In this guide, you learn how to use an if else function to change the HTTP status that is returned in your response. To determine the response status, you use a JSON string that is provided in the request. If the JSON includes an error, you return a 400 HTTP response code. In all other cases, you return the response code of the :status pseudo 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

Change the response status

  1. Create a payload that you later send as your request body.

      cat << EOF > data.json
{
  "error": {
   "message": "This is an error"
  }
}
EOF

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

    • Extract the message field from the data.json file that is sent in the request.
    • If the error message is not empty, return a 400 HTTP response code in the :status pseudo header.
    • In all other cases, do not change the :status pseudo 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:
          extractors: 
            message:
              body: {}
              mode: EXTRACT
              regex: '[\s\S]*(message)[\s\S]*'
              subgroup: 1
          headers:
           # We set the response status via the :status pseudo-header based on the response code
            :status:
              text: '{% if ( message ) != "" %}400{% else %}{{ header(":status") }}{% endif %}'
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:
          parseBodyBehavior: ParseAsJson
          headers:
           # We set the response status via the :status pseudo-header based on the response code
            ":status":
              text: '{% if {{ error }} != "" %}400{% else %}{{ header(":status") }}{% endif %}'
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
EOF

  3. Send a request to the httpbin app and include data.json file as your payload. Because the error.message field is not empty, a 400 HTTP response code is returned.

      curl -X POST -H "host: www.example.com:8080" -w "%{http_code}" \
 -H "Content-Type: application/json" \
 http://$INGRESS_GW_ADDRESS:8080/post -d @data.json | jq
  
      curl -vik localhost:8080/get -w "%{http_code}" \
-H "foo: bar" \
-H "host: www.example.com" \

    Example output:

       {
     "args": {},
     "headers": {
       "Accept": [
         "*/*"
       ],
        "Content-Length": [
         "49"
       ],
       "Content-Type": [
         "application/json"
       ],
       "Host": [
         "www.example.com:8080"
       ],
       "User-Agent": [
         "curl/8.7.1"
       ],
       "X-Envoy-Expected-Rq-Timeout-Ms": [
         "15000"
       ],
       "X-Forwarded-Proto": [
         "http"
       ],
       "X-Request-Id": [
         "e462eb36-0a36-4ffd-b37d-316737819532"
       ]
     },
     "origin": "10.0.2.124:53583",
     "url": "http://www.example.com:8080/post",
     "data": "{  \"error\": {   \"message\": \"This is an error\"  }}",
     "files": null,
    "form": null,
     "json": {
       "error": {
         "message": "This is an error"
       }
     }
   }
   400

  4. Update your payload file and remove the message so that the error field is empty.

      cat << EOF > data.json
{
  "error": {
  }
}
EOF

  5. Send another request to the httpbin app. Verify that this time a 200 HTTP response code is returned.

      curl -X POST -H "host: www.example.com:8080" -w "%{http_code}" \
 -H "Content-Type: application/json" \
 http://$INGRESS_GW_ADDRESS:8080/post -d @data.json | jq
  
      curl -vik localhost:8080/get -w "%{http_code}" \
-H "foo: bar" \
-H "host: www.example.com" \

    Example output:

       {
     "args": {},
     "headers": {
       "Accept": [
         "*/*"
       ],
        "Content-Length": [
         "49"
       ],
       "Content-Type": [
         "application/json"
       ],
       "Host": [
         "www.example.com:8080"
       ],
       "User-Agent": [
         "curl/8.7.1"
       ],
       "X-Envoy-Expected-Rq-Timeout-Ms": [
         "15000"
       ],
       "X-Forwarded-Proto": [
         "http"
       ],
       "X-Request-Id": [
         "e462eb36-0a36-4ffd-b37d-316737819532"
       ]
     },
     "origin": "10.0.2.124:53583",
     "url": "http://www.example.com:8080/post",
     "data": "{  \"error\": {   \"message\": \"This is an error\"  }}",
     "files": null,
    "form": null,
     "json": {
       "error": {
       }
     }
   }
   200

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