Mukan Erkin Törük
ef24c0b67e
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96 lines
3.2 KiB
Markdown
96 lines
3.2 KiB
Markdown
---
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order: 7
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---
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# Subscribing to events via Websocket
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CometBFT emits different events, which you can subscribe to via
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[Websocket](https://en.wikipedia.org/wiki/WebSocket). This can be useful
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for third-party applications (for analysis) or for inspecting state.
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[List of events](https://godoc.org/github.com/cometbft/cometbft/types#pkg-constants)
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To connect to a node via websocket from the CLI, you can use a tool such as
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[wscat](https://github.com/websockets/wscat) and run:
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```sh
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wscat -c ws://127.0.0.1:26657/websocket
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```
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NOTE: If your node's RPC endpoint is TLS-enabled, utilize the scheme `wss` instead of `ws`.
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You can subscribe to any of the events above by calling the `subscribe` RPC
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method via Websocket along with a valid query.
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```json
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{
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"jsonrpc": "2.0",
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"method": "subscribe",
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"id": 0,
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"params": {
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"query": "tm.event='NewBlock'"
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}
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}
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```
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Check out [API docs](https://docs.cometbft.com/v0.38/rpc/) for
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more information on query syntax and other options.
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You can also use tags, given you had included them into FinalizeBlock
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response, to query transaction results. See [Indexing
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transactions](../app-dev/indexing-transactions.md) for details.
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## Query parameter and event type restrictions
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While CometBFT imposes no restrictions on the application with regards to the type of
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the event output, there are several considerations that need to be taken into account
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when querying events with numeric values.
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- Queries convert all numeric event values to `big.Float` , provided by `math/big`. Integers
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are converted into a float with a precision equal to the number of bits needed
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to represent this integer. This is done to avoid precision loss for big integers when they
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are converted with the default precision (`64`).
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- When comparing two values, if either one of them is a float, the other one will be represented
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as a big float. Integers are again parsed as big floats with a precision equal to the number
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of bits required to represent them.
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- As with all floating point comparisons, comparing floats with decimal values can lead to imprecise
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results.
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- Queries cannot include negative numbers
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Prior to version `v0.38.x`, floats were not supported as query parameters.
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## ValidatorSetUpdates
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When validator set changes, ValidatorSetUpdates event is published. The
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event carries a list of pubkey/power pairs. The list is the same
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CometBFT receives from ABCI application (see [EndBlock
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section](https://github.com/cometbft/cometbft/blob/v0.38.x/spec/abci/abci++_methods.md#endblock) in
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the ABCI spec).
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Response:
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```json
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{
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"jsonrpc": "2.0",
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"id": 0,
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"result": {
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"query": "tm.event='ValidatorSetUpdates'",
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"data": {
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"type": "tendermint/event/ValidatorSetUpdates",
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"value": {
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"validator_updates": [
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{
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"address": "09EAD022FD25DE3A02E64B0FE9610B1417183EE4",
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"pub_key": {
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"type": "tendermint/PubKeyEd25519",
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"value": "ww0z4WaZ0Xg+YI10w43wTWbBmM3dpVza4mmSQYsd0ck="
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},
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"voting_power": "10",
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"proposer_priority": "0"
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}
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]
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}
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}
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}
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}
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```
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