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FRAME: Create TransactionExtension as a replacement for `SignedExte…
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…nsion` (#2280)

Closes paritytech#2160

First part of [Extrinsic
Horizon](paritytech/polkadot-sdk#2415)

Introduces a new trait `TransactionExtension` to replace
`SignedExtension`. Introduce the idea of transactions which obey the
runtime's extensions and have according Extension data (né Extra data)
yet do not have hard-coded signatures.

Deprecate the terminology of "Unsigned" when used for
transactions/extrinsics owing to there now being "proper" unsigned
transactions which obey the extension framework and "old-style" unsigned
which do not. Instead we have __*General*__ for the former and
__*Bare*__ for the latter. (Ultimately, the latter will be phased out as
a type of transaction, and Bare will only be used for Inherents.)

Types of extrinsic are now therefore:
- Bare (no hardcoded signature, no Extra data; used to be known as
"Unsigned")
- Bare transactions (deprecated): Gossiped, validated with
`ValidateUnsigned` (deprecated) and the `_bare_compat` bits of
`TransactionExtension` (deprecated).
  - Inherents: Not gossiped, validated with `ProvideInherent`.
- Extended (Extra data): Gossiped, validated via `TransactionExtension`.
  - Signed transactions (with a hardcoded signature).
  - General transactions (without a hardcoded signature).

`TransactionExtension` differs from `SignedExtension` because:
- A signature on the underlying transaction may validly not be present.
- It may alter the origin during validation.
- `pre_dispatch` is renamed to `prepare` and need not contain the checks
present in `validate`.
- `validate` and `prepare` is passed an `Origin` rather than a
`AccountId`.
- `validate` may pass arbitrary information into `prepare` via a new
user-specifiable type `Val`.
- `AdditionalSigned`/`additional_signed` is renamed to
`Implicit`/`implicit`. It is encoded *for the entire transaction* and
passed in to each extension as a new argument to `validate`. This
facilitates the ability of extensions to acts as underlying crypto.

There is a new `DispatchTransaction` trait which contains only default
function impls and is impl'ed for any `TransactionExtension` impler. It
provides several utility functions which reduce some of the tedium from
using `TransactionExtension` (indeed, none of its regular functions
should now need to be called directly).

Three transaction version discriminator ("versions") are now
permissible:
- 0b000000100: Bare (used to be called "Unsigned"): contains Signature
or Extra (extension data). After bare transactions are no longer
supported, this will strictly identify an Inherents only.
- 0b100000100: Old-school "Signed" Transaction: contains Signature and
Extra (extension data).
- 0b010000100: New-school "General" Transaction: contains Extra
(extension data), but no Signature.

For the New-school General Transaction, it becomes trivial for authors
to publish extensions to the mechanism for authorizing an Origin, e.g.
through new kinds of key-signing schemes, ZK proofs, pallet state,
mutations over pre-authenticated origins or any combination of the
above.

## Code Migration

### NOW: Getting it to build

Wrap your `SignedExtension`s in `AsTransactionExtension`. This should be
accompanied by renaming your aggregate type in line with the new
terminology. E.g. Before:

```rust
/// The SignedExtension to the basic transaction logic.
pub type SignedExtra = (
	/* snip */
	MySpecialSignedExtension,
);
/// Unchecked extrinsic type as expected by this runtime.
pub type UncheckedExtrinsic =
	generic::UncheckedExtrinsic<Address, RuntimeCall, Signature, SignedExtra>;
```

After:

```rust
/// The extension to the basic transaction logic.
pub type TxExtension = (
	/* snip */
	AsTransactionExtension<MySpecialSignedExtension>,
);
/// Unchecked extrinsic type as expected by this runtime.
pub type UncheckedExtrinsic =
	generic::UncheckedExtrinsic<Address, RuntimeCall, Signature, TxExtension>;
```

You'll also need to alter any transaction building logic to add a
`.into()` to make the conversion happen. E.g. Before:

```rust
fn construct_extrinsic(
		/* snip */
) -> UncheckedExtrinsic {
	let extra: SignedExtra = (
		/* snip */
		MySpecialSignedExtension::new(/* snip */),
	);
	let payload = SignedPayload::new(call.clone(), extra.clone()).unwrap();
	let signature = payload.using_encoded(|e| sender.sign(e));
	UncheckedExtrinsic::new_signed(
		/* snip */
		Signature::Sr25519(signature),
		extra,
	)
}
```

After:

```rust
fn construct_extrinsic(
		/* snip */
) -> UncheckedExtrinsic {
	let tx_ext: TxExtension = (
		/* snip */
		MySpecialSignedExtension::new(/* snip */).into(),
	);
	let payload = SignedPayload::new(call.clone(), tx_ext.clone()).unwrap();
	let signature = payload.using_encoded(|e| sender.sign(e));
	UncheckedExtrinsic::new_signed(
		/* snip */
		Signature::Sr25519(signature),
		tx_ext,
	)
}
```

### SOON: Migrating to `TransactionExtension`

Most `SignedExtension`s can be trivially converted to become a
`TransactionExtension`. There are a few things to know.

