Update request paths and methods

Change the request path and HTTP method when a request header is present. To update the path and HTTP method the :path and :method pseudo headers are used.

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. Follow the Get started guide to install kgateway.

2. Follow the Sample app guide to create a gateway proxy with an HTTP listener and deploy the httpbin sample app.

3. Get the external address of the gateway and save it in an environment variable.

   Cloud Provider LoadBalancerPort-forward for local testing

   export INGRESS_GW_ADDRESS=$(kubectl get svc -n kgateway-system http -o jsonpath="{.status.loadBalancer.ingress[0]['hostname','ip']}")
   echo $INGRESS_GW_ADDRESS  

   kubectl port-forward deployment/http -n kgateway-system 8080:8080

Update request paths and HTTP methods

1. Create a TrafficPolicy resource with the following transformation rules:

   • If the request contains the foo:bar header, the request path is rewritten to the /post path. In addition, the HTTP method is changed to the POST method.
   • If the request does not contain the foo:bar header, the request path and method do not change.

   kubectl apply -f- <<EOF  
   apiVersion: gateway.kgateway.dev/v1alpha1
   kind: TrafficPolicy
   metadata:
     name: transformation
     namespace: httpbin
   spec:
     targetRefs:
     - group: gateway.networking.k8s.io
       kind: HTTPRoute
       name: httpbin
     transformation:
       request:
         set:
         - name: ":path"
           value: '{% if request_header("foo") == "bar" %}/post{% else %}{{ header(":path") }}{% endif %}'
         - name: ":method"
           value: '{% if request_header("foo") == "bar" %}POST{% else %}{{ request_header(":method")}}{% endif %}'
   EOF

2. Send a request to the /get endpoint of the httpbin app. Include the foo: bar request header to trigger the request transformation. Verify that you get back a 200 HTTP response code and that your request path is rewritten to the /post endpoint. The /post endpoint accepts requests only if the HTTP POST method is used. The 200 HTTP response code therefore also indicates that the HTTP method was successfully changed from GET to POST.

   Cloud Provider LoadBalancerPort-forward for local testing

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

   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"
        ],
        "X-B3-Sampled": [
        "0"
        ],
        "X-B3-Spanid": [
        "5f36d131289dba78"
        ],
        "X-B3-Traceid": [
        "590047a63783206e5f36d131289dba78"
        ],
        "X-Forwarded-Proto": [
        "http"
        ],
        "X-Request-Id": [
        "6b7debde-6a8a-4d9e-90a4-33a9a35937d3"
        ]
    },
    "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 of the httpbin app. This time, you omit the foo: bar header. Verify that you get back a 200 HTTP response code and that the request path is not rewritten to the /post endpoint. The /get endpoint accepts requests only if the HTTP GET method is used. A 200 HTTP response code therefore also verifies that the HTTP method was not changed.

   Cloud Provider LoadBalancerPort-forward for local testing

   curl -vi http://$INGRESS_GW_ADDRESS:8080/get \
    -H "host: www.example.com:8080" 

   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"
        ],
        "X-B3-Sampled": [
        "0"
        ],
        "X-B3-Spanid": [
        "a83c35458cc4a47b"
        ],
        "X-B3-Traceid": [
        "bf14b3d3098cd639a83c35458cc4a47b"
        ],
        "X-Forwarded-Proto": [
        "http"
        ],
        "X-Request-Id": [
        "b91ecfcf-4f79-4b65-9727-09aafcaeb40e"
        ]
    },
    "origin": "127.0.0.6:46209",
    "url": "http://www.example.com:8080/get"
   }
   

Cleanup

kubectl delete TrafficPolicy transformation -n httpbin