Added decoder for chunked HTTP encoding

This decoder will join up a HTTP response sent using chunked transfer encoding, raised in issue #168.

This is useful when attempting to extract files or gzipped responses sent using chunked transfer encoding, particularly when combined with the gunzip operation.

src/core/operations/DechunkHTTP.mjs

@@ -0,0 +1,50 @@
+/**
+ * @author sevzero [sevzero@protonmail.com]
+ * @copyright Crown Copyright 2016
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation";
+
+/**
+ * Dechunk HTTP response operation
+ */
+class DechunkHTTP extends Operation {
+
+    /**
+     * DechunkHTTP constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Dechunk HTTP response";
+        this.module = "Default";
+        this.description = "Parses a HTTP response transferred using transfer-encoding:chunked";
+        this.inputType = "string";
+        this.outputType = "string";
+        this.args = [];
+    }
+
+    /**
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    run(input, args) {
+        var chunks = [];
+        var chunkSizeEnd = input.indexOf("\n") + 1;
+        var lineEndings = input.charAt(chunkSizeEnd - 2) == "\r" ? "\r\n" : "\n";
+        var lineEndingsLength = lineEndings.length;
+        var chunkSize = parseInt(input.slice(0, chunkSizeEnd), 16);
+        while (!isNaN(chunkSize)) {
+            chunks.push(input.slice(chunkSizeEnd, chunkSize + chunkSizeEnd)); 
+            input = input.slice(chunkSizeEnd + chunkSize + lineEndingsLength);
+            chunkSizeEnd = input.indexOf(lineEndings) + lineEndingsLength;
+            chunkSize = parseInt(input.slice(0, chunkSizeEnd), 16);
+        }
+        return chunks.join('') + input;
+    }
+
+}
+
+export default DechunkHTTP;