#ContextData - Sharing Request Data

It is often useful to store data throughout the life of a single request. This data could be used on multiple policies, handlers, or for logging. However, because the Zuplo runtime is asynchronous, you cannot simply create global variables and reference them in other modules if the value is unique accross requests. Additionally, using a traditional data structure like a Map is also not recommended as it can build up memory over time.

#ContextData

The ContextData utility allows safely storing data that is tied to a specific request. Additionally, this utility ensures that data stored is properly garbage collected (removed from memory) when the request is complete.

ContextData.set

ContextData.set(context, "my-data", { prop1: "hello world" });

ContextData.get

const data = ContextData.get(context, "my-data");

set (instance function)

const myData = new ContextData("my-data");
myData.set(context, { prop1: "hello world" });

get (instance function)

const myData = new ContextData("my-data");
const data = myData.get(context);

#Typing

The methods of ContextData support generics in order to support typing.

const myData = new ContextData<{ key: string }>("my-data");
ContextData.get<{ key: string }>(context, "my-data");
ContextData.set<{ key: string }>(context, "my-data", { key: "hello" });

#How NOT to Share Data

Below are a few examples of how NOT to share data in your API.

The first example uses a simple shared global variable called currentRequestId to store the current requestId. On the surface this looks straightforward. However, because the gateway is being shared among many requests who are all running at the same time, the value of currentRequestId is completely unpredictable when your API is under load.

let currentRequestId: string | undefined;

export function myFirstPolicy(request: ZuploRequest, context: ZuploContext) {
  currentRequestId = context.requestId;
  context.log.info(`The current requestId is: ${currentRequestId}`);
}

export function mySecondPolicy(request: ZuploRequest, context: ZuploContext) {
  currentRequestId = context.requestId;
  context.log.info(`The current requestId is: ${currentRequestId}`);
}

#Using ContextData

Below you will find examples of how to use ContextData to safely share data throughout the lifecycle of a request.

#Using static methods

import { ContextData, ZuploContext, ZuploRequest } from "@zuplo/runtime";

export function myFirstPolicy(request: ZuploRequest, context: ZuploContext) {
  ContextData.set(context, "currentRequestId", context.requestId);

  const currentRequestId = ContextData.get(context, "currentRequestId");
  context.log.info(`The current requestId is: ${currentRequestId}`);
}

#Using Shared Variable

Reusable class shared across modules The shared module allows other modules to access the same storage without passing the string name or type around.

export const myData = new ContextData<{ prop1: string }>("my-data");

Then use the class in another module.

import { myData } from "./my-module";
const data = myData.get(context);
myData.set(context, data);