# Events
Event
s 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.
# Pre-requisite Readings
# Subscribing to Events
# Cosmos and Tendermint Events
Check the Tendermint Websocket in the Clients documentation for reference.
It is possible to subscribe to Events
via Tendermint's
Websocket (opens new window).
This is done by calling the subscribe
RPC method via Websocket:
These events are triggered after a block is committed.
You can get the full list of event
categories and values here.
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 Evmos (MsgEthereumTx
) triggers an event
of type ethermint
and
has sender
and recipient
as attributes
. Subscribing to this event
would be done like so:
where hexAddress
is an Ethereum hex address (eg: 0x1122334455667788990011223344556677889900
).
# Ethereum Events
Evmos also supports the Ethereum JSON-RPC filters calls to subscribe to state logs (opens new window), blocks (opens new window) or pending transactions (opens new window) changes.
Under the hood, it uses the Tendermint RPC client's event system to process subscriptions that are then formatted to Ethereum-compatible events.
Then you can check if the state changes with the
eth_getFilterChanges
(opens new window) call:
# Websocket Connection
# Tendermint Websocket
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
):
Then, start a websocket subscription with ws (opens new window)
# Ethereum Websocket
Since Evmos 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 (opens new window), Evmos 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"
):
Then, start a websocket subscription with ws
(opens new window)