path: root/docs/externalapi/External-Api.md

# External API v2 (Draft)

The **News app** offers a RESTful API which can be used to sync folders, feeds and items. The API also supports [CORS](https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS) which means that you can access the API from your browser using JavaScript.

In addition, an updater API is exposed which enables API users to run feed updates in parallel using a REST API or ownCloud console API.

## Conventions
This document uses the following conventions:

* Object aliases as comments
* Error objects are omitted

### Object Aliases As Comments

In order to only specify the JSON objects once, comments are used to alias them.

There are two types of aliases:
* Objects
* Object arrays

**Objects**:
```js
{
    "folder": { /* folder object */ },
}
```

means that the folder attributes will be listed inside the **folder** object

**Object arrays**:
```js
{
    "folders": [ /* array of folder objects */ ],
}
```

means that folder objects will be listed inside the **folders** array.

### Error Objects Are Omitted

This means that the error object will not be explicitly shown in the examples. All HTTP 400 response status codes contain an error object:

```json
{
    "error": {
        "code": 1,
        "message": "error message"
    }
}
```

## API Stability Contract

The API level will **change** if the following occurs:

* a required HTTP request header is added
* a required request parameter is added
* a field of a response object is removed
* a field of a response object is changed to a different datatype
* an HTTP response header is removed
* an HTTP response header is changed to a different datatype
* the meaning of an API call changes (e.g. /sync will not sync any more but show a sync timestamp)

The API level will **not change** if:

* a new HTTP response header is added
* an optional new HTTP request header is added
* a new response parameter is added (e.g. each item gets a new field "something": 1)
* The order of the JSON attributes is changed on any level (e.g. "id":3 is not the first field anymore, but the last)

You have to design your app with these things in mind!:

* **Don't depend on the order** of object attributes. In JSON it does not matter where the object attribute is since you access the value by name, not by index
* **Don't limit your app to the currently available attributes**. New ones might be added. If you don't handle them, ignore them
* **Use a library to compare versions**, ideally one that uses semantic versioning

## Request Format
The base URL for all calls is:

    https://yourowncloud.com/index.php/apps/news/api/v2

Unless an absolute Url is specified, the relative Urls in the Specification are appended to this url. To access the route **/sync** for instance you'd use the following url:

    https://yourowncloud.com/index.php/apps/news/api/v2/sync

The required request headers are:
* **Accept**: application/json

Any request method except GET:
* **Content-Type**: application/json; charset=utf-8

Any route that allows caching:
* **If-None-Match**: an Etag, e.g. 6d82cbb050ddc7fa9cbb659014546e59. If no previous Etag is known, this header should be omitted

The request body is either passed in the URL in case of a **GET** request (e.g.: **?foo=bar&index=0**) or as JSON, e.g.:

```json
{
    "foo": "bar",
    "index": 0
}
```

**Note**: The current Etag implementation contains a unix timestamp in milliseconds. This is an implementation detail and you should not rely on it.

### API Level Detection
Check the [API level route](#api-level)

### Authentication
Because REST is stateless you have to re-send user and password each time you access the API. Therefore running ownCloud **with SSL is highly recommended** otherwise **everyone in your network can log your credentials**.

Credentials are passed as an HTTP header using [HTTP basic auth](https://en.wikipedia.org/wiki/Basic_access_authentication#Client_side):

    Authorization: Basic $CREDENTIALS

where $CREDENTIALS is:

    base64(USER:PASSWORD)

This authentication/authorization method will be the recommended default until core provides an easy way to do OAuth

**Note**: Even if login cookies are sent back to your client, they will not be considered for authentication.

## Response Format
The status codes are not always provided by the News app itself, but might also be returned because of ownCloud internal errors.

The following status codes can always be returned by ownCloud:
* **401**: The provided credentials to log into ownCloud are invalid.
* **403**: The user is not allowed to access the route. This can happen if for instance of only users in the admin group can access the route and the user is not in it.
* **404**: The route can not be found or the resource does not exist. Can also happen if for instance you are trying to delete a folder which does not exist.
* **5xx**: An internal server error occurred. This can happen if the server is in maintenance mode or because of other reasons.

The following status codes are returned by News:
* **200**: Everything went fine
* **304**: In case the resource was not modified, contains no response body. This means that you can ignore the request since everything is up to date.
* **400**: There was an app related error, check the **error** object if specified
* **409**: Conflict error which means that the resource exists already. Can be returned when updating (**PATCH**) or creating (**POST**) a resource, e.g. a folder

The response headers are:
* **Content-Type**: application/json; charset=utf-8
* **Etag**: A string containing a cache header of maximum length 64, e.g. 6d82cbb050ddc7fa9cbb659014546e59. The etag value will be assembled using the number of feeds, folders and the highest last modified timestamp in milliseconds, e.g. 2-3-123131923912392391239. However consider that a detail and dont rely on it.

The response body is a JSON structure that looks like this, which contains the actual data on the first level. The key is the resource in singular if it's a single resource or plural if its a collection. In case of HTTP 400, an error object is also present to help distinguishing between different error types:

```json
{
    "error": {
        "code": 1,
        "message": "error message"
    }
}
```

* **error**: Only present when an HTTP 400 is returned to help distinguishing between error causes
  * **code**: A unique error code
  * **message**: A translated error message. The user's configured locale is used.

In case of an **4xx** or **5xx** error the request was not successful and has to be retried. For instance marking items as read locally and syncing should send the same request again the next time the user syncs in case an error occurred.

## Security Guidelines
Read the following notes carefully to prevent being subject to security exploits:
* You should always enforce SSL certificate verification and never offer a way to turn it off. Certificate verification is important to prevent MITM attacks which is especially important in the mobile world where users are almost always connected to untrusted networks. In case a user runs a self-signed certificate on his server ask him to either install his certificate on his device or direct him to one of the many ways to sign his certificate for free (most notably letsencrypt.com)
* All string fields in a JSON response **expect an item's body** are **not sanitized**. This means that if you do not escape it properly before rendering you will be vulnerable to [XSS](https://www.owasp.org/index.php/Cross-site_Scripting_%28XSS%29) attacks
* Basic Auth headers can easily be decrypted by anyone since base64 is an encoding, not an encryption. Therefore only send them if you are accessing an HTTPS website or display an easy to understand warning if the user chooses HTTP
* When creating a feed you can choose to add basic auth authentication credentials. These must be stored in clear text so anyone with access to your database (however they might have achieved it, think of Sql injection) can read them and use them to access the website. You should warn th