Extract headers

Use extractors to retrieve request header values, transform them, and add them back as headers to the request.

In this guide, you use an extractor to retrieve the account ID from an account request header by using a regular expression. The extractor is then used to build a custom value for the x-account-solo header. You return the transformed header as a request header.

Before you begin

1. Follow the Get started guide to install Solo Enterprise for 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.

   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

Use extractors for headers

1. Create an EnterpriseKgatewayTrafficPolicy with the following transformation rules:

   • Use a regular expression to capture the value of the account request header and store that value in the account_id extractor.
   • Use the account_id extractor to build a custom string and add this string to the x-account-solo request header.

   kubectl apply -f- <<EOF
   apiVersion: enterprisekgateway.solo.io/v1alpha1
   kind: EnterpriseKgatewayTrafficPolicy
   metadata:
     name: transformation
     namespace: httpbin
   spec:
     targetRefs:
     - group: gateway.networking.k8s.io
       kind: HTTPRoute
       name: httpbin
     entTransformation:
       stages:
         early:
           requests:
           - transformation:
               template:
                 extractors:
                   account_id:
                     header: account
                     regex: '(\w+)'
                     subgroup: 1
                 headers:
                   x-account-solo: "account: {{ account_id }}-solo"
   EOF

2. Send a request to the httpbin app with the account: abc123 header. Verify that you see the transformed account value in the x-account-solo request header.

   curl -vik -H "host: www.example.com:8080" \
     -H "Content-Type: application/json" \
     -H "account:abc123" \
     http://$INGRESS_GW_ADDRESS:8080/headers  

   curl -vik localhost:8080/headers \
     -H "host: www.example.com" \
     -H "Content-Type: application/json" \
     -H "account:abc123" 

   Example output:

   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   < access-control-allow-credentials: true
   ...
   < 
   
   {
     "headers": {
       "Accept": [
        "*/*"
       ],
       "Account": [
         "abc123"
       ],
       "Host": [
         "www.example.com:8080"
       ],
       "X-Account-Solo": [
         "account: abc123-solo"
       ],
       "User-Agent": [
         "curl/8.7.1"
       ],
       "X-Envoy-Expected-Rq-Timeout-Ms": [
         "15000"
       ],
       "X-Forwarded-Proto": [
         "http"
       ],
       "X-Request-Id": [
         "7f2340db-c971-4449-b6cf-3bd8dd377f02"
       ]
     }
   }
   

Cleanup

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

kubectl delete EnterpriseKgatewayTrafficPolicy transformation -n httpbin