docs/developer-guide.rst

 
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RMR Developer Guide 
============================================================================================ 
 
The RIC Message Router (RMR) is a library for peer-to-peer 
communication. Applications use the library to send and 
receive messages where the message routing and endpoint 
selection is based on the message type rather than DNS host 
name-IP port combinations. 
 
This document contains information that developers need to 
know to contribute to the RMR project. 
 
Language 
-------------------------------------------------------------------------------------------- 
 
RMR is written in C, and thus a contributing developer to the 
core library should have an excellent working knowledge of C. 
There currently is one set of cross-languages bindings 
supporting Python, and a developer wishing to contribute to 
the bindings source should be familiar with Python (version 
3.7+) and with the Python *ctypes* library. 
 
Code Structure 
-------------------------------------------------------------------------------------------- 
 
RMR is designed to provide an insulation layer between user 
applications and the actual transport mechanism. Initially 
RMR was built on top of the third-party library Nanosmg, 
shortly after was ported to the third-party library NNG 
(Nanomsg Next Generation), and then was ported to an 
internally developed socket library called SI95. RMR presents 
the same API to the user application regardless of the 
underlying transport library, but the resulting output when 
compiling RMR is always a transport-specific library. As an 
example, librmr_nng.a is the library generated for use with 
the NNG transport. 
 
As such the library source is organised into multiple 
components: 
 
 
common 
   
  Source in the common directory is agnostic to the 
  underlying transport mechanism (Nanomsg, NNG, SI95, ..), 
  and thus can be used when generating either library. 
 
nano 
   
  Source which is tightly coupled with the underlying 
  Nanomsg library. (Nanomsg has been deprecated, but the RMR 
  source remains as an example.) 
 
nng 
   
  Source which is tightly coupled with the underlying NNG 
  library. (NNG has been deprecated, but the RMR source 
  remains as an example.) 
 
si 
   
  Source which is tightly coupled with the underlying SI95 
  library. 
 
 
 
Internal Function Exposure 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
 
The decision to limit as much as practical the exposure of 
truly internal RMR functions was made, and as a result most 
of the RMR functions carry a static label. In order to 
modularise the code as much as possible, this means that the 
primary module (e.g. rmr_nng.c) directly includes other RMR 
modules, rather than depending on referencing the internal 
functions during linking. While this is an infrequently used 
approach, it does mean that there are very few functions 
visible for the user application to reference, all of them 
having the prefix rmr\_. This allows internal functions to 
have shorter names while still being meaningful. 
 
Coding Style 
-------------------------------------------------------------------------------------------- 
 
There is a list of coding style guidelines in the top level 
directory, and as such they are not expanded upon here. The 
general practice is to follow the style when editing an 
existing module, respect the author's choice where style 
alternatives are not frowned upon. When creating new modules, 
select a style that fits the guidelines and is easy for you 
to work with. There are a few things that the RMR maintainers 
insist on, but for the most part style is up to the creator 
of a module. 
 
Building 
-------------------------------------------------------------------------------------------- 
 
RMR is constructed using CMake. While CMake's project 
description can be more cumbersome than most typical 
Makefiles, the tool provides convenience especially when it 
comes to creating DEB/RPM packages.