fix: stop reading closed channel for /watch devcontainers endpoint

DanielleMaywood · DanielleMaywood · commit 894b29839973 · 2025-08-15T09:44:55.000Z
Fixes #19372 We increase the read limit to 4MiB (we use this limit elsewhere). We also make sure to stop sending messages of `containersCh` becomes closed.
diff --git a/coderd/workspaceagents.go b/coderd/workspaceagents.go
@@ -896,7 +896,11 @@ func (api *API) watchWorkspaceAgentContainers(rw http.ResponseWriter, r *http.Re
 		case <-ctx.Done():
 			return
 
-		case containers := <-containersCh:
+		case containers, ok := <-containersCh:
+			if !ok {
+				return
+			}
+
 			if err := encoder.Encode(containers); err != nil {
 				api.Logger.Error(ctx, "encode containers", slog.Error(err))
 				return
diff --git a/codersdk/workspacesdk/agentconn.go b/codersdk/workspacesdk/agentconn.go
@@ -399,7 +399,8 @@ func (c *AgentConn) WatchContainers(ctx context.Context, logger slog.Logger) (<-
 	url := fmt.Sprintf("http://%s%s", host, "/api/v0/containers/watch")
 
 	conn, res, err := websocket.Dial(ctx, url, &websocket.DialOptions{
-		HTTPClient: c.apiClient(),
+		HTTPClient:      c.apiClient(),
+		CompressionMode: websocket.CompressionContextTakeover,
 	})
 	if err != nil {
 		if res == nil {
@@ -411,6 +412,8 @@ func (c *AgentConn) WatchContainers(ctx context.Context, logger slog.Logger) (<-
 		defer res.Body.Close()
 	}
 
+	conn.SetReadLimit(1 << 22) // 4MiB
+
 	d := wsjson.NewDecoder[codersdk.WorkspaceAgentListContainersResponse](conn, websocket.MessageText, logger)
 	return d.Chan(), d, nil
 }
