Extract query parameters

Documentation

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

Follow the Get started guide to install K8sGateway, set up a gateway resource, and deploy the httpbin sample app.

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

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

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:

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...
{
 "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

Decode base64 headers Update request paths and methods