Use extractors for headers

Use Gloo Gateway 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 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 extractors for headers

1. Create a RouteOption or VirtualHostOption resource that defines 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: 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: 
               parseBodyBehavior: "DontParse"
               extractors:
                 account_id:
                   header: account
                   regex: '(\w+)'
                   subgroup: 1
               headers:
                 x-account-solo:
                   text: "account: {{ account_id }}-solo"
     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:
               parseBodyBehavior: "DontParse"
               extractors:
                 account_id:
                   header: account
                   regex: '(\w+)'
                   subgroup: 1
               headers:
                 x-account-solo:
                   text: "account: {{ account_id }}-solo"
       targetRefs:
       - group: gateway.networking.k8s.io
         kind: Gateway
         name: http
         namespace: gloo-system
     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 virtualhostoption transformation -n gloo-system
kubectl delete routeoption transformation -n httpbin