Make sure frame examples compile for wasm (#5332)

* Make sure frame examples compile for wasm

This makes sure that `frame-example` and `frame-example-offchain-worker`
compile for wasm.

This also fixes compilation for these crates. The offchain worker
example doesn't use serde-json anymore as that is too heavy and breaks
`no_std` compilation.

* Apply suggestions from code review

Co-Authored-By: Nikolay Volf <nikvolf@gmail.com>

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

substrate/.gitlab-ci.yml

@@ -214,6 +214,24 @@ test-frame-staking:
     - WASM_BUILD_NO_COLOR=1 time cargo test --release --verbose --no-default-features --features std
     - sccache -s
 
+test-frame-examples-compile-to-wasm:
+  stage:                           test
+  <<:                              *docker-env
+  variables:
+    # Enable debug assertions since we are running optimized builds for testing
+    # but still want to have debug assertions.
+    RUSTFLAGS: -Cdebug-assertions=y
+    RUST_BACKTRACE: 1
+  except:
+    variables:
+      - $DEPLOY_TAG
+  script:
+    - cd frame/example-offchain-worker/
+    - cargo +nightly build --target=wasm32-unknown-unknown --no-default-features
+    - cd ../example
+    - cargo +nightly build --target=wasm32-unknown-unknown --no-default-features
+    - sccache -s
+
 test-wasmtime:
   stage:                           test
   <<:                              *docker-env

substrate/Cargo.lock

@@ -3063,6 +3063,15 @@ dependencies = [
  "linked-hash-map",
 ]
 
+[[package]]
+name = "lite-json"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "faa835713bb12ba5204013497da16caf2dd2eee25ca829d0efaa054fb38c4ddd"
+dependencies = [
+ "paste",
+]
+
 [[package]]
 name = "lock_api"
 version = "0.3.3"
@@ -4147,9 +4156,9 @@ version = "2.0.0-alpha.4"
 dependencies = [
  "frame-support",
  "frame-system",
+ "lite-json",
  "parity-scale-codec",
  "serde",
- "serde_json",
  "sp-core",
  "sp-io",
  "sp-runtime",
@@ -6718,18 +6727,18 @@ checksum = "f638d531eccd6e23b980caf34876660d38e265409d8e99b397ab71eb3612fad0"
 
 [[package]]
 name = "serde"
-version = "1.0.104"
+version = "1.0.105"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "414115f25f818d7dfccec8ee535d76949ae78584fc4f79a6f45a904bf8ab4449"
+checksum = "e707fbbf255b8fc8c3b99abb91e7257a622caeb20a9818cbadbeeede4e0932ff"
 dependencies = [
  "serde_derive",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.104"
+version = "1.0.105"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "128f9e303a5a29922045a830221b8f78ec74a5f544944f3d5984f8ec3895ef64"
+checksum = "ac5d00fc561ba2724df6758a17de23df5914f20e41cb00f94d5b7ae42fffaff8"
 dependencies = [
  "proc-macro2",
  "quote",

substrate/frame/example-offchain-worker/Cargo.toml

@@ -17,7 +17,7 @@ sp-core = { version = "2.0.0-alpha.4", default-features = false, path = "../../p
 sp-io = { version = "2.0.0-alpha.4", default-features = false, path = "../../primitives/io" }
 sp-runtime = { version = "2.0.0-alpha.4", default-features = false, path = "../../primitives/runtime" }
 sp-std = { version = "2.0.0-alpha.4", default-features = false, path = "../../primitives/std" }
-serde_json = { version = "1.0.46", default-features = false, features = ["alloc"] }
+lite-json = { version = "0.1", default-features = false }
 
