SetHook
The SetHook transaction allows users to install, update, delete, or perform other operations on hooks in Xahau.
[Source]
(Added by the [Hooks amendment][].)
Example
Field | JSON Type | [Internal Type][] | Description |
---|---|---|---|
| String | AccountID | The address of the account that will own the hook. |
| Array | Array | The array of hooks to be set. |
Special Transaction Cost
The SetHook transaction has a standard transaction cost, which is the minimum transaction cost required for all transactions.
Error Cases
Besides errors that can occur for all transactions, SetHook transactions can result in the following transaction result codes:
Error Code | Description |
---|---|
| Occurs if a hook with the same hash already exists. |
| Occurs if the owner's directory is full and cannot accommodate the new hook. |
| Occurs if the sending account does not exist. |
| Occurs if no hook exists with the specified hash. |
| Occurs if the Hooks Amendment is not enabled. |
| Occurs if the transaction is malformed. |
SetHook Operations
There are six possible operations: No Operation, Create, Update, Delete, Install and Namespace Delete
Each operation is specified by the inclusion or omission of certain HookSet Object fields. This might seem confusing at first but by working through a few examples the reader should find it intuitive; Essentially HookSet operations are a type of diff between a specific Hook's defaults, existing and newly specified fields.
Achieving each type of operation is explained in a subsection below.
No Operation
Occurs when:
The HookSet Object is empty
Behaviour:
No change of any kind is made.
Example:
JSON
Create Operation
Occurs when:
All of the following conditions are met:
The Corresponding Hook does not exist or
FLAG_OVERRIDE
is specified.CreateCode
field is specified and is not blank and contains the valid web assembly bytecode for a valid Hook.No instance of the same web assembly bytecode already exists on the XRPL. (If it does and all other requirements are met then interpret as an Install Operation — see below.)
Behaviour:
A reference counted
HookDefinition
object is created on the XRPL containing the fields in the HookSet Object, with all specified fields (Namespace, Parameters, HookOn) becoming defaults (but not Grants.)A
Hooks
array is created on the executing account, if it doesn't already exist. (This is the structure that contains the Corresponding Hooks.)A
Hook
object is created at the Corresponding Hook position if one does not already exist.The
Hook
object points at theHookDefinition
.The
Hook
object contains no fields exceptHookHash
which points at the createdHookDefinition
.If
hsfNSDELETE
flag is specified then any HookState entires in the destination namespace are deleted if they currently exist.
Example:
JSON
Install Operation
Occurs when:
All of the following conditions are met:
The Corresponding Hook does not exist or
FLAG_OVERRIDE
is specified.HookHash
field is specified and is not blank and contains the hash of a Hook that already exists as aHookDefinition
on the ledger orCreateCode
field is specified and is not blank and contains the valid web assembly bytecode for a valid hook that already exists on the ledger as aHookDefinition
.
Behaviour:
The reference count of the
HookDefinition
object is incremented.A
Hooks
array is created on the executing account, if it doesn't already exist. (This is the structure that contains the Corresponding Hooks.)A
Hook
object is created at the Corresponding Hook position if one does not already exist.The
Hook
object points at theHookDefinition
.The
Hook
object contains all the fields in the HookSet Object, except and unless:A field or key-pair within a field is identical to the Hook Defaults set on the
HookDefinition
, in which case it is omitted due to defaults.If
hsfNSDELETE
flag is specified then any HookState entires in the destination namespace are deleted if they currently exist.
Example:
JSON
Update Operation
Occurs when:
All of the following conditions are met:
The Corresponding Hook exists.
HookHash
is absent.CreateCode
is absent.One or more of
HookNamespace
,HookParameters
orHookGrants
is present.
General Behaviour:
The Corresponding Hook is updated in such a way that the desired changes are reflected in the Corresponding Hook.
Specific Behaviour:
If HookNamespace
is specified and differs from the Corresponding Hook's Namespace:
the Corresponding Hook's
HookNamespace
is updated, andif the
hsfNSDELETE
flag is specified all HookState entires in the old namespace are deleted.
