From 8c5fc11869aab91ede609f7f76d8cbd1af90e072 Mon Sep 17 00:00:00 2001
From: Samuel Williams <samuel.williams@oriontransfer.co.nz>
Date: Sat, 25 Jul 2026 09:05:57 +1200
Subject: [PATCH] Mask GOAWAY last stream id

---
 lib/protocol/http2/goaway_frame.rb  | 1 +
 releases.md                         | 4 ++++
 test/protocol/http2/goaway_frame.rb | 6 ++++++
 3 files changed, 11 insertions(+)

diff --git a/lib/protocol/http2/goaway_frame.rb b/lib/protocol/http2/goaway_frame.rb
index 0402beb..c316acc 100644
--- a/lib/protocol/http2/goaway_frame.rb
+++ b/lib/protocol/http2/goaway_frame.rb
@@ -33,6 +33,7 @@ def unpack
 				data = super
 				
 				last_stream_id, error_code = data.unpack(FORMAT)
+				last_stream_id &= 0x7fffffff
 				
 				return last_stream_id, error_code, data.slice(8, data.bytesize-8)
 			end
diff --git a/releases.md b/releases.md
index 20e4a35..9cccd4e 100644
--- a/releases.md
+++ b/releases.md
@@ -1,5 +1,9 @@
 # Releases
 
+## Unreleased
+
+  - Ignore the reserved high bit when decoding GOAWAY last stream IDs.
+
 ## v0.26.1
 
   - Improve `StreamError` messages for HTTP/2 stream reset error codes.
diff --git a/test/protocol/http2/goaway_frame.rb b/test/protocol/http2/goaway_frame.rb
index b968e1f..e1454ca 100644
--- a/test/protocol/http2/goaway_frame.rb
+++ b/test/protocol/http2/goaway_frame.rb
@@ -38,5 +38,11 @@ def before
 			
 			expect(frame.unpack).to be == [3, 2, data]
 		end
+		
+		it "ignores the reserved high bit of the last stream id" do
+			frame.pack 0x80000003, 2, data
+			
+			expect(frame.unpack).to be == [3, 2, data]
+		end
 	end
 end