 [features]
 default = ["std"]
@@ -26,6 +26,7 @@ std = [
 	"frame-support/std",
 	"frame-system/std",
 	"serde",
+	"lite-json/std",
 	"sp-core/std",
 	"sp-io/std",
 	"sp-runtime/std",

substrate/frame/example-offchain-worker/src/lib.rs

@@ -47,13 +47,14 @@ use frame_support::{
 	weights::SimpleDispatchInfo,
 };
 use frame_system::{self as system, ensure_signed, ensure_none, offchain};
-use serde_json as json;
 use sp_core::crypto::KeyTypeId;
 use sp_runtime::{
 	offchain::{http, Duration, storage::StorageValueRef},
 	traits::Zero,
 	transaction_validity::{InvalidTransaction, ValidTransaction, TransactionValidity},
 };
+use sp_std::{vec, vec::Vec};
+use lite_json::json::JsonValue;
 
 #[cfg(test)]
 mod tests;
@@ -320,7 +321,7 @@ impl<T: Trait> Module<T> {
 	}
 
 	/// A helper function to fetch the price and send signed transaction.
-	fn fetch_price_and_send_signed() -> Result<(), String> {
+	fn fetch_price_and_send_signed() -> Result<(), &'static str> {
 		use system::offchain::SubmitSignedTransaction;
 		// Firstly we check if there are any accounts in the local keystore that are capable of
 		// signing the transaction.
@@ -334,7 +335,7 @@ impl<T: Trait> Module<T> {
 
 		// Make an external HTTP request to fetch the current price.
 		// Note this call will block until response is received.
-		let price = Self::fetch_price().map_err(|e| format!("{:?}", e))?;
+		let price = Self::fetch_price().map_err(|_| "Failed to fetch price")?;
 
 		// Received price is wrapped into a call to `submit_price` public function of this pallet.
 		// This means that the transaction, when executed, will simply call that function passing
@@ -357,20 +358,18 @@ impl<T: Trait> Module<T> {
 	}
 
 	/// A helper function to fetch the price and send unsigned transaction.
-	fn fetch_price_and_send_unsigned(block_number: T::BlockNumber) -> Result<(), String> {
+	fn fetch_price_and_send_unsigned(block_number: T::BlockNumber) -> Result<(), &'static str> {
 		use system::offchain::SubmitUnsignedTransaction;
 		// Make sure we don't fetch the price if unsigned transaction is going to be rejected
 		// anyway.
 		let next_unsigned_at = <NextUnsignedAt<T>>::get();
 		if next_unsigned_at > block_number {
-			return Err(
-				format!("Too early to send unsigned transaction. Next at: {:?}", next_unsigned_at)
-			)?
+			return Err("Too early to send unsigned transaction")
 		}
 
 		// Make an external HTTP request to fetch the current price.
 		// Note this call will block until response is received.
-		let price = Self::fetch_price().map_err(|e| format!("{:?}", e))?;
+		let price = Self::fetch_price().map_err(|_| "Failed to fetch price")?;
 
 		// Received price is wrapped into a call to `submit_price_unsigned` public function of this
 		// pallet. This means that the transaction, when executed, will simply call that function
@@ -428,21 +427,17 @@ impl<T: Trait> Module<T> {
 		// Note that the return object allows you to read the body in chunks as well
 		// with a way to control the deadline.
 		let body = response.body().collect::<Vec<u8>>();
-		// Next we parse the response using `serde_json`. Even though it's possible to use
-		// `serde_derive` and deserialize to a struct it's not recommended due to blob size
-		// overhead introduced by such code. Deserializing to `json::Value` is much more
-		// lightweight and should be preferred, especially if we only care about a small number
-		// of properties from the response.
-		let val: Result<json::Value, _> = json::from_slice(&body);
-		// Let's parse the price as float value. Note that you should avoid using floats in the
-		// runtime, it's fine to do that in the offchain worker, but we do convert it to an integer
-		// before submitting on-chain.
-		let price = val.ok().and_then(|v| v.get("USD").and_then(|v| v.as_f64()));
-		let price = match price {
-			Some(pricef) => Ok((pricef * 100.) as u32),
+
+		// Create a str slice from the body.
+		let body_str = sp_std::str::from_utf8(&body).map_err(|_| {
+			debug::warn!("No UTF8 body");
+			http::Error::Unknown
+		})?;
+
+		let price = match Self::parse_price(body_str) {
+			Some(price) => Ok(price),
 			None => {
-				let s = core::str::from_utf8(&body);
-				debug::warn!("Unable to extract price from the response: {:?}", s);
+				debug::warn!("Unable to extract price from the response: {:?}", body_str);
 				Err(http::Error::Unknown)
 			}
 		}?;
@@ -452,6 +447,28 @@ impl<T: Trait> Module<T> {
 		Ok(price)
 	}
 
