// read key from data into entry key
_, err = r.Read(e.Key)
if err != nil {
return nil, err
}
// read value key from data into entry value
_, err = r.Read(e.Value)
if err != nil {
return nil, err
}
// make sure the crc checksum is valid
crc := checksum(append(e.Key, e.Value...))
if e.CRC != crc {
return nil, ErrBadChecksum
}
// return entry
return e, nil
}
func readEntryHeaderAt(r io.ReaderAt, offset int64, hdr *EntryHeader) (int, error) {
// make header buffer to read data into
buf := make([]byte, 16)
// read the header from the underlying reader into the buffer
n, err := r.ReadAt(buf, offset)
if err != nil {
return n, err
}
// decode key length
hdr.klen = binary.LittleEndian.Uint32(buf[0:4])
// decode value length
hdr.vlen = binary.LittleEndian.Uint32(buf[4:8])
// decode crc32 value
hdr.crc = binary.LittleEndian.Uint32(buf[8:12])
// skip the last 4 bytes (reserved for future use)
//
return n, nil
}
// readEntryAt reads the entry from the provided io.ReaderAt
// and returns the entry or nil and an error
func readEntryAt(r io.ReaderAt, offset int64) (*Entry, error) {
// make entry header
hdr := new(EntryHeader)
// reader entry header from r into EntryHeader
n, err := readEntryHeaderAt(r, offset, hdr)
if err != nil {
return nil, err
}
// update offset
offset += int64(n)
// make entry to read key and value into
e := &Entry{
Key: make([]byte, hdr.klen),
Value: make([]byte, hdr.vlen),
CRC: hdr.crc,
}
// read key from data into entry key
n, err = r.ReadAt(e.Key, offset)
if err != nil {
return nil, err
}
// update offset
offset += int64(n)
// read value key from data into entry value
n, err = r.ReadAt(e.Value, offset)
if err != nil {
return nil, err
}
// update offset
offset += int64(n)
// make sure the crc checksum is valid
crc := checksum(append(e.Key, e.Value...))
if e.CRC != crc {
return nil, ErrBadChecksum
}
// return entry
return e, nil
}
func writeEntryHeader(w io.Writer, hdr *EntryHeader) (int, error) {
// make header buffer to write data into
buf := make([]byte, 16)
// encode key length into header
binary.LittleEndian.PutUint32(buf[0:4], hdr.klen)
// encode value length into header
binary.LittleEndian.PutUint32(buf[4:8], hdr.vlen)
// encode crc32 value into header
binary.LittleEndian.PutUint32(buf[8:12], hdr.crc)
// skip the last 4 bytes (reserved for future use)
//
// write the header to the underlying writer
return w.Write(buf)
}
// writeEntry writes the provided entry to the provided io.Writer
func writeEntry(w io.WriteSeeker, e *Entry) (int64, error) {
// error check
if e == nil {
return -1, ErrNilEntry
}
// get the file pointer offset for the entry
offset, err := w.Seek(0, io.SeekCurrent)
if err != nil {
return -1, err
}
// make entry header
hdr := &EntryHeader{
klen: uint32(len(e.Key)),
vlen: uint32(len(e.Value)),
crc: e.CRC,
}
// write entry header
_, err = writeEntryHeader(w, hdr)
if err != nil {
return -1, err
}
// write entry key
_, err = w.Write(e.Key)
if err != nil {
return -1, err
}
// write entry value
_, err = w.Write(e.Value)
if err != nil {
return -1, err
}
// return offset
return offset, nil
}