Behind the `enableSrcObject` flag. This is revisiting a variant of what
was discussed in #11163.
Instead of supporting the [`srcObject`
property](https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/srcObject)
as a separate name, this adds an overload of `src` to allow objects to
be passed. The DOM needs to add separate properties for the object forms
since you read back but it doesn't make sense for React's write-only API
to do that. Similar to how we'll like add an overload for
`popoverTarget` instead of calling it `popoverTargetElement` and how
`style` accepts an object and it's not `styleObject={{...}}`.
There are a number of reason to revisit this.
- It's just way more convenient to have this built-in and it makes
conceptual sense. We typically support declarative APIs and polyfill
them when necessary.
- RSC supports Blobs and by having it built-in you don't need a Client
Component wrapper to render it where as doing it with effects would
require more complex wrappers. By picking Blobs over base64,
client-navigations can use the more optimized binary encoding in the RSC
protocol.
- The timing aspect of coordinating it with Suspensey images and image
decoding is a bit tricky to get right because if you set it in an effect
it's too late because you've already rendered it.
- SSR gets complicated when done in user space because you have to
handle both branches. Likely with `useSyncExternalStore`.
- By having it built-in we could optimize the payloads shared between
RSC payloads embedded in the HTML and data URLs.
This does not support objects for `<source src>` nor `<img srcset>`.
Those don't really have equivalents in the DOM neither. They're mainly
for picking an option when you don't know programmatically. However, for
this use case you're really better off picking a variant before
generating the blobs.
We may support Response objects in the future too as per
https://github.com/whatwg/fetch/issues/49
Currently you need to do one of either:
1. Install React DevTools
2. Install React Refresh
3. Add Profiler component
To opt in to component level profiling.
It was a bit confusing that some of the fixtures was doing 2 which made
them work while other was depending on if you had DevTools.
Really React Refresh shouldn't really opt you in I think.
Stacked on #31736.
<img width="1223" alt="Screenshot 2024-12-11 at 8 21 12 PM"
src="https://github.com/user-attachments/assets/a7cbc04b-c831-476b-aa2f-baddec9461c9"
/>
This emits a placeholder when we're deduping a component. This starts
when the parent's self time ends, where we would've started rendering
this component if it wasn't already started. The end time is when the
actual render ends since the parent is also blocked by it.
<img width="966" alt="Screenshot 2024-12-10 at 10 49 19 PM"
src="https://github.com/user-attachments/assets/27a21bdf-86b9-4203-893b-89523e698138">
This emits a tree view visualization of the timing information for each
Server Component provided in the RSC payload.
The unique thing about this visualization is that the end time of each
Server Component spans the end of the last child. Now what is
conceptually a blocking child is kind of undefined in RSC. E.g. if
you're not using a Promise on the client, or if it is wrapped in
Suspense, is it really blocking the parent?
Here I reconstruct parent-child relationship by which chunks reference
other chunks. A child can belong to more than one parent like when we
dedupe the result of a Server Component.
Then I wait until the whole RSC payload has streamed in, and then I
traverse the tree collecting the end time from children as I go and emit
the `performance.measure()` calls on the way up.
There's more work for this visualization in follow ups but this is the
basics. For example, since the Server Component time span includes async
work it's possible for siblings to execute their span in parallel (Foo
and Bar in the screenshot are parallel siblings). To deal with this we
need to spawn parallel work into separate tracks. Each one can be deep
due to large trees. This can makes this type of visualization unwieldy
when you have a lot of parallelism. Therefore I also plan another
flatter Timeline visualization in a follow up.
Prerendering in flight is similar to prerendering in Fizz. Instead of
receiving a result (the stream) immediately a promise is returned which
resolves to the stream when the prerender is complete. The promise will
reject if the flight render fatally errors otherwise it will resolve
when the render is completed or is aborted.
This was missed in the mount dev dispatcher. It was only in the rerender
dispatcher which means that it was only logged during the rerender.
Since DevTools can hide logs during rerenders, this hid the warning in
StrictMode.
This lets you click a stack frame on the client and see the Server
source code inline.
