github.com/scottcagno/storage@v1.8.0/pkg/_junk/_lsmtree/sstable/decode.go (about)

     1  package sstable
     2  
     3  import (
     4  	"encoding/binary"
     5  	"io"
     6  )
     7  
     8  func DecodeDataEntry(r io.Reader) (*sstDataEntry, error) {
     9  	// make buffer for decoding
    10  	buf := make([]byte, 16)
    11  	// read key length
    12  	_, err := r.Read(buf[0:8])
    13  	if err != nil {
    14  		return nil, err
    15  	}
    16  	// read val length
    17  	_, err = r.Read(buf[8:16])
    18  	if err != nil {
    19  		return nil, err
    20  	}
    21  	// decode key length
    22  	klen := binary.LittleEndian.Uint64(buf[0:8])
    23  	// decode val length
    24  	vlen := binary.LittleEndian.Uint64(buf[8:16])
    25  	// make buffer to load the key and value into
    26  	data := make([]byte, klen+vlen)
    27  	// read key and value
    28  	_, err = r.Read(data)
    29  	if err != nil {
    30  		return nil, err
    31  	}
    32  	// fill out sstDataEntry
    33  	ent := &sstDataEntry{
    34  		key:   string(data[0:klen]),
    35  		value: data[klen : klen+vlen],
    36  	}
    37  	// return
    38  	return ent, nil
    39  }
    40  
    41  func DecodeDataEntryAt(r io.ReaderAt, offset int64) (*sstDataEntry, error) {
    42  	// make buffer for decoding
    43  	buf := make([]byte, 16)
    44  	// read key length
    45  	n, err := r.ReadAt(buf[0:8], offset)
    46  	if err != nil {
    47  		return nil, err
    48  	}
    49  	// update offset for next read
    50  	offset += int64(n)
    51  	// read val length
    52  	n, err = r.ReadAt(buf[8:16], offset)
    53  	if err != nil {
    54  		return nil, err
    55  	}
    56  	// update offset for next read
    57  	offset += int64(n)
    58  	// decode key length
    59  	klen := binary.LittleEndian.Uint64(buf[0:8])
    60  	// decode val length
    61  	vlen := binary.LittleEndian.Uint64(buf[8:16])
    62  	// make buffer to load the key and value into
    63  	data := make([]byte, klen+vlen)
    64  	// read key and value
    65  	_, err = r.ReadAt(data, offset)
    66  	if err != nil {
    67  		return nil, err
    68  	}
    69  	// fill out sstDataEntry
    70  	ent := &sstDataEntry{
    71  		key:   string(data[0:klen]),
    72  		value: data[klen : klen+vlen],
    73  	}
    74  	// return
    75  	return ent, nil
    76  }
    77  
    78  func DecodeIndexEntry(r io.Reader) (*sstIndexEntry, error) {
    79  	// make buffer for decoding
    80  	buf := make([]byte, 16)
    81  	// read key length
    82  	_, err := r.Read(buf[0:8])
    83  	if err != nil {
    84  		return nil, err
    85  	}
    86  	// read data offset
    87  	_, err = r.Read(buf[8:16])
    88  	if err != nil {
    89  		return nil, err
    90  	}
    91  	// decode key length
    92  	keyLength := binary.LittleEndian.Uint64(buf[0:8])
    93  	// decode data offset
    94  	dataOffset := binary.LittleEndian.Uint64(buf[8:16])
    95  	// make buffer to load the key into
    96  	key := make([]byte, keyLength)
    97  	// read key
    98  	_, err = r.Read(key)
    99  	if err != nil {
   100  		return nil, err
   101  	}
   102  	// fill out sstIndexEntry
   103  	idx := &sstIndexEntry{
   104  		key:    string(key),
   105  		offset: int64(dataOffset),
   106  	}
   107  	return idx, nil
   108  }