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FRAME: Reintroduce
TransactionExtension as a replacement for `Signe…
…dExtension` (#3685) Original PR #2280 reverted in #3665 This PR reintroduces the reverted functionality with additional changes, related effort [here](#3623). Description is copied over from the original PR First part of [Extrinsic Horizon](#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) in extrinsic v4. - General transactions (without a hardcoded signature) in extrinsic v5. `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 (RFC [here](polkadot-fellows/RFCs#84)) in extrinsic version 5: - 0b00000100 or 0b00000101: 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. Available in both extrinsic versions 4 and 5. - 0b10000100: Old-school "Signed" Transaction: contains Signature, Extra (extension data) and an extension version byte, introduced as part of [RFC99](https://github.com/polkadot-fellows/RFCs/blob/main/text/0099-transaction-extension-version.md). Still available as part of extrinsic v4. - 0b01000101: New-school "General" Transaction: contains Extra (extension data) and an extension version byte, as per RFC99, but no Signature. Only available in extrinsic v5. 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. `UncheckedExtrinsic` still maintains encode/decode backwards compatibility with extrinsic version 4, where the first byte was encoded as: - 0b00000100 - Unsigned transactions - 0b10000100 - Old-school Signed transactions, without the extension version byte Now, `UncheckedExtrinsic` contains a `Preamble` and the actual call. The `Preamble` describes the type of extrinsic as follows: ```rust /// A "header" for extrinsics leading up to the call itself. Determines the type of extrinsic and /// holds any necessary specialized data. #[derive(Eq, PartialEq, Clone)] pub enum Preamble<Address, Signature, Extension> { /// An extrinsic without a signature or any extension. This means it's either an inherent or /// an old-school "Unsigned" (we don't use that terminology any more since it's confusable with /// the general transaction which is without a signature but does have an extension). /// /// NOTE: In the future, once we remove `ValidateUnsigned`, this will only serve Inherent /// extrinsics and thus can be renamed to `Inherent`. Bare(ExtrinsicVersion), /// An old-school transaction extrinsic which includes a signature of some hard-coded crypto. /// Available only on extrinsic version 4. Signed(Address, Signature, ExtensionVersion, Extension), /// A new-school transaction extrinsic which does not include a signature by default. The /// origin authorization, through signatures or other means, is performed by the transaction /// extension in this extrinsic. Available starting with extrinsic version 5. General(ExtensionVersion, Extension), } ``` ## 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 a `Call` type parameter. `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. - 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. --------- Signed-off-by: georgepisaltu <george.pisaltu@parity.io> Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com> Co-authored-by: Branislav Kontur <bkontur@gmail.com>
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