<img width="871" alt="Screenshot 2024-06-01 at 11 44 24 PM"
src="https://github.com/facebook/react/assets/63648/581281ce-0dce-40c0-a084-4a6d53ba1682">
<img width="840" alt="Screenshot 2024-06-01 at 11 43 37 PM"
src="https://github.com/facebook/react/assets/63648/00dc77af-07c1-4389-9ae0-cf1f45199efb">
We could do some logic on the server that sends a source map url for
every stack frame in the RSC payload. That would make the client
potentially config free. However regardless we need the config to
describe what url scheme to use since that’s not built in to the bundler
config. In practice you likely have a common pattern for your source
maps so no need to send data over and over when we can just have a
simple function configured on the client.
The server must return a source map, even if the file is not actually
compiled since the fake file is still compiled.
The source mapping strategy can be one of two models depending on if the
server’s stack traces (`new Error().stack`) are source mapped back to
the original (`—enable-source-maps`) or represents the location in
compiled code (like in the browser).
If it represents the location in compiled code it’s actually easier. You
just serve the source map generated for that file by the tooling.
If it is already source mapped it has to generate a source map where
everything points to the same location (as if not compiled) ideally with
a segment per logical ast node.
Upgrades the stability of Server Actions from experimental to canary.
- Turns on enableAsyncActions and enableFormActions
- Removes "experimental_" prefix from useOptimistic, useFormStatus, and
useFormState
If a Server Action is passed to useFormState, the action may be
submitted before it has hydrated. This will trigger a full page
(MPA-style) navigation. We can transfer the form state to the next page
by comparing the key path of the hook instance.
`ReactServerDOMServer.decodeFormState` is used by the server to extract
the form state from the submitted action. This value can then be passed
as an option when rendering the new page. It must be passed during both
SSR and hydration.
```js
const boundAction = await decodeAction(formData, serverManifest);
const result = await boundAction();
const formState = decodeFormState(result, formData, serverManifest);
// SSR
const response = createFromReadableStream(<App />);
const ssrStream = await renderToReadableStream(response, { formState })
// Hydration
hydrateRoot(container, <App />, { formState });
```
If the `formState` option is omitted, then the state won't be
transferred to the next page. However, it must be passed in both places,
or in neither; misconfiguring will result in a hydration mismatch.
(The `formState` option is currently prefixed with `experimental_`)
Client reference proxy should implement getOwnPropertyDescriptor. One
practical place where this shows up is when consuming CJS module.exports
in ESM modules. Node creates named exports it statically infers from the
underlying source but it only sets the named export if the CJS exports
hasOwnProperty. This trap will allow the proxy to respond affirmatively.
I did not add unit tests because contriving the ESM <-> CJS scenario in
Jest is challenging. I did add new components to the flight fixture
which demonstrate that the named exports are properly constructed with
the client reference whereas they were not before.
Currently, since we use a module cache for async modules, it doesn't
automatically get updated when the module registry gets updated (HMR).
This technique ensures that if Webpack replaces the module (HMR) then
we'll get the new Promise when we require it again.
This technique doesn't work for ESM and probably not Vite since ESM will
provide a new Promise each time you call `import()` but in the
Webpack/CJS approach this Promise is an entry in the module cache and
not a promise for the entry.
I tried to replicate the original issue in the fixture but it's tricky
to replicate because 1) we can't really use async modules the same way
without compiling both server and client 2) even then I'm not quite sure
how to repro the HMR issue.
This automatically exposes `$$FORM_ACTIONS` on Server References coming
from Flight. So that when they're used in a form action, we can encode
the ID for the server reference as a hidden field or as part of the name
of a button.
If the Server Action is a bound function it can have complex data
associated with it. In this case this additional data is encoded as
additional form fields.
To process a POST on the server there's now a `decodeAction` helper that
can take one of these progressive posts from FormData and give you a
function that is prebound with the correct closure and FormData so that
you can just invoke it.
I updated the fixture which now has a "Server State" that gets
automatically refreshed. This also lets us visualize form fields.
There's no "Action State" here for showing error messages that are not
thrown, that's still up to user space.
Use the Blob constructor + append with filename instead of File
constructor. Node.js doesn't expose a global File constructor but does
support it in this form.
Queue fields until we get the 'end' event from the previous file. We
rely on previous files being available by the time a field is resolved.
However, since the 'end' event in Readable is fired after two
micro-tasks, these are not resolved in order.
I use a queue of the fields while we're still waiting on files to
finish. This still doesn't resolve files and fields in order relative to
each other but that doesn't matter for our usage.
This lets you pass a function to `<form action={...}>` or `<button
formAction={...}>` or `<input type="submit formAction={...}>`. This will
behave basically like a `javascript:` URL except not quite implemented
that way. This is a convenience for the `onSubmit={e => {
e.preventDefault(); const fromData = new FormData(e.target); ... }`
pattern.
