Introduce fault header keys (#6876)

* Cleanup fault extractor

* Move to faults folder

* Extract fault header keys

* Cosmetics

* Approve API

* Dots can make real differences

src/NServiceBus.Core.Tests/ApprovalFiles/APIApprovals.ApproveNServiceBus.approved.txt

@@ -1152,7 +1152,14 @@ namespace NServiceBus.Faults
     }
     public static class FaultsHeaderKeys
     {
+        public const string ExceptionType = "NServiceBus.ExceptionInfo.ExceptionType";
         public const string FailedQ = "NServiceBus.FailedQ";
+        public const string HelpLink = "NServiceBus.ExceptionInfo.HelpLink";
+        public const string InnerExceptionType = "NServiceBus.ExceptionInfo.InnerExceptionType";
+        public const string Message = "NServiceBus.ExceptionInfo.Message";
+        public const string Source = "NServiceBus.ExceptionInfo.Source";
+        public const string StackTrace = "NServiceBus.ExceptionInfo.StackTrace";
+        public const string TimeOfFailure = "NServiceBus.TimeOfFailure";
     }
     public class ImmediateRetryMessage
     {

src/NServiceBus.Core/Recoverability/Faults/FaultMetadataExtractor.cs

@@ -0,0 +1,57 @@
+namespace NServiceBus
+{
+    using System;
+    using System.Collections;
+    using System.Collections.Generic;
+    using Faults;
+    using Transport;
+
+    class FaultMetadataExtractor(Dictionary<string, string> staticFaultMetadata, Action<Dictionary<string, string>> headerCustomizations)
+    {
+        public Dictionary<string, string> Extract(ErrorContext errorContext)
+        {
+            var metadata = new Dictionary<string, string>(staticFaultMetadata)
+            {
+                [FaultsHeaderKeys.FailedQ] = errorContext.ReceiveAddress
+            };
+
+            SetExceptionMetadata(metadata, errorContext.Exception);
+
+            headerCustomizations(metadata);
+
+            return metadata;
+        }
+
+        static void SetExceptionMetadata(Dictionary<string, string> headers, Exception e)
+        {
+            headers[FaultsHeaderKeys.ExceptionType] = e.GetType().FullName;
+
+            if (e.InnerException != null)
+            {
+                headers[FaultsHeaderKeys.InnerExceptionType] = e.InnerException.GetType().FullName;
+            }
+
+            headers[FaultsHeaderKeys.HelpLink] = e.HelpLink;
+            headers[FaultsHeaderKeys.Message] = Truncate(e.GetMessage(), 16384);
+            headers[FaultsHeaderKeys.Source] = e.Source;
+            headers[FaultsHeaderKeys.StackTrace] = e.ToString();
+            headers[FaultsHeaderKeys.TimeOfFailure] = DateTimeOffsetHelper.ToWireFormattedString(DateTimeOffset.UtcNow);
+
+            foreach (DictionaryEntry entry in e.Data)
+            {
+                if (entry.Value == null)
+                {
+                    continue;
+                }
+                headers[$"{FaultsHeaderKeys.ExceptionInfoDataPrefix}{entry.Key}"] = entry.Value.ToString();
+            }
+        }
+
+        static string Truncate(string value, int maxLength) =>
+            string.IsNullOrEmpty(value)
+                ? value
+                : value.Length <= maxLength
+                    ? value
+                    : value[..maxLength];
+    }
+}

src/NServiceBus.Core/Recoverability/Faults/FaultsHeaderKeys.cs

@@ -1,5 +1,7 @@
 namespace NServiceBus.Faults
 {
+    using System;
+
     /// <summary>
     /// Class holding keys to message headers for faults.
     /// </summary>
@@ -9,5 +11,43 @@ public static class FaultsHeaderKeys
         /// Header key for setting/getting the queue at which the message processing failed.
         /// </summary>
         public const string FailedQ = "NServiceBus.FailedQ";
+
+        /// <summary>
+        /// Header key for setting/getting the exception type that caused the message processing to fail.
+        /// </summary>
+        public const string ExceptionType = $"{ExceptionInfoPrefix}ExceptionType";
+
+        /// <summary>
+        /// Header key for setting/getting the inner exception type that caused the message processing to fail.
+        /// </summary>
+        public const string InnerExceptionType = $"{ExceptionInfoPrefix}InnerExceptionType";
+
+        /// <summary>
+        /// Header key for setting/getting the <see cref="Exception.HelpLink"/> of the exception that caused the message processing to fail.
+        /// </summary>
+        public const string HelpLink = $"{ExceptionInfoPrefix}HelpLink";
+
+        /// <summary>
+        /// Header key for setting/getting the <see cref="Exception.Message"/> of the exception that caused the message processing to fail.
+        /// </summary>
+        public const string Message = $"{ExceptionInfoPrefix}Message";
+
+        /// <summary>
+        /// Header key for setting/getting the <see cref="Exception.Source"/> of the exception that caused the message processing to fail.
+        /// </summary>
+        public const string Source = $"{ExceptionInfoPrefix}Source";
+
+        /// <summary>
+        /// Header key for setting/getting the <see cref="Exception.StackTrace"/> of the exception that caused the message processing to fail.
+        /// </summary>
+        public const string StackTrace = $"{ExceptionInfoPrefix}StackTrace";
+
+        /// <summary>
+        /// Header key for setting/getting the normalized time of the failure.
+        /// </summary>
+        public const string TimeOfFailure = "NServiceBus.TimeOfFailure";
+
+        const string ExceptionInfoPrefix = "NServiceBus.ExceptionInfo.";
+        internal const string ExceptionInfoDataPrefix = $"{ExceptionInfoPrefix}Data.";
     }
 }