core, trie: new trie

trie/secure_trie.go

@@ -16,46 +16,93 @@
 
 package trie
 
-import "github.com/ethereum/go-ethereum/crypto"
+import (
+	"hash"
 
-var keyPrefix = []byte("secure-key-")
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto/sha3"
+)
 
+var secureKeyPrefix = []byte("secure-key-")
+
+// SecureTrie wraps a trie with key hashing. In a secure trie, all
+// access operations hash the key using keccak256. This prevents
+// calling code from creating long chains of nodes that
+// increase the access time.
+//
+// Contrary to a regular trie, a SecureTrie can only be created with
+// New and must have an attached database. The database also stores
+// the preimage of each key.
+//
+// SecureTrie is not safe for concurrent use.
 type SecureTrie struct {
 	*Trie
+
+	hash       hash.Hash
+	secKeyBuf  []byte
+	hashKeyBuf []byte
 }
 
-func NewSecure(root []byte, backend Backend) *SecureTrie {
-	return &SecureTrie{New(root, backend)}
+// NewSecure creates a trie with an existing root node from db.
+//
+// If root is the zero hash or the sha3 hash of an empty string, the
+// trie is initially empty. Otherwise, New will panics if db is nil
+// and returns ErrMissingRoot if the root node cannpt be found.
+// Accessing the trie loads nodes from db on demand.
+func NewSecure(root common.Hash, db Database) (*SecureTrie, error) {
+	if db == nil {
+		panic("NewSecure called with nil database")
+	}
+	trie, err := New(root, db)
+	if err != nil {
+		return nil, err
+	}
+	return &SecureTrie{Trie: trie}, nil
 }
 
-func (self *SecureTrie) Update(key, value []byte) Node {
-	shaKey := crypto.Sha3(key)
-	self.Trie.cache.Put(append(keyPrefix, shaKey...), key)
-
-	return self.Trie.Update(shaKey, value)
-}
-func (self *SecureTrie) UpdateString(key, value string) Node {
-	return self.Update([]byte(key), []byte(value))
+// Get returns the value for key stored in the trie.
+// The value bytes must not be modified by the caller.
+func (t *SecureTrie) Get(key []byte) []byte {
+	return t.Trie.Get(t.hashKey(key))
 }
 
-func (self *SecureTrie) Get(key []byte) []byte {
-	return self.Trie.Get(crypto.Sha3(key))
-}
-func (self *SecureTrie) GetString(key string) []byte {
-	return self.Get([]byte(key))
+// Update associates key with value in the trie. Subsequent calls to
+// Get will return value. If value has length zero, any existing value
+// is deleted from the trie and calls to Get will return nil.
+//
+// The value bytes must not be modified by the caller while they are
+// stored in the trie.
+func (t *SecureTrie) Update(key, value []byte) {
+	hk := t.hashKey(key)
+	t.Trie.Update(hk, value)
+	t.Trie.db.Put(t.secKey(hk), key)
 }
 
-func (self *SecureTrie) Delete(key []byte) Node {
-	return self.Trie.Delete(crypto.Sha3(key))
-}
-func (self *SecureTrie) DeleteString(key string) Node {
-	return self.Delete([]byte(key))
+// Delete removes any existing value for key from the trie.
+func (t *SecureTrie) Delete(key []byte) {
+	t.Trie.Delete(t.hashKey(key))
 }
 
-func (self *SecureTrie) Copy() *SecureTrie {
-	return &SecureTrie{self.Trie.Copy()}
+// GetKey returns the sha3 preimage of a hashed key that was
+// previously used to store a value.
+func (t *SecureTrie) GetKey(shaKey []byte) []byte {
+	key, _ := t.Trie.db.Get(t.secKey(shaKey))
+	return key
 }
 
-func (self *SecureTrie) GetKey(shaKey []byte) []byte {
-	return self.Trie.cache.Get(append(keyPrefix, shaKey...))
+func (t *SecureTrie) secKey(key []byte) []byte {
+	t.secKeyBuf = append(t.secKeyBuf[:0], secureKeyPrefix...)
+	t.secKeyBuf = append(t.secKeyBuf, key...)
+	return t.secKeyBuf
+}
+
+func (t *SecureTrie) hashKey(key []byte) []byte {
+	if t.hash == nil {
+		t.hash = sha3.NewKeccak256()
+		t.hashKeyBuf = make([]byte, 32)
+	}
+	t.hash.Reset()
+	t.hash.Write(key)
+	t.hashKeyBuf = t.hash.Sum(t.hashKeyBuf[:0])
+	return t.hashKeyBuf
 }