trie: make stacktrie insert return errors instead of panic, make stackproof handle inexistence

trie/stackproof.go

@@ -87,6 +87,7 @@ func newStackTrieFromProof(rootHash common.Hash, key []byte, proofDb ethdb.KeyVa
 	if parent, err = resolveFromProof(proofDb, rootHash); err != nil {
 		return nil, err
 	}
+	var lastResolved common.Hash
 	stParent = nodeToStNode(parent, key)
 	stack.root = stParent
 	// Now we pursue the given key downwards, and populate the stacktrie too
@@ -94,9 +95,40 @@ func newStackTrieFromProof(rootHash common.Hash, key []byte, proofDb ethdb.KeyVa
 		keyrest, child = get(parent, key, false)
 		switch cld := child.(type) {
 		case nil:
-			return nil, errors.New("no node at given path")
+			/*
+				If the parent is a shortnode, it means that the 'next' key is not
+				going in here (because then the parent would be a fullnode). We cannot
+				leave the parent shortnode dangling without value: either we
+				revert it back to hashed form, or we leave it as an empty node.
+
+				There are a few cases to consider, this shortnode does prove the inexistence
+				of the 'origin', it does so by proving that the extension does not
+				point to 'origin'. However: it may point to
+				1. An existing leaf to the left of the 'origin'
+				2. An existing leaft to the right of the 'origin'.
+
+				In the former case, we do not want it here, it does not belong. We need
+				to replace it with it's hash.
+
+				In the latter case, we cannot replace it with a hash, because as soon
+				as we start feeding the leafs, the first one will hit the "trying to insert into hash" case.
+				So instead we must make it an emptyNode.
+			*/
+
+			if sn, ok := parent.(*shortNode); ok {
+				if bytes.Compare(sn.Key, key) < 0 {
+					// This is on the lower side of the proof-border. We must replace
+					// this with a hash, not an empty node
+					stParent.typ = hashedNode
+					stParent.val = lastResolved[:]
+				} else {
+					stParent.typ = emptyNode
+				}
+			}
+			return stack, nil
 		case hashNode:
-			child, err = resolveFromProof(proofDb, common.BytesToHash(cld))
+			lastResolved = common.BytesToHash(cld)
+			child, err = resolveFromProof(proofDb, lastResolved)
 			if err != nil {
 				return nil, err
 			}
@@ -217,9 +249,15 @@ func iterateProof(rootHash common.Hash, path []byte, ascending bool, proof ethdb
 		}
 		if hn, ok := n.(hashNode); ok {
 			n, _ = resolveFromProof(proof, common.Hash(hn))
-			if n == nil {
-				return nil, fmt.Errorf("proof node (hash %064x) missing", rootHash)
-			}
+		}
+		if n == nil {
+			// n is nil!
+			// At this point, we are following a path of nonexistence.
+			// nothing more to iterate here
+			// However, while iterating towards a non-present end leaf,
+			// we may have encountered an actual leaf here. Must we
+			// restore the hash for that one?
+			break
 		}
 	}
 	return paths, nil
@@ -312,15 +350,30 @@ func VerifyRangeProofWithStack(rootHash common.Hash, firstKey []byte, keys [][]b
 	if err != nil {
 		return false, fmt.Errorf("could not initate stacktrie: %v", err)
 	}
-	// Feed in the values, starting from 1 (do not re-add the proof-leaf)
-	for i := 1; i < len(keys); i++ {
-		if bytes.Compare(keys[i-1], keys[i]) >= 0 {
+	// Feed in the values
+	if bytes.Compare(firstKey, keys[0]) > 0 {
+		return false, errors.New("range is not monotonically increasing")
+	}
+	var pKey []byte
+	for i := 0; i < len(keys); i++ {
+		if bytes.Compare(pKey, keys[i]) >= 0 {
 			return false, errors.New("range is not monotonically increasing")
 		}
+		pKey = keys[i]
 		if len(values[i]) == 0 {
 			return false, errors.New("range contains deletion")
 		}
-		stTrie.Update(keys[i], values[i])
+		if err := stTrie.Update(keys[i], values[i]); err != nil {
+			return false, err
+		}
+	}
+	if !bytes.Equal(lastKey, keys[len(keys)-1]) {
+		// The method we have of inserting right-hand hashes only works
+		// if the proof indeed concerns the last element: otherwise it forces
+		// restructurings on the trie which result in insertion-into-hash.
+		// However, for snap-sync, we do not expect "right side proof-of-inexistence":
+		// the rhs proof should prove the last element that was sent along.
+		return false, fmt.Errorf("proofs must prove the last item")
 	}
 	// For the right-hand-side, we need a list of hashes ot inject
 	hps, err := iterateProof(rootHash, lastKey, false, proof)
@@ -330,7 +383,10 @@ func VerifyRangeProofWithStack(rootHash common.Hash, firstKey []byte, keys [][]b
 	slices.Reverse(hps)
 	// Insert into stacktrie
 	for _, hp := range hps {
-		stTrie.insert(stTrie.root, hp.path, hp.hash[:], nil, newHashed)
+		//fmt.Printf("Inserting at %x: hash %x \n", hp.path, hp.hash)
+		if err := stTrie.insert(stTrie.root, hp.path, hp.hash[:], nil, newHashed); err != nil {
+			return false, err
+		}
 	}
 	if have := stTrie.Hash(); have != rootHash {
 		return false, fmt.Errorf("invalid proof, want hash %x, got %x", rootHash, have)

