uSHET: A Malloc-Free SHET Client Library for Microcontrollers

A simple microcontroller-friendly C library for interfacing with SHET targeted at microcontrollers forked from SHETC and extended to support the complete SHET client protocol. uSHET intends to replace SHETSource as the de-facto microcontroller SHET interface.

uSHET supports the following key features:

• Transport-independent: The library simply expects to be fed strings received from a network device and will call a user-defined callback with strings to transmit. This means the library is suitable for use with any network interface/library.
• Malloc-free: The library does not use dynamic memory allocation and thus can have deterministic memory requirements and use only statically-allocated storage. This has the obvious side-effect that the library cannot handle arbitrarily large commands but this should not impact most applications.
• Small-ish: Though uSHET has not received any serious space optimisation passes, it is based on the compact jsmn JSON parser and avoids needlessly duplicating JSON strings.
• Complete SHET client protocol support: uSHET supports the full SHET client protocol and exposes a fairly sane high-level interface, unlike SHETSource. This comes with the trade-off that uSHET is heavier-weight than SHETSource in terms of network requirements, memory requirements and execution overhead since it deals with full JSON strings rather than a compact byte-stream.
• (Optional) High-Level Wrapper Macros: Includes EZSHET, a library of macros which hide much of the boilerplate required in handling dynamically typed input from SHET.

Documentation

Beginner's tutorials for the EZSHET and uSHET libraries are included in doc and these are the recommended starting point for new users to uSHET.

The uSHET and EZSHET libraries contain fairly extensive API documentation within their header files, shet.h and ezshet.h.

Teaser

The following snippet (which uses EZSHET) should give you a feel for the ease-of-use of the library.

void set_led(shet_state_t *shet, bool state) {
	digitalWrite(led_pin, state);
}
bool get_led(shet_state_t *shet) {
	return digitalRead(led_pin);
}
EZSHET_PROP("/arduino/led", led, SHET_BOOL);

This code creates a new boolean property in SHET at the path "/arduino/led" that controls the state of an LED in an Arduino project.

Test Suite

A test suite is included. It can be compiled and run as follows:

gcc -Wall -Wextra -Werror test.c -o test && ./test

Note that the testbench actually #includes the library sources in order to test a number of internal functions.