Static Metadata Validation (#478)

* metadata: Implement MetadataHashable for deterministic hashing Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Hash `scale_info::Field` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Hash `scale_info::Variant` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Hash `scale_info::TypeDef` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Hash pallet metadata Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Avoid data representation collision via unique identifiers Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Finalize hashing on recursive types Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Cache recursive calls Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Move `MetadataHashable` to codegen to avoid cyclic dependency Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Add pallet unique hash Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Wrap metadata as owned Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Use MetadataHashable wrapper for clients Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Generate runtime pallet uid from metadata Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Validate metadata compatibility at the pallet level Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Update polkadot.rs Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Modify examples and tests for the new API Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Implement metadata uid Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Update polkadot with TryFrom implementation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * client: Change `to_runtime_api` to reflect TryFrom changes Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * client: Skip full metadata validation option Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Add option to skip pallet validation for TransactionApi Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Add option to skip pallet validation for StorageApi Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Update polkadot.rs with ability to skip pallet validation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Change `MetadataHashable` to per function implementation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Use metadata hashes functions Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Use metadata hashes functions Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Make `get_type_uid` private Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen, subxt: Rename metadata functions `*_uid` to `*_hash` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Update `get_field_hash` to use `codec::Encode` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Update polkadot.rs Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen, subxt: Move metadata check from client to subxt::Metadata Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen, subxt: Rename metadata check functions to follow `*_hash` naming Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Update polkadot.rs to reflect naming changes Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Use `encode_to` for metadata generation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Update polkadot.rs to reflect `encode_to` changes Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Specific name for visited set Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Provide cache to hashing functions Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Compute metadata hash by sorted pallets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Get extrinsic hash Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Extend metadata hash with extrinsic and metadata type Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Add cache as metadata parameter Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen, subxt: Update metadata hash to use cache Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Implement Default trait for MetadataHasherCache Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Add cache for pallets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Move functionality to metadata crate Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen, subxt: Use subxt-metadata crate Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Remove metdata hashing functionality Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Add documentation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Fix vector capacity to include extrinisc and type hash Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Add empty CLI Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-cli: Fetch metadata from substrate nodes Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-cli: Log metadata hashes of provided nodes Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-cli: Group compatible nodes by metadata Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-cli: Simplify hash map insertion Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-cli: Move full metadata check to function Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-cli: Group metadata validation at the pallet level Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Persist metadata cache Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Move compatibility cli from subxt-metadata to subxt-cli Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Remove cli from subxt-metadata Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * cli: Fix clippy Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Fix compatible metadata when pallets are registered in different order Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * tests: Handle result of pallet hashing Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Remove type cache for deterministic hashing Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Add test assets from `substrate-node-template` tag `polkadot-v0.9.17` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-tests: Check cache hashing for Balances pallet Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Fix `get_type_hash` clippy issue Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-tests: Compare one time cache with persistent cache Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-test: Check metadata hash populates cache for pallets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-tests: Simplify `cache_deterministic_hash` test Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata-tests: Check deterministic metadata for different order pallets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Fix clippy Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Implement TransactionApiUnchecked for skipping pallet validation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Implement StorageApiUnchecked for skipping pallet validation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Remove skip_pallet_validation boolean Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Implement ClientUnchecked for skipping metadata validation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Update polkadot.rs Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Update examples of rpc_call to skip metadata Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Remove heck dependency Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Add pallet name as an identifier for pallet hashing Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Implement MetadataHashDetails Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Adjust testing to `MetadataHashDetails` interface Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Remove extra `pallet_name` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Update polkadot.rs Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Fix clippy issue Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Change