Extract query parameters

Extract query parameters, transform them, and add them to the response body.

The following example walks you through how to use an Inja template to find specific query parameters in a request, extract the parameter values, and to add these values to specific response headers.

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

Extract query parameters

1. Create a RouteOption or VirtualHostOption resource with your transformation rules. In the following example, you use a regular expression to find the foo and bar query parameters in the request path and to capture their values in the foo and bar extractors. Then, the extractor values are added to the response headers foo-response and bar-response.

   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:
             extractors:
               # This extracts the 'foo' query param to an extractor named 'foo'
               foo:
                 # The :path pseudo-header contains the URI
                 header: ':path'
                 # Use a nested capturing group to extract the query param
                 regex: '(.*foo=([^&]*).*)'
                 subgroup: 2
               # This extracts the 'bar' query param to an extractor named 'bar'
               bar:
                 # The :path pseudo-header contains the URI
                 header: ':path'
                 # Use a nested capturing group to extract the query param
                 regex: '(.*bar=([^&]*).*)'
                 subgroup: 2
             # Add two new headers with the values of the 'foo' and 'bar' extractions
             headers:
               foo-response:
                 text: '{{ foo }}'
               bar-response:
                 text: '{{ bar }}'
   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:
             extractors:
               # This extracts the 'foo' query param to an extractor named 'foo'
               foo:
                 # The :path pseudo-header contains the URI
                 header: ':path'
                 # Use a nested capturing group to extract the query param
                 regex: '(.*foo=([^&]*).*)'
                 subgroup: 2
               # This extracts the 'bar' query param to an extractor named 'bar'
               bar:
                 # The :path pseudo-header contains the URI
                 header: ':path'
                 # Use a nested capturing group to extract the query param
                 regex: '(.*bar=([^&]*).*)'
                 subgroup: 2
             # Add two new headers with the values of the 'foo' and 'bar' extractions
             headers:
               foo-response:
                 text: '{{ foo }}'
               bar-response:
                 text: '{{ bar }}'
     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 foo and bar query parameters. Verify that you get back a 200 HTTP response code and that the value of the foo and bar query parameters were added to the response headers foo-response and bar-response.

   curl -vik http://$INGRESS_GW_ADDRESS:8080/anything?foo=foo-value&bar=bar-value \
    -H "host: www.example.com:8080" 

   curl -vik localhost:8080/anything?foo=foo-value&bar=bar-value \
   -H "host: www.example.com" \

   Example output:

   ...
   {
    "args": {
      "bar": [
        "bar-value"
      ],
      "foo": [
        "foo-value"
      ]
    },
    "headers": {
      "Accept": [
        "*/*"
      ],
      "Bar-Response": [
        "bar-value"
      ],
      "Foo-Response": [
        "foo-value"
      ],
      "Host": [
        "www.example.com:8080"
      ],
      "User-Agent": [
        "curl/7.77.0"
      ],
      "X-B3-Sampled": [
        "0"
      ],
      "X-B3-Spanid": [
        "5003b7987ed56d7f"
      ],
      "X-B3-Traceid": [
        "eac0a28ecb32b9e15003b7987ed56d7f"
      ],
      "X-Forwarded-Proto": [
        "http"
      ],
      "X-Request-Id": [
        "b43982a7-cdb5-4bab-9ce5-cba0cf4c2ae5"
      ]
    },
    "origin": "127.0.0.6:41223",
    "url": "http://www.example.com:8080/anything?foo=foo-value&bar=bar-value",
    "data": "",
    "files": null,
    "form": null,
    "json": null
   }

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