kibana/dev_docs/tutorials/versioning_http_apis.mdx

---
id: kibDevTutorialVersioningHTTPAPIs
slug: /kibana-dev-docs/versioning-http-apis
title: Versioning HTTP APIs
description: This tutorial demonstrates how to create or migrate to versionable HTTP APIs.
date: 2023-02-09
tags: ['kibana', 'onboarding', 'dev', 'architecture']
---

All Kibana HTTP API developers and maintainers must ensure that past versions of HTTP APIs remain available.

<DocCallOut title="A note on internal vs public HTTP APIs">
  HTTP APIs may be intended for **internal** or **public** use. Different levels of rigour are appropriate when designing and managing changes for each. However, in both cases we must support some minimal set of past HTTP APIs.

  The exact number of past APIs and the length of time they are kept available will vary per use case. Generally, the length of time will be shorter for internal HTTP APIs than for public HTTP APIs.
</DocCallOut>

Versioned HTTP APIs should hold to the following set of properties. **Note:** how you meet these is properties is up to you. Use the examples provided as a guide.

### 1. Do not directly expose persistence schemas on your HTTP API endpoints

Consider this example of directly exposing a persisted schema over HTTP:

```ts
interface MyObject {
  foo: string;
  bar: number;
}
router.get(
  {
    path: '/api/myobject/{id}',
    validate: { params: schema.object({ id: schema.string() }) },
  },
  (ctx, req, res) => {
    const { savedObjects } = await ctx.core;
    const myObject = await savedObjects.client.get<MyObjectAttributes>('myObject', req.params.id);
    return res.ok({
      body: { ...myObject.attributes }, // <- Directly exposing SO attributes
    });
  }
);
```

#### Why is this problemetic for versioning?

Whenever we perform a data migration the body of this endpoint will change for all clients. This prevents us from being able to maintain past interfaces and gracefully introduce new ones.

#### There are several examples of persistence schemas:

* The shape of attributes in your Saved Object(s)
* The shape of the document source in an Elasticsearch index you manage, for example, a report
* The shape of the data whose storage you delegate to some other code
  * One example is the metadata stored on a `file` object exposed by the `src/plugins/files` plugin

Therefore a persistence schema is the _shape_ of any data your code directly, or indirectly _persists_. Think carefully about any persisted schemas your code might be using and ensure that none of them are exposed directly over your HTTP APIs.

Let's make the minimal changes to prepare the endpoint above for versioning:

```ts
interface MyObject {
  foo: string;
  bar: number;
}
// 1.
// We add a new interface for this HTTP APIs return value
// Note: this interface can live in your plugins top-level "common" directory
interface GetMyObjectResponse {
  foo: string;
  bar: number;
}
router.get(
  {
    path: '/api/myobject/{id}',
    validate: { params: schema.object({ id: schema.string() }) },
  },
  (ctx, req, res) => {
    const { savedObjects } = await ctx.core;
    const {
      attributes: { foo, bar },
    } = await savedObjects.client.get<MyObjectAttributes>('myObject', req.params.id);
    // 2.
    // Explicitly map to our HTTP body
    const body: GetMyObjectResponse = { foo, bar };
    return res.ok({ body });
  }
);
```

The changes are:

1. We created a **new interface** to represent our HTTP API contract. **Note:** Even though we duplicated some of our `MyObjectAttributes` in `GetMyObjectResponse`, it removed the risk that a data migration will break our current HTTP contract without TypeScript noticing.
2. We replaced object spread with **cherry-picking values** from our persistence schema. We now have a **translation layer** between our persistence schema and HTTP API interface.


These changes might seem subtle, but they are the difference between a versionable and unversionable HTTP API.

