fix: Implement basic error handling and user-friendly alerts

[sebmuehlbauer]

Fixes #5

This PR adds basic error handling for WebRTC connections, signaling server connectivity, and file transfer interruptions.

• Added a global showAlert function to display user-friendly error messages.
• Integrated WebSocket onerror and onclose listeners for signaling server failures.
• Added oniceconnectionstatechange to track WebRTC connection status.
• Added onerror handling for file reading operations.

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[Copilot]

Pull request overview

This PR aims to add user-friendly error handling for signaling/WebRTC/file transfer failures, but the current diff replaces the existing frontend UI and runtime (main.js) with a minimal index.html + new app.js that is not integrated with the current implementation.

Changes:

• Replaced client/index.html with a minimal page containing a custom alert box and a script tag for app.js.
• Added client/app.js implementing showAlert, plus basic WebSocket/WebRTC/FileReader error handlers (currently disconnected from the app’s real signaling/WebRTC/file-transfer flow).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
client/index.html	Replaces the full UI + module entrypoint with a minimal alert-only page and loads app.js.
client/app.js	Adds a new alert helper and placeholder signaling/WebRTC/file-transfer error handlers.

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[Copilot]

This change replaces the entire existing UI and removes all elements that the current frontend logic expects (e.g., connectionStatusIndicator, peersContainer, fileInput, modal/toast containers) while also no longer loading ./main.js as an ES module. As a result, the app’s peer discovery / transfer flow will not run at all. Instead of swapping the page to this minimal markup, keep the existing HTML/CSS structure and integrate the new user-facing error messaging into the current UI (e.g., via the existing toast container) while still loading ./main.js.

Suggested change

	<div id="alert-box"></div>
	<div id="app">
	<header>
	<h1>OpenDrop</h1>
	<div id="connectionStatusIndicator"></div>
	</header>
	<main>
	<section id="file-section">
	<input id="fileInput" type="file" multiple>
	</section>
	<section id="peers-section">
	<div id="peersContainer"></div>
	</section>
	</main>
	<div id="modal-root"></div>
	<div id="toast-container">
	<div id="alert-box" class="error" style="display: none;"></div>
	</div>
	</div>
	<script type="module" src="./main.js"></script>

[Copilot]

This diff is a large UI/asset rewrite (removes favicon/fonts/CSS, header/footer, and the whole interaction surface) rather than a targeted “basic error handling” change described in the PR. If the intent is only to add user-friendly alerts for signaling/WebRTC/file transfer errors, these UI deletions should be reverted and the error handling added to the existing implementation.

[Copilot]

new WebSocket('ws://your-server-url') is a non-functional placeholder and will break signaling in any real deployment. The existing codebase already derives the signaling URL from window.location.hostname (see client/main.js), so this should be wired into the real signaling URL/config rather than hardcoding a dummy string.

Suggested change

	const socket = new WebSocket('ws://your-server-url');
	const signalingProtocol = window.location.protocol === 'https:' ? 'wss://' : 'ws://';
	const signalingHost = window.location.hostname;
	const signalingPort = window.location.port ? `:${window.location.port}` : '';
	const signalingUrl = `${signalingProtocol}${signalingHost}${signalingPort}`;
	const socket = new WebSocket(signalingUrl);

[Copilot]

Creating a standalone RTCPeerConnection() here doesn’t attach error/state listeners to the real peer connections used for transfers, so it won’t surface actual connection failures to users (and may create unnecessary resources). To implement the intended behavior, the ICE/connection state handling needs to be registered on the peer connection instances created/used by the app’s WebRTC flow (rather than a new, unused connection).

Suggested change

	const peerConnection = new RTCPeerConnection();
	peerConnection.oniceconnectionstatechange = () => {
	if (peerConnection.iceConnectionState === 'failed' || peerConnection.iceConnectionState === 'disconnected') {
	showAlert('WebRTC connection failed.');
	}
	};
	function attachWebRTCErrorHandling(peerConnection) {
	if (!peerConnection) {
	return;
	}
	const handleICEConnectionStateChange = () => {
	if (
	peerConnection.iceConnectionState === 'failed' ||
	peerConnection.iceConnectionState === 'disconnected'
	) {
	showAlert('WebRTC connection failed.');
	}
	};
	peerConnection.addEventListener('iceconnectionstatechange', handleICEConnectionStateChange);
	}

[Copilot]

handleTransfer() is never called, and the FileReader created inside it never starts a read operation (no readAs* call). This means the added reader.onerror handler will never actually fire for real transfers. The error handling should be hooked into the existing file-slice reading logic used during sending, and also consider data-channel close/error events to detect interrupted transfers.

Suggested change

	// ... transfer logic
	reader.onload = (event) => {
	// Implement the actual transfer logic using event.target.result,
	// for example by sending the data over a WebRTC data channel.
	};
	reader.readAsArrayBuffer(file);