StorageApi to support `_unchecked` methods Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Change TransactionApi to support `_unchecked` methods Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Switch back from `TryFrom` to `From` for `subxt::Client` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen, subxt: Remove `ClientUnchecked` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Expose `validate_metadata` as validation of compatibility method Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * examples: Update to the new interface Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Update test integration to latest interface Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Update polkadot.rs Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Check different pallet index order Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Check recursive type hashing Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Check recursive types registered in different order Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Fix recursive types warning Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Remove test assets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Extend tests to verify cached pallet values Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * examples: Add metadata compatiblity example Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * examples: Revert balance_transfer to initial form Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Add ConstantsApi metadata check Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * tests: Modify tests to accomodate ConstantsApi changes Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * examples: Modify verified version Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Generate polkadot.rs from `0.9.18-4542a603cc-aarch64-macos` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * examples: Update polkadot_metadata.scale from `0.9.18-4542a603cc-aarch64-macos` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Update documentation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * tests: Modify default pallet usage Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Remove hex dependency Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Add MetadataTestType to capture complex types Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Update tests to use complex types Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Check metadata correctness via extending pallets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Extend pallet hash with Events Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Extend pallet hash with constants Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Extend pallet hash with error Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * examples: Extend metadata compatibiliy with StorageApi and ConstantsApi Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Modify comments and documentation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Benchmarks for full validation and pallet validation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/benches: Fix clippy Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Hash metadata just by inspecting the provided pallets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Make pallets generic over T for `AsRef<str>` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Expose the name of the pallets composing the metadata Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt/tests: Update polkadot.rs with pallets name Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen: Obtain metadata hash only by inspecting pallets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * codegen,subxt: Extend the metadata hash to utilize just pallets Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt/tests: Update polkadot.rs with client metadata has per pallet Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Test `get_metadata_per_pallet_hash` correctness Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Fix clippy Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/benches: Fix decode of metadata Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Fix clippy Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * [static metadata] validate storage, calls and constants per call (#507) * validate storage, calls and constants per call * fix typo * cache per-thing hashing, move an Arc, remove some unused bits * create hash_cache to simplify metadata call/constant/storage caching * simplify/robustify the caching logic to help prevent mismatch between get and set * cargo fmt * Fix clippy Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * bench the per-call metadata functions * metadata: Add test for `node_template_runtime_variant` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * ensure criteron cli opts work * group benchmarks and avoid unwrap issues * metadata: Check template runtime for handling the pallet swap order case Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Remove debug logs Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Optimise by removing field's name and type_name and type's path Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Refactor `get_type_hash` to break recursion earlier Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Add tests for `hash_cache` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Add tests for checking Metadata Inner cache Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Check semantic changes inside enum and struct fields Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Add enums named differently with compatible semantic meaning Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Guard testing of release versions for `node_template_runtime` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Improve documentation Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * Update polkadot.rs Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata/tests: Manually construct type of `node_template_runtimeL::Call` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * no more special Call handling, avoid a little cloning, and actually sort by name * remove unused deps and fmt * RuntimeMetadataLastVersion => RuntimeMetadataV14 * remove a bunch of allocations in the metadata hashing, speed up from ~17ms to ~5ms * update release docs to release metadata crate too * subxt: Remove codegen dependency Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Replace std RwLock with parking_lot Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt/tests: Add ws address to `TestNodeProcess` Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt/tests: Add metadata validation integration test Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Allow setting metadata on the ClientBuilder Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt/tests: Check incompatible metadatas Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * metadata: Fix constant hashing for deterministic output Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt/tests: Check metadata validation for constants Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt/tests: Test validation for calls Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt/tests: Test validation for storage Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Expose `set_metadata` for testing only Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> * subxt: Guard metadata tests under integration-tests Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io> Co-authored-by: James Wilson <james@jsdw.me>
2026-06-09 20:11:09 +00:00 · 2022-04-28 12:37:07 +03:00
parent 5605fbd308
commit 1fd1eee72a
44 changed files with 17760 additions and 4624 deletions
@@ -46,13 +46,13 @@ use codec::{
    Encode,
 };
 use derivative::Derivative;
-use std::sync::Arc;

