[Libosmscout-development] osmscout-server

[rinigus <rin...@gm...>]

Dear libosmscout developers:

I'd like to introduce a small libosmscout-based server that, in future, can
be used as a drop-in replacement for tile (and other relevant info) server
by programs that require such servers.

Rationale: We are missing a native application for offline navigation and
map viewing/exploring in Sailfish. At present, there are several
applications (at least 4) that are in part working to implement the
functionality. Out of them, some have focused on GUI and getting the best
support from online provided maps, and some have worked on all aspects
(backend and frontend, OSM Scout for Sailfish). The amount of developers is
very limited and through this server I would like to contribute by exposing
libosmscout backend to the frontends that have been focused on GUI.

What can it do: At present, the server registers a port and waits for HTTP
requests on it. So far, it knows how to serve tiles using slippy map
notation with small extensions. It can accept multiple requests
simultaneously and process them in parallel. This is done by
mutex-protecting calls to the database (
https://github.com/rinigus/osmscout-server/blob/master/src/dbmaster.cpp#L97)
and
drawing in parallel. On PC, it can load all CPUs without any problems when
accessed via modRana. Haven't tested multithreading in Sailfish yet due to
single-threaded access used in the app that I used for testing (Poor Maps).

Even when accessed via single thread, the server can feed the tile images
in PNG fomat with reasonable speed on mobile device. Through the extended
slippy map URL scheme, I can increase served tile sizes to optimize for
best performance. By using tile-oriented GUIs, all caching of generated
images has been taking care of and reducing the load on CPU further.

At present, the memory footprint was about 220-260MB RSS on mobile device.
I presume that it would be higher when multiple pixmaps are generated in
parallel.

Implementation: Please consider current implementation as a proof of
concept.

As an HTTP server API, I used QtWebApp which, as suggested by the lib
author, is incorporated into the code. This lib was selected since it is
simple to perform multi-threaded processing and, as majority of Sailfish
applications, it uses Qt. This choice can be altered if someone would like
to use some other API that has similar properties.

To compile, you need libosmscout libraries installed in the system. For
Sailfish, I made a simple packaging scripts to install libosmscout (qt
variant) and its development headers. That prevents distribution via
official store, but allows simpler development. There are other channels
that can be used for distribution and I intend to use them instead of the
store.

Further development: I plan to develop 2 interfaces - CLI and QML. QML
interface should allow to alter configuration settings (port, bound
interface, font size, ...) via GUI and simplify starting/stopping the
server on mobile device. CLI would read settings from configuration file
and run in terminal. That would allow using it for testing libosmscout on
PC.

License: LGPL
URL: https://github.com/rinigus/osmscout-server

As usual, everyone are welcome to join. Would be interesting to know
whether such project is of any interest to this community before I put a
lot of effort into it.

Best,

rinigus