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Gavin Wood
fd5f9292f5
Closes #2160 First part of [Extrinsic Horizon](https://github.com/paritytech/polkadot-sdk/issues/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. --------- Signed-off-by: georgepisaltu <george.pisaltu@parity.io> 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Phragmén Election Module
An election module based on sequential phragmen.
Term and Round
The election happens in rounds: every N blocks, all previous members are retired and a new set is elected (which may
or may not have an intersection with the previous set). Each round lasts for some number of blocks defined by
TermDuration storage item. The words term and round can be used interchangeably in this context.
TermDuration might change during a round. This can shorten or extend the length of the round. The next election
round's block number is never stored but rather always checked on the fly. Based on the current block number and
TermDuration, the condition BlockNumber % TermDuration == 0 being satisfied will always trigger a new election
round.
Voting
Voters can vote for any set of the candidates by providing a list of account ids. Invalid votes (voting for
non-candidates) are ignored during election. Yet, a voter might vote for a future candidate. Voters reserve a bond as
they vote. Each vote defines a value. This amount is locked from the account of the voter and indicates the weight of
the vote. Voters can update their votes at any time by calling vote() again. This keeps the bond untouched but can
optionally change the locked value. After a round, votes are kept and might still be valid for further rounds. A voter
is responsible for calling remove_voter once they are done to have their bond back and remove the lock.
Voters also report other voters as being defunct to earn their bond. A voter is defunct once all of the candidates that
they have voted for are neither a valid candidate anymore nor a member. Upon reporting, if the target voter is actually
defunct, the reporter will be rewarded by the voting bond of the target. The target will lose their bond and get
removed. If the target is not defunct, the reporter is slashed and removed. To prevent being reported, voters should
manually submit a remove_voter() as soon as they are in the defunct state.
Candidacy and Members
Candidates also reserve a bond as they submit candidacy. A candidate cannot take their candidacy back. A candidate can end up in one of the below situations:
- Winner: A winner is kept as a member. They must still have a bond in reserve and they are automatically counted as a candidate for the next election.
- Runner-up: Runners-up are the best candidates immediately after the winners. The number of runners_up to keep is
configurable. Runners-up are used, in order that they are elected, as replacements when a candidate is kicked by
[remove_member], or when an active member renounces their candidacy. Runners are automatically counted as a candidate for the next election. - Loser: Any of the candidate who are not a winner are left as losers. A loser might be an outgoing member or runner, meaning that they are an active member who failed to keep their spot. An outgoing will always lose their bond.
Renouncing candidacy
All candidates, elected or not, can renounce their candidacy. A call to [Module::renounce_candidacy] will always cause
the candidacy bond to be refunded.
Note that with the members being the default candidates for the next round and votes persisting in storage, the election
system is entirely stable given no further input. This means that if the system has a particular set of candidates C
and voters V that lead to a set of members M being elected, as long as V and C don't remove their candidacy and
votes, M will keep being re-elected at the end of each round.
Module Information
License: Apache-2.0