aspnetcore: StaticHtmlRenderer uses synchronous writes which eventually fails

All the prerendering logic inside StaticHtmlRenderer (and wrapper logic in EndpointHtmlRenderer’s WriteComponentHtml) performs synchronous writes against a TextWriter that wraps the output stream.

This works up to a point, but once you write too much content (presumably exceeding the writer’s internal buffer), the system will throw InvalidOperationException: Synchronous operations are disallowed. Call WriteAsync or set AllowSynchronousIO to true instead.. This can happen with or without streaming SSR.

Likely solutions:

• We may be able to change the prerendering logic to use asynchronous writes throughout
• Or we may need to write the prerendering output to a buffer and then asynchronously flush that to the response writer at the end of each batch