Abstract out stream related utils from render and web/utils (#35372)

The `readableStreamTee` util is only used by server/render.tsx, but ended up in the middleware runtime bundle. So it's better to add all the utils in one place, and we can remove them once upstream implementation of ReadableStream is ready.

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

packages/next/server/node-web-streams-helper.ts

@@ -0,0 +1,359 @@
+export function readableStreamTee<T = any>(
+  readable: ReadableStream<T>
+): [ReadableStream<T>, ReadableStream<T>] {
+  const transformStream = new TransformStream()
+  const transformStream2 = new TransformStream()
+  const writer = transformStream.writable.getWriter()
+  const writer2 = transformStream2.writable.getWriter()
+
+  const reader = readable.getReader()
+  function read() {
+    reader.read().then(({ done, value }) => {
+      if (done) {
+        writer.close()
+        writer2.close()
+        return
+      }
+      writer.write(value)
+      writer2.write(value)
+      read()
+    })
+  }
+  read()
+
+  return [transformStream.readable, transformStream2.readable]
+}
+
+export function pipeTo<T>(
+  readable: ReadableStream<T>,
+  writable: WritableStream<T>,
+  options?: { preventClose: boolean }
+) {
+  let resolver: () => void
+  const promise = new Promise<void>((resolve) => (resolver = resolve))
+
+  const reader = readable.getReader()
+  const writer = writable.getWriter()
+  function process() {
+    reader.read().then(({ done, value }) => {
+      if (done) {
+        if (options?.preventClose) {
+          writer.releaseLock()
+        } else {
+          writer.close()
+        }
+        resolver()
+      } else {
+        writer.write(value)
+        process()
+      }
+    })
+  }
+  process()
+  return promise
+}
+
+export function pipeThrough<Input, Output>(
+  readable: ReadableStream<Input>,
+  transformStream: TransformStream<Input, Output>
+) {
+  pipeTo(readable, transformStream.writable)
+  return transformStream.readable
+}
+
+export function chainStreams<T>(
+  streams: ReadableStream<T>[]
+): ReadableStream<T> {
+  const { readable, writable } = new TransformStream()
+
+  let promise = Promise.resolve()
+  for (let i = 0; i < streams.length; ++i) {
+    promise = promise.then(() =>
+      pipeTo(streams[i], writable, {
+        preventClose: i + 1 < streams.length,
+      })
+    )
+  }
+
+  return readable
+}
+
+export function streamFromArray(strings: string[]): ReadableStream<Uint8Array> {
+  // Note: we use a TransformStream here instead of instantiating a ReadableStream
+  // because the built-in ReadableStream polyfill runs strings through TextEncoder.
+  const { readable, writable } = new TransformStream()
+
+  const writer = writable.getWriter()
+  strings.forEach((str) => writer.write(encodeText(str)))
+  writer.close()
+
+  return readable
+}
+
+export async function streamToString(
+  stream: ReadableStream<Uint8Array>
+): Promise<string> {
+  const reader = stream.getReader()
+  let bufferedString = ''
+
+  while (true) {
+    const { done, value } = await reader.read()
+
+    if (done) {
+      return bufferedString
+    }
+
+    bufferedString += decodeText(value)
+  }
+}
+
+export function encodeText(input: string) {
+  return new TextEncoder().encode(input)
+}
+
+export function decodeText(input?: Uint8Array) {
+  return new TextDecoder().decode(input)
+}
+
+export function createTransformStream<Input, Output>({
+  flush,
+  transform,
+}: {
+  flush?: (
+    controller: TransformStreamDefaultController<Output>
+  ) => Promise<void> | void
+  transform?: (
+    chunk: Input,
+    controller: TransformStreamDefaultController<Output>
+  ) => Promise<void> | void
+}): TransformStream<Input, Output> {
+  const source = new TransformStream()
+  const sink = new TransformStream()
+  const reader = source.readable.getReader()
+  const writer = sink.writable.getWriter()
+
+  const controller = {
+    enqueue(chunk: Output) {
+      writer.write(chunk)
+    },
+
+    error(reason: Error) {
+      writer.abort(reason)
+      reader.cancel()
+    },
+
+    terminate() {
+      writer.close()
+      reader.cancel()
+    },
+
+    get desiredSize() {
+      return writer.desiredSize
+    },
+  }
+
+  ;(async () => {
+    try {
+      while (true) {
+        const { done, value } = await reader.read()
+
+        if (done) {
+          const maybePromise = flush?.(controller)
+          if (maybePromise) {
+            await maybePromise
+          }
+          writer.close()
+          return
+        }
+
+        if (transform) {
+          const maybePromise = transform(value, controller)
+          if (maybePromise) {
+            await maybePromise
+          }
+        } else {
+          controller.enqueue(value)
+        }
+      }
+    } catch (err) {
+      writer.abort(err)
+    }
+  })()
+
+  return {
+    readable: sink.readable,
+    writable: source.writable,
+  }
+}
+
+export function createBufferedTransformStream(): TransformStream<
+  Uint8Array,
