Fix SSE client cancellation (#9503)

Author: michaelstaib

src/HotChocolate/AspNetCore/src/Transport.Http/GraphQLHttpResponse.cs

@@ -165,7 +165,7 @@ public IAsyncEnumerable<OperationResult> ReadAsResultStreamAsync(CancellationTok
 
         if (contentType?.MediaType.EqualsOrdinal(ContentType.EventStream) ?? false)
         {
-            return new SseReader(_message);
+            return new SseReader(_message, cancellationToken);
         }
 
         // The server supports the newer graphql-response+json media type and users are free

src/HotChocolate/AspNetCore/src/Transport.Http/Sse/SseReader.cs

@@ -6,7 +6,9 @@
 
 namespace HotChocolate.Transport.Http;
 
-internal class SseReader(HttpResponseMessage message) : IAsyncEnumerable<OperationResult>
+internal class SseReader(
+    HttpResponseMessage message,
+    CancellationToken requestCancellationToken = default) : IAsyncEnumerable<OperationResult>
 {
     private static readonly StreamPipeReaderOptions s_options = new(
         pool: MemoryPool<byte>.Shared,
@@ -18,8 +20,11 @@ internal class SseReader(HttpResponseMessage message) : IAsyncEnumerable<Operati
     public async IAsyncEnumerator<OperationResult> GetAsyncEnumerator(
         CancellationToken cancellationToken = default)
     {
-        using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
-        await using var stream = await message.Content.ReadAsStreamAsync(cts.Token);
+        using var cts = CancellationTokenSource.CreateLinkedTokenSource(
+            requestCancellationToken,
+            cancellationToken);
+        await using var stream =
+            await message.Content.ReadAsStreamAsync(cts.Token).ConfigureAwait(false);
         using var eventBuffer = new PooledArrayWriter();
         var reader = PipeReader.Create(stream, s_options);
 

src/HotChocolate/AspNetCore/test/Transport.Http.Tests/GraphQLHttpClientTests.cs

@@ -713,7 +713,7 @@ mutation CreateReviewForEpisode(
         var canceled = false;
         try
         {
-            await foreach (var result in subscriptionResponse.ReadAsResultStreamAsync().WithCancellation(cts.Token))
+            await foreach (var result in subscriptionResponse.ReadAsResultStreamAsync(cts.Token))
             {
                 result.MatchInlineSnapshot(
                     """