react/packages/react-markup
Sebastian Markbåge 969a9790ad
[Flight] Track I/O Entry for the RSC Stream itself (#34425)
One thing that can suspend is the downloading of the RSC stream itself.
This tracks an I/O entry for each Promise (`SomeChunk<T>`) that
represents the request to the RSC stream. As the value we use the
`Response` for `createFromFetch` (or the `ReadableStream` for
`createFromReadableStream`). The start time is when you called those.

Since we're not awaiting the whole stream, each I/O entry represents the
part of the stream up until it got unblocked. However, in a production
environment with TLS packets and buffering in practice the chunks
received by the client isn't exactly at the boundary of each row. It's a
bit longer into larger chunks. From testing, it seems like multiples of
16kb or 64kb uncompressed are common. To simulate a production
environment we group into roughly 64kb chunks if they happen in rapid
sequence. Note that this might be too small to give a good idea because
of the throttle many boundaries might be skipped anyway so this might
show too many.

The React DevTools will see each I/O entry as separate but dedupe if an
outer boundary already depends on the same chunk. This deduping makes it
so that small boundaries that are blocked on the same chunk, don't get
treated as having unique suspenders. If you have a boundary with large
content, then that content will likely be in a separate chunk which is
not in the parent and then it gets marked as.

This is all just an approximation. The goal of this is just to highlight
that very large boundaries will very likely suspend even if they don't
suspend on any I/O on the server. In practice, these boundaries can
float around a lot and it's really any Suspense boundary that might
suspend but some are more likely than others which this is meant to
highlight.

It also just lets you inspect how many bytes needs to be transferred
before you can show a particular part of the content, to give you an
idea that it's not just I/O on the server that might suspend.

If you don't use the debug channel it can be misleading since the data
in development mode stream will have a lot more data in it which leads
to more chunking.

Similarly to "client references" these I/O infos don't have an "env"
since it's the client that has the I/O and so those are excluded from
flushing in the Server performance tracks.

Note that currently the same Response can appear many times in the same
Instance of SuspenseNode in DevTools when there are multiple chunks. In
a follow up I'll show only the last one per Response at any given level.

Note that when a separate debugChannel is used it has its own I/O entry
that's on the `_debugInfo` for the debug chunks in that channel.
However, if everything works correctly these should never leak into the
DevTools UI since they should never be propagated from a debug chunk to
the values waited by the runtime. This is easy to break though.
2025-09-09 16:46:11 -04:00
..
npm Move react-html to react-markup (#30688) 2024-08-14 19:22:44 +02:00
src [Flight] Track I/O Entry for the RSC Stream itself (#34425) 2025-09-09 16:46:11 -04:00
index.js Move react-html to react-markup (#30688) 2024-08-14 19:22:44 +02:00
package.json Bump next prerelease version numbers (#31676) 2024-12-12 14:10:46 -05:00
react-markup.react-server.js Move react-html to react-markup (#30688) 2024-08-14 19:22:44 +02:00
README.md Publish experimental_renderToHTML (#30690) 2024-08-15 08:50:56 +02:00

react-markup

This package provides the ability to render standalone HTML from Server Components for use in embedded contexts such as e-mails and RSS/Atom feeds. It cannot use Client Components and does not hydrate. It is intended to be paired with the generic React package, which is shipped as react to npm.

Installation

npm install react react-markup

Usage

import { experimental_renderToHTML as renderToHTML } from 'react-markup';
import EmailTemplate from './my-email-template-component.js'

async function action(email, name) {
  "use server";
  // ... in your server, e.g. a Server Action...
  const htmlString = await renderToHTML(<EmailTemplate name={name} />);
  // ... send e-mail using some e-mail provider
  await sendEmail({ to: email, contentType: 'text/html', body: htmlString });
}

Note that this is an async function that needs to be awaited - unlike the legacy renderToString in react-dom.

API

react-markup

See https://react.dev/reference/react-markup

Thanks

The React team thanks Nikolai Mavrenkov for donating the react-markup package name.