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/**
* Measures and separates static and dynamic content in a response stream
* by splitting on PPR boundary sentinel markers.
*
* This function is used in Partial Prerendering (PPR) tests to analyze the output
* of Next.js pages and verify that static and dynamic content are properly separated.
*
* @param fn - A function that returns a Promise resolving to a readable stream
* containing HTML with PPR boundary markers
* @returns An object containing the separated static and dynamic chunks
*
* @example
* const [staticPart, dynamicPart] = await splitResponseWithPPRSentinel(async () => {
* return fetch('/some-ppr-page').then(res => res.body)
* })
* console.log(staticPart) // Content before the boundary
* console.log(dynamicPart) // Content after the boundary
*/
export async function splitResponseWithPPRSentinel(
fn: () => Promise<NodeJS.ReadableStream>
): Promise<[staticPart: string, dynamicPart: string]> {
const stream = await fn()
const chunks: string[] = []
await new Promise<void>((resolve, reject) => {
stream.on('data', (chunk: Buffer | string) => {
if (typeof chunk !== 'string') {
chunk = chunk.toString('utf8')
}
chunks.push(chunk)
})
stream.on('end', resolve)
stream.on('error', reject)
})
// Combine all chunks and split on the PPR boundary sentinel
// The sentinel marks the boundary between static and dynamic content
const parts = chunks.join('').split('<!-- PPR_BOUNDARY_SENTINEL -->', 2)
return [parts[0] ?? '', parts[1] ?? '']
}
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