Enhancing SSR in Low-Thread Web Servers

Naive server-side rendering (SSR) techniques require a dedicated server thread per HTTP request, thereby limiting the number of concurrent requests to the available server threads. Furthermore, this approach proves impractical for modern low-thread servers like WebFlux, VertX, and Express Node.js. To achieve progressive rendering, asynchronous data models provided by non-blocking APIs must be utilized. Nevertheless, this method can introduce undesirable interleaving between template view processing and data access, potentially resulting in malformed HTML documents. Some template engines offer partial remedies through specific templating dialects, but they encounter two limitations. Firstly, their compatibility is confined to specific types of asynchronous APIs, such as the reactive stream Publisher API. Secondly, they typically support only a single asynchronous data model at a time. In this research, we propose an alternative web templating approach that embraces any asynchronous AP I (e.g., Publisher, promises, suspend functions, flow, etc.) and allows for multiple asynchronous data sources. Our approach is implemented on top of HtmlFlow, a Java-based DSL for writing type-safe HTML. We evaluated against state-of-the-art reactive servers, specifically WebFlux, and compared it with popular templating idioms like Thymeleaf and KotlinX.html. Our proposal effectively overcomes the limitations of existing approaches.