private async Task RenderLayoutAsync(
PageContext context,
ViewBufferTextWriter bodyWriter)
{
// A layout page can specify another layout page. We'll need to continue
// looking for layout pages until they're no longer specified.
var previousPage = razorPage;
var renderedLayouts = new List <TemplatePage>();
// This loop will execute Layout pages from the inside to the outside. With each
// iteration, bodyWriter is replaced with the aggregate of all the "body" content
// (including the layout page we just rendered).
while (!string.IsNullOrEmpty(previousPage.Layout))
{
if (!bodyWriter.IsBuffering)
{
// Once a call to RazorPage.FlushAsync is made, we can no longer render Layout pages - content has
// already been written to the client and the layout content would be appended rather than surround
// the body content. Throwing this exception wouldn't return a 500 (since content has already been
// written), but a diagnostic component should be able to capture it.
throw new InvalidOperationException("Layout cannot be rendered");
}
TemplatePage layoutPage = GetLayoutPage(previousPage.Layout);
if (renderedLayouts.Count > 0 &&
renderedLayouts.Any(l => string.Equals(l.Path, layoutPage.Path, StringComparison.Ordinal)))
{
// If the layout has been previously rendered as part of this view, we're potentially in a layout
// rendering cycle.
throw new InvalidOperationException("Layout has circular reference");
}
// Notify the previous page that any writes that are performed on it are part of sections being written
// in the layout.
previousPage.IsLayoutBeingRendered = true;
layoutPage.PreviousSectionWriters = previousPage.SectionWriters;
layoutPage.BodyContent = bodyWriter.Buffer;
bodyWriter = await RenderPageAsync(layoutPage, context, invokeViewStarts : false);
renderedLayouts.Add(layoutPage);
previousPage = layoutPage;
}
// Now we've reached and rendered the outer-most layout page. Nothing left to execute.
// Ensure all defined sections were rendered or RenderBody was invoked for page without defined sections.
foreach (var layoutPage in renderedLayouts)
{
layoutPage.EnsureRenderedBodyOrSections();
}
if (bodyWriter.IsBuffering)
{
// If IsBuffering - then we've got a bunch of content in the view buffer. How to best deal with it
// really depends on whether or not we're writing directly to the output or if we're writing to
// another buffer.
var viewBufferTextWriter = context.Writer as ViewBufferTextWriter;
if (viewBufferTextWriter == null || !viewBufferTextWriter.IsBuffering)
{
// This means we're writing to a 'real' writer, probably to the actual output stream.
// We're using PagedBufferedTextWriter here to 'smooth' synchronous writes of IHtmlContent values.
using (var writer = _bufferScope.CreateWriter(context.Writer))
{
await bodyWriter.Buffer.WriteToAsync(writer, _htmlEncoder);
}
}
else
{
// This means we're writing to another buffer. Use MoveTo to combine them.
bodyWriter.Buffer.MoveTo(viewBufferTextWriter.Buffer);
return;
}
}
}