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Bill of Materials

Bjorn Stahl edited this page Nov 15, 2022 · 1 revision

This page attempts to track the core dependencies, their level of coupling (necessary to build = high, optional = low), linking method (static, dynamic) along with licensing and security implications.

Component:

On a high level, Arcan is split into a core engine, its os integration platforms, a set of de-coupled services and protocol bridges as well as an IPC system (SHMIF) to tie these together. The coupling for integration platforms refers to when the specific platform path is chosen/built.

Engine (src/engine):

The engine is split into a user scripting layer, a core and a platform layer for system integration ("event"), one for graphics (drawing) one for video (display control), and one for audio. The selection of these are determined statically at build-time, where the selection is coupled into a tagged build (e.g. arcan-version-lua-audio-video) that is part of crash dumps and other user reporting forms.

Name Linking Coupling License Notes
Core N/A N/A 3-BSD
ALT (engine-Lua API) S High GPLv2
Lua51 OR LuaJit2.x S / D High MIT
STB (image formats) S High CC0 To be migrated to decode for security reasons.
Freetype, Harfbuzz D High FTL/oMIT (FTL = BSD + attribution) oMIT ("old" MIT)
Sqlite3 S / D High PD

Graphics (src/platform/agp):

The graphics platform is referred to as 'AGP' and provides 2D/3D rendering matched to about the hardware capabilities of embedded devices around 2013 as the lower bound in order to reach the widest reasonable audience. The intent is to expand these with a 'document format' based renderer as well as a software dedicated one to reach more devices.

Name Linking Coupling License Notes
GL21,GLES3 (MESA) D High MIT

Audio (src/platform/audio):

The audio layer has recently been broken out of the core engine as a step towards swapping it out for simpler and more permissible licenses. The current implementation relies on openAL-Soft due to its role in portable 3D audio (HRTFs) for intended VR applications. Where such are not needed, simpler options are being evaluated.

Name Linking Coupling License Notes
openal: OpenAL-soft D High LGPL

Video (src/platform/sdl2,egl-dri):

The video platform deals with negotiating optimal formats and timing parameters with the graphics rendering code. It is responsible for integration with an outer display server or native graphics drivers, depending on user preferences.

Name Linking Coupling License Notes
egl-dri: gbm/kms D High MIT
egl-dri: libbacklight S Low MIT
sdl2: sdl2 D High Zlib

Event (src/platform/sdl2,evdev,wscons): The event platform deals with input sources, sensors and low intensity output devices (LED indicators, backlight).

Name Linking Coupling License Notes
sdl2: sdl2 D High Zlib

SHMIF

The IPC system relies exclusively on OS(POSIX) based primitives and has no explicit other external dependencies. There is an extended form, arcan-shmif-ext for accelerated passing of hardware graphics resources, which follows GBM/KMS/Mesa (MIT) license.

A12

The protocol implementation (src/a12) and the support tool for client/server connection discovery and management.

Name Linking Coupling License Notes
zstd S High BSD
blake3 S High CC0 (dual-license, Apache license)
chacha(8,20) S High MIT vendored implementation chosen for ease of use, assumed to be swapped for stronger verified
x25519 (monocypher) S High CC0 Chosen over more popular nacl/libsodium due to size / simplicity
ffmpeg D Low GPL* Actual license depends on os / distribution provided, for higher security delegate to decode frameserver or passthrough to any other shmif capable application.

Decode (src/frameserver/decode/default):

The role of the decode frameserver is to provide a least privilege form of parsing of primarily media formats. Other components can and do delegate their media decode processing to this process. The default build act as a dependency / license sponge where are all build time optional, the coupling is low and all act as a separate program. As such the implementation itself can be swapped out or stubbed out with clear consequence (loss of performant formats to cover license concerns or gain of new ones) without changing the rest of the system. This decoupling/security intention applies to the other frameservers (encode, remoting, net) as well.

Name Linking Coupling License Notes
libvlc D Low LGPL2.1
espeak D Low Apache
mupdf D Low AGPL
uvc D/S Low BSD
nanosvg S Low Zlib
stb S Low Zlib
tinyobj S Low MIT

Encode:

The encode frameserver is the counterpart to decode and perform human-to-non-human transformations that are lossy and only partially reversible. It is also used for scrubbing or tampering with privacy affecting metadata. Its decoupling and security intentions are the same as for Decode.

Name Linking Coupling License Notes
FFMPEG D High GPL* GPL license version will vary with OS/distribution packaging
Libvncserver D Low GPLv2
Tesseract D Low Apache

Remoting:

The remoting frameserver is a simplified "specifically used for accessing shared remote desktops" which is mainly a different sandboxing profile than for other clients given its "only networking" use.

Name Linking Coupling License Notes
A12 S High BSD
libvncclient D Low GPL

Net

The net frameserver act as an engine to arcan-net/a12 implementation bridge with presets for making it easier to use from Arcan Lua scripts. Its bom/dependencies are thus the same as for A12.

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