C Implementation

The C implementation of “vad är klockan” can be found in the directory “src/c”. The same C source code is used both on Linux and on ESP32.

src/c/overlap_algorithm.[ch] is a port of the Python implementation in python/overlap.py to C.

The roughtime implementation is based on a project called “vroughtime” (https://github.com/oreparaz/vroughtime). vroughtime in turn uses some code from another project called “craggy” (https://github.com/nahojkap/craggy). “vroughtime” did not initially support newer draft versions of roughtime so the code was modified to also support draft version 07 and 06 of Roughtime.

The cryptographic primitives (Ed25516, SHA-512/256) used by vroughtime come from the library “tweetnacl”. Tweetnacl is in the public domain.

The remaingin files in the C implementation of “vad är klockan”, vroughtime and craggy are all licensed using the Apache License 2”.

C API

• C Overlap Algorithm
• vroughtime - a roughtime client in C
• tweetnacl - tiny crypto library

C on Linux

A an example C implementation for Linux can be found in examples/c. This implementation may also work on other Unix variants such as MacOS.

Some glue code needed to be written to run on Linux and for UDP communication via BSD sockets API. The code supports both IPv4 and IPv6.

Todo

Add instructions on how to compile and run the C code on Linux

C on ESP32

The C implementation for the ESP32 can be found in examples/esp32.

Some glue code needed to be written to use WiFi and UDP on the ESP32. The code so far only supports IPv4.

Todo

Add instructions on how to compile and run the C code on ESP32

Unit testing

Some of the c modules contain unit tests.

The test for overlap_algorithm reuses the test cases from the Python implementation. The C code is built into a dynamic library which is wrapped with a class which implements the same API as the Python implementation. The results from the Python and C implementations are compared to see that they perform identically. Additionally, some C code to replay the same test caes is generated to overlap_replay.c which is then compiled and run through valgrind to catch errors such as buffer overruns or memory leaks.

To run the test cases, install the following packages on a Debian or Ubuntu system:

apt-get install -y build-essential python3-cffi valgrind

Then run the test cases with:

cd src/c
python3 test_overlap_c.py