Add function for embedding the runtime version in a wasm blob (#9277)

* Add function for embedding the runtime version in a wasm blob

This function can be used to add the custom section to a wasm blob with
the runtime version in it.

* Review nitpick

substrate/primitives/version/src/embed.rs

@@ -0,0 +1,56 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2021 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Provides functionality to embed a [`RuntimeVersion`](crate::RuntimeVersion) as custom section
+//! into a WASM file.
+
+use codec::Encode;
+use parity_wasm::elements::{Module, deserialize_buffer, serialize};
+
+#[derive(Clone, Copy, Eq, PartialEq, Debug, thiserror::Error)]
+pub enum Error {
+	#[error("Deserializing wasm failed")]
+	Deserialize,
+	#[error("Serializing wasm failed")]
+	Serialize,
+}
+
+/// Embed the given `version` to the given `wasm` blob.
+///
+/// If there was already a runtime version embedded, this will be overwritten.
+///
+/// Returns the new WASM blob.
+pub fn embed_runtime_version(
+	wasm: &[u8],
+	mut version: crate::RuntimeVersion,
+) -> Result<Vec<u8>, Error> {
+	let mut module: Module = deserialize_buffer(wasm).map_err(|_| Error::Deserialize)?;
+
+	let apis = version.apis
+		.iter()
+		.map(Encode::encode)
+		.map(|v| v.into_iter())
+		.flatten()
+		.collect::<Vec<u8>>();
+
+	module.set_custom_section("runtime_apis", apis);
+
+	version.apis.to_mut().clear();
+	module.set_custom_section("runtime_version", version.encode());
+
+	serialize(module).map_err(|_| Error::Serialize)
+}

substrate/primitives/version/src/lib.rs

@@ -35,6 +35,9 @@ pub use sp_std;
 #[cfg(feature = "std")]
 use sp_runtime::{traits::Block as BlockT, generic::BlockId};
 
+#[cfg(feature = "std")]
+pub mod embed;
+
 /// An attribute that accepts a version declaration of a runtime and generates a custom wasm section
 /// with the equivalent contents.
 ///