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Extract the values of common pseudo headers to generate a redirect URL.

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