Permformance issue with StaticAssetDevelopmentRuntimeHandler.EnableSupport.

[maliming]

When StaticAssetDevelopmentRuntimeHandler.EnableSupport is enabled in the development environment, websites with many static resources may experience significant delays.

The delay occurs primarily during the first request due to an O(n^2) loop in the UpdateEndpoints process.

Each static resource endpoint builder invokes the AttachRuntimePatching method and then the FindOriginalAsset method to iterate through all descriptors.

If there are 10,000 static files(js/css/images) under the wwwroot folder, this leads to 10,000 x 10,000 iterations on the first request.

Thanks.

aspnetcore/src/StaticAssets/src/StaticAssetsEndpointRouteBuilderExtensions.cs

Lines 39 to 42 in af22eff

	if (StaticAssetDevelopmentRuntimeHandler.IsEnabled(result.IsBuildManifest, endpoints.ServiceProvider))
	{
	StaticAssetDevelopmentRuntimeHandler.EnableSupport(endpoints, result, environment, result.Descriptors);
	}

aspnetcore/src/StaticAssets/src/StaticAssetEndpointDataSource.cs

Lines 99 to 119 in af22eff

	private void UpdateEndpoints()
	{
	lock (_lock)
	{
	var endpoints = new List<Endpoint>();
	foreach (var asset in _descriptors)
	{
	// At this point the descriptor becomes immutable.
	asset.Freeze();
	endpoints.Add(_endpointFactory.Create(asset, _conventions, _finallyConventions));
	}
	var oldCancellationTokenSource = _cancellationTokenSource;
	_endpoints = endpoints;
	_cancellationTokenSource = new CancellationTokenSource();
	_changeToken = new CancellationChangeToken(_cancellationTokenSource.Token);
	oldCancellationTokenSource?.Cancel();
	oldCancellationTokenSource?.Dispose();
	}
	}

aspnetcore/src/StaticAssets/src/Development/StaticAssetDevelopmentRuntimeHandler.cs

Lines 29 to 38 in af22eff

	public void AttachRuntimePatching(EndpointBuilder builder)
	{
	var original = builder.RequestDelegate!;
	var asset = builder.Metadata.OfType<StaticAssetDescriptor>().Single();
	if (asset.HasContentEncoding())
	{
	// This is a compressed asset, which might get out of "sync" with the original uncompressed version.
	// We are going to find the original by using the weak etag from this compressed asset and locating an asset with the same etag.
	var eTag = asset.GetWeakETag();
	asset = FindOriginalAsset(eTag.Tag.Value!, descriptors);

aspnetcore/src/StaticAssets/src/Development/StaticAssetDevelopmentRuntimeHandler.cs

Lines 145 to 156 in af22eff

	private static StaticAssetDescriptor FindOriginalAsset(string tag, List<StaticAssetDescriptor> descriptors)
	{
	for (var i = 0; i < descriptors.Count; i++)
	{
	if (descriptors[i].HasETag(tag))
	{
	return descriptors[i];
	}
	}
	throw new InvalidOperationException("The original asset was not found.");
	}