transform-json

JSON field transform

Last modified: 2026-04-27

Demonstrates the json transform. The upstream is a static action that returns a canned post document, so the example runs offline. The transform reshapes the JSON before returning it to the client by renaming userId to author_id, removing the body field, and setting a new source field marking the response as proxied. The origin matches the json.local Host header on 127.0.0.1:8080.

Run

sbproxy serve -f sb.yml

Try it

# Upstream body (what the static action emits internally):
# {"userId":1,"id":1,"title":"first post","body":"this body field is removed by the transform"}

# Client response after the json transform:
$ curl -s -H 'Host: json.local' http://127.0.0.1:8080/posts/1
{"id":1,"title":"first post","author_id":1,"source":"sbproxy"}

# Headers reflect the JSON content type and the transform output
$ curl -sI -H 'Host: json.local' http://127.0.0.1:8080/posts/1
HTTP/1.1 200 OK
content-type: application/json

# Pretty-print to see the field rewrites applied:
$ curl -s -H 'Host: json.local' http://127.0.0.1:8080/posts/1 | jq
{
  "id": 1,
  "title": "first post",
  "author_id": 1,
  "source": "sbproxy"
}

What this exercises

• json transform with rename, remove, and set operations on the response body
• static action with json_body - the upstream is inline so no external service is needed
• Header / body content negotiation: the transform preserves application/json

See also

• docs/features.md - full feature reference
• docs/configuration.md - configuration schema