request-migrations

Rolling versions for your node.js apis

@oncehub/request-migrations is a Node.js middleware library for Express that simplifies API versioning by enabling smooth and controlled migrations of both incoming requests and outgoing responses. It allows you to define migrations for different API endpoints and versions, ensuring backward compatibility for older clients while you evolve your API. Read more about the versioning strategy on Stripe's blog.

┌─────────┐              ┌───────────────────────────────────────────────────────────────────┐
│         │              │ Your API                                                          │
│         │              │ ┌────────────────────────────────────┐             ┌────────────┐ │
│         │              │ │ request-migrations                 │             │ Codebase   │ │
│         │ v1.0 request │ │ ┌────┐   ┌────┐   ┌────┐   ┌────┐  │v1.3 request │            │ │
│ Client  │ ───────────► │ │ │v1.0├──►│v1.1├──►│v1.2├──►│v1.3│◄─┼─────────────┼─  v1.3     │ │
│         │ v1.0 response│ │ │    │   │    │   │    │   │    │  │v1.3 response│            │ │
│         │ ◄────────────┤ │ │    │◄──┤    │◄──┤    │◄──┤    ├──┼─────────────┼►           │ │
│         │              │ │ └────┘   └────┘   └────┘   └────┘  │             │            │ │
│         │              │ │                                    │             │            │ │
│         │              │ └────────────────────────────────────┘             └────────────┘ │
│         │              │                                                                   │
└─────────┘              └───────────────────────────────────────────────────────────────────┘

Key Features:

Request and Response Migrations: Define separate migrations for transforming incoming requests and outgoing responses.
Endpoint-Specific Migrations: Organize migrations by API endpoint (path and HTTP verb), making them easy to manage.
Version-Based Migrations: Apply migrations based on the client's requested API version (specified via a header).
Dynamic Path Matching: Supports migrations for routes with dynamic segments (e.g., /api/users/:id).
Flexible Verb Matching: Define migrations that apply to multiple HTTP verbs using regular expressions.
Sequential Migration Application: Migrations are applied in the correct order based on their version.
Error Handling: Includes error handling to prevent malformed responses in case of migration issues.

Installation

npm install @oncehub/request-migrations

Usage

Define your migrations:

Create a migrations directory in your project. Inside, create .ts files for each migration, following the naming convention:

<migration-description>.migration.ts

Example: split-user-name.migration.ts

Each migration file should export a Migration object:

import { Request } from "express";
import { Migration } from "@oncehub/request-migrations";

const migration: Migration = {
  path: "/api/users",
  verbs: "POST",
  version: "2023-06-15",
  description: "Separate user name to first and last name",
  migrateRequest: async (req: Request) => {
    if (req.body.name && !req.body.firstName && !req.body.lastName) {
      const [firstName, lastName] = req.body.name.split(" ", 2);
      req.body.firstName = firstName;
      req.body.lastName = lastName || "";
      delete req.body.name;
    }
    return req;
  },
  migrateResponse: async (req: Request, body: any) => {
    if (body.user && body.user.firstName && body.user.lastName) {
      body.user.name = `${body.user.firstName} ${body.user.lastName}`;
      delete body.user.firstName;
      delete body.user.lastName;
    }
    return body;
  },
};

export default migration;

Integrate the middleware into your Express app:

import express from "express";
import { requestMigrationMiddleware } from "@oncehub/request-migrations";
import path from "path";

const app = express();
app.use(express.json());

const migrationsDir = path.join(__dirname, "migrations");

app.use(requestMigrationMiddleware(migrationsDir));

app.post("/api/users", (req, res) => {
  // ... your route handler
});

// ... other routes

app.listen(3000, () => console.log("Server running on port 3000"));

Example Migration

This migration demonstrates how to transform a name field in a POST /api/users request into separate firstName and lastName fields for an older API version. Initial API (version < 2024-06-15):

{
  "name": "John Doe"
}

Later, you decided to change it to accept separate firstName and lastName fields:

New API (version >= 2024-06-15):

{
  "firstName": "John",
  "lastName": "Doe"
}

Write a migration file:

migrations/split-user-name-to-first-and-last-name.migration.ts:

import { Request } from "express";
import { Migration } from "@oncehub/request-migrations";

const migration: Migration = {
  path: "/api/users",
  verbs: "POST",
  version: "2024-06-15",
  description: "Separate user name to first and last name",
  migrateRequest: async (req: Request) => {
    if (req.body.name && !req.body.firstName && !req.body.lastName) {
      const [firstName, lastName] = req.body.name.split(" ", 2);
      req.body.firstName = firstName;
      req.body.lastName = lastName || "";
      delete req.body.name;
    }
    return req;
  },
  migrateResponse: async (req: Request, body: any) => {
    if (body.user && body.user.firstName && body.user.lastName) {
      body.user.name = `${body.user.firstName} ${body.user.lastName}`;
      delete body.user.firstName;
      delete body.user.lastName;
    }
    return body;
  },
};

export default migration;

API Reference

`requestMigrationMiddleware(migrationsDir, versionHeaderName, compareVersions)`

migrationsDir: (string) The directory containing your migration files.
versionHeaderName: (string, optional) The name of the HTTP header used to specify the API version. Defaults to "x-api-version".
compareVersions: ((v1: string, v2: string) => number, optional) A custom function for comparing version strings. Defaults to lexical comparison.

`Migration` Interface

path: (string) The API path this migration applies to (supports dynamic segments using path-to-regexp syntax, e.g., /api/users/:id).
verbs: (string) A regular expression specifying the HTTP verbs this migration applies to (e.g., "(GET|POST)").
description: (string) A brief description of the migration.
version: (string) The API version this migration is associated with.
migrateRequest: ((req: Request) => Promise<Request>) An async function that migrates the request object.
migrateResponse: ((req: Request, body: any) => Promise<any>) An async function that migrates the response body. It receives the potentially modified req object as its first argument.

Debug Logs

To see debug logs from the middleware, set the NODE_DEBUG environment variable:

NODE_DEBUG=request-migrations node your-app.js

This will print detailed information about which migrations are being loaded and applied.

Acknowledgements

This library was inspired by the following blog posts and other equivalent libraries in other languages:

License

This module is licensed under the MIT License. See the LICENSE file for details.

scheduleonce/request-migrations