add getOffset to DataStream

package.json

@@ -1,6 +1,6 @@
 {
   "name": "armarius-io",
-  "version": "1.1.0",
+  "version": "1.2.0",
   "description": "IO and compression library for Armarius",
   "repository": "github:aternosorg/armarius-io",
   "type": "module",

src/IO/DataStream.js

@@ -14,12 +14,24 @@ export default class DataStream {
     /**
      * Get the final length of the data stream.
      * Return null if the length is unknown.
+     *
      * @return {?number}
      * @abstract
      */
     getFinalLength() {
     }
 
+    /**
+     * Get the current offset within the data stream.
+     * (The number of bytes read so far since the stream was created/the last reset() call.)
+     *
+     * @return {number}
+     * @abstract
+     */
+    getOffset() {
+
+    }
+
     /**
      * @return {Promise<this>}
      * @abstract

src/IO/IO.js

@@ -280,5 +280,12 @@ export default class IO extends DataStream {
     getFinalLength() {
         return this.byteLength;
     }
+
+    /**
+     * @return {number}
+     */
+    getOffset() {
+        return this.offset;
+    }
 }