Developer’s 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.


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:


Source in the common directory is agnostic to the underlying transport mechanism (Nanomsg, NNG, SI95, ..), and thus can be used when generating either library.


Source which is tightly coupled with the underlying Nanomsg library. (Nanomsg has been deprecated, but the RMR source remains as an example.)


Source which is tightly coupled with the underlying NNG library. (NNG has been deprecated, but the RMR source remains as an example.)


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\$1_. 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.


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.