- Instead of a single trait like `SignedExtension`, you should now
implement two traits individually: `TransactionExtensionBase` and
`TransactionExtension`.
- Weights are now a thing and must be provided via the new function `fn
weight`.

#### `TransactionExtensionBase`

This trait takes care of anything which is not dependent on types
specific to your runtime, most notably `Call`.

- `AdditionalSigned`/`additional_signed` is renamed to
`Implicit`/`implicit`.
- Weight must be returned by implementing the `weight` function. If your
extension is associated with a pallet, you'll probably want to do this
via the pallet's existing benchmarking infrastructure.

#### `TransactionExtension`

Generally:
- `pre_dispatch` is now `prepare` and you *should not reexecute the
`validate` functionality in there*!
- You don't get an account ID any more; you get an origin instead. If
you need to presume an account ID, then you can use the trait function
`AsSystemOriginSigner::as_system_origin_signer`.
- You get an additional ticket, similar to `Pre`, called `Val`. This
defines data which is passed from `validate` into `prepare`. This is
important since you should not be duplicating logic from `validate` to
`prepare`, you need a way of passing your working from the former into
the latter. This is it.
- This trait takes two type parameters: `Call` and `Context`. `Call` is
the runtime call type which used to be an associated type; you can just
move it to become a type parameter for your trait impl. `Context` is not
currently used and you can safely implement over it as an unbounded
type.
- There's no `AccountId` associated type any more. Just remove it.

Regarding `validate`:
- You get three new parameters in `validate`; all can be ignored when
migrating from `SignedExtension`.
- `validate` returns a tuple on success; the second item in the tuple is
the new ticket type `Self::Val` which gets passed in to `prepare`. If
you use any information extracted during `validate` (off-chain and
on-chain, non-mutating) in `prepare` (on-chain, mutating) then you can
pass it through with this. For the tuple's last item, just return the
`origin` argument.

Regarding `prepare`:
- This is renamed from `pre_dispatch`, but there is one change:
- FUNCTIONALITY TO VALIDATE THE TRANSACTION NEED NOT BE DUPLICATED FROM
`validate`!!
- (This is different to `SignedExtension` which was required to run the
same checks in `pre_dispatch` as in `validate`.)

Regarding `post_dispatch`:
- Since there are no unsigned transactions handled by
`TransactionExtension`, `Pre` is always defined, so the first parameter
is `Self::Pre` rather than `Option<Self::Pre>`.

If you make use of `SignedExtension::validate_unsigned` or
`SignedExtension::pre_dispatch_unsigned`, then:
- Just use the regular versions of these functions instead.
- Have your logic execute in the case that the `origin` is `None`.
- Ensure your transaction creation logic creates a General Transaction
rather than a Bare Transaction; this means having to include all
`TransactionExtension`s' data.
- `ValidateUnsigned` can still be used (for now) if you need to be able
to construct transactions which contain none of the extension data,
however these will be phased out in stage 2 of the Transactions Horizon,
so you should consider moving to an extension-centric design.

## TODO

- [x] Introduce `CheckSignature` impl of `TransactionExtension` to
ensure it's possible to have crypto be done wholly in a
`TransactionExtension`.
- [x] Deprecate `SignedExtension` and move all uses in codebase to
`TransactionExtension`.
  - [x] `ChargeTransactionPayment`
  - [x] `DummyExtension`
  - [x] `ChargeAssetTxPayment` (asset-tx-payment)
  - [x] `ChargeAssetTxPayment` (asset-conversion-tx-payment)
  - [x] `CheckWeight`
  - [x] `CheckTxVersion`
  - [x] `CheckSpecVersion`
  - [x] `CheckNonce`
  - [x] `CheckNonZeroSender`
  - [x] `CheckMortality`
  - [x] `CheckGenesis`
  - [x] `CheckOnlySudoAccount`
  - [x] `WatchDummy`
  - [x] `PrevalidateAttests`
  - [x] `GenericSignedExtension`
  - [x] `SignedExtension` (chain-polkadot-bulletin)
  - [x] `RefundSignedExtensionAdapter`
- [x] Implement `fn weight` across the board.
- [ ] Go through all pre-existing extensions which assume an account
signer and explicitly handle the possibility of another kind of origin.
- [x] `CheckNonce` should probably succeed in the case of a non-account
origin.
- [x] `CheckNonZeroSender` should succeed in the case of a non-account
origin.
- [x] `ChargeTransactionPayment` and family should fail in the case of a
non-account origin.
  - [ ] 
- [x] Fix any broken tests.