You can still implement a custom `onSubmit` handler and if it calls
`preventDefault`, it won't invoke the action, just like it would if you
used a full page form navigation or javascript urls. It behaves just
like a navigation and we might implement it with the Navigation API in
the future.
Currently this is just a synchronous function but in a follow up this
will accept async functions, handle pending states and handle errors.
This is implemented by setting `javascript:` URLs, but these only exist
to trigger an error message if something goes wrong instead of
navigating away. Like if you called `stopPropagation` to prevent React
from handling it or if you called `form.submit()` instead of
`form.requestSubmit()` which by-passes the `submit` event. If CSP is
used to ban `javascript:` urls, those will trigger errors when these
URLs are invoked which would be a different error message but it's still
there to notify the user that something went wrong in the plumbing.
Next up is improving the SSR state with action replaying and progressive
enhancement.
Builds on top of https://github.com/facebook/react/pull/26661
This lets you pass FormData objects through the Flight Reply
serialization. It does that by prefixing each entry with the ID of the
reference and then the decoding side creates a new FormData object
containing only those fields (without the prefix).
Ideally this should be more generic. E.g. you should be able to pass
Blobs, Streams and Typed Arrays by reference inside plain objects too.
You should also be able to send Blobs and FormData in the regular Flight
serialization too so that they can go both directions. They should be
symmetrical. We'll get around to adding more of those features in the
Flight protocol as we go.
---------
Co-authored-by: Sophie Alpert <git@sophiebits.com>
Now that promises are renderable nodes, we can remove the `use` call
from the root of the Flight fixture.
Uncached promises will likely be accompanied by a warning when they are
rendered outside a transition. But this promise is the result of a
Flight response, so it's cached. And it's also a rendered as part of a
transition. So it's fine. Indeed, this is the canonical way to use this
feature.
This adds `encodeReply` to the Flight Client and `decodeReply` to the
Flight Server.
Basically, it's a reverse Flight. It serializes values passed from the
client to the server. I call this a "Reply". The tradeoffs and
implementation details are a bit different so it requires its own
implementation but is basically a clone of the Flight Server/Client but
in reverse. Either through callServer or ServerContext.
The goal of this project is to provide the equivalent serialization as
passing props through RSC to client. Except React Elements and
Components and such. So that you can pass a value to the client and back
and it should have the same serialization constraints so when we add
features in one direction we should mostly add it in the other.
Browser support for streaming request bodies are currently very limited
in that only Chrome supports it. So this doesn't produce a
ReadableStream. Instead `encodeReply` produces either a JSON string or
FormData. It uses a JSON string if it's a simple enough payload. For
advanced features it uses FormData. This will also let the browser
stream things like File objects (even though they're not yet supported
since it follows the same rules as the other Flight).
On the server side, you can either consume this by blocking on
generating a FormData object or you can stream in the
`multipart/form-data`. Even if the client isn't streaming data, the
network does. On Node.js busboy seems to be the canonical library for
this, so I exposed a `decodeReplyFromBusboy` in the Node build. However,
if there's ever a web-standard way to stream form data, or if a library
wins in that space we can support it. We can also just build a multipart
parser that takes a ReadableStream built-in.
On the server, server references passed as arguments are loaded from
Node or Webpack just like the client or SSR does. This means that you
can create higher order functions on the client or server. This can be
tokenized when done from a server components but this is a security
implication as it might be tempting to think that these are not fungible
but you can swap one function for another on the client. So you have to
basically treat an incoming argument as insecure, even if it's a
function.
I'm not too happy with the naming parity:
Encode `server.renderToReadableStream` Decode: `client.createFromFetch`
Decode `client.encodeReply` Decode: `server.decodeReply`
This is mainly an implementation details of frameworks but it's annoying
nonetheless. This comes from that `renderToReadableStream` does do some
"rendering" by unwrapping server components etc. The `create` part comes
from the parity with Fizz/Fiber where you `render` on the server and
`create` a root on the client.
Open to bike-shedding this some more.
---------
Co-authored-by: Josh Story <josh.c.story@gmail.com>
Previously when a called server reference function was rejected, the
emitted error chunk was not flushed, and the request was not properly
closed.
Co-authored-by: Sebastian Markbage <sebastian@calyptus.eu>
We always look up these references in a map so it doesn't matter what
their value is. It could be a hash for example.
