feat: add support for ResponseHeaderModifier Filter

docs/latest/user/http-request-headers.md

@@ -221,49 +221,7 @@ $ curl -vvv --header "Host: headers.example" "http://${GATEWAY_HOST}:8080/get" -
 
 ## Combining Filters
 
-Headers can be added/set/removed in separate filters on the same HTTPRoute and they will all perform as expected
-
-```shell
-cat <<EOF | kubectl apply -f -
-apiVersion: gateway.networking.k8s.io/v1beta1
-kind: HTTPRoute
-metadata:
-  name: http-headers
-spec:
-  parentRefs:
-  - name: eg
-  hostnames:
-  - headers.example
-  rules:
-  - matches:
-    - path:
-        type: PathPrefix
-        value: /
-    backendRefs:
-    - group: ""
-      kind: Service
-      name: backend
-      port: 3000
-      weight: 1
-    filters:
-    - type: RequestHeaderModifier
-      requestHeaderModifier:
-        add:
-        - name: "added-header"
-          value: "foo"
-    - type: RequestHeaderModifier
-      requestHeaderModifier:
-        set:
-        - name: "set-header"
-          value: "bar"
-    - type: RequestHeaderModifier
-      requestHeaderModifier:
-        remove:
-        - "removed-header"
-EOF
-```
-
-Alternatively, it is easier to combine all of the header operations into a single filter.
+Headers can be added/set/removed in a single filter on the same HTTPRoute and they will all perform as expected
 
 ```shell
 cat <<EOF | kubectl apply -f -

docs/latest/user/http-response-headers.md

@@ -0,0 +1,264 @@
+# HTTP Response Headers
+
+The [HTTPRoute][] resource can modify the headers of a response before responding it to the downstream service. To learn more about HTTP routing, refer to the [Gateway API documentation][].
+
+A [`ResponseHeaderModifier` filter][req_filter] instructs Gateways to modify the headers in responses that match the rule before responding to the downstream. Note that the `ResponseHeaderModifier` filter will only modify headers before the response is returned from Envoy to the downstream client and will not affect request headers forwarding to the upstream service.
+
+Follow the steps from the [Quickstart Guide](QUICKSTART.md) to install Envoy Gateway and then install the example resources used for this guide.
+
+## Adding Response Headers
+
+The `ResponseHeaderModifier` filter can add new headers to a response before it is sent to the upstream. If the response does not have the header configured by the filter, then that header will be added to the response. If the response already has the header configured by the filter, then the value of the header in the filter will be appended to the value of the header in the response.
+
+```shell
+cat <<EOF | kubectl apply -f -
+apiVersion: gateway.networking.k8s.io/v1beta1
+kind: HTTPRoute
+metadata:
+  name: http-headers
+spec:
+  parentRefs:
+  - name: eg
+  hostnames:
+  - headers.example
+  rules:
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /
+    backendRefs:
+    - group: ""
+      kind: Service
+      name: backend
+      port: 3000
+      weight: 1
+    filters:
+    - type: ResponseHeaderModifier
+      responseHeaderModifier:
+        add:
+        - name: "add-header"
+          value: "foo"
+EOF
+```
+
+The HTTPRoute status should indicate that it has been accepted and is bound to the example Gateway.
+
+```shell
+kubectl get httproute/http-headers -o yaml
+```
+
+Get the Gateway's address:
+
+```shell
+export GATEWAY_HOST=$(kubectl get gateway/eg -o jsonpath='{.status.addresses[0].value}')
+```
+
+Querying `headers.example/get` should result in a `200` response from the example Gateway and the output from the example
+app should indicate that the downstream client received the header `add-header` with the value: `foo`
+
+```console
+$ curl -vvv --header "Host: headers.example" "http://${GATEWAY_HOST}:8080/get" -H 'X-Echo-Set-Header: X-Foo: value1'
+...
+> GET /get HTTP/1.1
+> Host: headers.example
+> User-Agent: curl/7.81.0
+> Accept: */*
+> X-Echo-Set-Header: X-Foo: value1
+> 
+* Mark bundle as not supporting multiuse
+< HTTP/1.1 200 OK
+< content-type: application/json
+< x-content-type-options: nosniff
+< content-length: 474
+< x-envoy-upstream-service-time: 0
+< server: envoy
+< x-foo: value1
+< add-header: foo
+< 
+...
+ "headers": {
+  "Accept": [
+   "*/*"
+  ],
+  "X-Echo-Set-Header": [
+   "X-Foo: value1"
+  ]
+...
+```
+
+## Setting Response Headers
+
+Setting headers is similar to adding headers. If the response does not have the header configured by the filter, then it will be added, but unlike [adding response headers](#adding-response-headers) which will append the value of the header if the response already contains it, setting a header will cause the value to be replaced by the value configured in the filter.
+
+```shell
+cat <<EOF | kubectl apply -f -
+apiVersion: gateway.networking.k8s.io/v1beta1
+kind: HTTPRoute
+metadata:
+  name: http-headers
+spec:
+  parentRefs:
+  - name: eg
+  hostnames:
+  - headers.example
+  rules:
+  - backendRefs:
+    - group: ""
+      kind: Service
+      name: backend
+      port: 3000
+      weight: 1
+    matches:
+    - path:
+        type: PathPrefix
+        value: /
+    filters:
+    - type: ResponseHeaderModifier
+      responseHeaderModifier:
+        set:
+        - name: "set-header"
+          value: "foo"
+EOF
+```
+