_See "[Versioning interfaces](/kibana-dev-docs/versioning-interfaces)" for a more detailed strategy for managing multiple versions of TypeScript interfaces._

### 2. Strict input validation

Consider this example of an HTTP API that accepts unexpected values as input:

```ts
interface MyObjectAttributes {
  /** A user provided name */
  name: string;
  /** A number representing a length of time in milliseconds */
  duration: number;
}
router.post(
  {
    path: '/api/myobject',
    validate: { body: schema.object({ name: schema.string(), duration: schema.number() }) },
  },
  (ctx, req, res) => {
    const { savedObjects } = await ctx.core;
    const { id } = await savedObjects.client.create<MyObjectAttributes>('myObject', req.params.body);
    return res.ok({ body: id });
  }
);
```
#### Why is this problemetic for versioning?

This HTTP API currently accepts all numbers and strings as input which allows for unexpected inputs like negative numbers or non-URL friendly characters. This may break future migrations or integrations that assume your data will always be within certain parameters.

```ts
  {
    path: '/api/myobject',
    validate: {
      body: schema.object({
        name: schema.string({
          minLength: 3,
          maxLength: 100,
          validate: (name) => name.match(/^[a-z0-9]+$/),
        }),
        duration: schema.number({ min: 0 }),
      })
    },
  }
```

Adding this validation we negate the risk of unexpected values. It is not necessary to use `@kbn/config-schema`, as long as your validation mechanism provides finer grained controls than "number" or "string".

In summary: think about the acceptable paramaters for every input your HTTP API expects.

### 3. Keep interfaces as "narrow" as possible

```ts
const nameSchema = schema.string({ minLength: 1, });

router.get(
  {
    path: '/api/myobject/find',
    validate: { query: schema.object({ name: nameSchema, sort: schema.string() }) },
  },
  (ctx, req, res) => {
    const { savedObjects } = await ctx.core;
    const result = await savedObjects.client.find<MyObjectAttributes>({
      type: 'myObject',
      filter: `myObject.attributes.name: ${req.query.name}`,
      sortField: req.query.sort,
    });
    return res.ok({
      // Note: we observe the same translation for all our responses as in step 1.
      body: result.saved_objects.map(({ attributes: { foo, bar } }) => ({ foo, bar })),
    });
  }
);
```

The above code follows guidelines from steps 1 and 2, but it allows clients to specify ANY string by which to sort. This is a far "wider" API than we need for this endpoint.

#### Why is this problemetic for versioning?

Without telemetry it is impossible to know what values clients might be passing through &mdash; and what type of sort behaviour they are expecting.

Additionally, the `sortField` is leaking information about our persistence schema. As with step 1, we want to remove direct knowledge of persistence schema from clients. Consider the following changes:

```ts
import { escapeKuery } from '@kbn/es-query';
const nameSchema = schema.string({ minLength: 1, });
// 1.
// A stricter schema for the sort by field. Now it is a small, known set of values
const sortSchema = schema.oneOf([schema.literal('foo'), schema.literal('bar')]);

router.get(
  {
    path: '/api/myobject/find',
    validate: { query: schema.object({ name: nameSchema, sort: sortSchema }) },
  },
  (ctx, req, res) => {
    const { savedObjects } = await ctx.core;
    const result = await savedObjects.client.find<MyObjectAttributes>({
      type: 'myObject',
      // 2.
      // Bonus point: defend against injection attacks
      filter: `myObject.attributes.name: ${escapeKuery(req.query.name)}`,
      sortField: req.query.sort,
    });
    return res.ok({
      // Note: we observe the same translation for all our responses as in step 1.
      body: result.saved_objects.map(({ attributes: { foo, bar } }) => ({ foo, bar })),
    });
  }
);
```

The changes are:

1. New input validation accepts a known set of values. This makes our HTTP API far _narrower_ and specific to our use case. It does not matter that our `sortSchema` has the same values as our persistence schema, what matters is that we created a **translation layer** between our HTTP API and our internal schema. This faclitates easily versioning this endpoint.
2. **Bonus point**: we use the `escapeKuery` utility to defend against KQL injection attacks.

### 4. Use the versioned API spec

_Under construction, check back here soon!_