github.com/ava-labs/subnet-evm@v0.6.4/trie/tracer.go (about)

     1  // Copyright 2022 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  package trie
    18  
    19  import (
    20  	"github.com/ethereum/go-ethereum/common"
    21  )
    22  
    23  // tracer tracks the changes of trie nodes. During the trie operations,
    24  // some nodes can be deleted from the trie, while these deleted nodes
    25  // won't be captured by trie.Hasher or trie.Committer. Thus, these deleted
    26  // nodes won't be removed from the disk at all. Tracer is an auxiliary tool
    27  // used to track all insert and delete operations of trie and capture all
    28  // deleted nodes eventually.
    29  //
    30  // The changed nodes can be mainly divided into two categories: the leaf
    31  // node and intermediate node. The former is inserted/deleted by callers
    32  // while the latter is inserted/deleted in order to follow the rule of trie.
    33  // This tool can track all of them no matter the node is embedded in its
    34  // parent or not, but valueNode is never tracked.
    35  //
    36  // Besides, it's also used for recording the original value of the nodes
    37  // when they are resolved from the disk. The pre-value of the nodes will
    38  // be used to construct trie history in the future.
    39  //
    40  // Note tracer is not thread-safe, callers should be responsible for handling
    41  // the concurrency issues by themselves.
    42  type tracer struct {
    43  	inserts    map[string]struct{}
    44  	deletes    map[string]struct{}
    45  	accessList map[string][]byte
    46  }
    47  
    48  // newTracer initializes the tracer for capturing trie changes.
    49  func newTracer() *tracer {
    50  	return &tracer{
    51  		inserts:    make(map[string]struct{}),
    52  		deletes:    make(map[string]struct{}),
    53  		accessList: make(map[string][]byte),
    54  	}
    55  }
    56  
    57  // onRead tracks the newly loaded trie node and caches the rlp-encoded
    58  // blob internally. Don't change the value outside of function since
    59  // it's not deep-copied.
    60  func (t *tracer) onRead(path []byte, val []byte) {
    61  	t.accessList[string(path)] = val
    62  }
    63  
    64  // onInsert tracks the newly inserted trie node. If it's already
    65  // in the deletion set (resurrected node), then just wipe it from
    66  // the deletion set as it's "untouched".
    67  func (t *tracer) onInsert(path []byte) {
    68  	if _, present := t.deletes[string(path)]; present {
    69  		delete(t.deletes, string(path))
    70  		return
    71  	}
    72  	t.inserts[string(path)] = struct{}{}
    73  }
    74  
    75  // onDelete tracks the newly deleted trie node. If it's already
    76  // in the addition set, then just wipe it from the addition set
    77  // as it's untouched.
    78  func (t *tracer) onDelete(path []byte) {
    79  	if _, present := t.inserts[string(path)]; present {
    80  		delete(t.inserts, string(path))
    81  		return
    82  	}
    83  	t.deletes[string(path)] = struct{}{}
    84  }
    85  
    86  // reset clears the content tracked by tracer.
    87  func (t *tracer) reset() {
    88  	t.inserts = make(map[string]struct{})
    89  	t.deletes = make(map[string]struct{})
    90  	t.accessList = make(map[string][]byte)
    91  }
    92  
    93  // copy returns a deep copied tracer instance.
    94  func (t *tracer) copy() *tracer {
    95  	var (
    96  		inserts    = make(map[string]struct{})
    97  		deletes    = make(map[string]struct{})
    98  		accessList = make(map[string][]byte)
    99  	)
   100  	for path := range t.inserts {
   101  		inserts[path] = struct{}{}
   102  	}
   103  	for path := range t.deletes {
   104  		deletes[path] = struct{}{}
   105  	}
   106  	for path, blob := range t.accessList {
   107  		accessList[path] = common.CopyBytes(blob)
   108  	}
   109  	return &tracer{
   110  		inserts:    inserts,
   111  		deletes:    deletes,
   112  		accessList: accessList,
   113  	}
   114  }
   115  
   116  // deletedNodes returns a list of node paths which are deleted from the trie.
   117  func (t *tracer) deletedNodes() []string {
   118  	var paths []string
   119  	for path := range t.deletes {
   120  		// It's possible a few deleted nodes were embedded
   121  		// in their parent before, the deletions can be no
   122  		// effect by deleting nothing, filter them out.
   123  		_, ok := t.accessList[path]
   124  		if !ok {
   125  			continue
   126  		}
   127  		paths = append(paths, path)
   128  	}
   129  	return paths
   130  }