In this example, you use an if else function to determine the value of the :path and :method pseudo headers. If the bar request header is provided, you change the path and method. In all other cases, you preserve the value of both 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:

  • Pseudo headers must always start with a colon (:).
  • They must appear before regular headers in the HTTP/2 frame.
  • Pseudo headers 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 Gloo Gateway, set up a gateway resource, and deploy the httpbin sample app.

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

      export INGRESS_GW_ADDRESS=$(kubectl get svc -n gloo-system gloo-proxy-http -o jsonpath="{.status.loadBalancer.ingress[0]['hostname','ip']}")
echo $INGRESS_GW_ADDRESS  
  
      kubectl port-forward deployment/gloo-proxy-http -n gloo-system 8080:8080

Update request paths and HTTP methods

  1. Create a RouteOption or VirtualHostOption resource with the following transformation rules:

    • :path: If the request header foo equals the value bar, set the request path in the :path pseudo header to /post. In all other cases, set the request path to value of the :path pseudo header and return that value in the :path pseudo header.
    • :method: If the request header foo equals the value bar, set the HTTP method in the :method pseudo header to POST. In all other cases, set the method to the value of the :method pseudo header and return that value in the :method pseudo header.
        kubectl apply -f- <<EOF
apiVersion: gateway.solo.io/v1
kind: RouteOption
metadata:
  name: transformation
  namespace: httpbin
spec:
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: httpbin
  options:
    transformations:
      requestTransformation:
        transformationTemplate:
          headers:
            # If the foo: bar header is present, update the request path to /post. 
            # Otherwise, do not update the request path. 
            # Note that you must use the :path pseudo-header to update the request path.
            ":path":
               text: '{% if header("foo") == "bar" %}/post{% else %}{{ header(":path") }}{% endif %}'
            # If the foo: bar header is present, update the HTTP method to POST. 
            # Otherwise, do not update the HTTP method. 
            # Note that you must the :method pseudo-header to update the HTTP method of the request. 
            ":method":
               text: '{% if header("foo") == "bar" %}POST{% else %}{{ header(":method") }}{% endif %}'
EOF
  
        kubectl apply -n gloo-system -f- <<EOF
apiVersion: gateway.solo.io/v1
kind: VirtualHostOption
metadata:
  name: transformation
  namespace: gloo-system
spec:
  options:
    transformations:
      requestTransformation:
        transformationTemplate:
          headers:
            # If the foo: bar header is present, update the request path to /post. 
            # Otherwise, do not update the request path. 
            # Note that you must use the :path pseudo-header to update the request path.
            ":path":
               text: '{% if header("foo") == "bar" %}/post{% else %}{{ header(":path") }}{% endif %}'
            # If the foo: bar header is present, update the HTTP method to POST. 
            # Otherwise, do not update the HTTP method. 
            # Note that you must the :method pseudo-header to update the HTTP method of the request. 
            ":method":
               text: '{% if header("foo") == "bar" %}POST{% else %}{{ header(":method") }}{% endif %}'
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
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.

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

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

You can remove the resources that you created in this guide.

  kubectl delete virtualhostoption transformation -n gloo-system
kubectl delete routeoption transformation -n httpbin