Add Length Value Decoder Operatoin

This commit is contained in:
GCHQ 77703 2018-08-27 01:17:06 +01:00
parent 3905c01a0d
commit 032b4bed7f
3 changed files with 151 additions and 1 deletions

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@ -53,7 +53,8 @@
"To MessagePack",
"From MessagePack",
"To Braille",
"From Braille"
"From Braille",
"From Length Value"
]
},
{

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@ -0,0 +1,71 @@
/**
* @author gchq77703 []
* @copyright Crown Copyright 2018
* @license Apache-2.0
*/
const defaults = {
location: 0,
bytesInLength: 1,
basicEncodingRules: false
};
/**
* Length Value library
*/
export default class LengthValue {
/**
* LengthValue constructor
*/
constructor(input, options) {
this.input = input;
Object.assign(this, defaults, options);
}
/**
* @returns {Number}
*/
getLength() {
if (this.basicEncodingRules) {
const bit = this.input[this.location];
if (bit & 0x80) {
this.bytesInLength = bit & ~0x80;
} else {
this.location++;
return bit & ~0x80;
}
}
let length = 0;
for (let i = 0; i < this.bytesInLength; i++) {
length += this.input[this.location] * Math.pow(Math.pow(2, 8), i);
this.location++;
}
return length;
}
/**
* @param {Number} length
* @returns {Number[]}
*/
getValue(length) {
const value = [];
for (let i = 0; i < length; i++) {
value.push(this.input[this.location]);
this.location++;
}
return value;
}
/**
* @returns {Boolean}
*/
atEnd() {
return this.input.length <= this.location;
}
}

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@ -0,0 +1,78 @@
/**
* @author gchq77703 []
* @copyright Crown Copyright 2018
* @license Apache-2.0
*/
import Operation from "../Operation";
import LengthValue from "../lib/LengthValue";
/**
* From Length Value operation
*/
class FromLengthValue extends Operation {
/**
* FromLengthValue constructor
*/
constructor() {
super();
this.name = "From Length Value";
this.module = "Default";
this.description = "Converts a Length-Value (LV) encoded string into a line-delimited JSON (LDJSON / Streaming JSON) format";
this.infoURL = "";
this.inputType = "byteArray";
this.outputType = "string";
this.args = [
{
name: "Bytes in Length Value",
type: "populateOption",
value: [
{
name: "1 Byte",
value: "1"
},
{
name: "2 Bytes",
value: "2"
},
{
name: "4 Bytes",
value: "4"
}
]
},
{
name: "Use Basic Encoding Rules",
type: "boolean"
}
];
}
/**
* @param {byteArray} input
* @param {Object[]} args
* @returns {string}
*/
run(input, args) {
const bytesInLength = parseInt(args[0].split(" ")[0], 10);
const basicEncodingRules = args[2];
const lv = new LengthValue(input, { bytesInLength, basicEncodingRules });
const data = [];
while (!lv.atEnd()) {
const dataLength = lv.getLength();
const value = lv.getValue(dataLength);
data.push(value);
}
return data.map(line => line.map(value => ("00" + value.toString(16)).slice(-2)).join(" ")).join("\n");
}
}
export default FromLengthValue;