In pages functions avoid cloning the request when not necessary

[dario-piotrowicz]

Partially fixes #3259 (the full fix can only be applied as a breaking change so it'll have to wait for a wrangler major release unfortunately)

Supersedes #4861

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Example for the changes: https://github.com/dario-piotrowicz/cf-pages-functions-request-clone-repro

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TODO:

• understand why this only occurred in POST requests
• investigate alternative suggested in comment
• add tests for plugins

[changeset-bot]

🦋 Changeset detected

Latest commit: b489e23

The changes in this PR will be included in the next version bump.

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wrangler	Patch

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wrangler@3.26.0 includes the following runtime dependencies:

Package	Constraint	Resolved
miniflare	workspace:*	3.20240129.0
workerd	1.20240129.0	1.20240129.0
workerd --version	1.20240129.0	2024-01-29

Please ensure constraints are pinned, and miniflare/workerd minor versions match.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fcbde34) 70.62% compared to head (b489e23) 70.69%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4916      +/-   ##
==========================================
+ Coverage   70.62%   70.69%   +0.06%     
==========================================
  Files         292      292              
  Lines       15187    15187              
  Branches     3865     3865              
==========================================
+ Hits        10726    10736      +10     
+ Misses       4461     4451      -10     

see 7 files with indirect coverage changes

[Skye-31]

I wonder if we could use Request.bodyUsed alongside Request.body.cancel() to remove the warning in all cases, by cancelling the body streams of any requests where its not been read?

[russelldavis]

@Skye-31 that's an interesting idea. I think it would make the warnings go away (because the clones would be cleaned up right before the warning logic sees them), but unfortunately I think the underlying issue that is being warned about would remain. You'd still be calling request.clone() before each call to next(), and you'd only be able to safely call request.body.cancel() after the call to next() returns, which means the entire request would still get processed while clones of the stream exist, causing the problems mentioned in the warning message.

[GregBrimble]

There's two things in one here:

1. We can minimize the number of clones in a Pages Functions Worker. That can happen today. There shouldn't be any impact to users. We simply check the number of handlers. If < 2, then we don't need to clone. At a quick skim, that seems to be what the code of this PR does, and like I say, that could ship today because it's not a breaking change unless I'm misunderstanding something.

2. Foregoing automatic cloneing entirely. We can't do this, even with a major version bump, because Pages Functions is versioned independently (it currently is not versioned at all). This will need to wait until we figure out what we're doing with Pages Functions ownership long-term.