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SubscriptionExecutor.Subscription.cs
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SubscriptionExecutor.Subscription.cs
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using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Threading;
using System.Threading.Tasks;
using HotChocolate.Execution.Instrumentation;
using HotChocolate.Execution.Internal;
using HotChocolate.Fetching;
using HotChocolate.Types;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.ObjectPool;
namespace HotChocolate.Execution.Processing;
internal sealed partial class SubscriptionExecutor
{
private sealed class Subscription : ISubscription, IAsyncDisposable
{
private readonly ulong _id;
private readonly ObjectPool<OperationContext> _operationContextPool;
private readonly QueryExecutor _queryExecutor;
private readonly IExecutionDiagnosticEvents _diagnosticEvents;
private IDisposable? _subscriptionScope;
private readonly IRequestContext _requestContext;
private readonly ObjectType _subscriptionType;
private readonly ISelectionSet _rootSelections;
private readonly Func<object?> _resolveQueryRootValue;
private ISourceStream _sourceStream = default!;
private object? _cachedRootValue;
private IImmutableDictionary<string, object?> _scopedContextData =
ImmutableDictionary<string, object?>.Empty;
private bool _disposed;
private Subscription(
ObjectPool<OperationContext> operationContextPool,
QueryExecutor queryExecutor,
IRequestContext requestContext,
ObjectType subscriptionType,
ISelectionSet rootSelections,
Func<object?> resolveQueryRootValue,
IExecutionDiagnosticEvents diagnosticEvents)
{
unchecked
{
_id++;
}
_operationContextPool = operationContextPool;
_queryExecutor = queryExecutor;
_requestContext = requestContext;
_subscriptionType = subscriptionType;
_rootSelections = rootSelections;
_resolveQueryRootValue = resolveQueryRootValue;
_diagnosticEvents = diagnosticEvents;
}
/// <summary>
/// Subscribes to the pub/sub-system and creates a new <see cref="Subscription"/>
/// instance representing that subscriptions.
/// </summary>
/// <param name="operationContextPool">
/// The operation context pool to rent context pools for execution.
/// </param>
/// <param name="queryExecutor">
/// The query executor to process event payloads.
/// </param>
/// <param name="requestContext">
/// The original request context.
/// </param>
/// <param name="subscriptionType">
/// The object type that represents the subscription.
/// </param>
/// <param name="rootSelections">
/// The operation selection set.
/// </param>
/// <param name="resolveQueryRootValue">
/// A delegate to resolve the subscription instance.
/// </param>
/// <param name="diagnosticsEvents">
/// The internal diagnostic events to report telemetry.
/// </param>
/// <returns>
/// Returns a new subscription instance.
/// </returns>
public static async ValueTask<Subscription> SubscribeAsync(
ObjectPool<OperationContext> operationContextPool,
QueryExecutor queryExecutor,
IRequestContext requestContext,
ObjectType subscriptionType,
ISelectionSet rootSelections,
Func<object?> resolveQueryRootValue,
IExecutionDiagnosticEvents diagnosticsEvents)
{
var subscription = new Subscription(
operationContextPool,
queryExecutor,
requestContext,
subscriptionType,
rootSelections,
resolveQueryRootValue,
diagnosticsEvents);
subscription._subscriptionScope = diagnosticsEvents.ExecuteSubscription(subscription);
subscription._sourceStream = await subscription.SubscribeAsync().ConfigureAwait(false);
return subscription;
}
public IAsyncEnumerable<IQueryResult> ExecuteAsync()
=> new SubscriptionEnumerable(
_sourceStream,
OnEvent,
this,
_diagnosticEvents);
/// <inheritdoc />
public ulong Id => _id;
/// <inheritdoc />
public IOperation Operation => _requestContext.Operation!;
public async ValueTask DisposeAsync()
{
if (!_disposed)
{
await _sourceStream.DisposeAsync().ConfigureAwait(false);
_subscriptionScope?.Dispose();
_disposed = true;
}
}
/// <summary>
/// OnEvent is called whenever the event stream yields a payload and triggers an
/// execution of the subscription query.