 /// ClientBuilder for constructing a Client.
 #[derive(Default)]
 pub struct ClientBuilder {
    url: Option<String>,
    client: Option<RpcClient>,
+    metadata: Option<Metadata>,
    page_size: Option<u32>,
 }

@@ -62,6 +62,7 @@ impl ClientBuilder {
        Self {
            url: None,
            client: None,
+            metadata: None,
            page_size: None,
        }
    }
@@ -84,6 +85,15 @@ impl ClientBuilder {
        self
    }

+    /// Set the metadata.
+    ///
+    /// *Note:* Metadata will no longer be downloaded from the runtime node.
+    #[cfg(integration_tests)]
+    pub fn set_metadata(mut self, metadata: Metadata) -> Self {
+        self.metadata = Some(metadata);
+        self
+    }
+
    /// Creates a new Client.
    pub async fn build<T: Config>(self) -> Result<Client<T>, BasicError> {
        let client = if let Some(client) = self.client {
@@ -93,19 +103,23 @@ impl ClientBuilder {
            crate::rpc::ws_client(url).await?
        };
        let rpc = Rpc::new(client);
-        let (metadata, genesis_hash, runtime_version, properties) = future::join4(
-            rpc.metadata(),
+        let (genesis_hash, runtime_version, properties) = future::join3(
            rpc.genesis_hash(),
            rpc.runtime_version(None),
            rpc.system_properties(),
        )
        .await;
-        let metadata = metadata?;
+
+        let metadata = if let Some(metadata) = self.metadata {
+            metadata
+        } else {
+            rpc.metadata().await?
+        };

        Ok(Client {
            rpc,
            genesis_hash: genesis_hash?,
-            metadata: Arc::new(metadata),
+            metadata,
            properties: properties.unwrap_or_else(|_| Default::default()),
            runtime_version: runtime_version?,
            iter_page_size: self.page_size.unwrap_or(10),
@@ -119,7 +133,7 @@ impl ClientBuilder {
 pub struct Client<T: Config> {
    rpc: Rpc<T>,
    genesis_hash: T::Hash,
-    metadata: Arc<Metadata>,
+    metadata: Metadata,
    properties: SystemProperties,
    runtime_version: RuntimeVersion,
    iter_page_size: u32,
@@ -403,7 +403,7 @@ pub(crate) mod test_utils {
            ExtrinsicMetadata,
            PalletEventMetadata,
            PalletMetadata,
-            RuntimeMetadataLastVersion,
+            RuntimeMetadataV14,
        },
        RuntimeMetadataPrefixed,
    };
@@ -459,7 +459,7 @@ pub(crate) mod test_utils {
            signed_extensions: vec![],
        };

-        let v14 = RuntimeMetadataLastVersion::new(pallets, extrinsic, meta_type::<()>());
+        let v14 = RuntimeMetadataV14::new(pallets, extrinsic, meta_type::<()>());
        let runtime_metadata: RuntimeMetadataPrefixed = v14.into();

