Introduction

Events are an import functionality to help developers confirm, check, and search for the specific status of the smart contract.

Event Decoding

This section explains how to decode events and obtain the result from the transactionHistory database.

Solidity Event Example:

contract EventExampleContract {
    event Transfer(address indexed toAddress, uint256 amount);
    constructor() payable public{}
    function contractTransfer(address toAddress, uint256 amount){
        toAddress.transfer(amount);
        emit Transfer(toAddress, amount);
    }
}

Event Structure

Solidity uses LOG instruction to record event information in a transaction. The structure in protobuf is as follows:

message TransactionInfo {
  enum code {
    SUCESS = 0;
    FAILED = 1;
  }
  // LOG Structure represent single event
  message Log {
    bytes address = 1;
    repeated bytes topics = 2;
    bytes data = 3;
  }
  bytes id = 1;
  int64 fee = 2;
  int64 blockNumber = 3;
  int64 blockTimeStamp = 4;
  repeated bytes contractResult = 5;
  bytes contract_address = 6;
  ResourceReceipt receipt = 7;
  // A list of LOG represent list of events in a transaction
  repeated Log log = 8;
  code result = 9;
  bytes resMessage = 10;

  string assetIssueID = 14;
  int64 withdraw_amount = 15;
  int64 unfreeze_amount = 16;
  repeated InternalTransaction internal_transactions = 17;
  int64 exchange_received_amount = 18;
  int64 exchange_inject_another_amount = 19;
  int64 exchange_withdraw_another_amount = 20;
  int64 exchange_id = 21;
}

Decoding Events Example

The smart contract ABI for the solidity smart contract above is:

[{"constant":false,"inputs":[{"name":"toAddress","type":"address"},{"name":"amount","type":"uint256"}],"name":"contractTransfer","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"inputs":[],"payable":true,"stateMutability":"payable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"name":"toAddress","type":"address"},{"indexed":false,"name":"amount","type":"uint256"}],"name":"Transfer","type":"event"}]

The corresponding event ABI is:

{"anonymous":false,"inputs":[{"indexed":true,"name":"toAddress","type":"address"},{"indexed":false,"name":"amount","type":"uint256"}],"name":"Transfer","type":"event"}

Use gettransactioninfobyid to get the transaction result:

LogList:
address:
289C4D540B32C7BC56953E55631F8B141EB86434                          // contract address
data:
0000000000000000000000000000000000000000000000000000000000000001
TopicsList
69ca02dd4edd7bf0a4abb9ed3b7af3f14778db5d61921c7dc7cd545266326de2  // topics[0]
000000000000000000000000E552F6487585C2B58BC2C9BB4492BC1F17132CD0  // topics[1]

Check along with ABI:

• topics[0] is 69ca02dd4edd7bf0a4abb9ed3b7af3f14778db5d61921c7dc7cd545266326de2. It is the result of keccak("event(address,uint256)").

• topics[1] is 000000000000000000000000E552F6487585C2B58BC2C9BB4492BC1F17132CD0. It is the first indexed param (toAddress) with type address.

• data is 0000000000000000000000000000000000000000000000000000000000000001. It is the param without being indexed (amount) with type uint256.

Event Subscription Support

The Event Subscription supports event plug-ins, Kafka, and MongoDB plug-ins. Developers can customize their own plug-ins according to their own needs. It also supports subscription of chain data, such as block, transaction, contract log, contract event and so on. For transaction events, developers can retrieve information such as internal transactions, contract information, and so on. For contract events, developers could configure the contract addresses list or contract topic list to receive the specified events, and event subscription has low latency. The deployed Full Node receives event information immediately after the contract execution.

Event Subscription Description

Event types that support subscriptions:

• transactionTrigger: Transaction Event
• blockTrigger: Block Event, triggered when the block is submitted.
• contractLogTrigger: Smart Contract Log
• contractEventTrigger: Smart Contract Event

The transaction information is represented by TransactionLogTrigger and includes the following parameters:

• transactionId: transaction hash
• blockHash
• blockNunber
• energyUsage
• energyFee
• originEnergyUsage
• energyUsageTotal

The smart contract log object is represented by ContractLogTrigger and includes the following parameters:

• transactionID
• contractAddress
• callerAddress
• blockNumber
• blockTimestamp
• contractTopics: Solidity
• data:Solidity
• removed: True if the log has been deleted, false if the log is deleted

Event Plugin

• Kafka Plugin

• mongodb Plugin

Tron-EventQuery

• Deploy

• Tron Event Query Service