Add support for generating metadata from runtime wasm files (#1720)

closes #1660

macro/src/wasm_loader.rs

@@ -0,0 +1,55 @@
+// Copyright 2024 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+use std::{borrow::Cow, path::Path};
+
+use codec::Decode;
+use sc_executor::{WasmExecutionMethod, WasmExecutor};
+use sc_executor_common::runtime_blob::RuntimeBlob;
+use sp_maybe_compressed_blob::CODE_BLOB_BOMB_LIMIT;
+use subxt_codegen::{fetch_metadata::fetch_metadata_from_file_blocking, CodegenError, Metadata};
+
+/// Result type shorthand
+pub type WasmMetadataResult<A> = Result<A, CodegenError>;
+
+/// Uses wasm artifact produced by compiling the runtime to generate metadata
+pub fn from_wasm_file(wasm_file_path: &Path) -> WasmMetadataResult<Metadata> {
+    let wasm_file = fetch_metadata_from_file_blocking(wasm_file_path)
+        .map_err(Into::<CodegenError>::into)
+        .and_then(maybe_decompress)?;
+    call_and_decode(wasm_file)
+}
+
+fn call_and_decode(wasm_file: Vec<u8>) -> WasmMetadataResult<Metadata> {
+    let mut ext: sp_state_machine::BasicExternalities = Default::default();
+
+    let executor: WasmExecutor<sp_io::SubstrateHostFunctions> = WasmExecutor::builder()
+        .with_execution_method(WasmExecutionMethod::default())
+        .with_offchain_heap_alloc_strategy(sc_executor::HeapAllocStrategy::Dynamic {
+            maximum_pages: Some(64),
+        })
+        .with_max_runtime_instances(1)
+        .with_runtime_cache_size(1)
+        .build();
+
+    let runtime_blob =
+        RuntimeBlob::new(&wasm_file).map_err(|e| CodegenError::Wasm(e.to_string()))?;
+    let metadata_encoded = executor
+        .uncached_call(runtime_blob, &mut ext, true, "Metadata_metadata", &[])
+        .map_err(|_| CodegenError::Wasm("method \"Metadata_metadata\" doesnt exist".to_owned()))?;
+
+    let metadata = <Vec<u8>>::decode(&mut &metadata_encoded[..]).map_err(CodegenError::Decode)?;
+
+    decode(metadata)
+}
+
+fn decode(encoded_metadata: Vec<u8>) -> WasmMetadataResult<Metadata> {
+    Metadata::decode(&mut encoded_metadata.as_ref()).map_err(Into::into)
+}
+
+fn maybe_decompress(file_contents: Vec<u8>) -> WasmMetadataResult<Vec<u8>> {
+    sp_maybe_compressed_blob::decompress(file_contents.as_ref(), CODE_BLOB_BOMB_LIMIT)
+        .map_err(|e| CodegenError::Wasm(e.to_string()))
+        .map(Cow::into_owned)
+}