+  Uint8Array
+> {
+  let bufferedString = ''
+  let pendingFlush: Promise<void> | null = null
+
+  const flushBuffer = (controller: TransformStreamDefaultController) => {
+    if (!pendingFlush) {
+      pendingFlush = new Promise((resolve) => {
+        setTimeout(() => {
+          controller.enqueue(encodeText(bufferedString))
+          bufferedString = ''
+          pendingFlush = null
+          resolve()
+        }, 0)
+      })
+    }
+    return pendingFlush
+  }
+
+  return createTransformStream({
+    transform(chunk, controller) {
+      bufferedString += decodeText(chunk)
+      flushBuffer(controller)
+    },
+
+    flush() {
+      if (pendingFlush) {
+        return pendingFlush
+      }
+    },
+  })
+}
+
+export function createFlushEffectStream(
+  handleFlushEffect: () => Promise<string>
+): TransformStream<Uint8Array, Uint8Array> {
+  return createTransformStream({
+    async transform(chunk, controller) {
+      const extraChunk = await handleFlushEffect()
+      // those should flush together at once
+      controller.enqueue(encodeText(extraChunk + decodeText(chunk)))
+    },
+  })
+}
+
+export async function renderToStream({
+  ReactDOMServer,
+  element,
+  suffix,
+  dataStream,
+  generateStaticHTML,
+  flushEffectHandler,
+}: {
+  ReactDOMServer: typeof import('react-dom/server')
+  element: React.ReactElement
+  suffix?: string
+  dataStream?: ReadableStream<Uint8Array>
+  generateStaticHTML: boolean
+  flushEffectHandler?: () => Promise<string>
+}): Promise<ReadableStream<Uint8Array>> {
+  const closeTag = '</body></html>'
+  const suffixUnclosed = suffix ? suffix.split(closeTag)[0] : null
+  const renderStream: ReadableStream<Uint8Array> & {
+    allReady?: Promise<void>
+  } = await (ReactDOMServer as any).renderToReadableStream(element)
+
+  if (generateStaticHTML) {
+    await renderStream.allReady
+  }
+
+  const transforms: Array<TransformStream<Uint8Array, Uint8Array>> = [
+    createBufferedTransformStream(),
+    flushEffectHandler ? createFlushEffectStream(flushEffectHandler) : null,
+    suffixUnclosed != null ? createPrefixStream(suffixUnclosed) : null,
+    dataStream ? createInlineDataStream(dataStream) : null,
+    suffixUnclosed != null ? createSuffixStream(closeTag) : null,
+  ].filter(Boolean) as any
+
+  return transforms.reduce(
+    (readable, transform) => pipeThrough(readable, transform),
+    renderStream
+  )
+}
+
+export function createSuffixStream(
+  suffix: string
+): TransformStream<Uint8Array, Uint8Array> {
+  return createTransformStream({
+    flush(controller) {
+      if (suffix) {
+        controller.enqueue(encodeText(suffix))
+      }
+    },
+  })
+}
+
+export function createPrefixStream(
+  prefix: string
+): TransformStream<Uint8Array, Uint8Array> {
+  let prefixFlushed = false
+  let prefixPrefixFlushFinished: Promise<void> | null = null
+  return createTransformStream({
+    transform(chunk, controller) {
+      controller.enqueue(chunk)
+      if (!prefixFlushed && prefix) {
+        prefixFlushed = true
+        prefixPrefixFlushFinished = new Promise((res) => {
+          // NOTE: streaming flush
+          // Enqueue prefix part before the major chunks are enqueued so that
+          // prefix won't be flushed too early to interrupt the data stream
+          setTimeout(() => {
+            controller.enqueue(encodeText(prefix))
+            res()
+          })
+        })
+      }
+    },
+    flush(controller) {
+      if (prefixPrefixFlushFinished) return prefixPrefixFlushFinished
+      if (!prefixFlushed && prefix) {
+        prefixFlushed = true
+        controller.enqueue(encodeText(prefix))
+      }
+    },
+  })
+}
+
+export function createInlineDataStream(
+  dataStream: ReadableStream<Uint8Array>
+): TransformStream<Uint8Array, Uint8Array> {
+  let dataStreamFinished: Promise<void> | null = null
+  return createTransformStream({
+    transform(chunk, controller) {
+      controller.enqueue(chunk)
+
+      if (!dataStreamFinished) {
+        const dataStreamReader = dataStream.getReader()
+
+        // NOTE: streaming flush
+        // We are buffering here for the inlined data stream because the
+        // "shell" stream might be chunkenized again by the underlying stream
+        // implementation, e.g. with a specific high-water mark. To ensure it's
+        // the safe timing to pipe the data stream, this extra tick is
+        // necessary.
+        dataStreamFinished = new Promise((res) =>
+          setTimeout(async () => {
+            try {
+              while (true) {
+                const { done, value } = await dataStreamReader.read()
+                if (done) {
+                  return res()
+                }
+                controller.enqueue(value)
+              }
+            } catch (err) {
+              controller.error(err)
+            }
+            res()
+          }, 0)
+        )
+      }
+    },
+    flush() {
+      if (dataStreamFinished) {
+        return dataStreamFinished
+      }
+    },
+  })
+}