Update response body

Learn how to return a customized response body and how replace specific values in the body.

In this guide, you use the following methods to transform a JSON body:

Directly access fields in the JSON body and inject them into a custom JSON body.
Use extractors to capture values in a JSON body and use the SINGLE_REPLACE extractor mode to replace them with a specific text.
Use the replace_with_random Inja function to replace specific patterns in the JSON body.

This guide uses a subset of the supported transformation template attributes. To review all the attributes that you can set, see Templating language.

Before you begin

Follow the Get started guide to install Gloo Gateway, 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

Update response body

Send a request to the json endpoint of the httpbin app. The request returns a JSON body that you later transform.

curl -vik http://$INGRESS_GW_ADDRESS:8080/json \
 -H "host: www.example.com:8080"

curl -vik localhost:8080/json \
-H "host: www.example.com" \

Example output:

{
  "slideshow": {
    "author": "Yours Truly",
    "date": "date of publication",
   "slides": [
      {
        "title": "Wake up to WonderWidgets!",
        "type": "all"
      },
      {
        "items": [
          "Why <em>WonderWidgets</em> are great",
          "Who <em>buys</em> WonderWidgets"
        ],
        "title": "Overview",
        "type": "all"
      }
    ],
    "title": "Sample Slide Show"
  }
}

Create a RouteOption or VirtualHostOption resource that transforms the JSON body as follows:

A new body is created in the response with the values of the author, title, and slides fields.

To extract the values, you use dot notation. Because the response is parsed as a JSON file, no extractors need to be defined. Instead, you can access the fields directly.

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:
          parseBodyBehavior: ParseAsJson
          advancedTemplates: false
          body: 
            text: '{"author": "{{ slideshow.author }}", "title": "{{ slideshow.title }}", "slides": "{{ slideshow.slides }}}'
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
          advancedTemplates: false
          body: 
            text: '{"author": "{{ slideshow.author }}", "title": "{{ slideshow.title }}", "slides": "{{ slideshow.slides}}}'
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
EOF

Send another request to the json endpoint of the httpbin app. Verify that you see the transformed response body.

curl -vik http://$INGRESS_GW_ADDRESS:8080/json \
 -H "host: www.example.com:8080"

curl -vik localhost:8080/json \
-H "host: www.example.com" \

Example output:

{"author": "Yours Truly", "title": "Sample Slide Show", "slides": 
"[{"title":"Wake up to WonderWidgets!","type":"all"},{"items":
["Why <em>WonderWidgets</em> are great","Who <em>buys</em> WonderWidgets"],
"title":"Overview","type":"all"}]}

Update the RouteOption or VirtualHostOption resource to replace the word author with the word editor. The rest of the original response body is kept.

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:
            replaceAuthor:
              body: {}
              mode: SINGLE_REPLACE
              replacementText: 'editor'
              regex: '[\s\S]*(author)[\s\S]*'
              subgroup: 1
          body: 
            text: '{{ replaceAuthor }}'
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:
          extractors:
            replaceAuthor:
              body: {}
              mode: SINGLE_REPLACE
              replacementText: 'editor'
              regex: '[\s\S]*(author)[\s\S]*'
              subgroup: 1
          body: 
            text: '{{ replaceAuthor }}'
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
EOF

Send another request to the httpbin app. Verify that the author field is replaced with editor and that the rest of the response body is not changed.

curl -vik http://$INGRESS_GW_ADDRESS:8080/json \ class=s2>"host: www.example.com:8080"

curl -vik localhost:8080/json \ class=s2>"host: www.example.com" \

Example output:

{ "slideshow": { "editor": "Yours Truly", "date": "date of publication", "slides": [ { "title": "Wake up to WonderWidgets!", "type": "all" }, { "items": [ "Why <em>WonderWidgets</em> are great", "Who <em>buys</em> WonderWidgets" ], "title": "Overview", "type": "all" } ], "title": "Sample Slide Show" } >

Update the RouteOption or VirtualHostOption resource to replace the all pattern with a random string.

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:
          body:
            text: '{{ replace_with_random(body(), "all") }}'
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:
          extractors:
            replaceAuthor:
              body: {}
              mode: SINGLE_REPLACE
              replacementText: 'editor'
              regex: '[\s\S]*(author)[\s\S]*'
              subgroup: 1
          body:
            text: '{{ replace_with_random(body(), "all") }}'
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
EOF

Send another request to the httpbin app. Verify that every all value is replaced with a random string.

curl -vik http://$INGRESS_GW_ADDRESS:8080/json \
 -H "host: www.example.com:8080"

curl -vik localhost:8080/json \
-H "host: www.example.com" \

Example output:

{
  "slideshow": {
    "editor": "Yours Truly",
    "date": "date of publication",
    "slides": [
      {
        "title": "Wake up to WonderWidgets!",
        "type": "GGza0iF/51CsVwxovaiL1g"
      },
      {
        "items": [
          "Why <em>WonderWidgets</em> are great",
          "Who <em>buys</em> WonderWidgets"
        ],
        "title": "Overview",
        "type": "GGza0iF/51CsVwxovaiL1g"
      }
    ],
    "title": "Sample Slide Show"
  }
}

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

Change response status Enrich access logs