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Change request path and method

Use pseudo headers to conditionally rewrite the request path and HTTP method based on a request header value.

Change the request path and HTTP method when a request header is present by using CEL expressions. The example uses request.headers[], request.path, and request.method with a ternary expression to conditionally set the :path and :method pseudo headers.

About pseudo headers

Pseudo headers are special headers that are used in HTTP/2 to provide metadata about the request or response in a structured way. Although they look like traditional HTTP/1.x headers, they come with specific characteristics:

• Must always start with a colon (:).
• Must appear before regular headers in the HTTP/2 frame.
• Contain details about the request or response.

Common pseudo headers include:

• :method: The HTTP method that is used, such as GET or POST.
• :scheme: The protocol that is used, such as http or https.
• :authority: The hostname and port number that the request is sent to.
• :path: The path of the request.

Before you begin

1. Set up an agentgateway proxy.
2. Install the httpbin sample app.

Update request paths and HTTP methods

1. Create an AgentgatewayPolicy resource with your transformation rules. The policy rewrites the path to /post and the method to POST when the foo: bar request header is present. When the header is absent, the path and method are unchanged.

   kubectl apply -f- <<EOF
   apiVersion: agentgateway.dev/v1alpha1
   kind: AgentgatewayPolicy
   metadata:
     name: transformation
     namespace: httpbin
   spec:
     targetRefs:
     - group: gateway.networking.k8s.io
       kind: HTTPRoute
       name: httpbin
     traffic:
       transformation:
         request:
           set:
           - name: ":path"
             value: 'request.headers["foo"] == "bar" ? "/post" : request.path'
           - name: ":method"
             value: 'request.headers["foo"] == "bar" ? "POST" : request.method'
   EOF

2. Send a request to the /get endpoint and include the foo: bar header to trigger the transformation. Verify that you get back a 200 HTTP response code. The httpbin /post endpoint only accepts POST requests, so a 200 response confirms both the path rewrite and the method change succeeded.

   Cloud Provider LoadBalancerPort-forward for local testing

   curl -vi http://$INGRESS_GW_ADDRESS:80/get \
    -H "foo: bar" \
    -H "host: www.example.com:80"

   curl -vi localhost:8080/get \
   -H "foo: bar" \
   -H "host: www.example.com"

   Example output:

   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   ...
   {
     "args": {},
     "headers": {
        "Accept": [
          "*/*"
        ],
        "Content-Length": [
        "0"
        ],
        "Foo": [
        "bar"
        ],
        "Host": [
        "www.example.com:8080"
        ],
        "User-Agent": [
        "curl/7.77.0"
        ]
    },
    "origin": "127.0.0.6:48539",
    "url": "http://www.example.com:8080/post",
    "data": "",
    "files": null,
    "form": null,
    "json": null
   }
   

3. Send another request to the /get endpoint. This time, omit the foo: bar header. Verify that you get back a 200 HTTP response code and that the request path is not rewritten.

   Cloud Provider LoadBalancerPort-forward for local testing

   curl -vi http://$INGRESS_GW_ADDRESS:80/get \
    -H "host: www.example.com:80"

   curl -vi localhost:8080/get \
   -H "host: www.example.com"

   Example output:

   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   ...
   
   {
    "args": {},
    "headers": {
        "Accept": [
        "*/*"
        ],
        "Host": [
        "www.example.com:8080"
        ],
        "User-Agent": [
        "curl/7.77.0"
        ]
    },
    "origin": "127.0.0.6:46209",
    "url": "http://www.example.com:8080/get"
   }
   

Cleanup

kubectl delete AgentgatewayPolicy transformation -n httpbin