Another use case of a function is to use it as a processor for data streams. A stream may be sent out from any kind of sources, such as data buses or event buses. Kafka, Twitter, or blockchain (in our case, Ethereum) could be a source of data streams. An Ethereum blockchain could emit events specific to some smart contracts when a certain action is taken.
To observe these events in the form of data streams efficiently, we need to use a kind of reactive client. RxJava is one of them. Fortunately, web3j, the Ethereum client we are using, already has RxJava observables to receive streaming data from an Ethereum blockchain.
We call this component listener. The following diagram shows what we will implement around the Event Listener:
Figure 8.13: Diagram illustrating relations around the Event Listener
A requirement is that we run the agent (Event Listener) as a container on the same network as the blockchain. We use the agent to divert each transaction information to other endpoints...