        Metadata::try_from(runtime_metadata).unwrap()
@@ -0,0 +1,113 @@
+// Copyright 2019-2022 Parity Technologies (UK) Ltd.
+// This file is part of subxt.
+//
+// subxt 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.
+//
+// subxt 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 subxt.  If not, see <http://www.gnu.org/licenses/>.
+
+use parking_lot::RwLock;
+use std::{
+    borrow::Cow,
+    collections::HashMap,
+};
+
+/// A cache with the simple goal of storing 32 byte hashes against pallet+item keys
+#[derive(Default, Debug)]
+pub struct HashCache {
+    inner: RwLock<HashMap<PalletItemKey<'static>, [u8; 32]>>,
+}
+
+impl HashCache {
+    /// get a hash out of the cache by its pallet and item key. If the item doesn't exist,
+    /// run the function provided to obtain a hash to insert (or bail with some error on failure).
+    pub fn get_or_insert<F, E>(
+        &self,
+        pallet: &str,
+        item: &str,
+        f: F,
+    ) -> Result<[u8; 32], E>
+    where
+        F: FnOnce() -> Result<[u8; 32], E>,
+    {
+        let maybe_hash = self
+            .inner
+            .read()
+            .get(&PalletItemKey::new(pallet, item))
+            .copied();
+
+        if let Some(hash) = maybe_hash {
+            return Ok(hash)
+        }
+
+        let hash = f()?;
+        self.inner.write().insert(
+            PalletItemKey::new(pallet.to_string(), item.to_string()),
+            hash,
+        );
+
+        Ok(hash)
+    }
+}
+
+/// This exists so that we can look items up in the cache using &strs, without having to allocate
+/// Strings first (as you'd have to do to construct something like an `&(String,String)` key).
+#[derive(Debug, PartialEq, Eq, Hash)]
+struct PalletItemKey<'a> {
+    pallet: Cow<'a, str>,
+    item: Cow<'a, str>,
+}
+
+impl<'a> PalletItemKey<'a> {
+    fn new(pallet: impl Into<Cow<'a, str>>, item: impl Into<Cow<'a, str>>) -> Self {
+        PalletItemKey {
+            pallet: pallet.into(),
+            item: item.into(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn hash_cache_validation() {
+        let cache = HashCache::default();
+
+        let pallet = "System";
+        let item = "Account";
+        let mut call_number = 0;
+        let value = cache.get_or_insert(pallet, item, || -> Result<[u8; 32], ()> {
+            call_number += 1;
+            Ok([0; 32])
+        });
+
+        assert_eq!(
+            cache
+                .inner
+                .read()
+                .get(&PalletItemKey::new(pallet, item))
+                .unwrap(),
+            &value.unwrap()
+        );
+        assert_eq!(value.unwrap(), [0; 32]);
+        assert_eq!(call_number, 1);
+
+        // Further calls must be hashed.
+        let value = cache.get_or_insert(pallet, item, || -> Result<[u8; 32], ()> {
+            call_number += 1;
+            Ok([0; 32])
+        });
+        assert_eq!(call_number, 1);
+        assert_eq!(value.unwrap(), [0; 32]);
+    }
+}
@@ -14,41 +14,43 @@
 // You should have received a copy of the GNU General Public License
 // along with subxt.  If not, see <http://www.gnu.org/licenses/>.

-use std::{
-    collections::HashMap,
-    convert::TryFrom,
-};
-
+use super::hash_cache::HashCache;
+use crate::Call;
 use codec::Error as CodecError;
-
 use frame_metadata::{
    PalletConstantMetadata,
    RuntimeMetadata,
-    RuntimeMetadataLastVersion,
    RuntimeMetadataPrefixed,
+    RuntimeMetadataV14,
    StorageEntryMetadata,
    META_RESERVED,
 };
-
-use crate::Call;
 use scale_info::{
    form::PortableForm,
    Type,
    Variant,
 };
+use std::{
+    collections::HashMap,
+    convert::TryFrom,
+    sync::{
+        Arc,
+        RwLock,
+    },
+};

 /// Metadata error.
-#[derive(Debug, thiserror::Error)]
+#[derive(Debug, thiserror::Error, PartialEq)]
 pub enum MetadataError {
    /// Module is not in metadata.
-    #[error("Pallet {0} not found")]
-    PalletNotFound(String),
+    #[error("Pallet not found")]
+    PalletNotFound,
    /// Pallet is not in metadata.
    #[error("Pallet index {0} not found")]
    PalletIndexNotFound(u8),
    /// Call is not in metadata.
-    #[error("Call {0} not found")]
-    CallNotFound(&'static str),
+    #[error("Call not found")]
+    CallNotFound,
    /// Event is not in metadata.
    #[error("Pallet {0}, Event {0} not found")]
    EventNotFound(u8, u8),
@@ -56,8 +58,8 @@ pub enum MetadataError {
    #[error("Pallet {0}, Error {0} not found")]
    ErrorNotFound(u8, u8),
    /// Storage is not in metadata.
-    #[error("Storage {0} not found")]
-    StorageNotFound(&'static str),
+    #[error("Storage not found")]
+    StorageNotFound,
    /// Storage type does not match requested type.
    #[error("Storage type error")]
    StorageTypeError,
@@ -68,28 +70,48 @@ pub enum MetadataError {
    #[error("Failed to decode constant value: {0}")]
    ConstantValueError(CodecError),
    /// Constant is not in metadata.
-    #[error("Constant {0} not found")]
-    ConstantNotFound(&'static str),
+    #[error("Constant not found")]
+    ConstantNotFound,
    /// Type is not in metadata.
    #[error("Type {0} missing from type registry")]
    TypeNotFound(u32),
+    /// Runtime pallet metadata is incompatible with the static one.
+    #[error("Pallet {0} has incompatible metadata")]
+    IncompatiblePalletMetadata(&'static str),
+    /// Runtime metadata is not fully compatible with the static one.
+    #[error("Node metadata is not fully compatible")]
+    IncompatibleMetadata,
 }

