batch vaas
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Eric Wong
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@ -24,18 +24,14 @@ The Wormhole Core Layer effectively only has two important interactions -- (1) e
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### Emitting a VAA
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There are two forms that VAAs can be emitted within Wormhole:
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- Single VAA: this format should only be used for very simple transactions (i.e. sending tokens to a user's wallet)
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- Batch VAA: this format should be used for most transactions. Batch VAAs allow for easier compsability and better gas efficiency for transactions that contain multiple messages.
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- Single VAA: all messages will be emitted in this format
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- Batch VAA: messages that are generated from the same transaction will be emitted in this format. This feature was developed to provide an easier paradigm for composability and better gas efficiency for more involved cross-chain activity.
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To emit a VAA, always use `publishMessage` which takes in the following arguments:
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1. `nonce` (uint32): a number assigned to each message
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- The `nonce` gives the receving contract a mechanism by which to make sure it does not double process messages
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<!--
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TODO confirm how we want to describe how Batch VAAs are created - MVP or full functionality?
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-->
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- To emit
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- Batch VAAs allow for easier compsability and better gas efficiency of multiple messages. To do this, messages emitted within the same transaction with the same nonce are bundled together into one aggregate message. Messages with a nonce of `0` will not be included in a Batch VAA and emitted individually.
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- The `nonce` provides a mechanism by which to group messages together within a Batch VAA.
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- How Batch VAAs are generated based on a message's `nonce` is described below.
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2. `Consistency` (uint8): the number of blocks that Guardians will wait before signing a message
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- Each blockchain has different finality periods. In general, higher consistencies mean more security against blockchain reorgs.
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- [Here]() are the consistency levels by blockchain that are used by the xAsset layer to have a high level of guarantee against reorgs.
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@ -44,6 +40,32 @@ TODO confirm how we want to describe how Batch VAAs are created - MVP or full fu
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`publishMessage` will output a `sequence` (uint64) that is used in conjunction with `emitterChainID` and `emitterAddress` to retrive the generated VAA from the Guardian Network.
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> How Batch VAAs are generated
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>
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> There are two mechanisms that allow messages to be Batched together that represent a base and more advanced level of compsability.
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>
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> 1. All messages originating from the same transaction will be batched together.
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> 2. Messages that originate from the same transaction and are assigned the same nonce are additionally batched together.
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>
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> _Note: Single VAAs will always be emitted for each message within a transaction, regardless of if a message is included in a batch or not._
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>
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> Here is an example of how messages generated from the same transaction may be batched together:
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>
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> A transaction X that generates 6 messages [A, B, C, D, E, F] that are assigned `nonce` [1, 2, 2, 3, 3, 4] respectively will generate the following VAAs:
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> - (1) full transaction batch VAA
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> - [A, B, C, D, E, F]
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> - (2) smaller batch VAA
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> - [B, C]
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> - [D, E]
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> - (6) single VAA
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> - [A]
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> - [B]
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> - [C]
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> - [D]
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> - [E]
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> - [F]
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### Parsing and Verifying a VAA
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Parsing and Verifying a VAA will depend on the type of VAA that your application expects: a Single VAA or a Batch VAA.
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@ -71,6 +93,6 @@ Batch VAAs are designed so that relayers can choose to submit any subset of the
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---
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Code recommendation, write the code which expects to receive a VAA to utilize parseAndVerifyVM(? unsure if this is the correct call). That way, your code will be able to handle either type 1 VAAs (single VAAs), or type 3 VAAs (headless VAAs). This allows it to utilize both single & batch VAAs and dramatically increases composeability. \*this only requires like two or three lines of code, so this would be a good candidate for a code example which shows how to properly use batch vaas without breaking composeability. Should note that the module code still ALWAYS needs to verify, but should do so with the 'single' message verifying and then expose that function publicly in order to enable composeability.
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Code recommendation, write the code which expects to receive a VAA to utilize parseAndVerifyVM(? unsure if this is the correct call). That way, your code will be able to handle either type 1 VAAs (single VAAs), or type 3 VAAs (headless VAAs). This allows it to utilize both single & batch VAAs and dramatically increases composability. \*this only requires like two or three lines of code, so this would be a good candidate for a code example which shows how to properly use batch vaas without breaking composability. Should note that the module code still ALWAYS needs to verify, but should do so with the 'single' message verifying and then expose that function publicly in order to enable composability.
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-->
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@ -31,9 +31,27 @@ Because baseline VAAs have no destination, they are effectively multicast. They
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## Batch VAAs
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Certain blockchains support version 2 VAAs, also referred to as **Batch VAAs**. When multiple messages with the same nonce are emitted in the same transaction, a batch VAA will be created in addition to the individual VAAs. The Batch VAA contains the body of each individual VAA, but only has a single header. This reduces the gas cost of verifying the VAA, and simplifies the process of relaying and consuming multiple VAAs.
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Certain blockchains support version 2 VAAs, also referred to as **Batch VAAs** which are designed to provide an easier paradigm for composability and better gas efficiency when multiple cross-chain actions are involved in a single transaction.
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Batch VAAs are not currently live on mainnet, but will have initial support on all EVM chains when they launch.
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Batch VAAs are designed to be automatically generated for all messages that come from a single transaction.
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In an extreme composability scenario or advanced integration, there may be some messages in a transaction that may not be relevant to one another. To control the create of additional batches, some messages can be created with the same `nonce` to _additionally_ group them.
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It is of note that Single VAAs will always be emitted for each message generated, regardless of it they are contained in a Batch VAA or not.
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Go [here](../technical/evm/coreLayer.md) for a more detailed description of how Batch VAAs are generated.
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_Note: Batch VAAs are not currently live on mainnet, but will have initial support on all EVM chains when they launch._
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> How to leverage Batch VAAs
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>
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> Imagine a transaction generates three messages (A, B, C) that a consuming contract needs to know about.
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>
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> If each message is independent of each other, the consuming contract can handle and validate each of these VAAs individually like [A], [B], [C].
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>
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> If all of the messages are related to each other, the consuming contract can handle and validate the Batch VAA of the entire transaction that is automatically generated like [A, B, C].
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>
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> If only two of the messages are related to each other, say A and C, the same `nonce` can be used for those two messages to generate an additional Batch VAA and the consuming contract can then handle and validate two sets of VAAs like [A, C] and [B].
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---
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