+Querying `headers.example/get` should result in a `200` response from the example Gateway and the output from the example
+app should indicate that the downstream client received the header `set-header` with the original value `value1` replaced by `foo`.
+
+```console
+$ curl -vvv --header "Host: headers.example" "http://${GATEWAY_HOST}:8080/get" -H 'X-Echo-Set-Header: set-header: value1'
+...
+> GET /get HTTP/1.1
+> Host: headers.example
+> User-Agent: curl/7.81.0
+> Accept: */*
+> X-Echo-Set-Header: set-header: value1
+> 
+* Mark bundle as not supporting multiuse
+< HTTP/1.1 200 OK
+< content-type: application/json
+< x-content-type-options: nosniff
+< content-length: 474
+< x-envoy-upstream-service-time: 0
+< server: envoy
+< set-header: foo
+<
+ "headers": {
+  "Accept": [
+   "*/*"
+  ],
+  "X-Echo-Set-Header": [
+    "set-header": value1"
+  ]
+...
+```
+
+## Removing Response Headers
+
+Headers can be removed from a response by simply supplying a list of header names.
+
+Setting headers is similar to adding headers. If the response does not have the header configured by the filter, then it will be added, but unlike [adding response headers](#adding-response-headers) which will append the value of the header if the response already contains it, setting a header will cause the value to be replaced by the value configured in the filter.
+
+```shell
+cat <<EOF | kubectl apply -f -
+apiVersion: gateway.networking.k8s.io/v1beta1
+kind: HTTPRoute
+metadata:
+  name: http-headers
+spec:
+  parentRefs:
+  - name: eg
+  hostnames:
+  - headers.example
+  rules:
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /
+    backendRefs:
+    - group: ""
+      name: backend
+      port: 3000
+      weight: 1
+    filters:
+    - type: ResponseHeaderModifier
+      responseHeaderModifier:
+        remove:
+        - "remove-header"
+EOF
+```
+
+Querying `headers.example/get` should result in a `200` response from the example Gateway and the output from the example
+app should indicate that the header `remove-header` that was sent by curl
+was removed before the upstream received the response.
+
+```console
+$ curl -vvv --header "Host: headers.example" "http://${GATEWAY_HOST}:8080/get" -H 'X-Echo-Set-Header: remove-header: value1'
+...
+> GET /get HTTP/1.1
+> Host: headers.example
+> User-Agent: curl/7.81.0
+> Accept: */*
+> X-Echo-Set-Header: remove-header: value1
+>
+* Mark bundle as not supporting multiuse
+< HTTP/1.1 200 OK
+< content-type: application/json
+< x-content-type-options: nosniff
+< content-length: 474
+< x-envoy-upstream-service-time: 0
+< server: envoy
+< 
+
+ "headers": {
+  "Accept": [
+   "*/*"
+  ],
+  "X-Echo-Set-Header": [
+    "remove-header": value1"
+  ]
+...
+```
+
+## Combining Filters
+
+Headers can be added/set/removed in a single filter on the same HTTPRoute and they will all perform as expected
+
+```shell
+cat <<EOF | kubectl apply -f -
+apiVersion: gateway.networking.k8s.io/v1beta1
+kind: HTTPRoute
+metadata:
+  name: http-headers
+spec:
+  parentRefs:
+  - name: eg
+  hostnames:
+  - headers.example
+  rules:
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /
+    backendRefs:
+    - group: ""
+      kind: Service
+      name: backend
+      port: 3000
+      weight: 1
+    filters:
+    - type: ResponseHeaderModifier
+      responseHeaderModifier:
+        add:
+        - name: "add-header-1"
+          value: "foo"
+        set:
+        - name: "set-header-1"
+          value: "bar"
+        remove:
+        - "removed-header"
+EOF
+```
+
+[HTTPRoute]: https://gateway-api.sigs.k8s.io/api-types/httproute/
+[Gateway API documentation]: https://gateway-api.sigs.k8s.io/
+[req_filter]: https://gateway-api.sigs.k8s.io/references/spec/#gateway.networking.k8s.io/v1beta1.HTTPHeaderFilter

internal/gatewayapi/testdata/httproute-with-response-header-filter-adds.in.yaml

@@ -0,0 +1,57 @@
+gateways:
+- apiVersion: gateway.networking.k8s.io/v1beta1
+  kind: Gateway
+  metadata:
+    namespace: envoy-gateway
+    name: gateway-1
+  spec:
+    gatewayClassName: envoy-gateway-class
+    listeners:
+    - name: http
+      protocol: HTTP
+      port: 80
+      hostname: "*.envoyproxy.io"
+      allowedRoutes:
+        namespaces:
+          from: All
+httpRoutes:
+- apiVersion: gateway.networking.k8s.io/v1beta1
+  kind: HTTPRoute
+  metadata:
+    namespace: default
+    name: httproute-1
+  spec:
+    hostnames:
+    - gateway.envoyproxy.io
+    parentRefs:
+    - namespace: envoy-gateway
+      name: gateway-1
+      sectionName: http
+    rules:
+    - matches:
+      - path:
+          value: "/"
+      backendRefs:
+      - name: service-1
+        port: 8080
+      filters:
+      - type: ResponseHeaderModifier
+        responseHeaderModifier:
+          set: 
+          - name: "set-header-1"
+            value: "some-value"
+          - name: "set-header-2"
+            value: "some-value"
+          - name: "set-header-3"
+            value: "some-value"
+          - name: "set-header-4"
+            value: "some-value"
+          add:
+          - name: "Set-Header-1"
+            value: "some-value"
+          - name: "set-header-2"
+            value: "some-value"
+          - name: "set-header-3"
+            value: "some-value"
+          - name: "set-header-5"
+            value: "some-value"