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import { InvariantError } from '../../shared/lib/invariant-error'
/**
* This is a utility function to make scheduling sequential tasks that run back to back easier.
* We schedule on the same queue (setImmediate) at the same time to ensure no other events can sneak in between.
*/
export function prerenderAndAbortInSequentialTasks<R>(
prerender: () => Promise<R>,
abort: () => void
): Promise<R> {
if (process.env.NEXT_RUNTIME === 'edge') {
throw new InvariantError(
'`prerenderAndAbortInSequentialTasks` should not be called in edge runtime.'
)
} else {
return new Promise((resolve, reject) => {
let pendingResult: Promise<R>
setImmediate(() => {
try {
pendingResult = prerender()
pendingResult.catch(() => {})
} catch (err) {
reject(err)
}
})
setImmediate(() => {
abort()
resolve(pendingResult)
})
})
}
}
// React's RSC prerender function will emit an incomplete flight stream when using `prerender`. If the connection
// closes then whatever hanging chunks exist will be errored. This is because prerender (an experimental feature)
// has not yet implemented a concept of resume. For now we will simulate a paused connection by wrapping the stream
// in one that doesn't close even when the underlying is complete.
export class ReactServerResult {
private _stream: null | ReadableStream<Uint8Array>
constructor(stream: ReadableStream<Uint8Array>) {
this._stream = stream
}
tee() {
if (this._stream === null) {
throw new Error(
'Cannot tee a ReactServerResult that has already been consumed'
)
}
const tee = this._stream.tee()
this._stream = tee[0]
return tee[1]
}
consume() {
if (this._stream === null) {
throw new Error(
'Cannot consume a ReactServerResult that has already been consumed'
)
}
const stream = this._stream
this._stream = null
return stream
}
}
export type ReactServerPrerenderResolveToType = {
prelude: ReadableStream<Uint8Array>
}
export async function createReactServerPrerenderResult(
underlying: Promise<ReactServerPrerenderResolveToType>
): Promise<ReactServerPrerenderResult> {
const chunks: Array<Uint8Array> = []
const { prelude } = await underlying
const reader = prelude.getReader()
while (true) {
const { done, value } = await reader.read()
if (done) {
return new ReactServerPrerenderResult(chunks)
} else {
chunks.push(value)
}
}
}
export async function createReactServerPrerenderResultFromRender(
underlying: ReadableStream<Uint8Array>
): Promise<ReactServerPrerenderResult> {
const chunks: Array<Uint8Array> = []
const reader = underlying.getReader()
while (true) {
const { done, value } = await reader.read()
if (done) {
break
} else {
chunks.push(value)
}
}
return new ReactServerPrerenderResult(chunks)
}
export class ReactServerPrerenderResult {
private _chunks: null | Array<Uint8Array>
private assertChunks(expression: string): Array<Uint8Array> {
if (this._chunks === null) {
throw new InvariantError(
`Cannot \`${expression}\` on a ReactServerPrerenderResult that has already been consumed.`
)
}
return this._chunks
}
private consumeChunks(expression: string): Array<Uint8Array> {
const chunks = this.assertChunks(expression)
this.consume()
return chunks
}
consume(): void {
this._chunks = null
}
constructor(chunks: Array<Uint8Array>) {
this._chunks = chunks
}
asUnclosingStream(): ReadableStream<Uint8Array> {
const chunks = this.assertChunks('asUnclosingStream()')
return createUnclosingStream(chunks)
}
consumeAsUnclosingStream(): ReadableStream<Uint8Array> {
const chunks = this.consumeChunks('consumeAsUnclosingStream()')
return createUnclosingStream(chunks)
}
asStream(): ReadableStream<Uint8Array> {
const chunks = this.assertChunks('asStream()')
return createClosingStream(chunks)
}
consumeAsStream(): ReadableStream<Uint8Array> {
const chunks = this.consumeChunks('consumeAsStream()')
return createClosingStream(chunks)
}
}
function createUnclosingStream(
chunks: Array<Uint8Array>
): ReadableStream<Uint8Array> {
let i = 0
return new ReadableStream({
async pull(controller) {
if (i < chunks.length) {
controller.enqueue(chunks[i++])
}
// we intentionally keep the stream open. The consumer will clear
// out chunks once finished and the remaining memory will be GC'd
// when this object goes out of scope
},
})
}
function createClosingStream(
chunks: Array<Uint8Array>
): ReadableStream<Uint8Array> {
let i = 0
return new ReadableStream({
async pull(controller) {
if (i < chunks.length) {
controller.enqueue(chunks[i++])
} else {
controller.close()
}
},
})
}
export async function processPrelude(
unprocessedPrelude: ReadableStream<Uint8Array>
) {
const [prelude, peek] = unprocessedPrelude.tee()
const reader = peek.getReader()
const firstResult = await reader.read()
reader.cancel()
const preludeIsEmpty = firstResult.done === true
return { prelude, preludeIsEmpty }
}
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