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content:tech:serval_mesh_for_firefoxos

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Serval Mesh app for FirefoxOS

FirefoxOS is an attractive platform for Serval Mesh (app for Android) because it targets low-cost mobile devices and is likely to be adopted rapidly by vendors and carriers in developing countries who seek to avoid the compliance and commercial obligations imposed by Google, Apple and other platform suppliers.

A port of the Serval Mesh app to FirefoxOS would pose the following technical challenges:

  • the user interface (which for Android is written entirely in Java/XML using the Android API) would have to be rewritten in HTML5
  • interactions between Serval Mesh and the following FirefoxOS components would have to be made usable:
    • dialler screen for making and receiving calls
    • contact list for managing known Serval Identities
    • text message sending and receiving
    • app manager for auto-upgrade via Rhizome
    • gallery and camera for sending and receiving photos via Rhizome
    • file manager for sending and receiving files via Rhizome
  • the Serval DNA component could not be ported as a native executable because FirefoxOS does not and will never provide a native code facility
  • possibly the Emscripten C-to-JavaScript compiler could be used to port Serval DNA to FirefoxOS, but the following issues would have to be investigated to find out if this is feasible:
    • Serval DNA Posix file operations for persistent storage of the keyring file, configuration, logging, daemon control, and temporary storage of Rhizome payloads. How would these be achieved within JavaScript on FirefoxOS?
    • Serval DNA uses SQLite for persistent storage of Rhizome bundles. On Android, the native SQLite code contributes signficantly to the APK binary size and necessitates a great deal of extra overhead for data indexing and consistency. This may not scale well to low-end devices if executed as JavaScript.
    • Cryptographic operations such as signature verification and payload encryption are performed on Android using the native NaCl library which has been optimised for the ARM processor. This optimisation brings Serval's security features within reach of low-end devices. The Emscripten compiled code has known speed limitations, so how much CPU overhead will that introduce to crypographic operations? Would that make Serval Mesh for FirefoxOS unusable in practical terms due to slowness and battery drain?
    • Any port of Serval DNA must be controlled for quality using the automated test suite, which is a set of Bash scripts executed natively on the target platform. The Emscripten JavaScript port of Serval DNA would have to be invokable via the normal Serval DNA command-line interface, from an Emscripten port of Bash running the test framework script within a Posix environment that may include Emscripten ports of standard Posix utilities like grep, sed and awk.
    • The MDP packet assembly/disassembly code has been shown to be largely correct and portable to different-endian architectures (ARM, Sparc, Intel 32-bit and 64-bit) but it may not work correctly when compiled by Emscripten, so will need extensive testing on a heterogeneous network and may need some rewriting.
content/tech/serval_mesh_for_firefoxos.1378266473.txt.gz · Last modified: 03/09/2013 20:47 by Andrew Bettison