/// <summary>
/// Initializes a new instance of the <see cref="GraphMiddlewareInvoker{TContext}" /> class.
/// </summary>
/// <param name="middlewareComponent">The middleware component.</param>
/// <param name="next">The next.</param>
public GraphMiddlewareInvoker(
GraphMiddlewareDefinition <TContext> middlewareComponent,
GraphMiddlewareInvocationDelegate <TContext> next = null)
{
this.ComponentDefinition = Validation.ThrowIfNullOrReturn(middlewareComponent, nameof(middlewareComponent));
_singletonInstance = this.ComponentDefinition.Component;
this.Next = next;
if (this.Next == null)
{
this.Next = (_, __) => Task.CompletedTask;
}
}
public async Task InvokeAsync(TContext context, CancellationToken cancelToken)
{
// stop processing when cancelation is requested
if (cancelToken.IsCancellationRequested)
{
return;
}
// create and use the component, depending on the scope
// invoke it and return
var instance = _singletonInstance;
if (instance == null)
{
// no pre-instantiated component was provided
// generate the compoennt from the current context. If it was marked as a singleton scope
// store the reference for use on subsequent calls
instance = context?.ServiceProvider?
.GetService(this.ComponentDefinition.MiddlewareType) as IGraphMiddlewareComponent <TContext>;
if (this.ComponentDefinition.Lifetime == ServiceLifetime.Singleton)
{
lock (_locker)
{
if (_singletonInstance == null)
{
_singletonInstance = instance;
}
}
}
}
if (instance == null)
{
throw new GraphPipelineMiddlewareInvocationException(
this.ComponentDefinition.Name,
$"Unable to resolve an instance of the middleware compoent '{this.ComponentDefinition.Name}'. Either no instance was provided " +
"or one could not be created from the service provider on the request context.");
}
var task = instance.InvokeAsync(context, this.Next, cancelToken);
await task.ConfigureAwait(false);
}
/// <summary>
/// Initializes a new instance of the <see cref="GraphMiddlewareDefinition{TMiddlewareComponent}" /> class.
/// </summary>
/// <param name="component">The component.</param>
/// <param name="name">A friendly name to assign to this middleware component for easy reference.</param>
public GraphMiddlewareDefinition(IGraphMiddlewareComponent <TContext> component, string name = null)
{
this.Component = Validation.ThrowIfNullOrReturn(component, nameof(component));
this.Name = name?.Trim() ?? component.GetType().FriendlyName();
this.Lifetime = ServiceLifetime.Singleton;
}
