Rewrite Request Body

See the full example project on Github

This sample demonstrates how to rewrite the body of an incoming JSON request.

1/ Create Route

Create a route that uses the URL Rewrite Handler. The rewrite points to the Zuplo Echo API at

  "/rewrite-body": {
    "post": {
      "x-zuplo-route": {
        "corsPolicy": "none",
        "policies": {
          "inbound": [
        "handler": {
          "module": "$import(@zuplo/runtime)",
          "export": "urlRewriteHandler",
          "options": {
            "rewritePattern": ""

2/ Add Policy

Create a custom policy. This policy just takes body of the incoming request and adds two properties to the object.

  "name": "rewrite-body",
  "policyType": "custom-code-inbound",
  "handler": {
    "export": "default",
    "module": "$import(./modules/rewrite-body)"

Create an empty incoming policy called rewrite-body.ts and add the following code to the function.

// Read the incoming body
const body = await request.json();

// Create a new body with additional properties
const outbound = {
  id: crypto.randomUUID(),
  createdOn: new Date(),

// Return a new request with the modified body
return new Request(request, {
  body: JSON.stringify(outbound),

3/ Call the API

The API can now be called and will return the echoed response. Note, the echo API returns a serialized version of the entire request so you will get back the body, url, headers, etc. In this example, you will see that the body has the original hello property and two new properties id and createdOn

curl -X POST https://API_URL/rewrite-bod
   -H "Content-Type: application/json"
   -H "Authorization: user123"
   -d '{"hello": "world" }'


  "url": "",
  "method": "POST",
  "query": {},
  "body": {
    "hello": "world",
    "id": "d06b3a27-b40e-48f2-934a-1585ab993e8a",
    "createdOn": "2023-06-05T15:46:14.202Z"