Implement workflow-level exception handling

Fixes #4451

src/modules/Elsa.Workflows.Core/Extensions/WorkflowExecutionContextExtensions.cs

@@ -1,3 +1,4 @@
+using Elsa.Common.Contracts;
 using Elsa.Workflows.Core;
 using Elsa.Workflows.Core.Contracts;
 using Elsa.Workflows.Core.Models;
@@ -109,4 +110,36 @@ public static class WorkflowExecutionContextExtensions
     /// Returns true if all activities have completed or canceled, false otherwise.
     /// </summary>
     public static bool AllActivitiesCompleted(this WorkflowExecutionContext workflowExecutionContext) => workflowExecutionContext.ActiveActivityExecutionContexts.All(x => x.Status != ActivityStatus.Running);
+    
+    /// <summary>
+    /// Adds a new <see cref="WorkflowExecutionLogEntry"/> to the execution log of the current <see cref="WorkflowExecutionContext"/>.
+    /// </summary>
+    /// <param name="context">The <see cref="WorkflowExecutionContext"/></param> being extended.
+    /// <param name="eventName">The name of the event.</param>
+    /// <param name="message">The message of the event.</param>
+    /// <param name="payload">Any contextual data related to this event.</param>
+    /// <returns>Returns the created <see cref="WorkflowExecutionLogEntry"/>.</returns>
+    public static WorkflowExecutionLogEntry AddExecutionLogEntry(this WorkflowExecutionContext context, string eventName, string? message = default, object? payload = default)
+    {
+        var now = context.GetRequiredService<ISystemClock>().UtcNow;
+
+        var logEntry = new WorkflowExecutionLogEntry(
+            context.Id,
+            default,
+            context.Workflow.Id,
+            context.Workflow.Type,
+            context.Workflow.Identity.Version,
+            context.Workflow.Name,
+            context.Workflow.Identity.Id,
+            default,
+            now,
+            context.ExecutionLogSequence++,
+            eventName,
+            message,
+            context.Workflow.GetSource(),
+            payload);
+
+        context.ExecutionLog.Add(logEntry);
+        return logEntry;
+    }
 }

src/modules/Elsa.Workflows.Core/Features/WorkflowsFeature.cs

@@ -47,7 +47,9 @@ public class WorkflowsFeature : FeatureBase
     /// <summary>
     /// A delegate to configure the <see cref="IWorkflowExecutionPipeline"/>.
     /// </summary>
-    public Action<IWorkflowExecutionPipelineBuilder> WorkflowExecutionPipeline { get; set; } = builder => builder.UseDefaultActivityScheduler();
+    public Action<IWorkflowExecutionPipelineBuilder> WorkflowExecutionPipeline { get; set; } = builder => builder
+        .UseExceptionHandling()
+        .UseDefaultActivityScheduler();
     
     /// <summary>
     /// A delegate to configure the <see cref="IActivityExecutionPipeline"/>.

src/modules/Elsa.Workflows.Core/Middleware/Workflows/ExceptionHandlingMiddleware.cs

@@ -0,0 +1,60 @@
+using Elsa.Common.Contracts;
+using Elsa.Extensions;
+using Elsa.Workflows.Core.Contracts;
+using Elsa.Workflows.Core.Models;
+using Elsa.Workflows.Core.Pipelines.WorkflowExecution;
+using Elsa.Workflows.Core.State;
+using Microsoft.Extensions.Logging;
+
+namespace Elsa.Workflows.Core.Middleware.Workflows;
+
+/// <summary>
+/// Adds extension methods to <see cref="ExceptionHandlingMiddleware"/>.
+/// </summary>
+public static class ExceptionHandlingMiddlewareExtensions
+{
+    /// <summary>
+    /// Installs the <see cref="ExceptionHandlingMiddleware"/> component in the activity execution pipeline.
+    /// </summary>
+    public static IWorkflowExecutionPipelineBuilder UseExceptionHandling(this IWorkflowExecutionPipelineBuilder pipelineBuilder) => pipelineBuilder.UseMiddleware<ExceptionHandlingMiddleware>();
+}
+
+/// <summary>
+/// Catches any exceptions thrown by downstream components and transitions the workflow into the faulted state.
+/// </summary>
+public class ExceptionHandlingMiddleware : IWorkflowExecutionMiddleware
+{
+    private readonly WorkflowMiddlewareDelegate _next;
+    private readonly ISystemClock _systemClock;
+    private readonly ILogger<ExceptionHandlingMiddleware> _logger;
+
+    /// <summary>
+    /// Constructor.
+    /// </summary>
+    public ExceptionHandlingMiddleware(WorkflowMiddlewareDelegate next, ISystemClock systemClock, ILogger<ExceptionHandlingMiddleware> logger)
+    {
+        _next = next;
+        _systemClock = systemClock;
+        _logger = logger;
+    }
+
+    /// <inheritdoc />
+    public async ValueTask InvokeAsync(WorkflowExecutionContext context)
+    {
+        try
+        {
+            await _next(context);
+        }
+        catch (Exception e)
+        {
+            _logger.LogWarning(e, "An exception was caught from a downstream middleware component");
+            var exceptionState = ExceptionState.FromException(e);
+            var now = _systemClock.UtcNow;
+            var activity = context.Workflow;
+            var incident = new ActivityIncident(activity.Id, activity.Type, e.Message, exceptionState, now);
+            context.Incidents.Add(incident);
+            context.TransitionTo(WorkflowSubStatus.Faulted);
+            context.AddExecutionLogEntry("Faulted", e.Message, exceptionState);
+        }
+    }
+}

src/modules/Elsa.Workflows.Core/Models/WorkflowFaultState.cs

@@ -1,9 +0,0 @@
-namespace Elsa.Workflows.Core.Models;
-
-/// <summary>
-/// Holds information about a workflow fault.
-/// </summary>
-/// <param name="Exception">The exception that occurred</param>
-/// <param name="Message">A description about the fault. Usually the exception message, if there waa an exception.</param>
-/// <param name="FaultedActivityId">The ID of the activity that caused the workflow to fault.</param>
-public record WorkflowFault(Exception? Exception, string Message, string? FaultedActivityId);

src/modules/Elsa.Workflows.Core/Pipelines/WorkflowExecution/WorkflowExecutionPipeline.cs

@@ -33,5 +33,7 @@ public class WorkflowExecutionPipeline : IWorkflowExecutionPipeline
     /// <inheritdoc />
     public async Task ExecuteAsync(WorkflowExecutionContext context) => await Pipeline(context);
 
-    private WorkflowMiddlewareDelegate CreateDefaultPipeline() => Setup(x => x.UseDefaultActivityScheduler());
+    private WorkflowMiddlewareDelegate CreateDefaultPipeline() => Setup(x => x
+        .UseExceptionHandling()
+        .UseDefaultActivityScheduler());
 }

src/modules/Elsa.Workflows.Runtime/Extensions/WorkflowExecutionPipelineBuilderExtensions.cs

@@ -21,6 +21,7 @@ public static class WorkflowExecutionPipelineBuilderExtensions
             .UseBookmarkPersistence()
             .UseActivityExecutionLogPersistence()
             .UseWorkflowExecutionLogPersistence()
+            .UseExceptionHandling()
             .UseDefaultActivityScheduler();
 
     /// <summary>