Meta AsyncLocalStorage Package

Overview

meta-context-local-storage is a Node.js package that allows you to create asynchronous local storage for managing context that is scoped to the duration of an asynchronous operation. This can be useful for storing request-specific data such as user session, trace IDs, or other metadata across async calls, without manually passing it around.

Key Features

• Create isolated storage that persists across asynchronous execution based on ContextNameSapace.
• Maintain and retrieve data across async call chains.
• Use cases include logging, tracing, request-scoped data, and session management.

Installation

To install the package, run:

```bash npm install @meta-commons/meta-context-local-storage ```

Basic Usage

Here's a quick example to get started:

```javascript import { StorageContext } from '@meta-commons/meta-context-local-storage';

function someAsyncFunction() { return StorageContext.run(anotherAsyncFunction=> { StorageContext.setContextValue('requestId', '12345'); }); }

function anotherAsyncFunction() { setTimeout(() => { const requestId = StorageContext.getContextValue('requestId'); console.log('Request ID:', requestId ? requestId : 'No store'); }, 100); }

someAsyncFunction(); // Output: Request ID: 12345 ```

API Reference

StorageContext

It is a singleton instance wich manages the async storage context

StorageContext.run(nextFunction)

Runs the given nextFunction function within the context of the provided store. The store is typically a Map or any other data structure that holds context data.

• store: Any object to be used as the storage for the async context.
• nextFunction: Function to be executed within the context.

Example:

```javascript StorageContext.run(async()=>{ // Your code here }) ```

StorageContext.setContextValue(key: string, value: unknown, namespace: ClsContextNamespace)

Set the provided value for the ongoing asynchronous operation.

It expect a key and a value wich will be alocated in the ClsContextNamespace, if the name space is not provided the ClsContextNamespace.DEFAULT will be used, you can provide your own namespace justing passing a string value or use one of the pre-loaded availabel contexts found in ClsContextNamespace.

Example:

```javascript // 'myCustomNameSpace' is optional StorageContext.setContextValue('requestId', '123456', 'myCustomNameSapce') ```

StorageContext.getContextValue(key: string, nameSpace: ClsContextNamespace)

Retrieves the current value for the ongoing asynchronous operation. Returns undefined if called outside of an active store context.

It expect a key and a ClsContextNamespace, if the name space is not provided the ClsContextNamespace.DEFAULT will be used, you can provide your own namespace justing passing a string value or use one of the pre-loaded availabel contexts found in ClsContextNamespace.

Example:

```javascript const requestId = StorageContext.getContextValue('requestId') console.log(requestId) // it will output '123456' ```

Use Cases

1. Request/Response Tracing

You can use meta-context-local-storage to keep track of request-specific data across multiple asynchronous calls in an application.

```javascript app.use((req, res, next) => { return asyncLocalStorage.run(async () => { StorageContext.setContextValue('traceId', req.headers['x-trace-id'], ClsContextNamespace.LOGGER); next(); }); });

app.get('/', (req, res) => { const traceId = StorageContext.getContextValue('traceId', ClsContextNamespace.LOGGER) res.send(`Trace ID: ${traceId}`); }); ```

Compatibility

meta-context-local-storage works with Node.js v12.17.0 and above. It uses the built-in AsyncLocalStorage class available in the async_hooks module.

Meta

Meta is a Brazilian technology and innovation company with over 34 years of history, specializing in digital transformation solutions. With operations in eight countries, including Brazil, the United States, and Canada, the company employs around 3,000 people and serves more than 300 active clients across various sectors.

MIT License

Copyright (c) 2024 Meta

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.