nextjs-router-source-example-1.tsx

// packages/next/server/render.tsx
// pre-render하는 renderToHTML 함수
// https://github.com/vercel/next.js/blob/v12.3.4/packages/next/server/render.tsx#L351

export async function renderToHTML(
  req: IncomingMessage,
  res: ServerResponse,
  pathname: string,
  query: NextParsedUrlQuery,
  renderOpts: RenderOpts
): Promise<RenderResult | null> {
  // ...

  // SSG 여부 구분
  const isSSG = !!getStaticProps

  // ...

  // getServerSideProps fetch 처리
  if (getServerSideProps && !isFallback) {
    // ...
    try {
      // getServerSideProps 실행
      data = await getServerSideProps({
        // ...
      });
    } catch (serverSidePropsError: any) {
      // ...
    }
    // ...
  }

  // ...

  // document render
  // _document.tsx, _app.tsx, render하려는 페이지가 통합되어 render됨
  const documentResult = await renderDocument()

  // ...

  // documentResult로 stream 만들기
  const streams = [
    streamFromArray(prefix),
    await documentResult.bodyResult(renderTargetSuffix),
  ]

  // 최적화하기
  const postOptimize = (html: string) =>
    postProcessHTML(pathname, html, renderOpts, { inAmpMode, hybridAmp })

  // generateStaticHTML에 따라 pre-render 결과물이 달라짐
  if (generateStaticHTML) {
    const html = await streamToString(chainStreams(streams))
    const optimizedHtml = await postOptimize(html)
    return new RenderResult(optimizedHtml)
  }

  return new RenderResult(
    chainStreams(streams).pipeThrough(
      createBufferedTransformStream(postOptimize)
    )
  )
}