srml-contracts: Deferred actions (#3255)

* Switch to deferred actions

* Make restore_to a deferred action.

* Bump version.

* Review fixes.

substrate/srml/contracts/src/wasm/runtime.rs

@@ -586,6 +586,87 @@ define_env!(Env, <E: Ext>,
 		Ok(())
 	},
 
+	// Record a request to restore the caller contract to the specified contract.
+	//
+	// At the finalization stage, i.e. when all changes from the extrinsic that invoked this
+	// contract are commited, this function will compute a tombstone hash from the caller's
+	// storage and the given code hash and if the hash matches the hash found in the tombstone at
+	// the specified address - kill the caller contract and restore the destination contract and set
+	// the specified `rent_allowance`. All caller's funds are transfered to the destination.
+	//
+	// This function doesn't perform restoration right away but defers it to the end of the
+	// transaction. If there is no tombstone in the destination address or if the hashes don't match
+	// then restoration is cancelled and no changes are made.
+	//
+	// `dest_ptr`, `dest_len` - the pointer and the length of a buffer that encodes `T::AccountId`
+	// with the address of the to be restored contract.
+	// `code_hash_ptr`, `code_hash_len` - the pointer and the length of a buffer that encodes
+	// a code hash of the to be restored contract.
+	// `rent_allowance_ptr`, `rent_allowance_len` - the pointer and the length of a buffer that
+	// encodes the rent allowance that must be set in the case of successful restoration.
+	// `delta_ptr` is the pointer to the start of a buffer that has `delta_count` storage keys
+	// laid out sequentially.
+	ext_restore_to(
+		ctx,
+		dest_ptr: u32,
+		dest_len: u32,
+		code_hash_ptr: u32,
+		code_hash_len: u32,
+		rent_allowance_ptr: u32,
+		rent_allowance_len: u32,
+		delta_ptr: u32,
+		delta_count: u32
+	) => {
+		let dest = {
+			let dest_buf = read_sandbox_memory(ctx, dest_ptr, dest_len)?;
+			<<E as Ext>::T as system::Trait>::AccountId::decode(&mut &dest_buf[..])
+				.ok_or_else(|| sandbox::HostError)?
+		};
+		let code_hash = {
+			let code_hash_buf = read_sandbox_memory(ctx, code_hash_ptr, code_hash_len)?;
+			<CodeHash<<E as Ext>::T>>::decode(&mut &code_hash_buf[..])
+				.ok_or_else(|| sandbox::HostError)?
+		};
+		let rent_allowance = {
+			let rent_allowance_buf = read_sandbox_memory(
+				ctx,
+				rent_allowance_ptr,
+				rent_allowance_len
+			)?;
+			BalanceOf::<<E as Ext>::T>::decode(&mut &rent_allowance_buf[..])
+				.ok_or_else(|| sandbox::HostError)?
+		};
+		let delta = {
+			// We don't use `with_capacity` here to not eagerly allocate the user specified amount
+			// of memory.
+			let mut delta = Vec::new();
+			let mut key_ptr = delta_ptr;
+
+			for _ in 0..delta_count {
+				const KEY_SIZE: usize = 32;
+
+				// Read the delta into the provided buffer and collect it into the buffer.
+				let mut delta_key: StorageKey = [0; KEY_SIZE];
+				read_sandbox_memory_into_buf(ctx, key_ptr, &mut delta_key)?;
+				delta.push(delta_key);
+
+				// Offset key_ptr to the next element.
+				key_ptr = key_ptr.checked_add(KEY_SIZE as u32).ok_or_else(|| sandbox::HostError)?;
+			}
+
+			delta
+		};
+
+		ctx.ext.note_restore_to(
+			dest,
+			code_hash,
+			rent_allowance,
+			delta,
+		);
+
+		Ok(())
+	},
+
 	// Returns the size of the scratch buffer.
 	//
 	// For more details on the scratch buffer see `ext_scratch_copy`.