From cd791bd855b55b95afc8a5c8f56b8bf67863d099 Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Sun, 25 Sep 2016 20:49:02 +0200
Subject: core, trie: replace state caches with trie journal

---
 trie/hasher.go | 157 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 157 insertions(+)
 create mode 100644 trie/hasher.go

(limited to 'trie/hasher.go')

diff --git a/trie/hasher.go b/trie/hasher.go
new file mode 100644
index 000000000..87e02fb85
--- /dev/null
+++ b/trie/hasher.go
@@ -0,0 +1,157 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package trie
+
+import (
+	"bytes"
+	"hash"
+	"sync"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto/sha3"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+type hasher struct {
+	tmp *bytes.Buffer
+	sha hash.Hash
+}
+
+// hashers live in a global pool.
+var hasherPool = sync.Pool{
+	New: func() interface{} {
+		return &hasher{tmp: new(bytes.Buffer), sha: sha3.NewKeccak256()}
+	},
+}
+
+func newHasher() *hasher {
+	return hasherPool.Get().(*hasher)
+}
+
+func returnHasherToPool(h *hasher) {
+	hasherPool.Put(h)
+}
+
+// hash collapses a node down into a hash node, also returning a copy of the
+// original node initialzied with the computed hash to replace the original one.
+func (h *hasher) hash(n node, db DatabaseWriter, force bool) (node, node, error) {
+	// If we're not storing the node, just hashing, use avaialble cached data
+	if hash, dirty := n.cache(); hash != nil && (db == nil || !dirty) {
+		return hash, n, nil
+	}
+	// Trie not processed yet or needs storage, walk the children
+	collapsed, cached, err := h.hashChildren(n, db)
+	if err != nil {
+		return hashNode{}, n, err
+	}
+	hashed, err := h.store(collapsed, db, force)
+	if err != nil {
+		return hashNode{}, n, err
+	}
+	// Cache the hash and RLP blob of the ndoe for later reuse
+	if hash, ok := hashed.(hashNode); ok && !force {
+		switch cached := cached.(type) {
+		case shortNode:
+			cached.hash = hash
+			if db != nil {
+				cached.dirty = false
+			}
+			return hashed, cached, nil
+		case fullNode:
+			cached.hash = hash
+			if db != nil {
+				cached.dirty = false
+			}
+			return hashed, cached, nil
+		}
+	}
+	return hashed, cached, nil
+}
+
+// hashChildren replaces the children of a node with their hashes if the encoded
+// size of the child is larger than a hash, returning the collapsed node as well
+// as a replacement for the original node with the child hashes cached in.
+func (h *hasher) hashChildren(original node, db DatabaseWriter) (node, node, error) {
+	var err error
+
+	switch n := original.(type) {
+	case shortNode:
+		// Hash the short node's child, caching the newly hashed subtree
+		cached := n
+		cached.Key = common.CopyBytes(cached.Key)
+
+		n.Key = compactEncode(n.Key)
+		if _, ok := n.Val.(valueNode); !ok {
+			if n.Val, cached.Val, err = h.hash(n.Val, db, false); err != nil {
+				return n, original, err
+			}
+		}
+		if n.Val == nil {
+			n.Val = valueNode(nil) // Ensure that nil children are encoded as empty strings.
+		}
+		return n, cached, nil
+
+	case fullNode:
+		// Hash the full node's children, caching the newly hashed subtrees
+		cached := fullNode{dirty: n.dirty}
+
+		for i := 0; i < 16; i++ {
+			if n.Children[i] != nil {
+				if n.Children[i], cached.Children[i], err = h.hash(n.Children[i], db, false); err != nil {
+					return n, original, err
+				}
+			} else {
+				n.Children[i] = valueNode(nil) // Ensure that nil children are encoded as empty strings.
+			}
+		}
+		cached.Children[16] = n.Children[16]
+		if n.Children[16] == nil {
+			n.Children[16] = valueNode(nil)
+		}
+		return n, cached, nil
+
+	default:
+		// Value and hash nodes don't have children so they're left as were
+		return n, original, nil
+	}
+}
+
+func (h *hasher) store(n node, db DatabaseWriter, force bool) (node, error) {
+	// Don't store hashes or empty nodes.
+	if _, isHash := n.(hashNode); n == nil || isHash {
+		return n, nil
+	}
+	// Generate the RLP encoding of the node
+	h.tmp.Reset()
+	if err := rlp.Encode(h.tmp, n); err != nil {
+		panic("encode error: " + err.Error())
+	}
+	if h.tmp.Len() < 32 && !force {
+		return n, nil // Nodes smaller than 32 bytes are stored inside their parent
+	}
+	// Larger nodes are replaced by their hash and stored in the database.
+	hash, _ := n.cache()
+	if hash == nil {
+		h.sha.Reset()
+		h.sha.Write(h.tmp.Bytes())
+		hash = hashNode(h.sha.Sum(nil))
+	}
+	if db != nil {
+		return hash, db.Put(hash, h.tmp.Bytes())
+	}
+	return hash, nil
+}
-- 
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