cmd/k8s-operator,k8s-operator/sessionrecording: ensure recording header contains terminal size for terminal sessions (#12965)

* cmd/k8s-operator,k8s-operator/sessonrecording: ensure CastHeader contains terminal size

For tsrecorder to be able to play session recordings, the recording's
CastHeader must have '.Width' and '.Height' fields set to non-zero.
Kubectl (or whoever is the client that initiates the 'kubectl exec'
session recording) sends the terminal dimensions in a resize message that
the API server proxy can intercept, however that races with the first server
message that we need to record.
This PR ensures we wait for the terminal dimensions to be processed from
the first resize message before any other data is sent, so that for all
sessions with terminal attached, the header of the session recording
contains the terminal dimensions and the recording can be played by tsrecorder.

Updates tailscale/tailscale#19821

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

k8s-operator/sessionrecording/ws/conn_test.go

@@ -65,6 +65,7 @@ func Test_conn_Read(t *testing.T) {
 				log:  zl.Sugar(),
 			}
 			for i, input := range tt.inputs {
+				c.initialTermSizeSet = make(chan struct{})
 				if err := tc.WriteReadBufBytes(input); err != nil {
 					t.Fatalf("writing bytes to test conn: %v", err)
 				}
@@ -93,13 +94,15 @@ func Test_conn_Write(t *testing.T) {
 	}
 	cl := tstest.NewClock(tstest.ClockOpts{})
 	tests := []struct {
-		name          string
-		inputs        [][]byte
-		wantForwarded []byte
-		wantRecorded  []byte
-		firstWrite    bool
-		width         int
-		height        int
+		name              string
+		inputs            [][]byte
+		wantForwarded     []byte
+		wantRecorded      []byte
+		firstWrite        bool
+		width             int
+		height            int
+		hasTerm           bool
+		sendInitialResize bool
 	}{
 		{
 			name:          "single_write_control_frame",
@@ -144,12 +147,23 @@ func Test_conn_Write(t *testing.T) {
 			wantForwarded: []byte{0x2, 0x3, 0x1, 0x7, 0x8, 0x80, 0x6, 0x1, 0x1, 0x2, 0x3, 0x4, 0x5},
 			wantRecorded:  fakes.CastLine(t, []byte{0x7, 0x8, 0x1, 0x2, 0x3, 0x4, 0x5}, cl),
 		},
+		{
+			name:              "three_writes_stdout_data_message_with_split_fragment_cast_header_with_terminal",
+			inputs:            [][]byte{{0x2, 0x3, 0x1, 0x7, 0x8}, {0x80, 0x6, 0x1, 0x1, 0x2, 0x3}, {0x4, 0x5}},
+			wantForwarded:     []byte{0x2, 0x3, 0x1, 0x7, 0x8, 0x80, 0x6, 0x1, 0x1, 0x2, 0x3, 0x4, 0x5},
+			wantRecorded:      append(fakes.AsciinemaResizeMsg(t, 10, 20), fakes.CastLine(t, []byte{0x7, 0x8, 0x1, 0x2, 0x3, 0x4, 0x5}, cl)...),
+			height:            20,
+			width:             10,
+			hasTerm:           true,
+			firstWrite:        true,
+			sendInitialResize: true,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			tc := &fakes.TestConn{}
 			sr := &fakes.TestSessionRecorder{}
-			rec := tsrecorder.New(sr, cl, cl.Now(), true)
+			rec := tsrecorder.New(sr, cl, cl.Now(), true, zl.Sugar())
 			c := &conn{
 				Conn: tc,
 				log:  zl.Sugar(),
@@ -157,12 +171,17 @@ func Test_conn_Write(t *testing.T) {
 					Width:  tt.width,
 					Height: tt.height,
 				},
-				rec: rec,
+				rec:                rec,
+				initialTermSizeSet: make(chan struct{}),
+				hasTerm:            tt.hasTerm,
 			}
 			if !tt.firstWrite {
 				// This test case does not intend to test that cast header gets written once.
 				c.writeCastHeaderOnce.Do(func() {})
 			}
+			if tt.sendInitialResize {
+				close(c.initialTermSizeSet)
+			}
 			for i, input := range tt.inputs {
 				_, err := c.Write(input)
 				if err != nil {
@@ -221,7 +240,7 @@ func Test_conn_WriteRand(t *testing.T) {
 	}
 	cl := tstest.NewClock(tstest.ClockOpts{})
 	sr := &fakes.TestSessionRecorder{}
-	rec := tsrecorder.New(sr, cl, cl.Now(), true)
+	rec := tsrecorder.New(sr, cl, cl.Now(), true, zl.Sugar())
 	for i := range 100 {
 		tc := &fakes.TestConn{}
 		c := &conn{