/// </summary>
/// <param name="payload">
/// The event stream payload.
/// </param>
/// <returns>
/// Returns a query result which will be enqueued to the response stream.
/// </returns>
private async Task<IQueryResult> OnEvent(object payload)
{
using var es = _diagnosticEvents.OnSubscriptionEvent(new(this, payload));
using var serviceScope = _requestContext.Services.CreateScope();
var operationContext = _operationContextPool.Get();
try
{
var eventServices = serviceScope.ServiceProvider;
var dispatcher = eventServices.GetRequiredService<IBatchDispatcher>();
// we store the event payload on the scoped context so that it is accessible
// in the resolvers.
var scopedContextData =
_scopedContextData.SetItem(WellKnownContextData.EventMessage, payload);
// next we resolve the subscription instance.
var rootValue = RootValueResolver.Resolve(
_requestContext,
eventServices,
_subscriptionType,
ref _cachedRootValue);
// last we initialize a standard operation context to execute
// the subscription query with the standard query executor.
operationContext.Initialize(
_requestContext,
eventServices,
dispatcher,
_requestContext.Operation!,
_requestContext.Variables!,
rootValue,
_resolveQueryRootValue);
operationContext.Result.SetContextData(
WellKnownContextData.EventMessage,
payload);
var result = await _queryExecutor
.ExecuteAsync(operationContext, scopedContextData)
.ConfigureAwait(false);
_diagnosticEvents.SubscriptionEventResult(new(this, payload), result);
return result;
}
catch (OperationCanceledException ex)
{
operationContext = null;
_diagnosticEvents.SubscriptionEventError(
new SubscriptionEventContext(this, payload),
ex);
throw;
}
catch (Exception ex)
{
_diagnosticEvents.SubscriptionEventError(
new SubscriptionEventContext(this, payload),
ex);
throw;
}
finally
{
// if the operation context is null a cancellation has happened and we will
// abandon the operation context in order to not have leakage into the
// new operations.
if (operationContext is not null)
{
_operationContextPool.Return(operationContext);
}
}
}
// subscribe will use the subscribe resolver to create a source stream that yields
// the event messages from the underlying pub/sub-system.
private async ValueTask<ISourceStream> SubscribeAsync()
{
var operationContext = _operationContextPool.Get();
try
{
// first we will create the root value which essentially
// is the subscription object. In some cases this object is null.
var rootValue = RootValueResolver.Resolve(
_requestContext,
_requestContext.Services,
_subscriptionType,
ref _cachedRootValue);
// next we need to initialize our operation context so that we have access to
// variables services and other things.
// The subscribe resolver will use a noop dispatcher and all DataLoader are
// dispatched immediately.
operationContext.Initialize(
_requestContext,
_requestContext.Services,
NoopBatchDispatcher.Default,
_requestContext.Operation!,
_requestContext.Variables!,
rootValue,
_resolveQueryRootValue);
// next we need a result map so that we can store the subscribe temporarily
// while executing the subscribe pipeline.
var resultMap = operationContext.Result.RentObject(1);
var rootSelection = _rootSelections.Selections[0];
// we create a temporary middleware context so that we can use the standard
// resolver pipeline.
var middlewareContext = new MiddlewareContext();
middlewareContext.Initialize(
operationContext,
rootSelection,
resultMap,
1,
rootValue,
operationContext.PathFactory.New(rootSelection.ResponseName),
_scopedContextData);
// it is important that we correctly coerce the arguments before
// invoking subscribe.
if (!rootSelection.Arguments.TryCoerceArguments(
middlewareContext,
out var coercedArgs))
{
// the middleware context reports errors to the operation context,
// this means if we failed, we need to grab the coercion errors from there
// and just throw a GraphQLException.
throw new GraphQLException(operationContext.Result.Errors);
}
// if everything is fine with the arguments we still need to assign them.
middlewareContext.Arguments = coercedArgs;
// last but not least we can invoke the subscribe resolver which will subscribe
// to the underlying pub/sub-system yielding the source stream.
var sourceStream =
await rootSelection.Field.SubscribeResolver!
