BufferedRenderer Class — astro Architecture

Source Code

packages/astro/src/runtime/server/render/util.ts lines 191–245

class BufferedRenderer implements RenderDestination, RendererFlusher {
	private chunks: RenderDestinationChunk[] = [];
	private renderPromise: Promise<void> | void;
	private destination: RenderDestination;

	/**
	 * Determines whether buffer has been flushed
	 * to the final destination.
	 */
	private flushed = false;

	public constructor(destination: RenderDestination, renderFunction: RenderFunction) {
		this.destination = destination;
		this.renderPromise = renderFunction(this);

		if (isPromise(this.renderPromise)) {
			// Catch here in case it throws before `flush` is called,
			// to prevent an unhandled rejection.
			Promise.resolve(this.renderPromise).catch(noop);
		}
	}

	public write(chunk: RenderDestinationChunk): void {
		// Before the buffer has been flushed, we want to
		// append to the buffer, afterwards we'll write
		// to the underlying destination if subsequent
		// writes arrive.

		if (this.flushed) {
			this.destination.write(chunk);
		} else {
			this.chunks.push(chunk);
		}
	}

	public flush(): void | Promise<void> {
		if (this.flushed) {
			throw new Error('The render buffer has already been flushed.');
		}

		this.flushed = true;

		// Write the buffered chunks to the real destination
		for (const chunk of this.chunks) {
			this.destination.write(chunk);
		}

		// NOTE: We don't empty `this.chunks` after it's written as benchmarks show
		// that it causes poorer performance, likely due to forced memory re-allocation,
		// instead of letting the garbage collector handle it automatically.
		// (Unsure how this affects on limited memory machines)

		return this.renderPromise;
	}
}