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

Use pseudo headers for redirect URLs

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

    • Build a redirect URL with the values of the :authority and :path pseudo headers. These headers are extracted from the request with the request_header function that is provided in Gloo Gateway.
    • The :authority pseudo header contains the hostname that the request is sent to.
    • The :path pseudo header is set to the request path.
    • The redirect URL is added to the x-forwarded-uri response 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:
      responseTransformation:
        transformationTemplate:
           headers:
             x-forwarded-uri:
               text: 'https://{{ request_header(":authority") }}{{ request_header(":path") }}'
           parseBodyBehavior: "DontParse"
EOF
  
        kubectl apply -n gloo-system -f- <<EOF
apiVersion: gateway.solo.io/v1
kind: VirtualHostOption
metadata:
  name: transformation
  namespace: gloo-system
spec:
  options:
    transformations:
      responseTransformation:
        transformationTemplate:
          headers:
            x-forwarded-uri:
              text: 'https://{{ request_header(":authority") }}{{ request_header(":path") }}'
          parseBodyBehavior: "DontParse"
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
EOF

  2. Send a request to the httpbin app. Verify that you see the x-forwarded-uri response header that is set to the hostname and path that was used in the initial request.

      curl -vik -H "host: www.example.com:8080" \
  -H "Content-Type: application/json" \
  http://$INGRESS_GW_ADDRESS:8080/response-headers
  
      curl -vik localhost:8080/response-headers \
  -H "host: www.example.com" \
  -H "Content-Type: application/json" \

    Example output:

      ...
* Request completely sent off
< HTTP/1.1 200 OK
HTTP/1.1 200 OK
< access-control-allow-credentials: true
access-control-allow-credentials: true
< access-control-allow-origin: *
access-control-allow-origin: *
...
< x-forwarded-uri: https://www.example.com:8080/response-headers
x-forwarded-uri: https://www.example.com:8080/response-headers
< server: envoy
server: envoy
<

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