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package trie
import (
"bytes"
"errors"
"fmt"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/crypto/sha3"
"github.com/ethereum/go-ethereum/rlp"
)
// Prove constructs a merkle proof for key. The result contains all
// encoded nodes on the path to the value at key. The value itself is
// also included in the last node and can be retrieved by verifying
// the proof.
//
// The returned proof is nil if the trie does not contain a value for key.
// For existing keys, the proof will have at least one element.
func (t *Trie) Prove(key []byte) []rlp.RawValue {
// Collect all nodes on the path to key.
key = compactHexDecode(key)
nodes := []node{}
tn := t.root
for len(key) > 0 {
switch n := tn.(type) {
case shortNode:
if len(key) < len(n.Key) || !bytes.Equal(n.Key, key[:len(n.Key)]) {
// The trie doesn't contain the key.
return nil
}
tn = n.Val
key = key[len(n.Key):]
nodes = append(nodes, n)
case fullNode:
tn = n[key[0]]
key = key[1:]
nodes = append(nodes, n)
case nil:
return nil
case hashNode:
tn = t.resolveHash(n)
default:
panic(fmt.Sprintf("%T: invalid node: %v", tn, tn))
}
}
if t.hasher == nil {
t.hasher = newHasher()
}
proof := make([]rlp.RawValue, 0, len(nodes))
for i, n := range nodes {
// Don't bother checking for errors here since hasher panics
// if encoding doesn't work and we're not writing to any database.
n, _ = t.hasher.replaceChildren(n, nil)
hn, _ := t.hasher.store(n, nil, false)
if _, ok := hn.(hashNode); ok || i == 0 {
// If the node's database encoding is a hash (or is the
// root node), it becomes a proof element.
enc, _ := rlp.EncodeToBytes(n)
proof = append(proof, enc)
}
}
return proof
}
// VerifyProof checks merkle proofs. The given proof must contain the
// value for key in a trie with the given root hash. VerifyProof
// returns an error if the proof contains invalid trie nodes or the
// wrong value.
func VerifyProof(rootHash common.Hash, key []byte, proof []rlp.RawValue) (value []byte, err error) {
key = compactHexDecode(key)
sha := sha3.NewKeccak256()
wantHash := rootHash.Bytes()
for i, buf := range proof {
sha.Reset()
sha.Write(buf)
if !bytes.Equal(sha.Sum(nil), wantHash) {
return nil, fmt.Errorf("bad proof node %d: hash mismatch", i)
}
n, err := decodeNode(buf)
if err != nil {
return nil, fmt.Errorf("bad proof node %d: %v", i, err)
}
keyrest, cld := get(n, key)
switch cld := cld.(type) {
case nil:
return nil, fmt.Errorf("key mismatch at proof node %d", i)
case hashNode:
key = keyrest
wantHash = cld
case valueNode:
if i != len(proof)-1 {
return nil, errors.New("additional nodes at end of proof")
}
return cld, nil
}
}
return nil, errors.New("unexpected end of proof")
}
func get(tn node, key []byte) ([]byte, node) {
for len(key) > 0 {
switch n := tn.(type) {
case shortNode:
if len(key) < len(n.Key) || !bytes.Equal(n.Key, key[:len(n.Key)]) {
return nil, nil
}
tn = n.Val
key = key[len(n.Key):]
case fullNode:
tn = n[key[0]]
key = key[1:]
case hashNode:
return key, n
case nil:
return key, nil
default:
panic(fmt.Sprintf("%T: invalid node: %v", tn, tn))
}
}
return nil, tn.(valueNode)
}
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