node-crc16

Node CRC16 - (中文版README)

MODBUS is an application-layer messaging protocol, positioned at level 7 of the OSI model. It provides client/server communication between devices connected on different types of buses or networks.The CRC(Cyclic Redundancy Check) part in protocol, such as MODBUS over serial line(Page 42), and Modbus-RTU(Page 75), adopt the same one algorithm.

node-crc16 implement the c++ version of this algorithm by table look-up, and also provide a node native addon and a nodejs version wrapper.

This module has been well unit tested and documented.

Versions

If your version of node.js is lower than v8.x.x, please use the latest v1.x.x of this module, or you should select v2.x.x, which uses NAPI to implement native addon gracefully and compatibly.

Usage

Tips: the most intuitive decription about this module is the comment in src and the code in unit test :).

Install

npm install node-crc16

generate a sum by crc16.checkSum

checkSumaccept three params, the first two params (input, [encoding]) construct a Buffer

crc16.checkSum('utf8 string', 'utf8')

default encoding is hex

var sum = crc16.checkSum('a031ffb7');
sum.should.equal('726d');

the third param is option，which type is Object

• option.retType set the format of the returned sum
  • default is hex，two bytes BigEndian hex string, 726d
  • array, two unsigned char number of the returned sum，[114, 109]
  • int，one unsigned short number of the returned sum，29293
  • buffer，Buffer type of the returned sum，<Buffer 72 6d>

var sum = crc16.checkSum('a031ffb7', {retType: 'array'});
sum.should.eql([114, 109]);

verify a sum by crc16.verifySum

Params of verifySum is same as checkSum, the first two params are used to constructe a Buffer which contains the sum to be verified.

var stream = 'a031ffb7',
    sum = '726d';
var isValid = crc16.verifySum(stream + sum);
isValid.should.equal(true);

Contribution

get source code

# fork and clone the code to your local env 
git clone [e-mail]:imnemo/crc16.git
cd crc16

code structure

├── lib         //CRC16 algorithm implemention in c++
├── util        //Util functions
├── src         //Node Native Addon
├── test        //JS unit testing
├── test_cpp    //C++ unit testing
├── index.js    //Main entry of NodeJS module

install dependencies

npm install

C++ unit testing

The implemention of CRC16 checking and verifing algorithm in c++ is standalone in ./lib/crc16.cc. If you want to modify it, please write suitable unittest cases. You can reference Catch, and then run:

make test

Make sure all the unit testing case is passed after you modify.

JS unit testing

npm test or ./node_modules/.bin/mocha --reporter spec

Benchmark

use benchmark.js

 >>> npm run benchmark
 
> node-crc16@1.0.0 benchmark /Users/nemo/code/imnemo/crc16
> node benchmark/benchmark.js
 
CEC16#checkSum x 905,071 ops/sec ±2.00% (83 runs sampled)
CRC16#verifySum x 1,540,940 ops/sec ±19.92% (65 runs sampled)
Fastest is CRC16#verifySum

use nanobench

 >>> npm run nanobench
 
> node-crc16@1.0.0 nanobench /Users/nemo/code/imnemo/crc16
> node benchmark/nanobench.js
 
NANOBENCH version 2
> /Users/nemo/.nvm/versions/node/v8.1.2/bin/node benchmark/nanobench.js
 
# CRC16#checkSum 2,000,000 times 
ok ~3.17 s (3 s + 166422442 ns)
 
# CRC16#verifySum 2,000,000 times 
ok ~2.85 s (2 s + 848059820 ns)
 
all benchmarks completed
ok ~6.01 s (6 s + 14482262 ns)

pull request

You can pull a request when you complete all steps above.

TODO

• Add JS code lint
• Add changelog
• Add JS unit test
• Add JS unit test code covarage
• Add C++ unit test
• Add CI
• Add performance test
• Refactor node native addon part with NAPI
• Add index.js.d
• Add global module supported to provide a cli tool
• Add donate entry

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