---------

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35 changes: 23 additions & 12 deletions Cargo.lock

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1 change: 1 addition & 0 deletions bridges/bin/runtime-common/Cargo.toml
Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,7 @@ runtime-benchmarks = [
"pallet-bridge-messages/runtime-benchmarks",
"pallet-bridge-parachains/runtime-benchmarks",
"pallet-bridge-relayers/runtime-benchmarks",
"pallet-transaction-payment/runtime-benchmarks",
"pallet-utility/runtime-benchmarks",
"sp-runtime/runtime-benchmarks",
"xcm-builder/runtime-benchmarks",
Expand Down
72 changes: 41 additions & 31 deletions bridges/bin/runtime-common/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -105,43 +105,48 @@ macro_rules! generate_bridge_reject_obsolete_headers_and_messages {
($call:ty, $account_id:ty, $($filter_call:ty),*) => {
#[derive(Clone, codec::Decode, Default, codec::Encode, Eq, PartialEq, sp_runtime::RuntimeDebug, scale_info::TypeInfo)]
pub struct BridgeRejectObsoleteHeadersAndMessages;
impl sp_runtime::traits::SignedExtension for BridgeRejectObsoleteHeadersAndMessages {
impl sp_runtime::traits::TransactionExtensionBase for BridgeRejectObsoleteHeadersAndMessages {
const IDENTIFIER: &'static str = "BridgeRejectObsoleteHeadersAndMessages";
type AccountId = $account_id;
type Call = $call;
type AdditionalSigned = ();
type Implicit = ();
}
impl<Context> sp_runtime::traits::TransactionExtension<$call, Context> for BridgeRejectObsoleteHeadersAndMessages {
type Pre = ();

fn additional_signed(&self) -> sp_std::result::Result<
(),
sp_runtime::transaction_validity::TransactionValidityError,
> {
Ok(())
}
type Val = ();

fn validate(
&self,
_who: &Self::AccountId,
call: &Self::Call,
_info: &sp_runtime::traits::DispatchInfoOf<Self::Call>,
origin: <$call as sp_runtime::traits::Dispatchable>::RuntimeOrigin,
call: &$call,
_info: &sp_runtime::traits::DispatchInfoOf<$call>,
_len: usize,
) -> sp_runtime::transaction_validity::TransactionValidity {
let valid = sp_runtime::transaction_validity::ValidTransaction::default();
_context: &mut Context,
_self_implicit: Self::Implicit,
_inherited_implication: &impl codec::Encode,
) -> Result<
(
sp_runtime::transaction_validity::ValidTransaction,
Self::Val,
<$call as sp_runtime::traits::Dispatchable>::RuntimeOrigin,
), sp_runtime::transaction_validity::TransactionValidityError
> {
let tx_validity = sp_runtime::transaction_validity::ValidTransaction::default();
$(
let valid = valid
.combine_with(<$filter_call as $crate::BridgeRuntimeFilterCall<$call>>::validate(call)?);
let call_filter_validity = <$filter_call as $crate::BridgeRuntimeFilterCall<$call>>::validate(call)?;
let tx_validity = tx_validity.combine_with(call_filter_validity);
)*
Ok(valid)
Ok((tx_validity, (), origin))
}

fn pre_dispatch(
fn prepare(
self,
who: &Self::AccountId,
call: &Self::Call,
info: &sp_runtime::traits::DispatchInfoOf<Self::Call>,
len: usize,
_val: Self::Val,
_origin: &<$call as sp_runtime::traits::Dispatchable>::RuntimeOrigin,
_call: &$call,
_info: &sp_runtime::traits::DispatchInfoOf<$call>,
_len: usize,
_context: &Context,
) -> Result<Self::Pre, sp_runtime::transaction_validity::TransactionValidityError> {
self.validate(who, call, info, len).map(drop)
Ok(())
}
}
};
Expand All @@ -150,12 +155,14 @@ macro_rules! generate_bridge_reject_obsolete_headers_and_messages {
#[cfg(test)]
mod tests {
use crate::BridgeRuntimeFilterCall;
use frame_support::{assert_err, assert_ok};
use codec::Encode;
use frame_support::assert_err;
use sp_runtime::{
traits::SignedExtension,
traits::DispatchTransaction,
transaction_validity::{InvalidTransaction, TransactionValidity, ValidTransaction},
};