trie/stackproof_test.go

@@ -170,7 +170,7 @@ func testStackRangeProof(
 
 	var leftBorder = keybytesToHex(entries[0].k)
 	var rightBorder = keybytesToHex(entries[len(entries)-1].k)
-	writeFn := func(_ common.Hash, path []byte, hash common.Hash, blob []byte) {
+	writeFn := func(path []byte, hash common.Hash, blob []byte) {
 		if bytes.HasPrefix(leftBorder, path) {
 			fmt.Printf("path %x  tainted left (parent to %x)\n", path, leftBorder)
 			return

trie/stacktrie.go

@@ -17,9 +17,11 @@
 package trie
 
 import (
+	"bytes"
 	"errors"
 	"sync"
 
+	"fmt"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
@@ -59,8 +61,7 @@ func (t *StackTrie) Update(key, value []byte) error {
 	if len(value) == 0 {
 		panic("deletion not supported")
 	}
-	t.insert(t.root, k[:len(k)-1], value, nil, newLeaf)
-	return nil
+	return t.insert(t.root, k[:len(k)-1], value, nil, newLeaf)
 }
 
 // MustUpdate is a wrapper of Update and will omit any encountered error but
@@ -148,7 +149,7 @@ func (n *stNode) getDiffIndex(key []byte) int {
 
 // Helper function to that inserts a (key, value) pair into
 // the trie.
-func (t *StackTrie) insert(st *stNode, key, value []byte, prefix []byte, leafCtor func([]byte, []byte) *stNode) {
+func (t *StackTrie) insert(st *stNode, key, value []byte, prefix []byte, leafCtor func([]byte, []byte) *stNode) error {
 	switch st.typ {
 	case branchNode: /* Branch */
 		idx := int(key[0])
@@ -167,9 +168,8 @@ func (t *StackTrie) insert(st *stNode, key, value []byte, prefix []byte, leafCto
 		if st.children[idx] == nil {
 			st.children[idx] = leafCtor(key[1:], value)
 		} else {
-			t.insert(st.children[idx], key[1:], value, append(prefix, key[0]), leafCtor)
+			return t.insert(st.children[idx], key[1:], value, append(prefix, key[0]), leafCtor)
 		}
-
 	case extNode: /* Ext */
 		// Compare both key chunks and see where they differ
 		diffidx := st.getDiffIndex(key)
@@ -182,8 +182,7 @@ func (t *StackTrie) insert(st *stNode, key, value []byte, prefix []byte, leafCto
 		if diffidx == len(st.key) {
 			// Ext key and key segment are identical, recurse into
 			// the child node.
-			t.insert(st.children[0], key[diffidx:], value, append(prefix, key[:diffidx]...), leafCtor)
-			return
+			return t.insert(st.children[0], key[diffidx:], value, append(prefix, key[:diffidx]...), leafCtor)
 		}
 		// Save the original part. Depending if the break is
 		// at the extension's last byte or not, create an
@@ -240,8 +239,16 @@ func (t *StackTrie) insert(st *stNode, key, value []byte, prefix []byte, leafCto
 		// keys, 2) a fullnode selecting the path on which the
 		// keys differ, and 3) one leaf for the differentiated
 		// component of each key.
+
 		if diffidx >= len(st.key) {
-			panic("Trying to insert into existing key")
+			if diffidx == len(st.key) && bytes.Equal(st.val, value) {
+				// We can ignore this: it's not an overwrite, just reinsert.
+				//
+				// Sometimes a proof is initialized with a value, the
+				// same value is then fed in to the trie.
+				return nil
+			}
+			return errors.New("trying to insert into existing key")
 		}
 
 		// Check if the split occurs at the first nibble of the
@@ -283,11 +290,12 @@ func (t *StackTrie) insert(st *stNode, key, value []byte, prefix []byte, leafCto
 		st.val = value
 
 	case hashedNode:
-		panic("trying to insert into hash")
+		return fmt.Errorf("trying to insert into hash %x path %x %x", st.val, key, value)
 
 	default:
 		panic("invalid type")
 	}
+	return nil
 }
 
 // hash converts st into a 'hashedNode', if possible. Possible outcomes: