How to listen/get on-chain data in real time

Question

I know that I can use eosjs to read/query multi_index table data from the chain. However, my goal is to listen to/on these changes. Specifically, I want to receive a notification whenever something happens on-chain.

Therefore, I need a persistent connection to the chain, whether using web sockets, mqtt (pub-sub) or any other real-time protocol. How to do this? does the eosjs library support this?

Of course, I can write a while(true) loop, where I send RPC requests all the time to check if something has changed, but this is not a good solution, so I'm interested if other people already solved this issue.

Also, some websites like https://eosauthority.com/ show real-time data of what is happening on the eosio network. So, how do they do this?

Answer 1

dfuse.eosnation.io provides websocket and graphql push services which should accomplish what you are trying to do. See docs.dfuse.eosnation.io for details.

Answer 2

you would use the state history plugin which is a web socket of on chain events.

This is commonly referred to as a SHiP node (state history nodeos instance).

https://developers.eos.io/manuals/eos/v2.2/nodeos/plugins/state_history_plugin/index/?query=state%20history%20plugin&page=1#gatsby-focus-wrapper

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block one developed demux-js as well, but should still work https://github.com/EOSIO/demux-js

You can see other history tools here https://developers.eos.io/welcome/latest/tools/history-tools/history-tools

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If you want an example of storing certain information in a PostgreSQL database, you can see the atomic assets api: https://github.com/pinknetworkx/eosio-contract-api

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Here is an example script to run a SHiP node exposing the web socket on 8887.

#!/bin/bash
DATADIR="./blockchain"

if [ ! -d $DATADIR ]; then
  mkdir -p $DATADIR;
fi

nodeos \
--plugin eosio::producer_plugin \
--plugin eosio::chain_plugin \
--plugin eosio::chain_api_plugin \
--plugin eosio::http_plugin \
--plugin eosio::net_plugin \
--plugin eosio::state_history_plugin \
--data-dir $DATADIR"/data" \
--blocks-dir $DATADIR"/blocks" \
--config-dir $DATADIR"/config" \
--producer-name eosio \
--http-server-address 0.0.0.0:8888 \
--state-history-endpoint 0.0.0.0:8887 \
--access-control-allow-origin='*' \
--contracts-console \
--trace-history \
--chain-state-history \
--http-validate-host=false \
--p2p-peer-address $P2P_ADDRESS \
--verbose-http-errors \
--enable-stale-production \
--eos-vm-oc-enable \
--wasm-runtime eos-vm-jit \
--disable-replay-opts \
--genesis-json $DATADIR"/genesis.json" \
>> $DATADIR"/nodeos.log" 2>&1 & \
echo $! > $DATADIR"/eosd.pid"