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Custom Code Outbound Policy

Add your own custom outbound policy coded in TypeScript. See below for more details on how to build your own policy.

Configuration

The configuration shows how to configure the policy in the 'policies.json' document.

Code(json)
 
{
  "name": "my-custom-code-outbound-policy",
  "policyType": "custom-code-outbound",
  "handler": {
    "_name": "basic",
    "export": "default",
    "module": "$import(./modules/YOUR_MODULE)",
    "options": {
      "config1": "YOUR_VALUE",
      "config2": true
    }
  }
}

Policy Configuration

• name <string> - The name of your policy instance. This is used as a reference in your routes.
• policyType <string> - The identifier of the policy. This is used by the Zuplo UI. Value should be custom-code-outbound.
• handler.export <string> - The name of the exported type. Value should be YOUR_EXPORT.
• handler.module <string> - The module containing the policy. Value should be $import(./modules/YOUR_MODULE).
• handler.options <object> - The options for this policy. See Policy Options below.

Policy Options

The options for this policy are specified below. All properties are optional unless specifically marked as required.

Using the Policy

Writing A Policy

Custom policies can be written to extend the functionality of your gateway. This document is about outbound policies that can intercept the request and, if required, modify it before passing down the chain.

The outbound custom policy is similar to the inbound custom policy but also accepts a Response parameter. The outbound policy must return a valid Response (or throw an error, which will result in a 500 Internal Server Error for your consumer, not recommended).

Code(ts)
 
export type OutboundPolicyHandler<TOptions = any> = (
  response: Response,
  request: ZuploRequest,
  context: ZuploContext,
  options: TOptions,
  policyName: string,
) => Promise<ZuploRequest | Response>;

A common use case for outbound policies is to change the body of the response. In this example, we'll imagine we are proxying the /todos example api at https://jsonplaceholder.typicode.com/todos.

The format of the /todos response looks like this

Code(json)
 
[
  {
    "userId": 1,
    "id": 1,
    "title": "delectus aut autem",
    "completed": false
  },
  {
    "userId": 1,
    "id": 2,
    "title": "quis ut nam facilis et officia qui",
    "completed": false
  },

We will write an outbound policy that does two things

1. Removes the userId property
2. Adds a new outbound header called color

Here's the code:

Code(ts)
 
// /modules/my-first-policy.ts
export default async function (
  response: Response,
  request: ZuploRequest,
  context: ZuploContext,
  options: any,
  policyName: string,
) {
  if (response.status !== 200) {
    // if we get an unexpected response code, something went wrong, just let the response flow
    return response;
  }

  const data = (await response.json()) as any[]; // we know this is JSON and an array
  data.forEach((item) => {
    delete item.userId;
  });

  // create a new response
  const newResponse = new Response(JSON.stringify(data), {
    status: response.status,
    headers: response.headers,
  });

  // let's add an additional header as an example, for good measure
  newResponse.headers.set("color", "yellow");

  return newResponse;
}

Wiring up the policy on routes

Policies are activated by specifying them on routes in the route.oas.json file. Here's how we could wire up our new route:

Code(json)
 
// /config/policies.json
{
  "policies": [
    {
      "name": "my-first-policy",
      "policyType": "custom-code-outbound",
      "handler": {
        "export": "default",
        "module": "$import(./modules/my-first-policy)"
      }
    }
  ]
}

Code(json)
 
// /config/routes.oas.json
{
  ...
  "paths": {
  "x-zuplo-path": {
    "pathMode": "open-api"
  },
  "get": {
    "summary": "New Route",
    "description": "",
    "x-zuplo-route": {
      "corsPolicy": "none",
      "handler": {
        "export": "urlForwardHandler",
        "module": "$import(@zuplo/runtime)",
        "options": {
          "baseUrl": "https://getting-started.zuplo.io"
        }
      },
      "policies": {
        "inbound": [],
        "outbound": [
          "my-first-policy",
        ]
      }
    },
}

}

Custom Policy Options

In your policy configuration, you can specify additional information to configure your policy on the options property. In the example below we set an example object with some properties of type string and number. Note these objects can be as complicated as you like.

Code(json)
 
{
  "name": "my-first-policy",
  "policyType": "custom-code-outbound",
  "handler": {
    "export": "default",
    "module": "$import(./modules/my-first-policy)",
    "options": {
      "you": "can",
      "specify": "anything",
      "here": 0
    }
  }
}

The value of this property will be passed to your policy's handler as the options parameter. Sometimes it's useful to create a type as shown below.

Code(ts)
 
type MyPolicyOptionsType = {
  you: string;
  specify: string;
  here: number;
};
export default async function (
  response: Response,
  request: ZuploRequest,
  context: ZuploContext,
  options: MyPolicyOptionsType,
  policyName: string,
) {
  // your policy code goes here, and can use the options to perform any
  // configuration
  context.log.info(options.you);
}

You can also use the any type if you prefer not to create a type.

Adding headers

Note if you just need to add headers, it more efficient not read the body stream and reuse it, e.g.

Code(ts)
 
export default async function (
  response: Response,
  request: ZuploRequest,
  context: ZuploContext,
  options: any,
  policyName: string,
) {
  // create a new response
  const newResponse = new Response(response.body, {
    status: response.status,
    headers: response.headers,
  });

  // let's add an additional header as an example, for good measure
  newResponse.headers.set("color", "yellow");

  return newResponse;
}

Read more about how policies work