If HookParameters
is specified, then for each entry:
If
HookParameterName
exists butHookParameterValue
is absent and the Corresponding Hook's Parameters (either specifically or via defaults) contains thisHookParameterName
then the parameter is marked as deleted on the Corresponding Hook.If
HookParameterName
exists andHookParameterValue
exists then the Corresponding Hook's Parameters are modified to include the new or updated parameter.
If HookGrants
is specified then:
The Corresponding Hook's
HookGrants
array is replaced with the array.
Example:
JSON
Delete Operation
Occurs when:
All of the following conditions are met:
The Corresponding Hook exists.
hsfOVERRIDE
is specified.optionally
hsfNSDELETE
is also specified.HookHash
is absent.CreateCode
is present but empty.
Behaviour:
The reference count of the
HookDefinition
object is decremented.If the reference count is now zero the
HookDefintion
is removed from the ledger.The
Hook
object in the Corresponding Hook position is deleted, leaving an empty position.If
hsfNSDELETE
is specified the namespace and all HookState entries are also deleted.
Example:
JSON
Namespace Reset
Occurs when:
All of the following conditions are met:
flags
is present andhsfNSDELETE
is set.hsfOVERRIDE
can optionally also be specified if the Hook at this position is to be deleted.HookNamespace
is specified.CreateCode
is absent.HookHash
is absent.HookGrants
,HookParameters
,HookOn
andHookApiVersion
are absent.
Behaviour:
If the Corresponding Hook exists, it remains, nothing happens to it.
A subset of HookState objects and the HookState directory for the specified namespace are removed from the ledger, up to the defined limit (512). Further transactions are needed to continue the deletion process until all relevant records are removed. See
tesPARTIAL
.
Example:
JSON
Hook Fields
The following fields are used in the hook object:
Field | JSON Type | Internal Type | Description |
---|---|---|---|
| String | Hash256 | The hash of the hook. |
| String | Blob | The WebAssembly code for the hook. |
| Array | Array | The grants associated with the hook. |
| String | Hash256 | The namespace of the hook. |
| Array | Array | The parameters of the hook. |
| String | Hash256 | The event on which the hook is triggered. |
| Number | UInt16 | The API version of the hook. |
| Number | UInt32 | Additional flags for the hook. |
Flags
The Flags
field in the hook object specifies additional flags for the hook. The following flags are supported:
Flag Name | Description |
---|---|
| Allows the hook to be deleted even if it is referenced by other objects. |
| Deletes an entire namespace of hooks. |
| Collects the hook's associated objects. |
Hook Grants
The HookGrants
field is an array of objects that specify the grants associated with the hook. Each grant object has the following fields:
Field | JSON Type | Internal Type | Description |
---|---|---|---|
| String | Hash256 | The hook to apply the grant to. |
| String | AccountID | The address of the account that is granted access. |
| Number | Uint32 | Flags |
Hook Parameters
The HookParameters
field is an array of objects that specify the parameters of the hook. Each parameter object has the following fields:
Field | JSON Type | Internal Type | Description |
---|---|---|---|
| String | Blob | The name of the parameter. |
| String | Blob | The value of the parameter. |
Hook Executions
When Hooks execute they leave behind information about the status of that execution. This appears in the Originating Transaction metadata as an sfHookExecutions
block. This block contains the following fields:
Field | JSON Type | Internal Type | Description |
---|---|---|---|
| String | AccountID | The account the Hook ran on. |
| Number | UInt16 | The total number of Emitted Transactions produced by the Hook. |
| Number | UInt16 | The SHA512H of the Hook at the time it was executed. |
| String | Hash256 | The value of the parameter. |
| String | UInt64 | The total number of webassembly instructions that were executed when the Hook ran. |
| Number | UInt8 | Hooks can end in three ways: |
| String | UInt64 | The integer returned as the third parameter of |
| String | Blob | The string returned in the first two parameters of |
| Number | UInt16 | The number of Hook State changes the Hook made during execution. |
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