micurest

Application server for constrained platforms

Introduction

μcuREST is a C++11 library for implementing REST services on constrained platforms, such as bare metal applications on low-end MCUs. The library is platform-agnostic, zero-allocation, and has almost no external dependencies. It allows mapping hierarchically organized URIs to C/C++ variables, constants and methods, and exposing the URIs via a HTTP protocol.

μcuREST is a continuation of cojson project - it includes cojson as its integral part and uses many feature, itroduced in cojson.

HTTP standard

μcuREST implements a minimal subset of HTTP/1.1 specification, sufficient for serving GET requests from browsers, GET/PUT/POST requests from JavaScript via XMLHttpRequest and simple machine-to-machine communications.

JSON-RPC

μcuREST implements JSON-RPC 2.0 specification, enabling easy implementation of RPC for MCU applications over HTTP protocol.

Transport Layer

An application, implementing HTTP RESTful services with μcuREST needs a platform specific transport layer and a mediator (Session Layer in terms of OSI model) between μcuREST and the transport layer. The mediator must handle sessions and implement two μcuREST interfaces: istream and ostream.

Limitations

Query strings, cookies, absolute URLs, cache control, transfer encoding, and many other HTTP features are not supported. Depending on the transport layer in use, and mediator implementation, the HTTP message size could be limited to size of one MTU (~1460 bytes).

Requirements

• Compiler: μcuREST sources need a C++11 enabled compiler, such as g++-4.8 and up.
• Library: libstdc++ v3 highly desirable. But if not available a workaround exists
• Transport layer: A platform specific transport layer, such as TCP/IP, is required for implementing HTTP REST services.
• ROM/RAM space: on AVR platform μcuREST core takes 6K of ROM and 100 bytes of RAM. Size of the resource map starts with 3K/200 and grows with its complexity, taking in average 750 bytes of ROM and 250 bytes of RAM per entry.

Arduino Library

μcuREST library for Arduino is available for downloading on this link

Particle Library

μcuREST library for Spark Particle is available for downloading on this link

Tested On

• Debian i686, g++-4.9.2
• Controllino MAXI ATmega2560, avr-g++-4.8.1
• NodeMCU V3 ESP8266 xtensa-lx106-elf-g++-4.8.5
• Particle Photon STM32F205RGY6 arm-none-eabi-g++-4.9.3

Prebuilt Demos

Ready for flashing example applications can be downloaded via these links:

• Controllino MAXI atmega2560.controllino_maxi.micurest_demo.zip
• NodeMCU V3 esp8266.nodemcu_v3.micurest_demo.zip
• Particle Photon stm32f2.photon.micurest_demo.zip

Please visit project's home page and tutorial for more details

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cojson

C++ pull-type JSON parser/generator for constrained platforms

COJSON Introduction

cojson is a C++ pull-type JSON parser/serializer for constrained platforms, such as bare metal applications on low-end MCUs. It does not use memory allocation and has almost no external dependencies. It is not intrusive - it neither forces nor implies any particular design of the application. Instead it adapts to fit any existing application code. It is tolerant to data type mismatching. When such occurs, parser just skips mismatching data and makes best efforts to continue parsing.

The parser is recursive, e.g. nested JSON elements are handled with the recursion. However, this recursion is driven by the structure definition, not by the input data, which prevents stack faults on malformed input data.

cojson is character type neutral - it can work with signed or unsigned character, as well as with standard wide character types: wchar_t, char16_t and char32_t.

It is also transparent for UTF8 and properly handles BOM sequence.

cojson works against a user-defined structure which specifies hierarchy, data types, and data storage access methods. Thus, when parsing is complete, the data already delivered to the application and no further processing needed.

The same structure definition is also used for writing JSON. The JSON structure is defined with a set of templetized function.

Please visit project's home page and tutorial for more details

Requirements

• Compiler: cojson sources need a C++11 enabled compiler, such as g++-4.8 and up.
• Library: libstdc++ v3 highly desirable. But if not available a workaround exists
• Code space: Depending on the platform and JSON structure complexity varies from 4kB to 20kB.
• RAM space: 20-80 bytes per entry in the defined JSON structure

Tested On

• Debian i686, g++-4.9.2
• Arduino Mega ATmega2560, avr-g++-4.8.1
• Teensy 3.1 ARM Cortex-M4 arm-none-eabi-g++-4.8.3
• Carambola2 Atheros AR9331 mips-openwrt-linux-g++-4.8.3
• MSP430FR6989 MSP430FR6989 msp430-elf-g++-4.9.1
• NodeMCU V3 ESP8266 xtensa-lx106-elf-g++-4.8.5