Add multiple values to headers

Use the headersToAppend capability to add multiple values to the same header.

In this guide, you explore how to use the headersToAppend transformation template attribute to add multiple values to the same header. The values are separated with a comma.

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

Add multiple values to headers

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

   • Extract the value of the Host request header and use this value to build the customcookie2 string. Then, append the transformed string to the Set-Cookie request header.
   • Extract the value of the Host request header and use this value to build the customcookie3 string. Then, append the transformed string to the same Set-Cookie request 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: 
               headersToAppend:
               - key: Set-Cookie
                 value:
                   text: 'customcookie2={{ request_header("Host") }}'
               - key: Set-Cookie
                 value:
                   text: 'customcookie3={{ request_header("Host") }}'
     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:
               headersToAppend:
               - key: Set-Cookie
                 value:
                   text: 'customcookie2={{ request_header("Host") }}'
               - key: Set-Cookie
                 value:
                   text: 'customcookie3={{ request_header("Host") }}'
       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 multiple values in the Set-Cookie request header.

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

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

   Example output:

   {
     "headers": {
       "Accept": [
        "*/*"
       ],
       "Host": [
         "www.example.com:8080"
       ],
       "Set-Cookie": [
         "customcookie2=www.example.com:8080",
         "customcookie3=www.example.com:8080"
       ],
       "User-Agent": [
         "curl/8.7.1"
       ],
       "X-Envoy-Expected-Rq-Timeout-Ms": [
         "15000"
       ],
       "X-Forwarded-Proto": [
         "http"
       ],
       "X-Request-Id": [
         "09fbe5ed-5060-4cf5-835c-46729bf100db"
       ]
     }
   }

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