github.com/vescale/zgraph@v0.0.0-20230410094002-959c02d50f95/storage/mvcc/decoders.go (about)

     1  // Copyright 2022 zGraph Authors. All rights reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package mvcc
    16  
    17  import (
    18  	"bytes"
    19  
    20  	"github.com/cockroachdb/pebble"
    21  )
    22  
    23  // LockDecoder is used to decode Lock entry of low-level key-value store.
    24  type LockDecoder struct {
    25  	Lock      Lock
    26  	ExpectKey []byte
    27  }
    28  
    29  // Decode decodes the Lock value if current iterator is at expectKey::Lock.
    30  func (dec *LockDecoder) Decode(iter *pebble.Iterator) (bool, error) {
    31  	if iter.Error() != nil || !iter.Valid() {
    32  		return false, iter.Error()
    33  	}
    34  
    35  	iterKey := iter.Key()
    36  	key, ver, err := Decode(iterKey)
    37  	if err != nil {
    38  		return false, err
    39  	}
    40  	if !bytes.Equal(key, dec.ExpectKey) {
    41  		return false, nil
    42  	}
    43  	if ver != LockVer {
    44  		return false, nil
    45  	}
    46  
    47  	var lock Lock
    48  	val, err := iter.ValueAndErr()
    49  	if err != nil {
    50  		return false, err
    51  	}
    52  	err = lock.UnmarshalBinary(val)
    53  	if err != nil {
    54  		return false, err
    55  	}
    56  	dec.Lock = lock
    57  	iter.Next()
    58  	return true, nil
    59  }
    60  
    61  // ValueDecoder is used to decode the value entries. There will be multiple
    62  // versions of specified key.
    63  type ValueDecoder struct {
    64  	Value     Value
    65  	ExpectKey []byte
    66  }
    67  
    68  // Decode decodes a mvcc value if iter key is expectKey.
    69  func (dec *ValueDecoder) Decode(iter *pebble.Iterator) (bool, error) {
    70  	if iter.Error() != nil || !iter.Valid() {
    71  		return false, iter.Error()
    72  	}
    73  
    74  	key, ver, err := Decode(iter.Key())
    75  	if err != nil {
    76  		return false, err
    77  	}
    78  	if !bytes.Equal(key, dec.ExpectKey) {
    79  		return false, nil
    80  	}
    81  	if ver == LockVer {
    82  		return false, nil
    83  	}
    84  
    85  	var value Value
    86  	val, err := iter.ValueAndErr()
    87  	if err != nil {
    88  		return false, err
    89  	}
    90  	err = value.UnmarshalBinary(val)
    91  	if err != nil {
    92  		return false, err
    93  	}
    94  	dec.Value = value
    95  	iter.Next()
    96  	return true, nil
    97  }
    98  
    99  // SkipDecoder is used to decode useless versions of value entry.
   100  type SkipDecoder struct {
   101  	CurrKey []byte
   102  }
   103  
   104  // Decode skips the iterator as long as its key is currKey, the new key would be stored.
   105  func (dec *SkipDecoder) Decode(iter *pebble.Iterator) (bool, error) {
   106  	if iter.Error() != nil {
   107  		return false, iter.Error()
   108  	}
   109  	for iter.Valid() {
   110  		key, _, err := Decode(iter.Key())
   111  		if err != nil {
   112  			return false, err
   113  		}
   114  		if !bytes.Equal(key, dec.CurrKey) {
   115  			dec.CurrKey = key
   116  			return true, nil
   117  		}
   118  		iter.Next()
   119  	}
   120  	return false, nil
   121  }