ahriman/docs/architecture.md

Package structure

Packages have strict rules of importing:

• ahriman.application package must not be used anywhere except for itself.
• ahriman.core and ahriman.models packages don't have any import restriction. Actually we would like to totally restrict importing of core package from models, but it is impossible at the moment.
• ahriman.web package is allowed to be imported from ahriman.application (web handler only, only ahriman.web.web methods). It also must not be imported globally, only local import is allowed.

Full dependency diagram:

ahriman.application package

This package contains application (aka executable) related classes and everything for that. It also contains package called ahriman.application.handlers in which all available subcommands are described as separated classes derived from base ahriman.application.handlers.handler.Handler class. ahriman.application.ahriman contains only command line parses and executes specified Handler on success, ahriman.application.application.Application is a god class which provides interfaces for all repository related actions. ahriman.application.lock.Lock is additional class which provides file-based lock and also performs some common checks.

ahriman.core package

This package contains everything which is required for any time of application run and separated to several packages:

• ahriman.core.alpm package controls pacman related functions. It provides wrappers for pyalpm library and safe calls for repository tools (repo-add and repo-remove).
• ahriman.core.auth package provides classes for authorization methods used by web mostly. Base class is ahriman.core.auth.auth.Auth which must be called by load method.
• ahriman.core.build_tools is a package which provides wrapper for devtools commands.
• ahriman.core.report is a package with reporting classes. Usually it must be called by ahriman.core.report.report.Report.load method.
• ahriman.core.repository contains several traits and base repository (ahriman.core.repository.repository.Repository class) implementation.
• ahriman.core.sign package provides sign feature (only gpg calls are available).
• ahriman.core.status contains helpers and watcher class which are required for web application. Reporter must be initialized by using ahriman.core.status.client.Client.load method.
• ahriman.core.upload package provides sync feature, must be called by ahriman.core.upload.upload.Upload.load method.

This package also provides some generic functions and classes which may be used by other packages:

• ahriman.core.configuration.Configuration is an extension for standard configparser library.
• ahriman.core.exceptions provides custom exceptions.
• ahriman.core.spawn.Spawn is a tool which can spawn another ahriman process. This feature is used by web application.
• ahriman.core.tree is a dependency tree implementation.

ahriman.models package

It provides models for any other part of application. Unlike ahriman.core package classes from here provides only conversion methods (e.g. create class from another or convert to). Mostly case classes and enumerations.

ahriman.web package

Web application. It is important that this package is isolated from any other to allow it to be optional feature (i.e. dependencies which are required by the package are optional).

• ahriman.web.middlewares provides middlewares for request handlers.
• ahriman.web.views contains web views derived from aiohttp view class.
• ahriman.web.routes creates routes for web application.
• ahriman.web.web provides main web application functions (e.g. start, initialization).

Application run

• Parse command line arguments, find command and related handler which is set by parser.
• Call Handler.execute method.
• Define list of architectures to run. In case if there is more than one architecture specified run several subprocesses or process in current process otherwise. Class attribute ALLOW_MULTI_ARCHITECTURE_RUN controls whether application can be run in multiple processes or not - this feature is required for some handlers (e.g. Web) which should be able to spawn child process in daemon mode (it is impossible to do for daemonic processes).
• In each child process call lock functions.
• After success checks pass control to Handler.run method defined by specific handler class.
• Return result (success or failure) of each subprocess and exit from application.

In most cases handlers spawn god class ahriman.application.application.Application class and call required methods.

Application is designed to run from systemd services and provides parametrized by architecture timer and service file for that.

Basic flows

Add new packages or rebuild existing

Idea is to copy package to the directory from which it will be handled at the next update run. Different variants are supported:

• If supplied argument is file then application moves the file to the directory with built packages. Same rule applies for directory, but in this case it copies every package-like file from the specified directory.
• If supplied argument iis not file then application tries to lookup for the specified name in AUR and clones it into the directory with manual updates. This scenario can also handle package dependencies which are missing in repositories.

Rebuild packages

Same as add function for every package in repository. Optional filter by reverse dependency can be supplied.

Remove packages

This flow removes package from filesystem, updates repository database and also runs synchronization and reporting methods.

