Bring back SubmitSignedTransaction trait. (#3908)

* Bring back SubmitSignedTransaction.

* Fix long lines.

* Add missing docs.

* Update core/primitives/src/crypto.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/runtime/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/primitives/src/crypto.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/srml/system/src/offchain.rs

@@ -17,8 +17,8 @@
 //! Module helpers for offchain calls.
 
 use codec::Encode;
-use sr_primitives::app_crypto::RuntimeAppPublic;
-use sr_primitives::traits::Extrinsic as ExtrinsicT;
+use sr_primitives::app_crypto::{self, RuntimeAppPublic};
+use sr_primitives::traits::{Extrinsic as ExtrinsicT, IdentifyAccount};
 
 /// A trait responsible for signing a payload using given account.
 pub trait Signer<Public, Signature> {
@@ -28,17 +28,96 @@ pub trait Signer<Public, Signature> {
 	fn sign<Payload: Encode>(public: Public, payload: &Payload) -> Option<Signature>;
 }
 
+/// A `Signer` implementation for any `AppPublic` type.
+///
+/// This implementation additionaly supports conversion to/from multi-signature/multi-signer
+/// wrappers.
+/// If the wrapped crypto doesn't match `AppPublic`s crypto `None` is returned.
 impl<Public, Signature, AppPublic> Signer<Public, Signature> for AppPublic where
-	AppPublic: RuntimeAppPublic + From<Public>,
-	AppPublic::Signature: Into<Signature>,
+	AppPublic: RuntimeAppPublic
+		+ app_crypto::AppPublic
+		+ From<<AppPublic as app_crypto::AppPublic>::Generic>,
+	<AppPublic as RuntimeAppPublic>::Signature: app_crypto::AppSignature,
+	Signature: From<
+		<<AppPublic as RuntimeAppPublic>::Signature as app_crypto::AppSignature>::Generic
+	>,
+	Public: rstd::convert::TryInto<<AppPublic as app_crypto::AppPublic>::Generic>
 {
 	fn sign<Payload: Encode>(public: Public, raw_payload: &Payload) -> Option<Signature> {
 		raw_payload.using_encoded(|payload| {
-			AppPublic::from(public).sign(&payload).map(Into::into)
+			let public = public.try_into().ok()?;
+			AppPublic::from(public).sign(&payload)
+				.map(
+					<<AppPublic as RuntimeAppPublic>::Signature as app_crypto::AppSignature>
+					 ::Generic::from
+				)
+				.map(Signature::from)
 		})
 	}
 }
 
+/// Creates runtime-specific signed transaction.
+pub trait CreateTransaction<T: crate::Trait, Extrinsic: ExtrinsicT> {
+	/// A `Public` key representing a particular `AccountId`.
+	type Public;
+	/// A `Signature` generated by the `Signer`.
+	type Signature;
+
+	/// Attempt to create signed extrinsic data that encodes call from given account.
+	///
+	/// Runtime implementation is free to construct the payload to sign and the signature
+	/// in any way it wants.
+	/// Returns `None` if signed extrinsic could not be created (either because signing failed
+	/// or because of any other runtime-specific reason).
+	fn create_transaction<F: Signer<Self::Public, Self::Signature>>(
+		call: Extrinsic::Call,
+		public: Self::Public,
+		account: T::AccountId,
+		nonce: T::Index,
+	) -> Option<(Extrinsic::Call, Extrinsic::SignaturePayload)>;
+}
+
+type PublicOf<T, Call, X> = <
+	<X as SubmitSignedTransaction<T, Call>>::CreateTransaction as CreateTransaction<
+		T,
+		<X as SubmitSignedTransaction<T, Call>>::Extrinsic,
+	>
+>::Public;
+
+/// A trait to sign and submit transactions in offchain calls.
+pub trait SubmitSignedTransaction<T: crate::Trait, Call>
+where
+	PublicOf<T, Call, Self>: IdentifyAccount<AccountId=T::AccountId> + Clone,
+{
+	/// Unchecked extrinsic type.
+	type Extrinsic: ExtrinsicT<Call=Call> + codec::Encode;
+
+	/// A runtime-specific type to produce signed data for the extrinsic.
+	type CreateTransaction: CreateTransaction<T, Self::Extrinsic>;
+
+	/// A type used to sign transactions created using `CreateTransaction`.
+	type Signer: Signer<
+		PublicOf<T, Call, Self>,
+		<Self::CreateTransaction as CreateTransaction<T, Self::Extrinsic>>::Signature,
+	>;
+
+	/// Sign given call and submit it to the transaction pool.
+	///
+	/// Returns `Ok` if the transaction was submitted correctly
+	/// and `Err` if the key for given `id` was not found or the
+	/// transaction was rejected from the pool.
+	fn sign_and_submit(call: impl Into<Call>, public: PublicOf<T, Call, Self>) -> Result<(), ()> {
+		let call = call.into();
+		let id = public.clone().into_account();
+		let expected = <crate::Module<T>>::account_nonce(&id);
+		let (call, signature_data) = Self::CreateTransaction
+			::create_transaction::<Self::Signer>(call, public, id, expected)
+			.ok_or(())?;
+		let xt = Self::Extrinsic::new(call, Some(signature_data)).ok_or(())?;
+		runtime_io::submit_transaction(xt.encode())
+	}
+}
+
 /// A trait to submit unsigned transactions in offchain calls.
 pub trait SubmitUnsignedTransaction<T: crate::Trait, Call> {
 	/// Unchecked extrinsic type.
@@ -67,6 +146,19 @@ impl<S, C, E> Default for TransactionSubmitter<S, C, E> {
 	}
 }
 
+/// A blanket implementation to simplify creation of transaction signer & submitter in the runtime.
+impl<T, E, S, C, Call> SubmitSignedTransaction<T, Call> for TransactionSubmitter<S, C, E> where
+	T: crate::Trait,
+	C: CreateTransaction<T, E>,
+	S: Signer<<C as CreateTransaction<T, E>>::Public, <C as CreateTransaction<T, E>>::Signature>,
+	E: ExtrinsicT<Call=Call> + codec::Encode,
+	<C as CreateTransaction<T, E>>::Public: IdentifyAccount<AccountId=T::AccountId> + Clone,
+{
+	type Extrinsic = E;
+	type CreateTransaction = C;
+	type Signer = S;
+}
+
 /// A blanket impl to use the same submitter for usigned transactions as well.
 impl<T, E, S, C, Call> SubmitUnsignedTransaction<T, Call> for TransactionSubmitter<S, C, E> where
 	T: crate::Trait,