The afm-user-daemon

version: 1
Date:    30 mai 2016
Author:  José Bollo

Foreword

This document describes application framework user daemon fundamentals. FCF (Fully Conform to Specification) implementation is still under development. It may happen that current implementation somehow diverges with specifications.

Introduction

The daemon afm-user-daemon is in charge of handling applications on behalf of a user. Its main tasks are:

The afm-user-daemon takes its orders from the session instance of D-Bus.

The figure below summarizes the situation of afm-user-daemon in the system.

+------------------------------------------------------------+
|                          User                              |
|                                 +---------------------+    |
|     +---------------------+     |   Smack isolated    |    |
|     |   D-Bus   session   +     |    APPLICATIONS     |    |
|     +----------+----------+     +---------+-----------+    |
|                |                          |                |
|                |                          |                |
|     +----------+--------------------------+-----------+    |
|     |                                                 |    |
|     |                  afm-user-daemon                |    |
|     |                                                 |    |
|     +----------+----------------------+----------+----+    |
|                |                      |          :         |
|                |                      |          :         |
:================|======================|==========:=========:
|                |                      |          :         |
|     +----------+----------+     +-----+-----+    :         |
|     |   D-Bus   system    +-----+  CYNARA   |    :         |
|     +----------+----------+     +-----+-----+    :         |
|                |                      |          :         |
|     +----------+---------+    +-------+----------+----+    |
|     | afm-system-daemon  +----+   SECURITY-MANAGER    |    |
|     +--------------------+    +-----------------------+    |
|                                                            |
|                          System                            |
+------------------------------------------------------------+

Tasks of afm-user-daemon

Maintaining list of applications

At start afm-user-daemon scans the directories containing applications and load in memory a list of avaliable applications accessible by current user.

When afm-system-daemon installs or removes an application. On success it sends the signal org.AGL.afm.system.changed. When receiving such a signal, afm-user-daemon rebuilds its applications list.

afm-user-daemon provides the data it collects about applications to its clients. Clients may either request the full list of avaliable applications or a more specific information about a given application.

Launching application

afm-user-daemon launches application. Its builds a secure environment for the application before starting it within a secured environment.

Different kind of applications can be launched.

This is set using a configuration file that describes how to launch an application of a given kind within a given mode.

There is two launching modes: local or remote.

Launching an application locally means that the application and its binder are launched together.

Launching application remotely translates in only launching the application binder. The UI by itself has to be activated remotely by the requested (ie: HTML5 homescreen in a browser)

Once launched, running instances of application receive a runid that identify them.

Managing instances of running applications

afm-user-daemon manages the list of applications that it launched.

When owning the right permissions, a client can get the list of running instances and details about a specific running instance. It can also terminates, stops or continues a given application.

Installing and uninstalling applications

If the client own the right permissions, afm-user-daemon delegates that task to afm-system-daemon.

Starting afm-user-daemon

afm-user-daemon is launched as a systemd service attached to user sessions. Normally, the service file is located at /usr/lib/systemd/user/afm-user-daemon.service.

The options for launching afm-user-daemon are:

-a
--application directory

 Includes the given application directory to
 the database base of applications.

 Can be repeated.

-r
--root directory 

 Includes root application directory or directories when
 passing multiple rootdir to
 applications database.

 Note that default root directory for
 applications is always added. In current version
 /usr/share/afm/applications is used as default.

-m
--mode (local|remote)

 Set the default launch mode.
 The default value is 'local'

-d
--daemon

 Daemonizes the process. It is not needed by sytemd.

-q
--quiet

 Reduces the verbosity (can be repeated).

-v
--verbose

 Increases the verbosity (can be repeated).

-h
--help

 Prints a short help.

Launcher Configuration

It contains rules for launching applications. When afm-user-daemon has to launch an application, it looks for launch mode (local or remote), as well as for the type of application describe in config.xml widget configuration file.

