Weak and Strong

Which Hooks are allowed to run and when?

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Hook Design Philosophy

Every party affected by a transaction should have the opportunity to have their Hooks executed.

Transactional Stake Holders (TSH) are parties that somehow have a stake in or are otherwise affected by a transaction. Their particular stake may be a weak or strong. The degree of connection with the transaction dictates whether the party has the right to have their Hooks executed and who has to pay for that execution.

For example:

• In a conventional direct XRP Payment transaction the two TSH are the originating account and the destination account.
• In a SetSignerList transaction the TSH are the originating account and each account whose address appears in the signer list, where such accounts are active on the ledger.
• In an OfferCreate transaction, other account's offers which are crossed by the originating transaction are all weak TSH and may opt for weak execution.

Due to the heterogenous nature of transactions on the XRP Ledger, TSH come in all shapes and sizes and can be exotic and non-intuitive. This becomes more true as time passes and more transaction types are added to the Ledger.

Weak and Strong

Each TSH has either a weak or a strong connection to the transaction.

A Strong connection means:

1. The originating transaction must pay the fee for the execution of the TSH Hook Chain
2. The TSH has the right to rollback the whole transaction by calling rollback() from their Hook during execution.

A Weak connection means:

1. The originating transaction does not pay for the execution of the TSH Hook Chain.
2. The TSH pays for the execution of their own Hook Chain through a feature called Collect Call Hooks.
3. The TSH must have set an account flag asfTshCollect prior to the execution of the originating transaction.
4. The TSH does not have the right to rollback the whole transaction by calling rollback() from their Hook during execution (but can still modify their own Hook state and Emit transactions.)

Before or After

Strong TSHes have their hooks executed before the originating transaction is applied to the ledger. This means they have the ability to rollback the transaction (because it hasn't yet been applied.) This gives strongly executed hooks the ability to completely block a transaction from occurring.

Weak TSHes have their hooks executed after the originating transaction has been applied to the ledger. This means they have access to the transaction metadata but cannot prevent the transaction from occurring.

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Hint

Strongly executed hooks can call hook_again to be executed a second time as a weak execution after the originating transaction has been applied.

Execution Context

The uint32_t parameter in hook(uint32_t) and cbak(uint32_t) carries important context information from the Hooks Amendment to your Hook.

During the execution of hook:

• 0 means the Hook is being executed strongly
• 1 means the Hook is being executed weakly
• 2 means the Hook is being executed weakly after being executed strongly due to a hook_again call.

During the execution of cbak:

• 0 means the Hook is being called back after a transaction it emitted was successfully accepted into a ledger.
• 1 means the Hook is being called back after a transaction it emitted was marked as never able to be applied to any ledger (EmitFailure).

Reference Table

If a Transaction Type does not appear in the table then it has no TSHes other than its originating account.

Transaction Type	TSH Type	Who is the TSH
AccountDelete	Strong	Destination account funds are paid out to after deletion
AccountSet	None	N/A
CheckCancel	Weak	Destination account
CheckCash	None	N/A
CheckCreate	Strong	Destination account
ClaimReward	Strong	Issuer Account
DepositPreauth	Strong	Authorized account
EscrowCancel	Weak	Destination account
EscrowCreate	Strong	Destination account
EscrowFinish	Strong	Destination account
GenesisMint	Weak	Each Destination in the GenesisMints Array
Import	Strong	Issuer Account
Invoke	Strong	Destination account
OfferCancel	None	N/A
OfferCreate	Weak	Accounts whose offers were crossed by this action.
Payment	Strong + Weak	Strong: Destination account. Weak: Any non-issuer the payment is rippled through.
PaymentChannelClaim	Weak	Destination account
PaymentChannelCreate	Strong	Destination account
PaymentChannelFund	Weak	Destination account
SetHook	None	N/A
SetRegularKey	Strong	The account whose address is being set as the key.
SignerListSet	Strong	Accounts whose addresses are set as signing keys (if they exist and have Hooks set on them).
TicketCreate	None	N/A
TrustSet	Weak	Issuer account
URITokenCancelSellOffer	None	N/A
URITokenCreateSellOffer	Strong	Destination account, Issuer if tfBurnable Flag is set
URITokenBurn	Strong	Issuer if tfBurnable Flag is set
URITokenBuy	Strong	Owner account, Issuer if tfBurnable Flag is set
URITokenMint	None	N/A

AccountSet

OTXN	TSH	AccountSet
Account	Account	Strong

AccountDelete

OTXN	TSH	AccountDelete
Account	Account	None
Account	Beneficiary	Strong

Check

OTXN	TSH	CheckCancel	CheckCreate	CheckCash
Account	Account	Strong	Strong	None
Account	Destination	Weak	Strong	None
Destination	Destination	Strong	None	Strong
Destination	Account	Weak	None	Weak

ClaimReward

OTXN	TSH	ClaimReward
Account	Account	Strong
Account	Issuer	Strong

DepositPreauth

OTXN	TSH	DepositPreauth
Account	Account	Strong
Account	Authorized	Strong

Escrow

OTXN	TSH	EscrowCancel	EscrowCreate	EscrowFinish
Account	Account	Strong	Strong	Strong
Account	Destination	Weak	Strong	Weak
Destination	Destination	Strong	None	Strong
Destination	Account	Weak	None	Weak

GenesisMint

OTXN	TSH	GenesisMint
Account	Account	Strong
Account	Destination	Strong
Account	Beneficiary	Weak

Import

OTXN	TSH	Import
Account	Account	Strong
Account	Issuer	Strong

Invoke

OTXN	TSH	Invoke
Account	Account	Strong
Account	Destination	Weak

Offer

OTXN	TSH	OfferCancel	OfferCreate
Account	Account	Strong	Strong
Account	Crossed	None	Weak

Payment

OTXN	TSH	Payment
Account	Account	Strong
Account	Destination	Strong
Account	Crossed	Weak

PaymentChannel

OTXN	TSH	PaymentChannelClaim	PaymentChannelCreate	PaymentChannelFund
Account	Account	Strong	Strong	Strong
Account	Destination	Weak	Strong	Weak
Destination	Destination	Strong	None	None
Destination	Account	Weak	None	None

SetHook

OTXN	TSH	SetHook
Account	Account	Strong

SetRegularKey

OTXN	TSH	SetRegularKey
Account	Account	Strong
Account	RegularKey	Strong

SignersListSet

OTXN	TSH	SignerListSet
Account	Account	Strong
Account	Signer	Strong

Ticket

OTXN	TSH	TicketCreate
Account	Account	Strong

TrustSet

OTXN	TSH	TrustSet
Account	Account	Strong
Account	Issuer	Weak

URIToken

OTXN	Burnable	TSH	Mint	Burn	Buy	Sell	Cancel
Owner	False	Owner	None	Strong	Strong	Strong	Strong
Owner	False	Issuer	None	Weak	Weak	Weak	None
Owner	False	Buyer	None	None	None	Strong	Weak
Owner	True	Buyer	None	None	None	Strong	Weak
Owner	True	Owner	None	Strong	Strong	Strong	Strong
Owner	True	Issuer	None	Weak	Strong	Strong	None
Issuer	False	Owner	None	None	None	None	None
Issuer	False	Issuer	Strong	None	None	None	None
Issuer	False	Buyer	Weak	None	None	None	None
Issuer	True	Owner	None	Weak	None	None	None
Issuer	True	Issuer	Strong	Strong	None	None	None
Issuer	True	Buyer	Weak	None	None	None	None
Buyer	True	Buyer	None	None	Strong	None	None
Buyer	True	Owner	None	None	Weak	None	None