The loaders now encode a single $$id instead of filepath + name.
This changes the react-client-manifest to have a single level. The value
inside the map is still split into module id + export name because
that's what gets looked up in webpack.
The react-ssr-manifest is still two levels because that's a reverse
lookup.
Builds on #26257.
To do this we need access to a manifest for which scripts and CSS are
used for each "page" (entrypoint).
The initial script to bootstrap the app is inserted with
`bootstrapScripts`. Subsequent content are loaded using the chunks
mechanism built-in.
The stylesheets for each pages are prepended to each RSC payload and
rendered using Float. This doesn't yet support styles imported in
components that are also SSR:ed nor imported through Server Components.
That's more complex and not implemented in the node loader.
HMR doesn't work after reloads right now because the SSR renderer isn't
hot reloaded because there's no idiomatic way to hot reload ESM modules
in Node.js yet. Without killing the HMR server. This leads to hydration
mismatches when reloading the page after a hot reload.
Notably this doesn't show serializing the stream through the HTML like
real implementations do. This will lead to possible hydration mismatches
based on the data. However, manually serializing the stream as a string
isn't exactly correct due to binary data. It's not the idiomatic way
this is supposed to work. This will all be built-in which will make this
automatic in the future.
This proxies requests through the global server instead of requesting
RSC responses from the regional server. This is a bit closer to
idiomatic, and closer to SSR.
This also wires up HMR using the Middleware technique instead of server.
This will be an important part of RSC compatibility because there will
be a `react-refresh` aspect to the integration.
This convention uses `Accept` header to branch a URL between HTML/RSC
but it could be anything really. Special headers, URLs etc. We might be
more opinionated about this in the future but now it's up to the router.
Some fixes for Node 16/17 support in the loader and fetch polyfill.
This is the first of a series of PRs, that let you pass functions, by
reference, to the client and back. E.g. through Server Context. It's
like client references but they're opaque on the client and resolved on
the server.
To do this, for security, you must opt-in to exposing these functions to
the client using the `"use server"` directive. The `"use client"`
directive lets you enter the client from the server. The `"use server"`
directive lets you enter the server from the client.
This works by tagging those functions as Server References. We could
potentially expand this to other non-serializable or stateful objects
too like classes.
This only implements server->server CJS imports and server->server ESM
imports. We really should add a loader to the webpack plug-in for
client->server imports too. I'll leave closures as an exercise for
integrators.
You can't "call" a client reference on the server, however, you can
"call" a server reference on the client. This invokes a callback on the
Flight client options called `callServer`. This lets a router implement
calling back to the server. Effectively creating an RPC. This is using
JSON for serializing those arguments but more utils coming from
client->server serialization.
This updates the Flight fixture to support the new ESM loaders in newer
versions of Node.js.
It also uses native fetch since react-fetch is gone now. (This part
requires Node 18 to run the fixture.)
I also updated everything to use the `"use client"` convention instead
of file name based convention.
The biggest hack here is that the Webpack plugin now just writes every
`.js` file in the manifest. This needs to be more scoped. In practice,
this new convention effectively requires you to traverse the server
graph first to find the actual used files. This is enough to at least
run our own fixture though.
I didn't update the "blocks" fixture.
More details in each commit message.
* [Flight] Move from suspensey readRoot() to use(thenable)
* Update noop tests
These are no longer sync so they need some more significant updating.
Some of these tests are written in a non-idiomatic form too which is not
great.
* Update Relay tests
I kept these as sync for now and just assume a sync Promise.
* Updated the main tests
* Gate tests
* We need to cast through any because Thenable doesn't support unknown strings
* Move files
* Update paths
* Rename import variables
* Rename /server to /writer
This is mainly because "React Server Server" is weird so we need another
dimension.
* Use "react-server" convention to enforce that writer is only loaded in a server
* Basic scan of the file system to find Client modules
This does a rudimentary merge of the plugins. It still uses the global
scan and writes to file system.
Now the plugin accepts a search path or a list of referenced client files.
In prod, the best practice is to provide a list of files that are actually
referenced rather than including everything possibly reachable. Probably
in dev too since it's faster.
This is using the same convention as the upstream ContextModule - which
powers the require.context helpers.
* Add neo-async to dependencies
* Remove react/unstable_cache
We're probably going to make it available via the dispatcher. Let's remove this for now.
* Add readContext() to the dispatcher
On the server, it will be per-request.
