ethereum-event-azure-function-trigger/EthereumEventListener

EthereumEventListener.cs

public class EthereumEventListener : IListener
{
	private const int EventPollingDelay = 1000;

	private readonly ITriggeredFunctionExecutor _executor;
	private readonly EthereumEventTriggerAttribute _attribute;
	private CancellationTokenSource _cts = null;
	private Event _event = null;
	private HexBigInteger _filter = null;

	public EthereumEventListener(ITriggeredFunctionExecutor executor, EthereumEventTriggerAttribute attribute)
	{
		_executor = executor;
		_attribute = attribute;
	}

	public void Cancel()
	{
		StopAsync(CancellationToken.None).Wait();
	}

	public void Dispose() { }

	public async Task StartAsync(CancellationToken cancellationToken)
	{
		_cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);

		var web3 = new Web3(_attribute.Url);
		var contract = web3.Eth.GetContract(_attribute.Abi, _attribute.ContractAddress);

		_event = contract.GetEvent(_attribute.EventName);
		_filter = await _event.CreateFilterAsync();

		ListenAsync(_cts.Token);
	}

	public Task StopAsync(CancellationToken cancellationToken)
	{
		_cts.Cancel();

		return Task.CompletedTask;
	}

	private async void ListenAsync(CancellationToken cancellationToken)
	{
		await Task.Run(async () =>
		{
			while (!cancellationToken.IsCancellationRequested)
			{
				var eventsData = await _event.GetFilterChangeDefault(_filter);

				ProcessEvents(eventsData, cancellationToken);
				await Task.Delay(EventPollingDelay);
			}
		});
	}

	private void ProcessEvents(List<EventLog<List<ParameterOutput>>> eventsData, CancellationToken cancellationToken)
	{
		eventsData
			.Select(eventData => ExtractEventData(eventData.Event, eventData.Log))
			.ToList()
			.ForEach(ethereumEventData => _executor.TryExecuteAsync(new TriggeredFunctionData { TriggerValue = ethereumEventData }, cancellationToken));
	}

	private EthereumEventData ExtractEventData(List<ParameterOutput> eventParams, FilterLog log)
	{
		Dictionary<string, string> values = eventParams.ToDictionary(eventParam => eventParam.Parameter.Name, eventParam => eventParam.Result.ToString());

		return new EthereumEventData
		{
			Values = values,
			BlockNumber = log.BlockNumber
		};
	}
}