This tuple mode+type allows to select the adequate rule.

Configuration file is /etc/afm/afm-launch.conf.

It contains sections and rules. It can also contain comments and empty lines to improve readability.

The separators are space and tabulation, any other character should have a meaning.

The format is line oriented. The new line character separate the lines.

Lines having only separators are blank lines and ignored. Line having character #(sharp) at first position are comment lines and ignored.

Lines not starting with a separator are different from lines starting with a separator character.

The grammar of the configuration file is defined below:

CONF: *COMMENT *SECTION

SECTION: MODE *RULE

RULE: +TYPE VECTOR ?VECTOR

MODE: 'mode' +SEP ('local' | 'remote') *SEP EOL

TYPE: DATA *SEP EOL

VECTOR: +SEP DATA *(+SEP NDATA) *SEP EOL

DATA: CHAR *NCHAR
NDATA: +NCHAR

EOL: NL *COMMENT
COMMENT: *SEP CMT *(SEP | NCHAR) NL

NL: '\x0a'
SEP: '\x20' | '\x09'
CMT: '#'
CHAR: '\x00'..'\x08' | '\x0b'..'\x1f' | '\x21' | '\x22' | '\x24'..'\xff'
NCHAR: CMT | CHAR

Here is a sample of configuration file for defining how to launch an application of types application/x-executable, text/x-shellscript and text/html in local mode:

mode local

application/x-executable
text/x-shellscript
%r/%c

text/html
/usr/bin/afb-daemon --mode=local --readyfd=%R --alias=/icons:%I --port=%P --rootdir=%r --token=%S --sessiondir=%D/.afb-daemon
/usr/bin/web-runtime http://localhost:%P/%c?token=%S

This shows that:

mode local

Within this mode, the launchers have either one or two description vectors. All of those vectors are treated as programs and are executed with ‘execve’ system call.

The first vector is the leader vector and it defines the process group. The second vector (if any) is attached to the group defined by this first vector.

mode remote

Within this mode, the launchers have either one or two vectors describing them.

The first vector is process as a program and is executed with system call ‘execve’.

The second vector (if any) defines a text that is returned to the caller. This mechanism can be used to return a uri for remote UI to connect on the newly launched application.

The daemon afm-user-daemon allocates a port for each new remote application. The current implementation port allocation is incremental. A smarter (cacheable and discoverable) allocation should be defined.

%substitutions

Vectors can include sequences of 2 characters that have a special meaning. These sequences are named %substitution because their first character is the percent sign (%) and because each occurrence of the sequence is replaced, at launch time, by the value associated to sequences.

Here is the list of %substitutions:

The D-Bus interface

Overview of the dbus interface

afm-user-daemon takes its orders from the session instance of D-Bus. D-Bus is nice to use in this context because it allows discovery and signaling.

The dbus session is by default addressed by environment variable DBUS_SESSION_BUS_ADDRESS. Using systemd variable DBUS_SESSION_BUS_ADDRESS is automatically set for user sessions.

The afm-user-daemon is listening on destination name org.AGL.afm.user at object path /org/AGL/afm/user on interface org.AGL.afm.user for following members: runnables, detail, start, terminate, stop, continue, runners, state, install and uninstall.

D-Bus is mainly used for signaling and discovery. Its optimized typed protocol is not used except for transmission of standalone strings.

Clients and Services are using JSON serialisation to exchange data.

The D-Bus interface is defined by:

The signature of any member of the interface is string -> string for JSON -> JSON.

This is the normal case. In case of error, the current implementation returns a dbus error as a string.

Here an example using dbus-send to query data on installed applications.

dbus-send --session --print-reply \
--dest=org.AGL.afm.user \
/org/AGL/afm/user \
org.AGL.afm.user.runnables string:true

Using afm-util

The command line tool afm-util uses dbus-send to send orders to afm-user-daemon. This small scripts allows to send command to afm-user-daemon either interactively at shell prompt or scriptically.

