Fix smol-dot#2035

lib/src/trie/proof_decode.rs

@@ -43,6 +43,8 @@ use super::{nibble, trie_node, TrieEntryVersion};
 use alloc::vec::Vec;
 use core::{fmt, iter, ops};
 
+mod tests;
+
 /// Configuration to pass to [`decode_and_verify_proof`].
 pub struct Config<I> {
     /// List of node values of nodes found in the trie. At least one entry corresponding to the
@@ -1218,11 +1220,11 @@ impl<T: AsRef<[u8]>> DecodedTrieProof<T> {
                             // If the child isn't present in the proof, then the proof is
                             // incomplete. While in some situations we could prove that the child
                             // is necessarily the next key, there is no way to know its full key.
-                            if children_present_in_proof_bitmap & (1 << key_before_nibble) == 0 {
+                            if children_present_in_proof_bitmap & (1 << child_num) == 0 {
                                 return Err(IncompleteProofError());
                             }
 
-                            for c in 0..key_before_nibble {
+                            for c in 0..child_num {
                                 if children_present_in_proof_bitmap & (1 << c) != 0 {
                                     iter_entry += 1;
                                     iter_entry += self.entries[iter_entry].child_entries_follow_up;

lib/src/trie/proof_decode/tests.rs

@@ -0,0 +1,59 @@
+// Smoldot
+// Copyright (C) 2024  Pierre Krieger
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program 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 General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#![cfg(test)]
+
+use super::*;
+
+#[test]
+fn issue_2035() {
+    // Repro for <https://github.com/smol-dot/smoldot/issues/2035>.
+    let proof = include_bytes!("./issue_2035_proof");
+    let state_root_hash: [u8; 32] = [
+        247, 47, 169, 142, 251, 242, 60, 33, 209, 98, 166, 105, 10, 36, 18, 208, 178, 227, 210,
+        231, 105, 202, 180, 106, 126, 182, 0, 65, 56, 235, 237, 167,
+    ];
+    let key: [u8; 32] = [
+        0x63, 0xf7, 0x8c, 0x98, 0x72, 0x3d, 0xdc, 0x90, 0x73, 0x52, 0x3e, 0xf3, 0xbe, 0xef, 0xda,
+        0x0c, 0xa9, 0x5d, 0xac, 0x46, 0xc0, 0x7a, 0x40, 0xd9, 0x15, 0x06, 0xe7, 0x63, 0x7e, 0xc4,
+        0xba, 0x57,
+    ];
+
+    let decoded = decode_and_verify_proof(Config { proof }).unwrap();
+
+    let next_key = decoded.next_key(
+        &state_root_hash,
+        crate::trie::bytes_to_nibbles(key.iter().copied()),
+        false,
+        iter::empty(),
+        false,
+    );
+
+    assert_eq!(
+        next_key.unwrap().unwrap().collect::<Vec<_>>(),
+        crate::trie::bytes_to_nibbles(
+            [
+                0x63, 0xf7, 0x8c, 0x98, 0x72, 0x3d, 0xdc, 0x90, 0x73, 0x52, 0x3e, 0xf3, 0xbe, 0xef,
+                0xda, 0x0c, 0xa9, 0x5d, 0xac, 0x46, 0xc0, 0x7a, 0x40, 0xd9, 0x15, 0x06, 0xe7, 0x63,
+                0x7e, 0xc4, 0xba, 0x57, 0x07, 0x1c, 0xef, 0xf5, 0xb0, 0xf6, 0x4d, 0x36, 0x2e, 0x08,
+                0x00, 0x00
+            ]
+            .iter()
+            .copied()
+        ).collect::<Vec<_>>()
+    );
+}