State
The trigger module manages the state of every trigger.
Trigger
A Trigger is the main data structure used by the module. It keeps track of the owner, event, and actions for a single Trigger. Every Trigger gets its own unique identifier, and a unique entry within the Event Listener and Gas Limit tables. The Event Listener table allows the event detection system to quickly filter applicable Triggers by name and type. A trigger can vary in size making it difficult to calculate gas usage on store, thus we opted to store remaining transaction gas in the Gas Limit table. It gives us a predictable way to calculate and store remaining gas.
The excess gas on a MsgCreateTrigger transaction will be used for the Trigger's Gas Limit table. The maximum Gas Limit for a Trigger is 2000000.
- Trigger:
0x01 | Trigger ID (8 bytes) -> ProtocolBuffers(Trigger) - Trigger ID:
0x05 -> uint64(TriggerID) - Event Listener:
0x02 | Event Type (32 bytes) | Order (8 bytes) -> []byte{} - Gas Limit:
0x04 | Trigger ID (8 bytes) -> uint64(GasLimit)
TriggerEventI
A Trigger must have an event that implements the TriggerEventI interface. Currently, the system supports BlockHeightEvent, BlockTimeEvent, and TransactionEvent.
BlockHeightEvent
The BlockHeightEvent allows the user to configure their Trigger to fire when the current block's Block Height is greater than or equal to the defined one.
BlockTimeEvent
The BlockTimeEvent allows the user to configure their Trigger to fire when the current block's Block Time is greater than or equal to the defined one.
TransactionEvent
The TransactionEvent allows the user to configure their Trigger to fire when a transaction event matching the user defined one has been emitted.
Attribute
The Attribute is used by the TransactionEvent to allow the user to configure which attributes must be present on the transaction event. An Attribute with an empty value will only require the name to match.
Queue
The Queue is an internal structure that we use to store and throttle the execution of Triggers on the BeginBlock. We store each Trigger as a QueuedTrigger, and then manipulate the Queue Start Index and Queue Length whenever we add or remove from the Queue. When we add to the Queue, the new element is added to the QueueStartIndex + Length. The QueueLength is then incremented by one. When we dequeue from the Queue, the QueueStartIndex will be incremented by 1 and the QueueLength is decremented by 1. We also ensure the key of the dequeued element is removed.
- Queue Item:
0x03 | Queue Index (8 bytes) -> ProtocolBuffers(QueuedTrigger) - Queue Start Index:
0x06 -> uint64(QueueStartIndex) - Queue Length:
0x07 -> uint64(QueueLength)