Improved error handling

samples/GraphQL.Samples.Http/Program.cs

@@ -1,4 +1,7 @@
 using System.Runtime.CompilerServices;
+
+using Microsoft.AspNetCore.Mvc;
+
 using Tanka.GraphQL.Executable;
 using Tanka.GraphQL.Server;
 
@@ -59,7 +62,7 @@
 app.Run();
 
 // simple subscription generating numbers from 0 to the given number
-static async IAsyncEnumerable<int> Count(int to, [EnumeratorCancellation] CancellationToken cancellationToken)
+static async IAsyncEnumerable<int> Count(int to, [FromServices]ILogger<Program> logger, [EnumeratorCancellation] CancellationToken cancellationToken)
 {
     var i = 0;
     while (!cancellationToken.IsCancellationRequested)

src/GraphQL.Server/WebSockets/ServerMethods.cs

@@ -1,6 +1,8 @@
 using System.Collections.Concurrent;
 
 using Microsoft.AspNetCore.Http;
+
+using Tanka.GraphQL.Fields;
 using Tanka.GraphQL.Server.WebSockets.WebSocketPipe;
 using Tanka.GraphQL.Validation;
 
@@ -56,40 +58,32 @@ await Channel.Complete(
     private async Task Execute(Subscribe subscribe, CancellationTokenSource unsubscribeOrAborted)
     {
         var cancellationToken = unsubscribeOrAborted.Token;
+        var context = new GraphQLRequestContext
+        {
+            HttpContext = _httpContext,
+            RequestServices = _httpContext.RequestServices,
+            Request = new()
+            {
+                InitialValue = null,
+                Document = subscribe.Payload.Query,
+                OperationName = subscribe.Payload.OperationName,
+                Variables = subscribe.Payload.Variables
+            }
+        };
 
         try
         {
-            var context = new GraphQLRequestContext
-            {
-                HttpContext = _httpContext,
-                RequestServices = _httpContext.RequestServices,
-                Request = new()
-                {
-                    InitialValue = null,
-                    Document = subscribe.Payload.Query,
-                    OperationName = subscribe.Payload.OperationName,
-                    Variables = subscribe.Payload.Variables
-                }
-            };
-
             await _requestDelegate(context);
             await using var enumerator = context.Response.GetAsyncEnumerator(cancellationToken);
 
             while (await enumerator.MoveNextAsync())
             {
-                await Client.Next(new Next()
-                {
-                    Id = subscribe.Id,
-                    Payload = enumerator.Current
-                }, cancellationToken);
+                await Client.Next(new Next() { Id = subscribe.Id, Payload = enumerator.Current }, cancellationToken);
             }
 
             if (!cancellationToken.IsCancellationRequested)
             {
-                await Client.Complete(new Complete()
-                {
-                    Id = subscribe.Id
-                }, cancellationToken);
+                await Client.Complete(new Complete() { Id = subscribe.Id }, cancellationToken);
             }
         }
         catch (OperationCanceledException)
@@ -99,26 +93,36 @@ await Client.Complete(new Complete()
         catch (ValidationException x)
         {
             var validationResult = x.Result;
-            await Client.Error(new Error()
-            {
-                Id = subscribe.Id,
-                Payload = validationResult.Errors.Select(ve => ve.ToError()).ToArray()
-            }, cancellationToken);
+            await Client.Error(
+                new Error()
+                {
+                    Id = subscribe.Id, 
+                    Payload = validationResult.Errors.Select(ve => ve.ToError()).ToArray()
+                }, cancellationToken);
         }
         catch (QueryException x)
         {
-            await Client.Error(new Error()
-            {
-                Id = subscribe.Id,
-                Payload = new[]
+            await Client.Error(
+                new Error()
+                {
+                    Id = subscribe.Id,
+                    Payload = new[]
+                    {
+                        context.Errors?.FormatError(x)!
+                    }
+                }, cancellationToken);
+        }
+        catch (Exception x)
+        {
+            await Client.Error(
+                new Error()
                 {
-                    new ExecutionError()
+                    Id = subscribe.Id,
+                    Payload = new[]
                     {
-                        Path = x.Path.Segments.ToArray(),
-                        Message = x.Message
+                        context.Errors?.FormatError(x)!
                     }
-                }
-            }, cancellationToken);
+                }, cancellationToken);
         }
         finally
         {

src/GraphQL/ErrorCollectorFeature.cs

@@ -18,6 +18,11 @@ public IEnumerable<ExecutionError> GetErrors()
         return _bag.Select(DefaultFormatError);
     }
 
