Merge pull request #1915 from Oshawk/take-nth-bytes

Add 'Take nth bytes' operation

src/core/config/Categories.json

@@ -327,6 +327,7 @@
             "Pseudo-Random Number Generator",
             "Sleep",
             "File Tree",
+            "Take nth bytes",
             "Drop nth bytes"
         ]
     },

src/core/operations/TakeNthBytes.mjs

@@ -0,0 +1,79 @@
+/**
+ * @author Oshawk [[email protected]]
+ * @copyright Crown Copyright 2019
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation.mjs";
+import OperationError from "../errors/OperationError.mjs";
+
+/**
+ * Take nth bytes operation
+ */
+class TakeNthBytes extends Operation {
+
+    /**
+     * TakeNthBytes constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Take nth bytes";
+        this.module = "Default";
+        this.description = "Takes every nth byte starting with a given byte.";
+        this.infoURL = "";
+        this.inputType = "byteArray";
+        this.outputType = "byteArray";
+        this.args = [
+            {
+                name: "Take every",
+                type: "number",
+                value: 4
+            },
+            {
+                name: "Starting at",
+                type: "number",
+                value: 0
+            },
+            {
+                name: "Apply to each line",
+                type: "boolean",
+                value: false
+            }
+        ];
+    }
+
+    /**
+     * @param {byteArray} input
+     * @param {Object[]} args
+     * @returns {byteArray}
+     */
+    run(input, args) {
+        const n = args[0];
+        const start = args[1];
+        const eachLine = args[2];
+
+        if (parseInt(n, 10) !== n || n <= 0) {
+            throw new OperationError("'Take every' must be a positive integer.");
+        }
+        if (parseInt(start, 10) !== start || start < 0) {
+            throw new OperationError("'Starting at' must be a positive or zero integer.");
+        }
+
+        let offset = 0;
+        const output = [];
+        for (let i = 0; i < input.length; i++) {
+            if (eachLine && input[i] === 0x0a) {
+                output.push(0x0a);
+                offset = i + 1;
+            } else if (i - offset >= start && (i - (start + offset)) % n === 0) {
+                output.push(input[i]);
+            }
+        }
+
+        return output;
+    }
+
+}
+
+export default TakeNthBytes;

tests/operations/index.mjs

@@ -150,6 +150,7 @@ import "./tests/StripUDPHeader.mjs";
 import "./tests/Subsection.mjs";
 import "./tests/SwapCase.mjs";
 import "./tests/SymmetricDifference.mjs";
+import "./tests/TakeNthBytes.mjs";
 import "./tests/TextEncodingBruteForce.mjs";
 import "./tests/ToFromInsensitiveRegex.mjs";
 import "./tests/TranslateDateTimeFormat.mjs";

tests/operations/tests/TakeNthBytes.mjs

@@ -0,0 +1,123 @@
+/**
+ * @author Oshawk [[email protected]]
+ * @copyright Crown Copyright 2019
+ * @license Apache-2.0
+ */
+
+import TestRegister from "../../lib/TestRegister.mjs";
+
+/**
+ * Take nth bytes tests
+ */
+TestRegister.addTests([
+    {
+        name: "Take nth bytes: Nothing",
+        input: "",
+        expectedOutput: "",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 0, false],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Nothing (apply to each line)",
+        input: "",
+        expectedOutput: "",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 0, true],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Basic single line",
+        input: "0123456789",
+        expectedOutput: "048",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 0, false],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Basic single line (apply to each line)",
+        input: "0123456789",
+        expectedOutput: "048",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 0, true],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Complex single line",
+        input: "0123456789",
+        expectedOutput: "59",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 5, false],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Complex single line (apply to each line)",
+        input: "0123456789",
+        expectedOutput: "59",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 5, true],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Basic multi line",
+        input: "01234\n56789",
+        expectedOutput: "047",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 0, false],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Basic multi line (apply to each line)",
+        input: "01234\n56789",
+        expectedOutput: "04\n59",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 0, true],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Complex multi line",
+        input: "01234\n56789",
+        expectedOutput: "\n8",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 5, false],
+            },
+        ],
+    },
+    {
+        name: "Take nth bytes: Complex multi line (apply to each line)",
+        input: "012345\n6789ab",
+        expectedOutput: "5\nb",
+        recipeConfig: [
+            {
+                op: "Take nth bytes",
+                args: [4, 5, true],
+            },
+        ],
+    }
+]);