RPC api for offchain storage (#4694)

* Rpc api for offchain storage

* Replace Vec<u8> to Bytes, replace Mutex to RwLock

* Remove pub

* Modify copyright year

substrate/client/rpc/src/offchain/mod.rs

@@ -0,0 +1,67 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Substrate offchain API.
+
+#[cfg(test)]
+mod tests;
+
+/// Re-export the API for backward compatibility.
+pub use sc_rpc_api::offchain::*;
+use self::error::{Error, Result};
+use sp_core::{
+	Bytes,
+	offchain::{OffchainStorage, StorageKind},
+};
+use parking_lot::RwLock;
+use std::sync::Arc;
+
+/// Offchain API
+#[derive(Debug)]
+pub struct Offchain<T: OffchainStorage> {
+	/// Offchain storage
+	storage: Arc<RwLock<T>>,
+}
+
+impl<T: OffchainStorage> Offchain<T> {
+	/// Create new instance of Offchain API.
+	pub fn new(storage: T) -> Self {
+		Offchain {
+			storage: Arc::new(RwLock::new(storage)),
+		}
+	}
+}
+
+impl<T: OffchainStorage + 'static> OffchainApi for Offchain<T> {
+	/// Set offchain local storage under given key and prefix.
+	fn set_local_storage(&self, kind: StorageKind, key: Bytes, value: Bytes) -> Result<()> {
+		let prefix = match kind {
+			StorageKind::PERSISTENT => sp_offchain::STORAGE_PREFIX,
+			StorageKind::LOCAL => return Err(Error::UnavailableStorageKind),
+		};
+		self.storage.write().set(prefix, &*key, &*value);
+		Ok(())
+	}
+
+	/// Get offchain local storage under given key and prefix.
+	fn get_local_storage(&self, kind: StorageKind, key: Bytes) -> Result<Option<Bytes>> {
+		let prefix = match kind {
+			StorageKind::PERSISTENT => sp_offchain::STORAGE_PREFIX,
+			StorageKind::LOCAL => return Err(Error::UnavailableStorageKind),
+		};
+		Ok(self.storage.read().get(prefix, &*key).map(Into::into))
+	}
+}