1 files changed, 58 insertions, 1 deletions
diff --git a/tools/http2_interop/s6.5.go b/tools/http2_interop/s6.5.go
index 8145b6e031..4295c46f73 100644
--- a/tools/http2_interop/s6.5.go
+++ b/tools/http2_interop/s6.5.go
@@ -1,6 +1,7 @@
 package http2interop
 
 import (
+	"fmt"
 	"time"
 )
 
@@ -11,7 +12,6 @@ func testSmallMaxFrameSize(ctx *HTTP2InteropCtx) error {
 		return err
 	}
 	defer conn.Close()
-	conn.Log = ctx.T.Log
 	conn.SetDeadline(time.Now().Add(defaultTimeout))
 
 	sf := &SettingsFrame{
@@ -31,3 +31,60 @@ func testSmallMaxFrameSize(ctx *HTTP2InteropCtx) error {
 
 	return nil
 }
+
+// Section 6.5.3 says all settings frames must be acked.
+func testAllSettingsFramesAcked(ctx *HTTP2InteropCtx) error {
+	conn, err := connect(ctx)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+	conn.SetDeadline(time.Now().Add(defaultTimeout))
+
+	sf := &SettingsFrame{}
+	if err := http2Connect(conn, sf); err != nil {
+		return err
+	}
+
+	// The spec says "The values in the SETTINGS frame MUST be processed in the order they
+	// appear. [...] Once all values have been processed, the recipient MUST immediately
+	// emit a SETTINGS frame with the ACK flag set."  From my understanding, processing all
+	// of no values warrants an ack per frame.
+	for i := 0; i < 10; i++ {
+		if err := streamFrame(conn, sf); err != nil {
+			return err
+		}
+	}
+
+	var settingsFramesReceived = 0
+	// The server by default sends a settings frame as part of the handshake, and another
+	// after the receipt of the initial settings frame as part of our conneection preface.
+	// This means we expected 1 + 1 + 10 = 12 settings frames in return, with all but the
+	// first having the ack bit.
+	for settingsFramesReceived < 12 {
+		f, err := parseFrame(conn)
+		if err != nil {
+			return err
+		}
+
+		// Other frames come down the wire too, including window update.  Just ignore those.
+		if f, ok := f.(*SettingsFrame); ok {
+			settingsFramesReceived += 1
+			if settingsFramesReceived == 1 {
+				if f.Header.Flags&SETTINGS_FLAG_ACK > 0 {
+					return fmt.Errorf("settings frame should not have used ack: %v")
+				}
+				continue
+			}
+
+			if f.Header.Flags&SETTINGS_FLAG_ACK == 0 {
+				return fmt.Errorf("settings frame should have used ack: %v", f)
+			}
+			if len(f.Params) != 0 {
+				return fmt.Errorf("settings ack cannot have params: %v", f)
+			}
+		}
+	}
+
+	return nil
+}