 /// Runtime metadata.
 #[derive(Clone, Debug)]
 pub struct Metadata {
-    metadata: RuntimeMetadataLastVersion,
+    inner: Arc<MetadataInner>,
+}
+
+// We hide the innards behind an Arc so that it's easy to clone and share.
+#[derive(Debug)]
+struct MetadataInner {
+    metadata: RuntimeMetadataV14,
    pallets: HashMap<String, PalletMetadata>,
    events: HashMap<(u8, u8), EventMetadata>,
    errors: HashMap<(u8, u8), ErrorMetadata>,
+    // The hashes uniquely identify parts of the metadata; different
+    // hashes mean some type difference exists between static and runtime
+    // versions. We cache them here to avoid recalculating:
+    cached_metadata_hash: RwLock<Option<[u8; 32]>>,
+    cached_call_hashes: HashCache,
+    cached_constant_hashes: HashCache,
+    cached_storage_hashes: HashCache,
 }

 impl Metadata {
    /// Returns a reference to [`PalletMetadata`].
    pub fn pallet(&self, name: &'static str) -> Result<&PalletMetadata, MetadataError> {
-        self.pallets
+        self.inner
+            .pallets
            .get(name)
-            .ok_or_else(|| MetadataError::PalletNotFound(name.to_string()))
+            .ok_or(MetadataError::PalletNotFound)
    }

    /// Returns the metadata for the event at the given pallet and event indices.
@@ -99,6 +121,7 @@ impl Metadata {
        event_index: u8,
    ) -> Result<&EventMetadata, MetadataError> {
        let event = self
+            .inner
            .events
            .get(&(pallet_index, event_index))
            .ok_or(MetadataError::EventNotFound(pallet_index, event_index))?;
@@ -112,6 +135,7 @@ impl Metadata {
        error_index: u8,
    ) -> Result<&ErrorMetadata, MetadataError> {
        let error = self
+            .inner
            .errors
            .get(&(pallet_index, error_index))
            .ok_or(MetadataError::ErrorNotFound(pallet_index, error_index))?;
@@ -120,12 +144,90 @@ impl Metadata {

    /// Resolve a type definition.
    pub fn resolve_type(&self, id: u32) -> Option<&Type<PortableForm>> {
-        self.metadata.types.resolve(id)
+        self.inner.metadata.types.resolve(id)
    }