+    public ExecutionError FormatError(Exception x)
+    {
+        return DefaultFormatError(x);
+    }
+
     public ExecutionError DefaultFormatError(Exception exception)
     {
         var rootCause = exception.GetBaseException();

src/GraphQL/ExceptionExtensions.cs

@@ -1,5 +1,4 @@
-using Tanka.GraphQL.Fields;
-using Tanka.GraphQL.Language.Nodes;
+using Tanka.GraphQL.Language.Nodes;
 using Tanka.GraphQL.Language.Nodes.TypeSystem;
 using Tanka.GraphQL.ValueResolution;
 

src/GraphQL/ExecutionError.cs

@@ -11,7 +11,7 @@ public class ExecutionError
 
     [JsonPropertyName("locations")]
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
-    public List<Location>? Locations { get; set; }
+    public List<SerializedLocation>? Locations { get; set; }
 
     [JsonPropertyName("message")] public string Message { get; set; } = string.Empty;
 
@@ -23,4 +23,28 @@ public void Extend(string key, object value)
 
         Extensions[key] = value;
     }
+}
+
+public class SerializedLocation
+{
+    public int Line { get; set; }
+
+    public int Column { get; set; }
+
+    public static implicit operator SerializedLocation(Location location)  
+    {
+        return new()
+        {
+            Line = location.Line,
+            Column = location.Column
+        };
+    }
+}
+
+public static class ExecutionErrorExtensions
+{
+    public static List<SerializedLocation> ToSerializedLocations(this IEnumerable<Location> locations)
+    {
+        return [.. locations];
+    }
 }

src/GraphQL/Executor.ExecuteSubscription.cs

@@ -1,4 +1,7 @@
-using System.Runtime.CompilerServices;
+using System;
+using System.Runtime.CompilerServices;
+
+using Microsoft.VisualBasic.FileIO;
 
 using Tanka.GraphQL.Features;
 using Tanka.GraphQL.Language.Nodes;
@@ -15,11 +18,11 @@ public partial class Executor
     /// </summary>
     /// <param name="context"></param>
     /// <returns></returns>
-    public static Task ExecuteSubscription(QueryContext context)
+    public static async Task ExecuteSubscription(QueryContext context)
     {
         context.RequestCancelled.ThrowIfCancellationRequested();
 
-        IAsyncEnumerable<object?> sourceStream = CreateSourceEventStream(
+        IAsyncEnumerable<object?> sourceStream = await CreateSourceEventStream(
             context,
             context.RequestCancelled);
 
@@ -29,7 +32,6 @@ public static Task ExecuteSubscription(QueryContext context)
             context.RequestCancelled);
 
         context.Response = responseStream;
-        return Task.CompletedTask;
     }
 
 
@@ -40,9 +42,9 @@ public static Task ExecuteSubscription(QueryContext context)
     /// <param name="cancellationToken"></param>
     /// <returns></returns>
     /// <exception cref="QueryException"></exception>
-    public static async IAsyncEnumerable<object?> CreateSourceEventStream(
+    public static async Task<IAsyncEnumerable<object?>> CreateSourceEventStream(
         QueryContext context,
-        [EnumeratorCancellation] CancellationToken cancellationToken)
+        CancellationToken cancellationToken)
     {
         ArgumentNullException.ThrowIfNull(context.Schema.Subscription);
 
@@ -56,9 +58,9 @@ public static Task ExecuteSubscription(QueryContext context)
         );
 
         List<FieldSelection> fields = groupedFieldSet.Values.First();
-        Name fieldName = fields.First().Name;
         FieldSelection fieldSelection = fields.First();
-
+        Name fieldName = fieldSelection.Name;
+
         IReadOnlyDictionary<string, object?> coercedArgumentValues = ArgumentCoercion.CoerceArgumentValues(
             context.Schema,
             subscriptionType,
@@ -68,7 +70,7 @@ public static Task ExecuteSubscription(QueryContext context)
         FieldDefinition? field = context.Schema.GetField(subscriptionType.Name, fieldName);
 
         if (field is null)
-            yield break;
+            return AsyncEnumerableEx.Empty<object?>();
 
         var path = new NodePath();
         Subscriber? subscriber = context.Schema.GetSubscriber(subscriptionType.Name, fieldName);
@@ -92,13 +94,60 @@ public static Task ExecuteSubscription(QueryContext context)
             QueryContext = context
         };
 
