feat: example of polling mirror node to simulate TopicMessageQuery

[ivaylonikolov7]

Description:
Polling mirror node rest api to stimulate TopicMessageQuery

Notes for reviewer:

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[lfdt-bot]

🎉 Snyk checks have passed. No issues have been found so far.

✅ security/snyk check is complete. No issues have been found. (View Details)

[codecov]

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[ivaylonikolov7]

@CodiumAI-Agent /improve

[CodiumAI-Agent]

PR Code Suggestions ✨

Category	Suggestion	Impact
Security	Remove client-side key usage Exposing the private operator key on the client is a security risk; move Hedera transaction signing to a secure server or cloud function and only expose non-sensitive data to the frontend. examples/frontend-examples/src/app/topic/message-query/page.js [25-27] -const operatorKey = PrivateKey.fromStringED25519( - process.env.NEXT_PUBLIC_OPERATOR_KEY, -); +// On client: call secure API endpoint instead of using PrivateKey directly +// Example: +// const response = await fetch('/api/create-topic', { method: 'POST' }); +// const { topicId } = await response.json(); +// setTopicId(topicId); Suggestion importance[1-10]: 9 __ Why: Exposing the operator private key in the client is a critical security vulnerability and should be moved to a secure backend.	High
Possible issue	Prevent listener re-registration Move emitter instantiation into a stable ref and subscribe inside a useEffect with cleanup to prevent re-registering listeners on every render and avoid memory leaks. examples/frontend-examples/src/app/components/TopicListener.js [8-23] -const dataEmitter = new EventEmitter(); -dataEmitter.on("newMessages", (message) => { - setMessages((prevMessages) => [...prevMessages, message]); +const dataEmitter = useRef(new EventEmitter()).current; + +useEffect(() => { + const handler = (message) => { + setMessages(prev => [...prev, message]); setLastUpdate(new Date()); -}); + }; + dataEmitter.on("newMessages", handler); + return () => { + dataEmitter.off("newMessages", handler); + }; +}, [dataEmitter]); Suggestion importance[1-10]: 8 __ Why: This prevents the EventEmitter listener from being re-registered on every render, avoiding memory leaks and duplicate message handling.	Medium
	Emit all new messages When new batches have more than one message, only the first one is processed; iterate over the slice to emit all new messages and update lastMessagesLength after processing. examples/frontend-examples/src/app/components/TopicListener.js [171-177] -const newMessages = data.messages.slice(lastMessagesLength)[0]; -const decodedMessage = Buffer.from( - newMessages.message, - "base64", -).toString("utf-8"); -dataEmitter.emit("newMessages", decodedMessage); +const newBatch = data.messages.slice(lastMessagesLength); +newBatch.forEach(msg => { + const decoded = Buffer.from(msg.message, "base64").toString("utf-8"); + dataEmitter.emit("newMessages", decoded); +}); lastMessagesLength = currentMessagesLength; Suggestion importance[1-10]: 8 __ Why: Looping over the new messages ensures no incoming messages are dropped, fixing a functional bug when multiple messages arrive in one poll.	Medium
General	Support polling cancellation Add an AbortController signal to pollMirrorNode and break the loop when the component unmounts to avoid runaway polling. Pass the controller’s signal to the function and check signal.aborted in the loop. examples/frontend-examples/src/app/components/TopicListener.js [147-152] -async function pollMirrorNode(dataEmitter, topicId) { +async function pollMirrorNode(dataEmitter, topicId, signal) { let lastMessagesLength = 0; - // eslint-disable-next-line no-constant-condition - while (true) { + while (!signal.aborted) { // ... } } +// In the component: +useEffect(() => { + const controller = new AbortController(); + pollMirrorNode(dataEmitter, topicId, controller.signal); + return () => controller.abort(); +}, [dataEmitter, topicId]); + Suggestion importance[1-10]: 7 __ Why: Adding an AbortController allows the infinite polling loop to be cleanly stopped on unmount, preventing runaway requests but is a lower-severity enhancement.	Medium

[venilinvasilev]

Suggestion: Consider using a setInterval stored in a constant so it can be cleared when needed. As it stands, this while (true) loop will run indefinitely once executed, which isn’t ideal for an example. If this is meant to demonstrate polling behavior, it's better to follow best practices by including a way to stop or clean up the polling loop.

[venilinvasilev]

How about assigning this interval to a timer variable that is passed as a dependency trought the function so it can be cleared when polling is no longer needed (for example when the user navigates from a page). WDYT?

[ivaylonikolov7]

eslint cries that we have added a constant that doesn't get used. I think the user can handle this and will set it to a constant and pass it to clearInterval when needed.

[venilinvasilev]

How about assign this to a const variable e.g. something like POLLING_INTERVAL?