While most builds of Flight and Fizz schedule work in new tasks some do
execute work synchronously. While this is necessary for legacy APIs like
renderToString for modern APIs there really isn't a great reason to do
this synchronously.
We could schedule works as microtasks but we actually want to yield so
the runtime can run events and other things that will unblock additional
work before starting the next work loop.
This change updates all non-legacy uses to be async using the best
availalble macrotask scheduler.
Browser now uses postMessage
Bun uses setTimeout because while it also supports setImmediate the
scheduling is not as eager as the same API in node
the FB build also uses setTimeout
This change required a number of changes to tests which were utilizing
the sync nature of work in the Browser builds to avoid having to manage
timers and tasks. I added a patch to install MessageChannel which is
required by the browser builds and made this patched version integrate
with the Scheduler mock. This way we can effectively use `act` to flush
flight and fizz work similar to how we do this on the client.
This adds support in Flight for serializing four kinds of streams:
- `ReadableStream` with objects as a model. This is a single shot
iterator so you can read it only once. It can contain any value
including Server Components. Chunks are encoded as is so if you send in
10 typed arrays, you get the same typed arrays out on the other side.
- Binary `ReadableStream` with `type: 'bytes'` option. This supports the
BYOB protocol. In this mode, the receiving side just gets `Uint8Array`s
and they can be split across any single byte boundary into arbitrary
chunks.
- `AsyncIterable` where the `AsyncIterator` function is different than
the `AsyncIterable` itself. In this case we assume that this might be a
multi-shot iterable and so we buffer its value and you can iterate it
multiple times on the other side. We support the `return` value as a
value in the single completion slot, but you can't pass values in
`next()`. If you want single-shot, return the AsyncIterator instead.
- `AsyncIterator`. These gets serialized as a single-shot as it's just
an iterator.
`AsyncIterable`/`AsyncIterator` yield Promises that are instrumented
with our `.status`/`.value` convention so that they can be synchronously
looped over if available. They are also lazily parsed upon read.
We can't do this with `ReadableStream` because we use the native
implementation of `ReadableStream` which owns the promises.
The format is a leading row that indicates which type of stream it is.
Then a new row with the same ID is emitted for every chunk. Followed by
either an error or close row.
`AsyncIterable`s can also be returned as children of Server Components
and then they're conceptually the same as fragment arrays/iterables.
They can't actually be used as children in Fizz/Fiber but there's a
separate plan for that. Only `AsyncIterable` not `AsyncIterator` will be
valid as children - just like sync `Iterable` is already supported but
single-shot `Iterator` is not. Notably, neither of these streams
represent updates over time to a value. They represent multiple values
in a list.
When the server stream is aborted we also close the underlying stream.
However, closing a stream on the client, doesn't close the underlying
stream.
A couple of possible follow ups I'm not planning on doing right now:
- [ ] Free memory by releasing the buffer if an Iterator has been
exhausted. Single shots could be optimized further to release individual
items as you go.
- [ ] We could clean up the underlying stream if the only pending data
that's still flowing is from streams and all the streams have cleaned
up. It's not very reliable though. It's better to do cancellation for
the whole stream - e.g. at the framework level.
- [ ] Implement smarter Binary Stream chunk handling. Currently we wait
until we've received a whole row for binary chunks and copy them into
consecutive memory. We need this to preserve semantics when passing
typed arrays. However, for binary streams we don't need that. We can
just send whatever pieces we have so far.
The internal file ReactSharedSubset is what the `react` module resolves
to when imported from a Server Component environment. We gave it this
name because, originally, the idea was that Server Components can access
a subset of the APIs available on the client.
However, since then, we've also added APIs that can _only_ by accessed
on the server and not the client. In other words, it's no longer a
subset, it's a slightly different overlapping set.
So this commit renames ReactSharedSubet to ReactServer and updates all
the references. This does not affect the public API, only our internal
implementation.
I do this by simply renaming the secret export name in the "subset"
bundle and this renamed version is what the FlightServer uses.
This requires us to be more diligent about always using the correct
instance of "react" in our tests so there's a bunch of clean up for
that.
Currently when we SSR a Flight response we do not emit any resources for
module imports. This means that when the client hydrates it won't have
already loaded the necessary scripts to satisfy the Imports defined in
the Flight payload which will lead to a delay in hydration completing.