On the client, there will be some way to shadow it.
For now, I provide it on the server, and throw on the client.
* Use readContext() from react-fetch
This makes it work on the server (but not on the client until we implement it there.)
Updated the test to use Server Components. Now it passes.
* Fixture: Add fetch from a Server Component
* readCache -> getCacheForType<T>
* Add React.unstable_getCacheForType
* Add a feature flag
* Fix Flow
* Add react-suspense-test-utils and port tests
* Remove extra Map lookup
* Unroll async/await because build system
* Add some error coverage and retry
* Add unstable_getCacheForType to Flight entry
* Rename "name"->"filepath" field on Webpack module references
This field name will get confused with the imported name or the module id.
* Switch back to transformSource instead of getSource
getSource would be more efficient in the cases where we don't need to read
the original file but we'll need to most of the time.
Even then, we can't return a JS file if we're trying to support non-JS
loader because it'll end up being transformed.
Similarly, we'll need to parse the file and we can't parse it before it's
transformed. So we need to chain with other loaders that know how.
* Add acorn dependency
This should be the version used by Webpack since we have a dependency on
Webpack anyway.
* Parse exported names of ESM modules
We need to statically resolve the names that a client component will
export so that we can export a module reference for each of the names.
For export * from, this gets tricky because we need to also load the
source of the next file to parse that. We don't know exactly how the
client is built so we guess it's somewhat default.
* Handle imported names one level deep in CommonJS using a Proxy
We use a proxy to see what property the server access and that will tell
us which property we'll want to import on the client.
* Add export name to module reference and Webpack map
To support named exports each name needs to be encoded as a separate
reference. It's possible with module splitting that different exports end
up in different chunks.
It's also possible that the export is renamed as part of minification.
So the map also includes a map from the original to the bundled name.
* Special case plain CJS requires and conditional imports using __esModule
This models if the server tries to import .default or a plain require.
We should replicate the same thing on the client when we load that
module reference.
* Dedupe acorn-related deps
Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>
This lets the Flight fixture run as "type": "module" or "commonjs".
Experimental loaders can be used similar to require.extensions to do the
transpilation and replacement of .client.js references.
* Expand fixture
Use .server convention. /server/index.js should really change too so it can be compiled but for now we treat it as bootstrapping code outside the compiled code.
Move App.server. It's part of the application code rather than the infra.
Add hybrid component used in both server/client and an extra component shared by multiple entry points.
* Use require.extensions to replace .client imports
The simplest server doesn't need AOT compilation. Instead we can just
configure require.extensions. This is probably not the best idea to use
in prod but is enough to show the set up.
* Rename Flight to Transport
Flight is still the codename for the implementation details (like Fiber).
However, now the public package is react-transport-... which is only
intended to be used directly by integrators.
* Rename names
Originally the idea was to hide all suspending behind getters or proxies.
However, this has some issues with perf on hot code like React elements.
It also makes it too easy to accidentally access it the first time in an
effect or callback where things aren't allowed to suspend. Making it
an explicit method call avoids this issue.
All other suspending has moved to explicit lazy blocks (and soon elements).
The only thing remaining is the root. We could require the root to be an
element or block but that creates an unfortunate indirection unnecessarily.
Instead, I expose a readRoot method on the response. Typically we try to
avoid virtual dispatch but in this case, it's meant that you build
abstractions on top of a Flight response so passing it a round is useful.
This replaces the HTML renderer with instead resolving host elements into
arrays tagged with the react.element symbol. These turn into proper
React Elements on the client.
The symbol is encoded as the magical value "$". This has security implications
so this special value needs to remain escaped for other strings.
We could just encode the element as {$$typeof: "$", key: key props: props}
but that's a lot more bytes. So instead I encode it as:
["$", key, props] and then convert it back.
It would be nicer if React's reconciler could just accept these tuples.
* Move Flight DOM to Webpack Specific Packagee
We'll have Webpack specific coupling so we need to ensure that it can be
versioned separately from various Webpack versions. We'll also have builds
for other bundlers in the future.
* Move to peerDep
* Move DOM Flight Tests
* Merge ReactFlightIntegration into ReactFlightDOM
This was an integration test. We can add to it.
* Fix fixture paths
Sebastian MarkbågeandGitHub
Josh StoryandGitHub
Sebastian SilbermannandGitHub
Andrew ClarkandGitHub
Sebastian MarkbågeandGitHub
Dan AbramovandGitHub
