feat: Implement requestBuffer

[markwinter]

What this PR does / why we need it:

This implements the new requestBuffer API using the Envoy's Buffer and BufferPerRoute filters.
API PR: #5537

Which issue(s) this PR fixes:

Fixes #3706

Release Notes: Yes

[codecov]

Codecov Report

Attention: Patch coverage is 62.13592% with 39 lines in your changes missing coverage. Please review.

Project coverage is 65.34%. Comparing base (096cb8d) to head (f1f1283).
Report is 54 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/xds/translator/request_buffer.go	61.90%	22 Missing and 10 partials ⚠️
internal/gatewayapi/backendtrafficpolicy.go	56.25%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5661      +/-   ##
==========================================
+ Coverage   65.19%   65.34%   +0.14%     
==========================================
  Files         214      220       +6     
  Lines       34321    35092     +771     
==========================================
+ Hits        22377    22932     +555     
- Misses      10591    10749     +158     
- Partials     1353     1411      +58     

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[zhaohuabing]

@markwinter Thanks so much for working on this great feature — really appreciate the effort you’re putting in!

If the BTP has a Gateway as a target, then we will configure the Buffer filter on the Listener. If the BTP has a HTTPRoute as a target, then we will configure the BufferPerRoute filter for that particular route. The BufferPerRoute will take precedence - I've tested having both applied and the BufferPerRoute maxBytes won.

This behavior is different than other types of settings in the BackendTrafficPolicy, where the settings targeting Gateway apply to all xRoutes. This inconsistent behavior of BackendTrafficPolicy could confuse users. We also can't apply a default RequestBuffer for all the xRoutes under a Gateway.

Another small thing: when the Buffer filter is applied at the Gateway level, it’s configured on all Listeners. While this makes sense (since BackendTrafficPolicy doesn’t target Listeners directly), it might be a bit unexpected from a user perspective.

I prefer keeping the same "Override" behavior as the other settings, and adding a Shared field in the RequestBuffer, similar to what we have done with the shared global ratelimit. We'll need to implement a "merge" mechanism to allow two-level request buffer settings. This is tracked at #1934 .

Shared global rate limit:

gateway/api/v1alpha1/ratelimit_types.go

Lines 55 to 62 in 61474e3

	// Shared determines whether the rate limit rules apply across all the policy targets.
	// If set to true, the rule is treated as a common bucket and is shared across all policy targets (xRoutes).
	// Default: false.
	//
	// +optional
	// +notImplementedHide
	// +kubebuilder:default=false
	Shared *bool `json:"shared,omitempty"`

cc @envoyproxy/gateway-maintainers

[arkodg]

hey @markwinter as @zhaohuabing suggested, can the implementation push all the intent to per Route, and we can enhance this in the future with a shared api field to be able to set common per gateway buffers ?

[markwinter]

@arkodg @zhaohuabing Thanks for the feedback. On holiday for a week and will return to the PR afterwards 👍

[arkodg]

hey @markwinter hope you had a good break, feature freeze for v1.4 is April 30th, curious if you youd be able to complete this by then or prefer moving this to v1.5 ?

[markwinter]

@arkodg @zhaohuabing Sorry for the little bit of delay in getting back.

I've updated the request buffer xds patching.

Now the patchHCM will add the Buffer filter but in a Disabled: true state if there exists a route with request buffering. This is required to make any request buffering work at all, as BufferPerRoutes filters on routes by themselves are not enough. Then in patchRoute it will add the BufferPerRoute filter using that route's settings (if any) which will enable Buffer for that route.

If the BTP target was a Gateway all routes get the BufferPerRoute filter applied, and if the BTP target was just a Route, it gets added for just that route.

I took inspiration from how BasicAuth filter works which also adds a HCM filter in Disabled state, but then overrides the per route config.

[markwinter]

/retest

[zhaohuabing]

LGTM thanks!

[arkodg]

LGTM thanks for adding this ! this will be part of v1.4 😅