The syntax is simple: it accept a command and when requires attached arguments.

Here is the summary of afm-util:

Here is how to list applications using afm-util:

afm-util runnables

The protocol over D-Bus

Recall:


Method org.AGL.afm.user.detail

Description: Get details about an application from its id.

Input: the id of the application as below.

Either just a string:

"appli@x.y"

Or an object having the field “id” of type string:

{"id":"appli@x.y"}

Output: A JSON object describing the application containing the fields described below.

{
  "id":          string, the application id (id@version)
  "version":     string, the version of the application
  "width":       integer, requested width of the application
  "height":      integer, resqueted height of the application
  "name":        string, the name of the application
  "description": string, the description of the application
  "shortname":   string, the short name of the application
  "author":      string, the author of the application
}

Method org.AGL.afm.user.runnables

Description: Get the list of applications that can be run.

Input: any valid json entry, can be anything except null.

output: An array of description of the runnable applications. Each item of the array contains an object containing the detail of an application as described above for the method org.AGL.afm.user.detail.


Method org.AGL.afm.user.install

Description: Install an application from its widget file.

If an application of the same id and version exists, it is not reinstalled except when force=true.

Applications are installed in the subdirectories of the common directory reserved for applications. If root is specified, the application is installed under sub-directories of defined root.

Note that this methods is a simple accessor to the method org.AGL.afm.system.install of afm-system-daemon.

After the installation and before returning to the sender, afm-user-daemon sends the signal org.AGL.afm.user.changed.

Input: The path of widget file to be installed. Optionally, a flag to force reinstallation and/or a root directory.

Simple form a simple string containing the absolute widget path:

"/a/path/driving/to/the/widget"

Or an object:

{
  "wgt": "/a/path/to/the/widget",
  "force": false,
  "root": "/a/path/to/the/root"
}

“wgt” and “root” MUST be absolute paths.

output: An object containing field “added” to use as application ID.

{"added":"appli@x.y"}

Method org.AGL.afm.user.uninstall

Description: Uninstall an application from its id.

Note that this methods is a simple accessor to org.AGL.afm.system.uninstall method from afm-system-daemon.

After the uninstallation and before returning to the sender, afm-user-daemon sends the signal org.AGL.afm.user.changed.

Input: the id of the application and, optionally, the path to application root.

Either a string:

"appli@x.y"

Or an object:

{
  "id": "appli@x.y",
  "root": "/a/path/to/the/root"
}

output: the value ‘true’.


Method org.AGL.afm.user.start

Description:

Input: the id of the application and, optionally, the start mode as below.

Either just a string:

"appli@x.y"

Or an object containing field “id” of type string and optionally a field mode:

{"id":"appli@x.y","mode":"local"}

The field “mode” is a string equal to either “local” or “remote”.

output: The runid of the application launched. runid is an integer.


Method org.AGL.afm.user.terminate

Description: Terminates the application attached to runid.

Input: The runid (an integer) of running instance to terminate.

output: the value ‘true’.


Method org.AGL.afm.user.stop

Description: Stops the application attached to runid until terminate or continue.

Input: The runid (integer) of the running instance to stop.

output: the value ‘true’.


Method org.AGL.afm.user.continue

Description: Continues the application attached to runid previously stopped.

Input: The runid (integer) of the running instance to continue.

output: the value ‘true’.


Method org.AGL.afm.user.state

Description: Get informations about a running instance of runid.

Input: The runid (integer) of the running instance inspected.

output: An object describing instance state. It contains: the runid (integer), the id of the running application (string), the state of the application (string either: “starting”, “running”, “stopped”).

Example of returned state:

{
  "runid": 2,
  "state": "running",
  "id": "appli@x.y"
}

Method org.AGL.afm.user.runners

Description: Get the list of currently running instances.

Input: anything.

output: An array of states, one per running instance, as returned by the methodd org.AGL.afm.user.state.