Hook

[Source]

(Added by the Hooks amendment.)

A Hook object describes a smart contract, which can be triggered by a transaction to perform predefined operations. The operations are defined by the Hook creator and can interact with the ledger and transactions.

Example JSON

{
  "Account": "rUn84CUYbNjRoTQ6mSW7BVJPSVJNLb1QLo",
  "OwnerNode": "0000000000000000",
  "PreviousTxnID": "5463C6E08862A1FAE5EDAC12D70ADB16546A1F674930521295BC082494B62924",
  "PreviousTxnLgrSeq": 6,
  "Hooks": [
    {
      "HookHash": "46060241FABCF692D4D934BA2A6C4427CD4279083E38C77CBE642243E43BE291",
      "HookParameters": []
    }
  ],
  "LedgerEntryType": "Hook",
  "index": "49647F0D748DC3FE26BDACBC57F251AADEFFF391403EC9BF87C97F67E9977FB0"
}

Fields

A Hook object has the following fields:

Field	JSON Type	Internal Type	Required?	Description
Account	String	Account	Yes	The account that created the Hook.
OwnerNode	String	UInt64	Yes	A hint indicating which page of the owner’s directory links to this object, in case the directory consists of multiple pages.
PreviousTxnID	String	Hash256	Yes	The ID of the transaction that most recently modified this object.
PreviousTxnLgrSeq	Number	UInt32	Yes	The ledger index of the ledger that contains the transaction that most recently modified this object.
Hooks	Array	Array	Yes	An array of hook objects. Each object has the following fields: HookHash, CreateCode, HookGrants, HookNamespace, HookParameters, HookOn, HookOnIncoming, HookOnOutgoing, HookCanEmit, HookName, HookApiVersion, Flags.
LedgerEntryType	String	UInt16	Yes	The value 0x0043, mapped to the string Hook, indicates that this object is a Hook object.

Hook Fields

The following fields are used in the hook object:

Field	JSON Type	Internal Type	Description
HookHash	String	Hash256	The hash of the hook.
CreateCode	String	Blob	The hex-encoded WebAssembly binary (WASM) that defines the hook’s logic. Present when the hook was installed with inline code rather than referencing an existing HookDefinition object.
HookGrants	Array	Array	An array of grant objects specifying which accounts are permitted to set or modify this hook on the hook account’s behalf.
HookNamespace	String	Hash256	A 32-byte (64 hex character) namespace that segregates this hook’s state data from other hooks on the same account. Must be unique per hook slot.
HookParameters	Array	Array	The parameters of the hook.
HookApiVersion	Number	UInt16	The version of the Hooks API used by this hook. Determines which hook API functions are available to the WASM binary at runtime.
HookOn	String	Hash256	The transaction type(s) on which the hook is triggered. Mutually exclusive with HookOnIncoming/HookOnOutgoing.
HookOnIncoming	String	Hash256	(HookOnV2) Same syntax as HookOn. Triggers the hook on transactions originating from another account. Mutually exclusive with HookOn.
HookOnOutgoing	String	Hash256	(HookOnV2) Same syntax as HookOn. Triggers the hook on transactions originating from the Hook account itself. Mutually exclusive with HookOn.
HookCanEmit	String	Hash256	Same syntax as HookOn. Controls which transaction types the hook is allowed to emit. If absent, the hook may emit any transaction type.
HookName	String	Blob	(NamedHooks) UTF-8 string (4–16 bytes, hex-encoded) assigned to this hook slot. When present, the hook only executes if the triggering transaction carries a matching top-level HookName field.
Flags	Number	UInt32	Additional flags for the hook.

Hook ID Format

The ID of a Hook object is the SHA-512Half of the following values, concatenated in order:

• The Hook space key (0x0048)
• The AccountID of the sender of the SetHook transaction that created the Hook object