Arsse/README.md

# The Advanced RSS Environment

The Arsse is a news aggregator server which implements multiple synchronization protocols, including [version 1.2][NCNv1] of [NextCloud News][NCN]' protocol and the [Tiny Tiny RSS][TTRSS] protocol (details below). Unlike most other aggregator servers, The Arsse does not include a Web front-end (though one is planned as a separate project), and it relies on existing protocols to maximize compatibility with existing clients.

At present the software should be considered in an "alpha" state: though its core subsystems are covered by unit tests and should be free of major bugs, not everything has been rigorously tested. Additionally, many features one would expect from other similar software have yet to be implemented. Areas of future work include:

- Providing more sync protocols (Google Reader, Fever, others)
- Better packaging and configuration samples
- A user manual

## Requirements

The Arsse has the following requirements:

- A Linux server utilizing systemd and Nginx (tested on Ubuntu 16.04)
- PHP 7.0.7 or later with the following extensions:
    - [intl](http://php.net/manual/en/book.intl.php), [json](http://php.net/manual/en/book.json.php), [hash](http://php.net/manual/en/book.hash.php), and [pcre](http://php.net/manual/en/book.pcre.php)
    - [dom](http://php.net/manual/en/book.dom.php), [simplexml](http://php.net/manual/en/book.simplexml.php), and [iconv](http://php.net/manual/en/book.iconv.php) (for picoFeed)
    - One of:
        - [sqlite3](http://php.net/manual/en/book.sqlite3.php) or [pdo_sqlite](http://php.net/manual/en/ref.pdo-sqlite.php) for SQLite databases
        - [pgsql](http://php.net/manual/en/book.pgsql.php) or [pdo_pgsql](http://php.net/manual/en/ref.pdo-pgsql.php) for PostgreSQL 10 or later databases
        - [mysqli](http://php.net/manual/en/book.mysqli.php) or [pdo_mysql](http://php.net/manual/en/ref.pdo-mysql.php) for MySQL 8.0.7 or later databases
- Privileges to create and run daemon processes on the server

## Installation

At present, installation of The Arsse is rather manual. We hope to improve this in the future, but for now the steps below should help get you started. The instructions and configuration samples assume you will be using Ubuntu 16.04 (or equivalent Debian) and Nginx; we hope to expand official support for different configurations in the future as well.

### Initial setup

1. Extract the tar archive to `/usr/share`
2. If desired, create `/usr/share/arsse/config.php` using  `config.defaults.php` as a guide. The file you create only needs to contain non-default settings. The `userPreAuth` setting may be of particular interest
3. Copy `/usr/share/arsse/dist/arsse.service` to `/lib/systemd/system`
4. In a terminal, execute the following to start the feed fetching service:

``` sh
sudo systemctl enable arsse
sudo systemctl start arsse
```

### Configuring the Web server and PHP

Sample configuration parameters for Nginx can be found in `arsse/dist/nginx.conf` and `arsse/dist/nginx-fcgi.conf`; the samples assume [a server group](http://nginx.org/en/docs/http/ngx_http_upstream_module.html#upstream) has already been defined for PHP. How to configure an Nginx service to use PHP and install the required PHP extensions is beyond the scope of this document, however.

### Adding users

The Arsse includes a `user add <username> [<password>]` console command to add users to the database; for example running `php arsse.php user add admin password` will add the user `admin` with the password `pasword` to the database. Other commands for managing users are also available.

Alternatively, if the Web server is configured to handle authentication, you may set the configuration option `userPreAuth` to `true` and The Arsse will defer to the Web server and automatically add any missing users as it encounters them.

## Installation from source

If installing from the Git repository rather than a download package, you will need to follow extra steps before the instructions in the section above.

First, you must install [Composer] to fetch required PHP libraries. Once Composer is installed, dependencies may be downloaded with the following command:

``` sh
php composer.phar install -o --no-dev --no-scripts
```

Second, you may wish to create an example configuration file using the following command:

``` sh
php ./arsse.php conf save-defaults "./config.defaults.php"
```

## License

The Arsse is made available under the permissive MIT license.  See the `LICENSE` and `AUTHORS` files included with the distribution or source code for exact legal text and copyright holders. Dependencies included in the distribution may be governed by other licenses.

## Contributing

Please refer to `CONTRIBUTING.md` for guidelines on contributing code to The Arsse.

## Database compatibility notes

Functionally there is no reason to prefer either SQLite or PostgreSQL over the other. SQLite is significantly simpler to set up in most cases, requiring only read and write access to a containing directory in order to function; PostgreSQL may perform better than SQLite when serving hundreds of users or more, though this has not been tested.