    /// Return the runtime metadata.
-    pub fn runtime_metadata(&self) -> &RuntimeMetadataLastVersion {
-        &self.metadata
+    pub fn runtime_metadata(&self) -> &RuntimeMetadataV14 {
+        &self.inner.metadata
+    }
+
+    /// Obtain the unique hash for a specific storage entry.
+    pub fn storage_hash<S: crate::StorageEntry>(
+        &self,
+    ) -> Result<[u8; 32], MetadataError> {
+        self.inner
+            .cached_storage_hashes
+            .get_or_insert(S::PALLET, S::STORAGE, || {
+                subxt_metadata::get_storage_hash(
+                    &self.inner.metadata,
+                    S::PALLET,
+                    S::STORAGE,
+                )
+                .map_err(|e| {
+                    match e {
+                        subxt_metadata::NotFound::Pallet => MetadataError::PalletNotFound,
+                        subxt_metadata::NotFound::Item => MetadataError::StorageNotFound,
+                    }
+                })
+            })
+    }
+
+    /// Obtain the unique hash for a constant.
+    pub fn constant_hash(
+        &self,
+        pallet: &str,
+        constant: &str,
+    ) -> Result<[u8; 32], MetadataError> {
+        self.inner
+            .cached_constant_hashes
+            .get_or_insert(pallet, constant, || {
+                subxt_metadata::get_constant_hash(&self.inner.metadata, pallet, constant)
+                    .map_err(|e| {
+                        match e {
+                            subxt_metadata::NotFound::Pallet => {
+                                MetadataError::PalletNotFound
+                            }
+                            subxt_metadata::NotFound::Item => {
+                                MetadataError::ConstantNotFound
+                            }
+                        }
+                    })
+            })
+    }
+
+    /// Obtain the unique hash for a call.
+    pub fn call_hash<C: crate::Call>(&self) -> Result<[u8; 32], MetadataError> {
+        self.inner
+            .cached_call_hashes
+            .get_or_insert(C::PALLET, C::FUNCTION, || {
+                subxt_metadata::get_call_hash(
+                    &self.inner.metadata,
+                    C::PALLET,
+                    C::FUNCTION,
+                )
+                .map_err(|e| {
+                    match e {
+                        subxt_metadata::NotFound::Pallet => MetadataError::PalletNotFound,
+                        subxt_metadata::NotFound::Item => MetadataError::CallNotFound,
+                    }
+                })
+            })
+    }
+
+    /// Obtain the unique hash for this metadata.
+    pub fn metadata_hash<T: AsRef<str>>(&self, pallets: &[T]) -> [u8; 32] {
+        if let Some(hash) = *self.inner.cached_metadata_hash.read().unwrap() {
+            return hash
+        }
+
+        let hash = subxt_metadata::get_metadata_per_pallet_hash(
+            self.runtime_metadata(),
+            pallets,
+        );
+        *self.inner.cached_metadata_hash.write().unwrap() = Some(hash);
+
+        hash
    }
 }

@@ -159,28 +261,26 @@ impl PalletMetadata {
        let fn_index = *self
            .calls
            .get(C::FUNCTION)
-            .ok_or(MetadataError::CallNotFound(C::FUNCTION))?;
+            .ok_or(MetadataError::CallNotFound)?;
        Ok(fn_index)
    }

    /// Return [`StorageEntryMetadata`] given some storage key.
    pub fn storage(
        &self,
-        key: &'static str,
+        key: &str,
    ) -> Result<&StorageEntryMetadata<PortableForm>, MetadataError> {
-        self.storage
-            .get(key)
-            .ok_or(MetadataError::StorageNotFound(key))
+        self.storage.get(key).ok_or(MetadataError::StorageNotFound)
    }

    /// Get a constant's metadata by name.
    pub fn constant(
        &self,
-        key: &'static str,
+        key: &str,
    ) -> Result<&PalletConstantMetadata<PortableForm>, MetadataError> {
        self.constants
            .get(key)
-            .ok_or(MetadataError::ConstantNotFound(key))
+            .ok_or(MetadataError::ConstantNotFound)
    }
 }

@@ -359,11 +459,134 @@ impl TryFrom<RuntimeMetadataPrefixed> for Metadata {
            })
            .collect();

