HTTP Request Header Manipulate

This document explains FSM Gateway’s feature to modify HTTP request headers with filter, including adding, setting, and removing headers, with examples.

The HTTP header manipulation feature allows you to fine-tune incoming and outgoing request and response headers.

In Gateway API, the HTTPRoute resource utilities two HTTPHeaderFilter filter for request and response header manipulation.

The both filters supports add, set and remove operation. The combination of them is also available.

This document will introduce the HTTP request header manipulation function of FSM Gateway. The introduction of HTTP response header manipulation is located in doc HTTP Response Header Manipulate.

Prerequisites

  • Kubernetes cluster version v1.21.0 or higher.
  • kubectl CLI
  • FSM Gateway installed via guide doc.

Demonstration

We will follow the sample in HTTP Routing.

In backend service, there is a path /headers which will respond all request headers.

curl -H 'host:foo.example.com' http://$GATEWAY_IP:8000/headers
{
  "headers": {
    "Accept": "*/*",
    "Connection": "keep-alive",
    "Host": "10.42.0.15:80",
    "User-Agent": "curl/8.1.2"
  }
}

Add HTTP Request header

With header adding feature, let’s try to add a new header to request by add HTTPHeaderFilter filter.

Modifying the HTTPRoute http-route-foo and add RequestHeaderModifier filter.

kubectl apply -n httpbin -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: http-route-foo
spec:
  parentRefs:
  - name: simple-fsm-gateway
    port: 8000
  hostnames:
  - foo.example.com
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - name: httpbin
      port: 8080
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        add: 
        - name: "header-2-add"
          value: "foo"
EOF

Now request the path /headers again and you will get the new header injected by gateway.

Thought HTTP header name is case insensitive but it will be converted to capital mode.

curl -H 'host:foo.example.com' http://$GATEWAY_IP:8000/headers
{
  "headers": {
    "Accept": "*/*",
    "Connection": "keep-alive",
    "Header-2-Add": "foo",
    "Host": "10.42.0.15:80",
    "User-Agent": "curl/8.1.2"
  }
}

Set HTTP Request header

set operation is used to update the value of specified header. If the header not exist, it will do as add operation.

Let’s update the HTTPRoute resource again and set two headers with new value. One does not exist and another does.

kubectl apply -n httpbin -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: http-route-foo
spec:
  parentRefs:
  - name: simple-fsm-gateway
    port: 8000
  hostnames:
  - foo.example.com
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - name: httpbin
      port: 8080
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        set: 
        - name: "header-2-set"
          value: "foo"
        - name: "user-agent"
          value: "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Safari/605.1.15"
EOF

In the response, we can get the two headers updated.

curl -H 'host:foo.example.com' http://$GATEWAY_IP:8000/headers
{
  "headers": {
    "Accept": "*/*",
    "Connection": "keep-alive",
    "Header-2-Set": "foo",
    "Host": "10.42.0.15:80",
    "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Safari/605.1.15"
  }
}

Remove HTTP Request header

The last operation is remove, which can remove the header of client sending.

Let’s update the HTTPRoute resource to remove user-agent header directly to hide client type from backend service.

kubectl apply -n httpbin -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: http-route-foo
spec:
  parentRefs:
  - name: simple-fsm-gateway
    port: 8000
  hostnames:
  - foo.example.com
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - name: httpbin
      port: 8080
    filters:
    - type: RequestHeaderModifier
      requestHeaderModifier:
        remove:
        - "user-agent"
EOF

With resource udpated, the user agent is invisible on backend service side.

curl -H 'host:foo.example.com' http://$GATEWAY_IP:8000/headers
{
  "headers": {
    "Accept": "*/*",
    "Connection": "keep-alive",
    "Host": "10.42.0.15:80"
  }
}

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Last modified June 18, 2024: fix workflow issue (c83135d)