MySQL, on the other hand, is **not recommended** due to its relatively constrained index prefix limits which may cause some newsfeeds which would otherwise work to be rejected. If using MySQL, special care should also be taken when performing schema upgrades, as errors during the process can leave the database in a half-upgraded state which The Arsse cannot itself recover from.

Note that MariaDB is not compatible with The Arsse: its support for common table expressions is, as of this writing, not sufficient for our needs.

## Protocol compatibility notes

###  General

#### Type casting

The Arsse does not guarantee it will handle type casting of input in the same way as reference implementations for its supported protocols. As a general rule, clients should endeavour to send only correct input.

The Arsse does, however, guarantee _output_ to be of the same type. If it is not, this is [a bug][newIssue] and should be reported.

#### Content sanitization

The Arsse makes use of the [picoFeed] newsfeed parsing library to sanitize article content. The exact sanitization parameters may differ from those of reference implementations for protocols The Arsse supports.

### NextCloud News v1.2

As a general rule, The Arsse should yield the same output as the reference implementation for all valid inputs (otherwise you've found [a bug][newIssue]), but there are exception, either because the NextCloud News (hereafter "NCN") [protocol description][NCNv1] is at times ambiguous or incomplete, or because implementation details necessitate it differ; this section along with the General section above detail these differences.

#### Differences

- Article GUID hashes are not hashes like in NCN; they are integers rendered as strings
- Article fingerprints are a combination of hashes rather than a single hash
- When marking articles as starred the feed ID is ignored, as they are not needed to establish uniqueness
- The feed updater ignores the `userId` parameter: feeds in The Arsse are deduplicated, and have no owner
- The `/feeds/all` route lists only feeds which should be checked for updates, and it also returns all `userId` attributes as empty strings: feeds in The Arsse are deduplicated, and have no owner
- The API's "updater" routes do not require administrator priviledges as The Arsse has no concept of user classes
- The "updater" console commands mentioned in the protocol specification are not implemented, as The Arsse does not implement the required NextCloud subsystems
- The `lastLoginTimestamp` attribute of the user metadata is always the current time: The Arsse's implementation of the protocol is fully stateless
- Syntactically invalid JSON input will yield a `400 Bad Request` response instead of falling back to GET parameters
- Folder names consisting only of whitespace are rejected along with the empty string
- Feed titles consisting only of whitespace or the empty string are rejected with a `422 Unprocessable Entity` reponse instead of being accepted
- Bulk-marking operations without a `newestItemId` argument result in a `422 Unprocessable Entity` reponse instead of silently failing
- Creating a feed in a folder which does not exist places the feed in the root folder rather than suppressing the feed
- Moving a feed to a folder which does not exist results in a `422 Unprocessable Entity` reponse rather than suppressing the feed

### Tiny Tiny RSS

As a general rule, The Arsse should yield the same output as the reference implementation for all valid inputs (otherwise you've found [a bug][newIssue]), but there are exception, either because the Tiny Tiny RSS (hereafter "TTRSS") [protocol description][TTRSS] is incomplete, erroneous, or out of date, or because TTRSS itself is buggy, or because implementation details necessitate The Arsse differ; this section along with the General section above detail these differences.

#### Extended functionality

The Arsse supports both [the set of extensions][ext-feedreader] to the TTRSS protocol defined by [FeedReader], as well as [the `getCompactHeadlines` operation][ext-newsplus] defined by [News+].

We are not aware of any other extensions to the TTRSS protocol. If you know of any more, please [let us know][newIssue].

#### Missing features

- The `getPref` operation is not implemented; it returns `UNKNOWN_METHOD`
- The `shareToPublished` operation is not implemented; it returns `UNKNOWN_METHOD`
- Setting an article's "published" flag with the `updateArticle` operation is not implemented and will gracefully fail
- The `sanitize`, `force_update`, and `has_sandbox` parameters of the `getHeadlines` operation are ignored
- String `feed_id` values for the `getCompactHeadlines` operation are not supported and will yield an `INCORRECT_USAGE` error
- Articles are limited to a single attachment rather than multiple attachments

#### Differences

- Input that cannot be parsed as JSON normally returns a `NOT_LOGGED_IN` error; The Arsse returns a non-standard `MALFORMED_INPUT` error instead
- Feed, category, and label names are normally unrestricted; The Arsse rejects empty strings, as well as strings composed solely of whitespace
- Discovering multiple feeds during `subscribeToFeed` processing normally produces an error; The Arsse instead chooses the first feed it finds
- Providing the `setArticleLabel` operation with an invalid label normally silently fails; The Arsse returns an `INVALID_USAGE` error instead
- Processing of the `search` parameter of the `getHeadlines` operation differs in the following ways:
    - Values other than `"true"` or `"false"` for the `unread`, `star`, and `pub` special keywords treat the entire token as a search term rather than as `"false"`
    - Invalid dates are ignored rather than assumed to be `"1970-01-01"`
    - Only a single negative date is allowed (this is a known bug rather than intentional)
    - Dates are always relative to UTC
    - Full-text search is not yet employed with any database, including PostgreSQL
- Article hashes are normally SHA1; The Arsse uses SHA256 hashes
- Article attachments normally have unique IDs; The Arsse always gives attachments an ID of `"0"`
- The default sort order of the `getHeadlines` operation normally uses custom sorting for "special" feeds; The Arsse's default sort order is equivalent to `feed_dates` for all feeds
- The `getCounters` operation normally omits members with zero unread; The Arsse includes everything to appease some clients

