Add Length Value Decoder Operatoin

src/core/config/Categories.json

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

src/core/lib/LengthValue.mjs

@@ -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;
+    }
+}

src/core/operations/LengthValueDecoder.mjs

@@ -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;