+	/// Parse the price from the given JSON string using `lite-json`.
+	///
+	/// Returns `None` when parsing failed or `Some(price in cents)` when parsing is successful.
+	fn parse_price(price_str: &str) -> Option<u32> {
+		let val = lite_json::parse_json(price_str);
+		let price = val.ok().and_then(|v| match v {
+			JsonValue::Object(obj) => {
+				let mut chars = "USD".chars();
+				obj.into_iter()
+					.find(|(k, _)| k.iter().all(|k| Some(*k) == chars.next()))
+					.and_then(|v| match v.1 {
+						JsonValue::Number(number) => Some(number),
+						_ => None,
+					})
+			},
+			_ => None
+		})?;
+
+		let exp = price.fraction_length.checked_sub(2).unwrap_or(0);
+		Some(price.integer as u32 * 100 + (price.fraction / 10_u64.pow(exp)) as u32)
+	}
+
 	/// Add new price to the list.
 	fn add_price(who: T::AccountId, price: u32) {
 		debug::info!("Adding to the average: {}", price);

substrate/frame/example-offchain-worker/src/tests.rs

@@ -132,7 +132,7 @@ fn should_make_http_call_and_parse_result() {
 		// when
 		let price = Example::fetch_price().unwrap();
 		// then
-		assert_eq!(price, 15522);
+		assert_eq!(price, 15523);
 	});
 }
 
@@ -164,7 +164,7 @@ fn should_submit_signed_transaction_on_chain() {
 		assert!(pool_state.read().transactions.is_empty());
 		let tx = Extrinsic::decode(&mut &*tx).unwrap();
 		assert_eq!(tx.signature.unwrap().0, 0);
-		assert_eq!(tx.call, Call::submit_price(15522));
+		assert_eq!(tx.call, Call::submit_price(15523));
 	});
 }
 
@@ -186,7 +186,7 @@ fn should_submit_unsigned_transaction_on_chain() {
 		assert!(pool_state.read().transactions.is_empty());
 		let tx = Extrinsic::decode(&mut &*tx).unwrap();
 		assert_eq!(tx.signature, None);
-		assert_eq!(tx.call, Call::submit_price_unsigned(1, 15522));
+		assert_eq!(tx.call, Call::submit_price_unsigned(1, 15523));
 	});
 }
 
@@ -208,3 +208,19 @@ fn price_oracle_response(state: &mut testing::OffchainState) {
 		..Default::default()
 	});
 }
+
+#[test]
+fn parse_price_works() {
+	let test_data = vec![
+		("{\"USD\":6536.92}", Some(653692)),
+		("{\"USD\":65.92}", Some(6592)),
+		("{\"USD\":6536.924565}", Some(653692)),
+		("{\"USD\":6536}", Some(653600)),
+		("{\"USD2\":6536}", None),
+		("{\"USD\":\"6432\"}", None),
+	];
+
+	for (json, expected) in test_data {
+		assert_eq!(expected, Example::parse_price(json));
+	}
+}

substrate/frame/example/Cargo.toml

@@ -20,7 +20,7 @@ sp-std = { version = "2.0.0-alpha.4", default-features = false, path = "../../pr
 sp-io = { version = "2.0.0-alpha.4", default-features = false, path = "../../primitives/io" }
 
 [dev-dependencies]
-sp-core = { version = "2.0.0-alpha.4", path = "../../primitives/core" }
+sp-core = { version = "2.0.0-alpha.4", path = "../../primitives/core", default-features = false }
 
 [features]
 default = ["std"]