This change updates `react-server-dom-webpack` and
`react-server-dom-esm` to emit async script tags in the head when we
encounter a modules in the flight response.
To support this we need some additional server configuration. We need to
know the path prefix for chunk loading and whether the chunks will load
with CORS or not (and if so with what configuration).
We already did this for Server References on the Client so this brings
us parity with that. This gives us some more flexibility with changing
the runtime implementation without having to affect the loaders.
We can also do more in the runtime such as adding `.bind()` support to
Server References.
I also moved the CommonJS Proxy creation into the runtime helper from
the register so that it can be handled in one place.
This lets us remove the forks from Next.js since the loaders can be
simplified there to just use these helpers.
This PR doesn't change the protocol or shape of the objects. They're
still specific to each bundler but ideally we should probably move this
to shared helpers that can be used by multiple bundler implementations.
This uses the same mechanism as [large
strings](https://github.com/facebook/react/pull/26932) to encode chunks
of length based binary data in the RSC payload behind a flag.
I introduce a new BinaryChunk type that's specific to each stream and
ways to convert into it. That's because we sometimes need all chunks to
be Uint8Array for the output, even if the source is another array buffer
view, and sometimes we need to clone it before transferring.
Each type of typed array is its own row tag. This lets us ensure that
the instance is directly in the right format in the cached entry instead
of creating a wrapper at each reference. Ideally this is also how
Map/Set should work but those are lazy which complicates that approach a
bit.
We assume both server and client use little-endian for now. If we want
to support other modes, we'd convert it to/from little-endian so that
the transfer protocol is always little-endian. That way the common
clients can be the fastest possible.
So far this only implements Server to Client. Still need to implement
Client to Server for parity.
NOTE: This is the first time we make RSC effectively a binary format.
This is not compatible with existing SSR techniques which serialize the
stream as unicode in the HTML. To be compatible, those implementations
would have to use base64 or something like that. Which is what we'll do
when we move this technique to be built-in to Fizz.
This introduces a Text row (T) which is essentially a string blob and
refactors the parsing to now happen at the binary level.
```
RowID + ":" + "T" + ByteLengthInHex + "," + Text
```
Today, we encode all row data in JSON, which conveniently never has
newline characters and so we use newline as the line terminator. We
can't do that if we pass arbitrary unicode without escaping it. Instead,
we pass the byte length (in hexadecimal) in the leading header for this
row tag followed by a comma.
We could be clever and use fixed or variable-length binary integers for
the row id and length but it's not worth the more difficult
debuggability so we keep these human readable in text.
Before this PR, we used to decode the binary stream into UTF-8 strings
before parsing them. This is inefficient because sometimes the slices
end up having to be copied so it's better to decode it directly into the
format. The follow up to this is also to add support for binary data and
then we can't assume the entire payload is UTF-8 anyway. So this
refactors the parser to parse the rows in binary and then decode the
result into UTF-8. It does add some overhead to decoding on a per row
basis though.
Since we do this, we need to encode the byte length that we want decode
- not the string length. Therefore, this requires clients to receive
binary data and why I had to delete the string option.
It also means that I had to add a way to get the byteLength from a chunk
since they're not always binary. For Web streams it's easy since they're
always typed arrays. For Node streams it's trickier so we use the
byteLength helper which may not be very efficient. Might be worth
eagerly encoding them to UTF8 - perhaps only for this case.
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>
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.
This splits out the Edge and Node implementations of Flight Client into
their own implementations. The Node implementation now takes a Node
Stream as input.
I removed the bundler config from the Browser variant because you're
never supposed to use that in the browser since it's only for SSR.
Similarly, it's required on the server. This also enables generating a
SSR manifest from the Webpack plugin. This is necessary for SSR so that
you can reverse look up what a client module is called on the server.
I also removed the option to pass a callServer from the server. We might
want to add it back in the future but basically, we don't recommend
calling Server Functions from render for initial render because if that
happened client-side it would be a client-side waterfall. If it's never
called in initial render, then it also shouldn't ever happen during SSR.
This might be considered too restrictive.
~This also compiles the unbundled packages as ESM. This isn't strictly
necessary because we only need access to dynamic import to load the
modules but we don't have any other build options that leave
`import(...)` intact, and seems appropriate that this would also be an
ESM module.~ Went with `import(...)` in CJS instead.
Josh Story
Sebastian Markbåge
Andrew Clark
Ricky
