Add support for ext_trie_blake2_256_verify_proof host functions

Implement ext_trie_blake2_256_verify_proof_version_1 and _version_2
which were previously stubbed with host_fn_not_implemented!(). These
host functions are needed by runtimes that perform Merkle proof
verification, such as Polkadot Bulletin Chain's pallet-transaction-storage.

The implementation uses smoldot's existing proof_decode module to decode
and verify the proof, then looks up the key and compares against the
expected value. For state version V1 (version_2 only), hashed storage
values (>= 33 bytes) are handled by comparing blake2b hashes.

Author: x3c41a

lib/src/executor/host.rs

@@ -2108,8 +2108,59 @@ impl ReadyToRun {
                     },
                 }
             }
-            HostFunction::ext_trie_blake2_256_verify_proof_version_1 => host_fn_not_implemented!(),
-            HostFunction::ext_trie_blake2_256_verify_proof_version_2 => host_fn_not_implemented!(),
+            HostFunction::ext_trie_blake2_256_verify_proof_version_1
+            | HostFunction::ext_trie_blake2_256_verify_proof_version_2 => {
+                let state_version = if matches!(
+                    host_fn,
+                    HostFunction::ext_trie_blake2_256_verify_proof_version_2
+                ) {
+                    expect_state_version!(4)
+                } else {
+                    TrieEntryVersion::V0
+                };
+
+                let root = expect_pointer_constant_size!(0, 32);
+                let proof = expect_pointer_size!(1).as_ref().to_vec();
+                let key = expect_pointer_size!(2).as_ref().to_vec();
+                let value = expect_pointer_size!(3).as_ref().to_vec();
+
+                let outcome = match trie::proof_decode::decode_and_verify_proof(
+                    trie::proof_decode::Config { proof: &proof },
+                ) {
+                    Ok(decoded) => match decoded.trie_node_info(
+                        &root,
+                        trie::bytes_to_nibbles(key.iter().copied()),
+                    ) {
+                        Ok(info) => match info.storage_value {
+                            trie::proof_decode::StorageValue::Known {
+                                value: found_value,
+                                ..
+                            } => found_value == &value[..],
+                            trie::proof_decode::StorageValue::HashKnownValueMissing(hash) => {
+                                // The proof contains only the hash of the value.
+                                // This happens with state version V1 where values
+                                // >= 33 bytes are stored as their blake2b hash.
+                                // Verify by hashing the expected value and comparing.
+                                matches!(state_version, TrieEntryVersion::V1)
+                                    && *hash
+                                        == <[u8; 32]>::try_from(
+                                            blake2_rfc::blake2b::blake2b(32, &[], &value)
+                                                .as_bytes(),
+                                        )
+                                        .unwrap_or_else(|_| unreachable!())
+                            }
+                            trie::proof_decode::StorageValue::None => false,
+                        },
+                        Err(_) => false,
+                    },
+                    Err(_) => false,
+                };
+
+                HostVm::ReadyToRun(ReadyToRun {
+                    resume_value: Some(vm::WasmValue::I32(if outcome { 1 } else { 0 })),
+                    inner: self.inner,
+                })
+            }
             HostFunction::ext_trie_keccak_256_verify_proof_version_1 => host_fn_not_implemented!(),
             HostFunction::ext_trie_keccak_256_verify_proof_version_2 => host_fn_not_implemented!(),
             HostFunction::ext_misc_print_num_version_1 => {

wasm-node/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Added
+
+- Add support for the `ext_trie_blake2_256_verify_proof_version_1` and `ext_trie_blake2_256_verify_proof_version_2` host functions. These are used by runtimes that perform Merkle proof verification (e.g. Polkadot Bulletin Chain's `pallet-transaction-storage`).
+
 ## 2.0.40 - 2025-12-02
 
 ### Added