Update packages

This feature is divided into to stages: check AUR for updates and run rebuild for required packages. Whereas check does not do anything except for check itself, update flow is the following:

1. Process every built package first. Those packages are usually added manually.
2. Run sync and report methods.
3. Generate dependency tree for packages to be built.
4. For each level of tree it does:
   1. Download package data from AUR.
   2. Build every package in clean chroot.
   3. Sign packages if required.
   4. Add packages to database and sign database if required.
   5. Process sync and report methods.

After any step any package data is being removed.

Core functions reference

Configuration

ahriman.core.configuration.Configuration class provides some additional methods (e.g. getpath and getlist) and also combines multiple files into single configuration dictionary using architecture overrides. It is recommended to read class related settings from the class, not outside.

Utils

For every external command run (which is actually not recommended if possible) custom wrapper for subprocess is used. Additional functions ahriman.core.auth.helpers provide safe calls for aiohttp_security methods and are required to make this dependency optional.

Submodules

Some packages provide different behaviour depending on configuration settings. In this cases inheritance is used and recommended way to deal with them is to call class method load from base classes.

Authorization

The package provides several authorization methods: disabled, based on configuration and OAuth2.

Disabled (default) authorization provider just allows everything for everyone and does not have any specific configuration (it uses some default configuration parameters though). It also provides generic interface for derived classes.

Mapping (aka configuration) provider uses hashed passwords with salt from configuration file in order to authenticate users. This provider also enables user permission checking (read/write) (authorization). Thus, it defines the following methods:

• check_credentials - user password validation (authentication).
• verify_access - user permission validation (authorization).

Passwords must be stored in configuration as hash(password + salt), where password is user defined password (taken from user input), salt is random string (any length) defined globally in configuration and hash is secure hash function. Thus, the following configuration

[auth:read]
username = $6$rounds=656000$mWBiecMPrHAL1VgX$oU4Y5HH8HzlvMaxwkNEJjK13ozElyU1wAHBoO/WW5dAaE4YEfnB0X3FxbynKMl4FBdC3Ovap0jINz4LPkNADg0

means that there is user username with read access and password password hashed by sha512 with salt salt.

OAuth provider uses library definitions (aioauth-client) in order authenticate users. It still requires user permission to be set in configuration, thus it inherits mapping provider without any changes. Whereas we could override check_credentials (authentication method) by something custom, OAuth flow is a bit more complex than just forward request, thus we have to implement the flow in login form.

OAuth's implementation also allows authenticating users via username + password (in the same way as mapping does) though it is not recommended for end-users and password must be left blank. In particular this feature is used by service reporting (aka robots).

In order to configure users there is special command.

Additional features

Some features require optional dependencies to be installed:

• Version control executables (e.g. git, svn) for VCS packages.
• gnupg application for package and repository sign feature.
• rsync application for rsync based repository sync.
• boto3 python package for S3 sync.
• Jinja2 python package for HTML report generation (it is also used by web application).

Web application

Web application requires the following python packages to be installed:

• Core part requires aiohttp (application itself), aiohttp_jinja2 and Jinja2 (HTML generation from templates).
• In addition, authorization feature requires aiohttp_security, aiohttp_session and cryptography.
• In addition to base authorization dependencies, OAuth2 also requires aioauth-client library.

Middlewares

Service provides some custom middlewares, e.g. logging every exception (except for user ones) and user authorization.

Web views

All web views are defined in separated package and derived from ahriman.web.views.base.Base class which provides typed interfaces for web application.

REST API supports both form and JSON data, but the last one is recommended.

Different APIs are separated into different packages:

• ahriman.web.views.service provides views for application controls.
• ahriman.web.views.status package provides REST API for application reporting.
• ahriman.web.views.user package provides login and logout methods which can be called without authorization.

Templating

Package provides base jinja templates which can be overridden by settings. Vanilla templates are actively using bootstrap library.

Requests and scopes

Service provides optional authorization which can be turned on in settings. In order to control user access there are two levels of authorization - read-only (only GET-like requests) and write (anything).

If this feature is configured any request except for whitelisted will be prohibited without authentication. In addition, configuration flag auth.allow_read_only can be used in order to allow seeing main page without authorization (this page is in default white list).

For authenticated users it uses encrypted session cookies to store tokens; encryption key is generated each time at the start of the application.

External calls

Web application provides external calls to control main service. It spawns child process with specific arguments and waits for its termination. This feature must be used either with authorization or in safe (i.e. when status page is not available world-wide) environment.