Offchain execution extensions (#4145)

* Pass Extensions instead of individual objects.

* Move TransactionPool to a separate ExternalitiesExtension.

* Fix compilation.?

* Clean up.

* Refactor testing utilities.

* Add docs, fix tests.

* Fix doctest.

* Fix formatting and add some logs.

* Add some docs.

* Remove unused files.

substrate/primitives/sr-primitives/src/offchain/http.rs

@@ -516,8 +516,10 @@ impl<'a> HeadersIterator<'a> {
 mod tests {
 	use super::*;
 	use runtime_io::TestExternalities;
-	use substrate_offchain::testing;
-	use primitives::offchain::OffchainExt;
+	use primitives::offchain::{
+		OffchainExt,
+		testing,
+	};
 
 	#[test]
 	fn should_send_a_basic_request_and_get_response() {

substrate/primitives/sr-primitives/src/offchain/mod.rs

@@ -14,6 +14,29 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
-//! A collection of higher lever helpers for offchain workers.
+//! A collection of higher lever helpers for offchain calls.
+
+use crate::{
+	traits,
+	generic::BlockId,
+};
 
 pub mod http;
+
+/// An abstraction for transaction pool.
+///
+/// This trait is used by offchain calls to be able to submit transactions.
+/// The main use case is for offchain workers, to feed back the results of computations,
+/// but since the transaction pool access is a separate `ExternalitiesExtension` it can
+/// be also used in context of other offchain calls. For one may generate and submit
+/// a transaction for some misbehavior reports (say equivocation).
+pub trait TransactionPool<Block: traits::Block>: Send + Sync {
+	/// Submit transaction.
+	///
+	/// The transaction will end up in the pool and be propagated to others.
+	fn submit_at(
+		&self,
+		at: &BlockId<Block>,
+		extrinsic: Block::Extrinsic,
+	) -> Result<(), ()>;
+}