Events
Events are objects that contain information about the execution of the application. They are mainly used by service providers like block explorers and wallet to track the execution of various messages and index transactions.
It is possible to subscribe to
Events via Tendermint's Websocket. This is done by calling the subscribe RPC method via Websocket:{
"jsonrpc": "2.0",
"method": "subscribe",
"id": "0",
"params": {
"query": "tm.event='<event_value>' AND eventType.eventAttribute='<attribute_value>'"
}
}
These events are triggered after a block is committed.
The
type and attribute value of the query allow you to filter the specific event you are looking for. For example, a an Ethereum transaction on BlockX (MsgEthereumTx) triggers an event of type ethermint and has sender and recipient as attributes. Subscribing to this event would be done like so:{
"jsonrpc": "2.0",
"method": "subscribe",
"id": "0",
"params": {
"query": "tm.event='Tx' AND ethereum.recipient='hexAddress'"
}
}
where
hexAddress is an Ethereum hex address (eg: 0x1122334455667788990011223344556677889900).BlockX also supports the Ethereum JSON-RPC filters calls to subscribe to state logs, block or pending transactions changes.
Under the hood, it uses the Tendermint RPC client's event system to process subscriptions that are then formatted to Ethereum-compatible events.
curl -X POST --data '{"jsonrpc":"2.0","method":"eth_newBlockFilter","params":[],"id":1}' -H "Content-Type: application/json" http://localhost:8545
{"jsonrpc":"2.0","id":1,"result":"0x3503de5f0c766c68f78a03a3b05036a5"}
Then you can check if the state changes with the
eth_getFilterChanges call:curl -X POST --data '{"jsonrpc":"2.0","method":"eth_getFilterChanges","params":["0x3503de5f0c766c68f78a03a3b05036a5"],"id":1}' -H "Content-Type: application/json" http://localhost:8545
{"jsonrpc":"2.0","id":1,"result":["0x7d44dceff05d5963b5bc81df7e9f79b27e777b0a03a6feca09f3447b99c6fa71","0x3961e4050c27ce0145d375255b3cb829a5b4e795ac475c05a219b3733723d376","0xd7a497f95167d63e6feca70f344d9f6e843d097b62729b8f43bdcd5febf142ab","0x55d80a4ba6ef54f2a8c0b99589d017b810ed13a1fda6a111e1b87725bc8ceb0e","0x9e8b92c17280dd05f2562af6eea3285181c562ebf41fc758527d4c30364bcbc4","0x7353a4b9d6b35c9eafeccaf9722dd293c46ae2ffd4093b2367165c3620a0c7c9","0x026d91bda61c8789c59632c349b38fd7e7557e6b598b94879654a644cfa75f30","0x73e3245d4ddc3bba48fa67633f9993c6e11728a36401fa1206437f8be94ef1d3"]}
To start a connection with the Tendermint websocket you need to define the address with the
--rpc.laddr flag when starting the node (default tcp://127.0.0.1:26657):# connect to tendermint websocket at port 8080 as defined above
ws ws://localhost:8080/websocket
# subscribe to new Tendermint block headers
> { "jsonrpc": "2.0", "method": "subscribe", "params": ["tm.event='NewBlockHeader'"], "id": 1 }
Since BlockX runs uses Tendermint Core as it's consensus Engine and it's built with the Cosmos SDK framework, it inherits the event format from them. However, in order to support the native Web3 compatibility for websockets of the Ethereum's PubSubAPI, BlockX needs to cast the Tendermint responses retrieved into the Ethereum types.
You can start a connection with the Ethereum websocket using the
--json-rpc.ws-address flag when starting the node (default "0.0.0.0:8546"):blockxd start --json-rpc.address"0.0.0.0:8545" --json-rpc.ws-address="0.0.0.0:8546" --evm.rpc.api="eth,web3,net,txpool,debug" --json-rpc.enable
# connect to tendermint websocet at port 8546 as defined above
ws ws://localhost:8546/
# subscribe to new Ethereum-formatted block Headers
> {"id": 1, "method": "eth_subscribe", "params": ["newHeads", {}]}
< {"jsonrpc":"2.0","result":"0x44e010cb2c3161e9c02207ff172166ef","id":1}
Last modified 8mo ago