.Invoke(middlewareContext)
.ConfigureAwait(false);
_scopedContextData = middlewareContext.ScopedContextData;
if (operationContext.Result.Errors.Count > 0)
{
// again if we have any errors we will just throw them and not opening
// any subscription context.
try
{
// we make sure that we unsubscribe again by disposing the stream.
await sourceStream.DisposeAsync().ConfigureAwait(false);
}
catch
{
// we ignore any errors here since already are in error state.
}
throw new GraphQLException(operationContext.Result.Errors);
}
return sourceStream;
}
catch
{
// if there is an error we will just dispose our instrumentation scope
// the error is reported in the request level in this case.
_subscriptionScope?.Dispose();
_subscriptionScope = null;
throw;
}
finally
{
operationContext.Result.DiscardResult();
_operationContextPool.Return(operationContext);
}
}
}
private sealed class SubscriptionEnumerable : IAsyncEnumerable<IQueryResult>
{
private readonly ISourceStream _sourceStream;
private readonly Func<object, Task<IQueryResult>> _onEvent;
private readonly Subscription _subscription;
private readonly IExecutionDiagnosticEvents _diagnosticEvents;
public SubscriptionEnumerable(
ISourceStream sourceStream,
Func<object, Task<IQueryResult>> onEvent,
Subscription subscription,
IExecutionDiagnosticEvents diagnosticEvents)
{
_sourceStream = sourceStream;
_onEvent = onEvent;
_subscription = subscription;
_diagnosticEvents = diagnosticEvents;
}
public IAsyncEnumerator<IQueryResult> GetAsyncEnumerator(
CancellationToken cancellationToken = default)
{
try
{
var eventStreamEnumerator =
_sourceStream.ReadEventsAsync()
.GetAsyncEnumerator(cancellationToken);
return new SubscriptionEnumerator(
eventStreamEnumerator,
_onEvent,
_subscription,
_diagnosticEvents,
cancellationToken);
}
catch (Exception ex)
{
_diagnosticEvents.SubscriptionEventError(_subscription, ex);
return new ErrorSubscriptionEnumerator();
}
}
}
private sealed class SubscriptionEnumerator : IAsyncEnumerator<IQueryResult>
{
private readonly IAsyncEnumerator<object> _eventEnumerator;
private readonly Func<object, Task<IQueryResult>> _onEvent;
private readonly Subscription _subscription;
private readonly IExecutionDiagnosticEvents _diagnosticEvents;
private readonly CancellationToken _requestAborted;
private bool _disposed;
public SubscriptionEnumerator(
IAsyncEnumerator<object> eventEnumerator,
Func<object, Task<IQueryResult>> onEvent,
Subscription subscription,
IExecutionDiagnosticEvents diagnosticEvents,
CancellationToken requestAborted)
{
_eventEnumerator = eventEnumerator;
_onEvent = onEvent;
_subscription = subscription;
_diagnosticEvents = diagnosticEvents;
_requestAborted = requestAborted;
}
public IQueryResult Current { get; private set; } = default!;
public async ValueTask<bool> MoveNextAsync()
{
if (_requestAborted.IsCancellationRequested)
{
return false;
}
try
{
if (await _eventEnumerator.MoveNextAsync().ConfigureAwait(false))
{
Current = await _onEvent(_eventEnumerator.Current).ConfigureAwait(false);
return true;
}
}
catch (Exception ex)
{
_diagnosticEvents.SubscriptionEventError(_subscription, ex);
throw;
}
return false;
}
public async ValueTask DisposeAsync()
{
if (!_disposed)
{
await _eventEnumerator.DisposeAsync().ConfigureAwait(false);
_disposed = true;
}
}
}
private sealed class ErrorSubscriptionEnumerator : IAsyncEnumerator<IQueryResult>
{
public IQueryResult Current => default!;
public ValueTask<bool> MoveNextAsync() => new(false);
public ValueTask DisposeAsync() => default;
}
}