#### Other notes

- TTRSS accepts base64-encoded passwords, though this is undocumented; The Arsse accepts base64-encoded passwords as well
- TTRSS sometimes returns an incorrect count from the `setArticleLabel` operation; The Arsse returns a correct count in all cases
- TTRSS sometimes returns out-of-date cached information; The Arsse does not use caches as TTRSS does, so information is always current
- TTRSS returns results for _feed_ ID `-3` when providing the `getHeadlines` operation with _category_ ID `-3`; The Arsse retuns the correct results
- The protocol doucmentation advises not to use `limit` or `skip` together with `unread_only` for the `getFeeds` operation as it produces unpredictable results; The Arsse produces predictable results by first retrieving all unread feeds and then applying `skip` and `limit`
- The protocol documentation on values for the `view_mode` parameter of the `getHeadlines` operation is out of date; The Arsse matches the actual implementation and supports the undocumented `published` and `has_note` values exposed by the Web user interface
- The protocol documentation makes mention of a `search_mode` parameter for the `getHeadlines` operation, but this seems to be ignored; The Arsse does not implement it
- The protocol documentation makes mention of an `output_mode` parameter for the `getCounters` operation, but this seems to be ignored; The Arsse does not implement it
- The documentation for the `getCompactHeadlines` operation states the default value for `limit` is 20, but the reference implementation defaults to unlimited; The Arsse also defaults to unlimited
- It is assumed TTRSS exposes other undocumented behaviour; unless otherwise noted The Arsse only implements documented behaviour

#### Interaction with HTTP authentication

Tiny Tiny RSS itself is unaware of HTTP authentication: if HTTP authentication is used in the server configuration, it has no effect on authentication in the API. The Arsse, however, makes use of HTTP authentication for NextCloud News, and can do so for TTRSS as well. In a default configuration The Arsse functions in the same way as TTRSS: HTTP authentication and API authentication are completely separate and independent. Alternative behaviour is summarized below:

- With default settings:
    - Clients may optionally provide HTTP credentials
    - API authentication proceeds as normal
    - All feed icons are visible to unauthenticated clients
- If the `userHTTPAuthRequired` setting is `true`:
    - Clients must pass HTTP authentication
    - API authentication proceeds as normal
    - Feed icons are visible only to their owners
- If the `userSessionEnforced` setting is `false`:
    - Clients may optionally provide HTTP credentials
    - If HTTP authentication succeeded API authentication is skipped: tokens are issued upon login, but ignored for HTTP-authenticated requests
    - All feed icons are visible to unauthenticated clients
- If the `userHTTPAuthRequired` setting is `true` and the `userSessionEnforced` setting is `false`:
    - Clients must pass HTTP authentication
    - API authentication is skipped: tokens are issued upon login, but thereafter ignored
    - Feed icons are visible only to their owners
- If the `userPreAuth` setting is `true`:
    - The Web server asserts HTTP authentication was successful
    - API authentication only checks that HTTP and API user names match
    - Feed icons are visible only to their owners
- If the `userPreAuth` setting is `true` and the `userSessionEnforced` setting is `false`:
    - The Web server asserts HTTP authentication was successful
    - API authentication is skipped: tokens are issued upon login, but thereafter ignored
    - Feed icons are visible only to their owners

In all cases, supplying invalid HTTP credentials will result in a 401 response.

[newIssue]: https://code.mensbeam.com/MensBeam/arsse/issues/new
[Composer]: https://getcomposer.org/
[picoFeed]: https://github.com/miniflux/picoFeed/
[NCN]: https://github.com/nextcloud/news
[NCNv1]: https://github.com/nextcloud/news/blob/master/docs/externalapi/Legacy.md
[CORS]: https://fetch.spec.whatwg.org/#http-cors-protocol
[TTRSS]: https://git.tt-rss.org/git/tt-rss/wiki/ApiReference
[FeedReader]: https://jangernert.github.io/FeedReader/
[News+]: https://github.com/noinnion/newsplus/
[ext-feedreader]: https://github.com/jangernert/FeedReader/tree/master/data/tt-rss-feedreader-plugin
[ext-newsplus]: https://github.com/hrk/tt-rss-newsplus-plugin