Extensions & Hooks

#Runtime Extensions

While most configuration in your Zuplo gateway is set on a per-route or per-policy basis, there are times when behaviors need to be modified globally. To plug into the global initialization of your gateway, create a file called zuplo.runtime.ts in the modules folder with the following code.

Any error thrown in the runtimeInit method will prevent the gateway from starting and yield a 500 error for all requests. Be sure to add only reliable code here and use try/catch as appropriate to handle any recoverable exceptions.

import { RuntimeExtensions } from "@zuplo/runtime";

export function runtimeInit(runtime: RuntimeExtensions) {
  // Extensions go here
}

The name of the export must be runtimeInit and must conform to the above function signature.

The following configurations are available.

#Custom Problem (Error) Response Formatter

Zuplo includes built-in error handling that returns errors in the format of the Problem Details for HTTP APIs proposed standard. This means that HTTP errors (or other exceptions) will return responses that look like the following.

{
  "type": "https://httpproblems.com/http-status/404",
  "title": "Not Found",
  "status": 404,
  "detail": "Not Found",
  "instance": "/not-a-path",
  "trace": {
    "timestamp": "2023-03-14T15:49:38.581Z",
    "requestId": "05968b6d-6f82-4ae3-8e13-f92e0d0499c5",
    "buildId": "a9b200a3-734c-413a-a1ae-ce171d53e5a7",
    "rayId": "7a7daaf3bac2f325"
  }
}

json

If you want to customize this format, you can configure the problemResponseFormat function and return a Response in the format of your choice.

import { RuntimeExtensions } from "@zuplo/runtime";

export function runtimeInit(runtime: RuntimeExtensions) {
  runtime.problemResponseFormat = (
    { problem, statusText, additionalHeaders },
    request,
    context,
  ) => {
    // Build the response body
    const body = JSON.stringify(problem, null, 2);

    // Send the response with headers and status
    return new Response(body, {
      status: problem.status,
      statusText,
      headers: {
        ...additionalHeaders,
        "content-type": "application/problem+json",
      },
    });
  };
}

#Hooks

Hooks allow code to be run as part of the request/response pipeline. Hooks can be created at the API level in zuplo.runtime.ts as shown below or can be added via a plugin.

All hooks can be either synchronous or asynchronous. To make your hook asynchronous simply add the async keyword on the function.

The following hooks can be set globally in the zuplo.runtime.ts:

#Hook: OnRequest

Runs when a request is received, before any plugins or handlers.

import { RuntimeExtensions } from "@zuplo/runtime";

export function runtimeInit(runtime: RuntimeExtensions) {
  runtime.addRequestHook((request, context) => {
    // Code here

    // Can return a request or a response. If a response is returned the
    // pipeline stops and the response is returned.
    return request;
  });
}

#Hooks: OnResponseSending

Runs before a response is sent. Response can be modified. More details.

import { RuntimeExtensions } from "@zuplo/runtime";

export function runtimeInit(runtime: RuntimeExtensions) {
  runtime.addResponseSendingHook((response, request, context) => {
    // Code here
    return response;
  });
}

#Hooks: OnResponseSendingFinal

Runs before a response is sent. The response cannot be modified. More details.

import { RuntimeExtensions } from "@zuplo/runtime";

export function runtimeInit(runtime: RuntimeExtensions) {
  runtime.addResponseSendingFinalHook((response, request, context) => {
    // Code here
  });
}

#Plugin and Handler Extensions

Built-in and custom plugins and handlers can expose their own extensibility. For example, AWS Lambda handler exposes the ability to customize the event that is sent when invoking the Lambda function.

The example below shows how to use a route's custom property to set the path on the outgoing event to a custom value.

import {
  AwsLambdaHandlerExtensions,
  RuntimeExtensions,
  ContextData,
} from "@zuplo/runtime";

export function runtimeInit(runtime: RuntimeExtensions) {
  AwsLambdaHandlerExtensions.addSendingAwsLambdaEventHook(
    async (request, context, event: AwsLambdaEventV1) => {
      const lambdaPath = ContextData.get(context, "lambdaPath");
      event.path = lambdaPath ?? event.path;
      return event;
    },
  );
}

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