http2: HEADERS without END_STREAM after the block that opens a request resets the stream, so its fields no longer land in the body

src/protocols/ioxide.http2/Http2Connection.Frames.cs

@@ -190,6 +190,14 @@ private void HandleHeaders(in FrameHeader header, ReadOnlySpan<byte> payload)
             }
             return;
         }
+        else if ((header.Flags & FrameFlags.EndStream) == 0)
+        {
+            // RFC 9113 8.1: after the block that opens a request come only trailers, which end its stream.
+            _discardBlock.StreamId = header.StreamId;
+            DiscardHeaderBlock(header, block);
+            ResetStream(header.StreamId, Http2Error.ProtocolError);
+            return;
+        }
 
         // A header block can span HEADERS + CONTINUATION frames, and HPACK cannot be decoded
         // piecewise - the whole block has to be in hand first.

tests/Ioxide.Tests.Unit/Http2TrailerTests.cs

@@ -195,6 +195,56 @@ public static void Register(Runner runner)
             gate.SetResult();
             peer.Close(run);
         });
+
+        // RFC 9113 8.1. Its fields landed in the arena the body was being appended to, and the body's range ran across them.
+        runner.Test("h2 buffered request: HEADERS without END_STREAM after the opening block resets the stream, and its body never reaches a handler", () =>
+        {
+            var served = new List<string>();
+
+            using var peer = new Peer(new Http2Options());
+            Task run = peer.Connection.RunAsync(request =>
+            {
+                served.Add($"{Ascii(request.Path)} {Fields(request)}");
+                return Http2Response.Text("ok");
+            });
+
+            peer.Open();
+            peer.Headers(1, Request("/up"), endStream: false);
+            peer.Data(1, 400, endStream: false);
+            peer.Headers(1, Field("x-a", "abc", index: true), endStream: false);
+            peer.Data(1, 400, endStream: true);
+            peer.Headers(3, [.. Request("/next"), 0xBE], endStream: true);   // the block was decoded, so x-a is at index 62
+            peer.Close(run);
+
+            Assert.Equal("1 PROTOCOL_ERROR", Resets(peer));
+            Assert.Equal("", GoAways(peer));
+            Assert.True(served.SequenceEqual(["/next x-a: abc"]), $"the handler was handed: {string.Join(", ", served)}");
+        });
+
+        // The block's CONTINUATION is still owed after the reset, and has to reach the decoder, not end the connection.
+        runner.Test("h2 buffered request: HEADERS without END_STREAM split over CONTINUATION still keeps HPACK in step", () =>
+        {
+            var served = new List<string>();
+
+            using var peer = new Peer(new Http2Options());
+            Task run = peer.Connection.RunAsync(request =>
+            {
+                served.Add($"{Ascii(request.Path)} {Fields(request)}");
+                return Http2Response.Text("ok");
+            });
+
+            peer.Open();
+            peer.Headers(1, Request("/up"), endStream: false);
+            byte[] block = Field("x-a", "abc", index: true);
+            peer.HeadersOpen(1, block[..3], endStream: false);
+            peer.Continuation(1, block[3..]);
+            peer.Headers(3, [.. Request("/next"), 0xBE], endStream: true);
+            peer.Close(run);
+
+            Assert.Equal("1 PROTOCOL_ERROR", Resets(peer));
+            Assert.Equal("", GoAways(peer));
+            Assert.True(served.SequenceEqual(["/next x-a: abc"]), $"the handler was handed: {string.Join(", ", served)}");
+        });
     }
 
     // :method POST and :scheme http from the static table, and :path as a literal on its static
@@ -343,6 +393,10 @@ public void Headers(int streamId, byte[] block, bool endStream)
 
         public void Continuation(int streamId, byte[] block) => Feed(FrameBytes(0x9, 0x4, streamId, block));
 
+        /// <summary>A HEADERS frame without END_HEADERS: a CONTINUATION ends its block.</summary>
+        public void HeadersOpen(int streamId, byte[] block, bool endStream)
+            => Feed(FrameBytes(0x1, (byte)(endStream ? 0x1 : 0), streamId, block));
+
         public void Data(int streamId, int bytes, bool endStream)
             => Feed(FrameBytes(0x0, (byte)(endStream ? 0x1 : 0), streamId, Enumerable.Repeat((byte)'z', bytes).ToArray()));