feat: add solution for ex10

Author: tdelabro

exercises/ex10-offchain-worker/pallet-price-oracle/src/lib.rs

@@ -47,7 +47,12 @@ pub mod pallet {
 	#[pallet::hooks]
 	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
 		fn offchain_worker(_n: BlockNumberFor<T>) {
-			// TODO: call `fetch_btc_price_and_send_unsigned_transaction` and log any error
+			match Self::fetch_btc_price_and_send_unsigned_transaction() {
+				Ok(_) => {},
+				Err(e) => {
+					log::error!("Failed to fetch and set BTC price: {e}");
+				},
+			};
 		}
 	}
 
@@ -58,10 +63,11 @@ pub mod pallet {
 	impl<T: Config> Pallet<T> {
 		#[pallet::weight(0)]
 		pub fn set_btc_price(origin: OriginFor<T>, btc_price: FixedI64) -> DispatchResult {
-			// TODO:
-			// - ensure origin is none
-			// - set BTCPrice storage
-			// - emit `BtcPriceSet` event
+			ensure_none(origin)?;
+
+			BTCPrice::<T>::set(Some(btc_price));
+
+			Self::deposit_event(Event::<T>::BtcPriceSet(btc_price));
 
 			Ok(())
 		}
@@ -77,10 +83,24 @@ pub mod pallet {
 		/// here we make sure that some particular calls (the ones produced by offchain worker)
 		/// are being whitelisted and marked as valid.
 		fn validate_unsigned(source: TransactionSource, call: &Self::Call) -> TransactionValidity {
-			// TODO: implemente some kind of validation
-			// It should accept calls to `set_btc_price` and refuse any other
-
-			InvalidTransaction::Call.into()
+			if source == TransactionSource::External {
+				return InvalidTransaction::Call.into()
+			}
+
+			const UNSIGNED_TXS_PRIORITY: TransactionPriority = u64::MAX;
+			let valid_tx = |provide| {
+				ValidTransaction::with_tag_prefix("price-oracle")
+					.priority(UNSIGNED_TXS_PRIORITY)
+					.and_provides([&provide])
+					.longevity(1) // Only valid for this block
+					.propagate(false) // Should not be gossiped
+					.build()
+			};
+
+			match call {
+				Call::set_btc_price { .. } => valid_tx(b"set_btc_price".to_vec()),
+				_ => InvalidTransaction::Call.into(),
+			}
 		}
 	}
 }

exercises/ex10-offchain-worker/pallet-price-oracle/src/offchain_worker/mod.rs

@@ -22,20 +22,30 @@ struct CoinbaseResponseBody {
 }
 
 pub(crate) fn fetch_btc_price() -> Result<FixedI64, OffchainWorkerError> {
-	// TODO:
-	// - do an http get request to `"https://api.coinbase.com/v2/prices/BTC-USD/buy`
-	// - extract the price form the response body
-	// - convert it to `FixedI64` before returning it
+	let res = http::Request::get(&"https://api.coinbase.com/v2/prices/BTC-USD/buy")
+		.send()?
+		.wait()?;
+	let body_bytes = res.body().collect::<Vec<u8>>();
+	let body: CoinbaseResponseBody = serde_json::from_slice(&body_bytes)?;
 
-	Ok(Default::default())
+	if &body.data.base != "BTC" || &body.data.currency != "USD" {
+		return Err(OffchainWorkerError::WrongPair)
+	}
+
+	let price: f64 = body.data.amount.parse().map_err(|e| OffchainWorkerError::ParsePrice(e))?;
+
+	Ok(f64_to_fixed_i64(price))
 }
 
 impl<T: Config> Pallet<T> {
 	pub(crate) fn fetch_btc_price_and_send_unsigned_transaction() -> Result<(), String> {
-		// Todo: call `fetch_btc_price` and use the return to submit an unsigned transaction
-		// containing a call to `set_btc_price`
+		let btc_price = fetch_btc_price().map_err(|e| e.to_string())?;
 
-		Ok(())
+		let call = Call::set_btc_price { btc_price };
+		frame_system::offchain::SubmitTransaction::<T, Call<T>>::submit_unsigned_transaction(
+			call.into(),
+		)
+		.map_err(|_| String::from("Failed to submit unsigned `set_btc_price` call"))
 	}
 }