-        Ok(Self {
-            metadata,
-            pallets,
-            events,
-            errors,
+        Ok(Metadata {
+            inner: Arc::new(MetadataInner {
+                metadata,
+                pallets,
+                events,
+                errors,
+                cached_metadata_hash: Default::default(),
+                cached_call_hashes: Default::default(),
+                cached_constant_hashes: Default::default(),
+                cached_storage_hashes: Default::default(),
+            }),
        })
    }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::StorageEntryKey;
+
+    fn load_metadata() -> Metadata {
+        let bytes = test_runtime::METADATA;
+        let meta: RuntimeMetadataPrefixed =
+            codec::Decode::decode(&mut &*bytes).expect("Cannot decode scale metadata");
+
+        Metadata::try_from(meta)
+            .expect("Cannot translate runtime metadata to internal Metadata")
+    }
+
+    #[test]
+    fn metadata_inner_cache() {
+        // Note: Dependency on test_runtime can be removed if complex metadata
+        // is manually constructed.
+        let metadata = load_metadata();
+
+        let hash = metadata.metadata_hash(&["System"]);
+        // Check inner caching.
+        assert_eq!(
+            metadata.inner.cached_metadata_hash.read().unwrap().unwrap(),
+            hash
+        );
+
+        // Currently the caching does not take into account different pallets
+        // as the intended behavior is to use this method only once.
+        // Enforce this behavior into testing.
+        let hash_old = metadata.metadata_hash(&["Balances"]);
+        assert_eq!(hash_old, hash);
+    }
+
+    #[test]
+    fn metadata_call_inner_cache() {
+        let metadata = load_metadata();
+
+        #[derive(codec::Encode)]
+        struct ValidCall;
+        impl crate::Call for ValidCall {
+            const PALLET: &'static str = "System";
+            const FUNCTION: &'static str = "fill_block";
+        }
+
+        let hash = metadata.call_hash::<ValidCall>();
+
+        let mut call_number = 0;
+        let hash_cached = metadata.inner.cached_call_hashes.get_or_insert(
+            "System",
+            "fill_block",
+            || -> Result<[u8; 32], MetadataError> {
+                call_number += 1;
+                Ok([0; 32])
+            },
+        );
+
+        // Check function is never called (e.i, value fetched from cache).
+        assert_eq!(call_number, 0);
+        assert_eq!(hash.unwrap(), hash_cached.unwrap());
+    }
+
+    #[test]
+    fn metadata_constant_inner_cache() {
+        let metadata = load_metadata();
+
+        let hash = metadata.constant_hash("System", "BlockWeights");
+
+        let mut call_number = 0;
+        let hash_cached = metadata.inner.cached_constant_hashes.get_or_insert(
+            "System",
+            "BlockWeights",
+            || -> Result<[u8; 32], MetadataError> {
+                call_number += 1;
+                Ok([0; 32])
+            },
+        );
+
+        // Check function is never called (e.i, value fetched from cache).
+        assert_eq!(call_number, 0);
+        assert_eq!(hash.unwrap(), hash_cached.unwrap());
+    }
+
+    #[test]
+    fn metadata_storage_inner_cache() {
+        let metadata = load_metadata();
+
+        #[derive(codec::Encode)]
+        struct ValidStorage;
+        impl crate::StorageEntry for ValidStorage {
+            const PALLET: &'static str = "System";
+            const STORAGE: &'static str = "Account";
+            type Value = ();
+
+            fn key(&self) -> StorageEntryKey {
+                unreachable!("Should not be called");
+            }
+        }
+
+        let hash = metadata.storage_hash::<ValidStorage>();
+
+        let mut call_number = 0;
+        let hash_cached = metadata.inner.cached_storage_hashes.get_or_insert(
+            "System",
+            "Account",
+            || -> Result<[u8; 32], MetadataError> {
+                call_number += 1;
+                Ok([0; 32])
+            },
+        );
+
+        // Check function is never called (e.i, value fetched from cache).
+        assert_eq!(call_number, 0);
+        assert_eq!(hash.unwrap(), hash_cached.unwrap());
+    }
+}
@@ -0,0 +1,27 @@
+// Copyright 2019-2022 Parity Technologies (UK) Ltd.
+// This file is part of subxt.
+//
+// subxt 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.
+//
+// subxt 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 subxt.  If not, see <http://www.gnu.org/licenses/>.
+
+mod hash_cache;
+mod metadata_type;
+
+pub use metadata_type::{
+    ErrorMetadata,
+    EventMetadata,
+    InvalidMetadataError,
+    Metadata,
+    MetadataError,
+    PalletMetadata,
+};