#[derive(Encode)]
pub struct MockCall {
data: u32,
}
Expand Down Expand Up @@ -206,17 +213,20 @@ mod tests {
);

assert_err!(
BridgeRejectObsoleteHeadersAndMessages.validate(&(), &MockCall { data: 1 }, &(), 0),
BridgeRejectObsoleteHeadersAndMessages.validate_only((), &MockCall { data: 1 }, &(), 0),
InvalidTransaction::Custom(1)
);

assert_err!(
BridgeRejectObsoleteHeadersAndMessages.validate(&(), &MockCall { data: 2 }, &(), 0),
BridgeRejectObsoleteHeadersAndMessages.validate_only((), &MockCall { data: 2 }, &(), 0),
InvalidTransaction::Custom(2)
);

assert_ok!(
BridgeRejectObsoleteHeadersAndMessages.validate(&(), &MockCall { data: 3 }, &(), 0),
assert_eq!(
BridgeRejectObsoleteHeadersAndMessages
.validate_only((), &MockCall { data: 3 }, &(), 0)
.unwrap()
.0,
ValidTransaction { priority: 3, ..Default::default() }
)
}
Expand Down
2 changes: 1 addition & 1 deletion bridges/bin/runtime-common/src/mock.rs
Original file line number Diff line number Diff line change
Expand Up @@ -164,6 +164,7 @@ impl pallet_balances::Config for TestRuntime {
type AccountStore = System;
}

#[derive_impl(pallet_transaction_payment::config_preludes::TestDefaultConfig as pallet_transaction_payment::DefaultConfig)]
impl pallet_transaction_payment::Config for TestRuntime {
type OnChargeTransaction = pallet_transaction_payment::CurrencyAdapter<Balances, ()>;
type OperationalFeeMultiplier = ConstU8<5>;
Expand All @@ -176,7 +177,6 @@ impl pallet_transaction_payment::Config for TestRuntime {
MinimumMultiplier,
MaximumMultiplier,
>;
type RuntimeEvent = RuntimeEvent;
}

impl pallet_bridge_grandpa::Config for TestRuntime {
Expand Down
11 changes: 7 additions & 4 deletions bridges/bin/runtime-common/src/priority_calculator.rs
Original file line number Diff line number Diff line change
Expand Up @@ -169,20 +169,23 @@ mod integrity_tests {
// nodes to the proof (x0.5 because we expect some nodes to be reused)
let estimated_message_size = 512;
// let's say all our messages have the same dispatch weight
let estimated_message_dispatch_weight =
Runtime::WeightInfo::message_dispatch_weight(estimated_message_size);
let estimated_message_dispatch_weight = <Runtime as pallet_bridge_messages::Config<
MessagesInstance,
>>::WeightInfo::message_dispatch_weight(
estimated_message_size
);
// messages proof argument size is (for every message) messages size + some additional
// trie nodes. Some of them are reused by different messages, so let's take 2/3 of default
// "overhead" constant
let messages_proof_size = Runtime::WeightInfo::expected_extra_storage_proof_size()
let messages_proof_size = <Runtime as pallet_bridge_messages::Config<MessagesInstance>>::WeightInfo::expected_extra_storage_proof_size()
.saturating_mul(2)
.saturating_div(3)
.saturating_add(estimated_message_size)
.saturating_mul(messages as _);

// finally we are able to estimate transaction size and weight
let transaction_size = base_tx_size.saturating_add(messages_proof_size);
let transaction_weight = Runtime::WeightInfo::receive_messages_proof_weight(
let transaction_weight = <Runtime as pallet_bridge_messages::Config<MessagesInstance>>::WeightInfo::receive_messages_proof_weight(
&PreComputedSize(transaction_size as _),
messages as _,
estimated_message_dispatch_weight.saturating_mul(messages),
Expand Down
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