[Diagnostics] Give every batch item its own request span

src/HotChocolate/Diagnostics/src/Diagnostics.Core/Spans/Http/ExecuteHttpRequestSpan.cs

@@ -61,6 +61,15 @@ internal sealed class ExecuteHttpRequestSpan(
         return new ExecuteHttpRequestSpan(activity, httpContext, kind, enricher, options);
     }
 
+    /// <summary>
+    /// Specifies whether this span covers more than one GraphQL request. The items of a
+    /// batch execute concurrently, so they must not write their own operation details
+    /// onto this shared span.
+    /// </summary>
+    public bool IsBatch { get; private set; }
+
+    public void MarkAsBatch() => IsBatch = true;
+
     public void SetSingleRequestDetails(GraphQLRequest request)
     {
         Activity.SetTag(GraphQL.Http.Request.Type, GraphQL.Http.Request.Types.Single);
@@ -122,13 +131,13 @@ public void SetBatchRequestDetails(IReadOnlyList<GraphQLRequest> batch)
             if (request.DocumentId is not null
                 && (options.RequestDetails & RequestDetails.Id) == RequestDetails.Id)
             {
-                Activity.SetTag(GraphQL.Http.Request.BatchRequest.QueryId(i), request.DocumentId.Value);
+                Activity.SetTag(GraphQL.Http.Request.BatchRequest.QueryId(i), request.DocumentId.Value.Value);
             }
 
             if (request.DocumentHash is not null
                 && (options.RequestDetails & RequestDetails.Hash) == RequestDetails.Hash)
             {
-                Activity.SetTag(GraphQL.Http.Request.BatchRequest.QueryHash(i), request.DocumentHash.Value);
+                Activity.SetTag(GraphQL.Http.Request.BatchRequest.QueryHash(i), request.DocumentHash.Value.Value);
             }
 
             if (request.Document is not null

src/HotChocolate/Diagnostics/src/Diagnostics/Listeners/ActivityExecutionDiagnosticListener.cs

@@ -31,10 +31,12 @@ public override IDisposable ExecuteRequest(RequestContext context)
                 return EmptyScope;
             }
 
-            // A GraphQL over HTTP request reuses the transport span as the root request
-            // span instead of emitting a second one. A transport that has no span of its
-            // own, like a WebSocket session, falls through to a dedicated request span.
-            if (httpContext.Features.Get<ExecuteHttpRequestSpan>() is { } httpRequestSpan)
+            // A single GraphQL over HTTP request reuses the transport span as the root
+            // request span instead of emitting a second one. A batch shares one transport
+            // span across concurrently executing items, and a transport without a span of
+            // its own, like a WebSocket session, has nothing to reuse, so both fall
+            // through to a dedicated request span.
+            if (httpContext.Features.Get<ExecuteHttpRequestSpan>() is { IsBatch: false } httpRequestSpan)
             {
                 httpContextActivity = httpRequestSpan.Activity;
             }

src/HotChocolate/Diagnostics/src/Diagnostics/Listeners/ActivityServerDiagnosticListener.cs

@@ -43,8 +43,14 @@ public override void StartSingleRequest(HttpContext context, GraphQLRequest requ
 
     public override void StartBatchRequest(HttpContext context, IReadOnlyList<GraphQLRequest> batch)
     {
-        if (options.IncludeRequestDetails
-            && context.Features.Get<ExecuteHttpRequestSpan>() is { } span)
+        if (context.Features.Get<ExecuteHttpRequestSpan>() is not { } span)
+        {
+            return;
+        }
+
+        span.MarkAsBatch();
+
+        if (options.IncludeRequestDetails)
         {
             span.SetBatchRequestDetails(batch);
         }
@@ -55,8 +61,14 @@ public override void StartOperationBatchRequest(
         GraphQLRequest request,
         IReadOnlyList<string> operations)
     {
-        if (options.IncludeRequestDetails
-            && context.Features.Get<ExecuteHttpRequestSpan>() is { } span)
+        if (context.Features.Get<ExecuteHttpRequestSpan>() is not { } span)
+        {
+            return;
+        }
+
+        span.MarkAsBatch();
+
+        if (options.IncludeRequestDetails)
         {
             span.SetOperationBatchRequestDetails(request, operations);
         }

src/HotChocolate/Diagnostics/test/Diagnostics.Tests/ActivityServerDiagnosticListenerTests.cs

@@ -154,6 +154,37 @@ public async Task Http_Get_PersistedOperationEndpoint_GetHeroName_Default()
         }
     }
 
+    [Fact]
+    public async Task Http_Post_BatchRequest_Should_Give_Every_Item_Its_Own_Request_Span_Default()
+    {
+        using (CaptureActivities(out var activities))
+        {
+            // arrange
+            // batch items execute concurrently and share one transport span, so with the
+            // default scopes they must not fold their operation details into it
+            using var server = CreateInstrumentedServer();
+            using var client = server.CreateClient();
+            client.BaseAddress = new Uri("http://localhost:5000");
+
+            const string batch =
+                """
+                [{"query":"query A { hero { name } }"},
+                 {"query":"query B { human(id: \"1000\") { name } }"}]
+                """;
+
+            // act
+            using var content = new StringContent(batch, Encoding.UTF8, "application/json");
+            using var response = await client.PostAsync(
+                "/graphql",
+                content,
+                TestContext.Current.CancellationToken);
+            await response.Content.ReadAsStringAsync(TestContext.Current.CancellationToken);
+
+            // assert
+            activities.MatchSnapshot(Postfix([NET11_0]));
+        }
+    }
+
     [Fact]
     public async Task Http_Post_Variables_Are_Not_Automatically_Added_To_Activities()
     {