[Segment Cache] Support third-party redirects in output: "export" mode (#81247)
In output: "export" mode, we can't use headers to request a particular
segment. Instead, we encode the extra request information into the URL.
This is not part of the "public" interface of the app; it's an internal
Next.js implementation detail that the app developer should not need to
concern themselves with.
For example, to request a segment:
- Path passed to <Link>: /path/to/page
- Path passed to fetch: /path/to/page/__next-segments/_tree
*(This is not the exact protocol, just an illustration.)*
Before we do that, though, we need to account for redirects. Even in
output: "export" mode, a proxy might redirect the page to a different
location, but we shouldn't assume or expect that they also redirect all
the segment files, too.
To check whether the page is redirected, we perform a range request of
the first N bytes of the HTML document, just enough to verify the
document comes from the same build. The canonical URL is determined from
the response.
Then we can use the canonical URL to request the route tree.
Note: We could embed the route tree into the HTML document, to avoid a
second request. We're not doing that currently because it would make the
HTML document larger and affect normal page loads.
next.js
5557bdda - [Segment Cache] Support third-party redirects in output: "export" mode (#81247)
