Extract query parameters

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 link

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 link

1. Create a 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. Then, these values are added to the response headers foo-response and bar-response.

     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 link

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

  kubectl delete virtualhostoption transformation -n gloo-system