-        await subscriber(resolverContext, cancellationToken);
+        try
+        {
+            await subscriber(resolverContext, cancellationToken);
 
-        if (resolverContext.ResolvedValue is null)
-            yield break;
+            if (resolverContext.ResolvedValue is null)
+                return AsyncEnumerableEx.Empty<object?>();
+        }
+        catch (Exception exception)
+        {
+            if (exception is not FieldException)
+                throw new FieldException(exception.Message, exception)
+                {
+                    ObjectDefinition = subscriptionType,
+                    Field = field,
+                    Selection = fieldSelection,
+                    Path = path
+                };
+
+            throw;
+        }
+
+        return Core(resolverContext, cancellationToken);
+
+        static async IAsyncEnumerable<object?> Core(SubscriberContext resolverContext, [EnumeratorCancellation]CancellationToken cancellationToken)
+        {
+            await using var e = resolverContext.ResolvedValue!.GetAsyncEnumerator(cancellationToken);
 
-        await foreach (object? evnt in resolverContext.ResolvedValue.WithCancellation(cancellationToken))
-            yield return evnt;
+            while (true)
+            {
+                try
+                {
+                    if (!await e.MoveNextAsync())
+                    {
+                        yield break;
+                    }
+
+                }
+                catch (Exception exception)
+                {
+                    if (exception is not FieldException)
+                        throw new FieldException(exception.Message, exception)
+                        {
+                            ObjectDefinition = resolverContext.ObjectDefinition,
+                            Field = resolverContext.Field,
+                            Selection = resolverContext.Selection,
+                            Path = resolverContext.Path
+                        };
+
+                    throw;
+                }
+
+                yield return e.Current;
+            }
+        }
     }
 
     /// <summary>
@@ -109,25 +158,36 @@ public static Task ExecuteSubscription(QueryContext context)
     /// <param name="sourceStream"></param>
     /// <param name="cancellationToken"></param>
     /// <returns></returns>
-    public static async IAsyncEnumerable<ExecutionResult> MapSourceToResponseEventStream(
+    public static IAsyncEnumerable<ExecutionResult> MapSourceToResponseEventStream(
         QueryContext context,
         IAsyncEnumerable<object?> sourceStream,
-        [EnumeratorCancellation] CancellationToken cancellationToken)
+        CancellationToken cancellationToken)
     {
         ArgumentNullException.ThrowIfNull(context.Schema.Subscription);
 
         ObjectDefinition? subscriptionType = context.Schema.Subscription;
         SelectionSet selectionSet = context.OperationDefinition.SelectionSet;
 
-        await foreach (object? sourceEvnt in sourceStream.WithCancellation(cancellationToken))
+        return Core(context, sourceStream, subscriptionType, selectionSet, cancellationToken);
+
+        static async IAsyncEnumerable<ExecutionResult> Core(
+            QueryContext context,
+            IAsyncEnumerable<object?> sourceStream,
+            ObjectDefinition subscriptionType,
+            SelectionSet selectionSet,
+            [EnumeratorCancellation] CancellationToken cancellationToken)
         {
-            var path = new NodePath();
-            yield return await ExecuteSourceEvent(
-                context,
-                selectionSet,
-                subscriptionType,
-                sourceEvnt,
-                path);
+
+            await foreach (var sourceEvnt in sourceStream.WithCancellation(cancellationToken))
+            {
+                var path = new NodePath();
+                yield return await ExecuteSourceEvent(
+                    context,
+                    selectionSet,
+                    subscriptionType,
+                    sourceEvnt,
+                    path);
+            }
         }
     }
 

src/GraphQL/Features/IErrorCollectorFeature.cs

@@ -4,4 +4,5 @@ public interface IErrorCollectorFeature
 {
     void Add(Exception error);
     IEnumerable<ExecutionError> GetErrors();
+    ExecutionError FormatError(Exception x);
 }