feat(api): add addIfAbsent header action in ClientTrafficPolicy #7978
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**What type of PR is this?** Feature - adds new API field and functionality **What this PR does / why we need it**: This PR adds support for the `addIfAbsent` header action in `HTTPHeaderFilter`, which adds headers only if they don't already exist. This maps to Envoy's [`ADD_IF_ABSENT`](https://www.envoyproxy.io/docs/envoy/v1.36.2/api-v3/config/core/v3/base.proto#enum-config-core-v3-headervalueoption-headerappendaction) action. **Use Case:** Set default headers (e.g., `Content-Security-Policy`, `X-Frame-Options`) at the gateway level that can be overridden by backend responses. Unlike `add` which appends to existing headers, or `set` which overwrites them, `addIfAbsent` is a no-op if the header is already present. **Changes:** - Added `AddIfAbsent` field to `HTTPHeaderFilter` in `api/v1alpha1/shared_types.go` - Added `AddIfAbsent` field to IR `AddHeader` struct in `internal/ir/xds.go` - Updated `translateHeaderModifier()` in `internal/gatewayapi/clienttrafficpolicy.go` - Updated `buildXdsAddedHeaders()` in `internal/xds/translator/route.go` - Updated `buildHeaderMutationRules()` in `internal/xds/translator/header_mutation.go` - Added documentation in `site/content/en/latest/tasks/traffic/http-response-headers.md` - Added testdata files for Gateway API and XDS translator tests **Example usage:** ```yaml apiVersion: gateway.envoyproxy.io/v1alpha1 kind: ClientTrafficPolicy metadata: name: default-headers spec: targetRef: group: gateway.networking.k8s.io kind: Gateway name: eg headers: lateResponseHeaders: addIfAbsent: - name: "content-security-policy" value: "default-src 'self'" ``` Which issue(s) this PR fixes: Fixes envoyproxy#7656 Release Notes: Yes Signed-off-by: Michal Skalski <michal@skalski.org>
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
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+ Coverage 72.81% 72.83% +0.01%
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Lines 35475 35505 +30
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- Misses 7801 7805 +4
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Signed-off-by: Michal Skalski <michal@skalski.org>
Signed-off-by: Michal Skalski <michal@skalski.org>
Signed-off-by: Michal Skalski <michal@skalski.org>
Contributor
Author
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/retest |
arkodg
reviewed
Jan 17, 2026
| port: 10080 | ||
| hostnames: | ||
| - "*" | ||
| headers: |
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can we also add an example for earlyRequestHeaders
arkodg
reviewed
Jan 17, 2026
| namespace: envoy-gateway | ||
| name: target-gateway-1 | ||
| spec: | ||
| headers: |
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can we also add an example for earlyRequestHeaders
Contributor
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hey PR looks great, added a minor comment to add 1 more test case to make sure this also works for |
Signed-off-by: Michal Skalski <michal@skalski.org>
zirain
approved these changes
Jan 18, 2026
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can you add release notes for this? |
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Author
Added in release-notes/current.yaml:29. Happy to adjust the wording if needed. |
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Author
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/retest |
Member
my bad, I missed it. |
Contributor
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Thanks @michalskalski, this is going to be really useful! |
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What type of PR is this?
Feature - adds new API field and functionality
What this PR does / why we need it:
This PR adds support for the
addIfAbsentheader action inHTTPHeaderFilter, which adds headers only if they don't already exist. This maps to Envoy'sADD_IF_ABSENTaction.Use Case:
Set default headers (e.g.,
Content-Security-Policy,X-Frame-Options) at the gateway level that can be overridden by backend responses. Unlikeaddwhich appends to existing headers, orsetwhich overwrites them,addIfAbsentis a no-op if the header is already present.Changes:
AddIfAbsentfield toHTTPHeaderFilterinapi/v1alpha1/shared_types.goAddIfAbsentfield to IRAddHeaderstruct ininternal/ir/xds.gotranslateHeaderModifier()ininternal/gatewayapi/clienttrafficpolicy.gobuildXdsAddedHeaders()ininternal/xds/translator/route.gobuildHeaderMutationRules()ininternal/xds/translator/header_mutation.gosite/content/en/latest/tasks/traffic/http-response-headers.mdExample usage:
Which issue(s) this PR fixes:
Fixes #7656
Release Notes: Yes