The following example walks you through how to use extractors to extract request header values by using regular expressions. The captured header values are then added to the response body by using the mergeExtractorsToBody setting. You can use the extractors to also indicate where you want to place the request header values in the body.

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].ip}')
echo $INGRESS_GW_ADDRESS  
  
      export INGRESS_GW_ADDRESS=$(kubectl get svc -n gloo-system gloo-proxy-http -o jsonpath='{.status.loadBalancer.ingress[0].hostname}')
echo $INGRESS_GW_ADDRESS
  
      kubectl port-forward deployment/gloo-proxy-http -n gloo-system 8080:8080

Add header values to the response body

  1. Create a VirtualHostOption resource with your transformation rules. In the following example, you extract the root and nested request headers and add them to the response body by using the mergeExtractorsToBody setting. The dot notation that you use for the extractor names determines the placement of the header in the body. For example, if no dot notation is used, such as in root, the header is added to the body’s root level. If dot notation is used, such as in payload.nested, the extractor is added under the payload.nested field.

      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:
          # Merge the specified extractors to the request body
          mergeExtractorsToBody: {}
          extractors:
            # The name of this attribute determines where the value will be nested in the body. 
            # Because no dots are specified, such as root.nested, the root header value is added to the body's root level. 
            root:
              # Name of the header to extract
              header: 'root'
              # Regex to apply to it. This value is required and is configured to capture the entire header. 
              regex: '.*'
            # The name of this attribute determines where the value will be nested in the body. 
            # Because dot notation is used, the nested header is placed under the placeholder.nested field in the body. 
            payload.nested:
              # Name of the header to extract
              header: 'nested'
              # Regex to apply to it. This value is required and is configured to capture the entire header.
              regex: '.*'
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
EOF

  2. Send a request to the httpbin app and include the root and nested request headers. Verify that you get back a 200 HTTP response code and that the value of the root header is added to the body’s root level, and that the nested header value is added under the payload.nested field in your response.

      curl -X POST -H "host: www.example.com:8080" \
-H "Content-Type: application/json" \
-H "root: root-val" \
-H "nested: nested-val" http://$INGRESS_GW_ADDRESS:8080/post -d @data.json | jq
  
      curl -X POST localhost:8080/post \
-H "host: www.example.com" \
-H "Content-Type: application/json" \
-H "root: root-val" \
-H "nested: nested-val" -d @data.json | jq

    Example output:

       ...
   "json": {
    "payload": {
      "nested": "nested-val"
    },
    "root": "root-val"
   }

Cleanup

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

  kubectl delete virtualhostoption transformation -n gloo-system