cd2c8eac55
Co-authored-by: Marko <marko@baricevic.me> Co-authored-by: Julien Robert <julien@rbrt.fr>
46 lines
2.2 KiB
Markdown
46 lines
2.2 KiB
Markdown
# Prepare Proposal
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`PrepareProposal` handles construction of the block, meaning that when a proposer
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is preparing to propose a block, it requests the application to evaluate a
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`RequestPrepareProposal`, which contains a series of transactions from CometBFT's
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mempool. At this point, the application has complete control over the proposal.
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It can modify, delete, and inject transactions from its own app-side mempool into
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the proposal or even ignore all the transactions altogether. What the application
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does with the transactions provided to it by `RequestPrepareProposal` has no
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effect on CometBFT's mempool.
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Note, that the application defines the semantics of the `PrepareProposal` and it
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MAY be non-deterministic and is only executed by the current block proposer.
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Now, reading mempool twice in the previous sentence is confusing, lets break it down.
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CometBFT has a mempool that handles gossiping transactions to other nodes
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in the network. The order of these transactions is determined by CometBFT's mempool,
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using FIFO as the sole ordering mechanism. It's worth noting that the priority mempool
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in Comet was removed or deprecated.
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However, since the application is able to fully inspect
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all transactions, it can provide greater control over transaction ordering.
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Allowing the application to handle ordering enables the application to define how
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it would like the block constructed.
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The Cosmos SDK defines the `DefaultProposalHandler` type, which provides applications with
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`PrepareProposal` and `ProcessProposal` handlers. If you decide to implement your
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own `PrepareProposal` handler, you must ensure that the transactions
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selected DO NOT exceed the maximum block gas (if set) and the maximum bytes provided
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by `req.MaxBytes`.
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```go reference
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https://github.com/cosmos/cosmos-sdk/blob/v0.52.0-beta.1/baseapp/abci_utils.go
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```
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This default implementation can be overridden by the application developer in
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favor of a custom implementation in [`app_di.go`](https://docs.cosmos.network/main/build/building-apps/app-go-di):
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```go
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prepareOpt := func(app *baseapp.BaseApp) {
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abciPropHandler := baseapp.NewDefaultProposalHandler(mempool, app)
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app.SetPrepareProposal(abciPropHandler.PrepareProposalHandler())
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}
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baseAppOptions = append(baseAppOptions, prepareOpt)
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```
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