Add skip() method to ByteStream

io/bytestream.js

@@ -66,10 +66,12 @@ export class ByteStream {
     this.littleEndian_ = true;
   }
 
+  /** Big-Endian is sometimes called Motorola-style. */
   setBigEndian() {
     this.littleEndian_ = false;
   }
 
+  /** Little-Endian is sometimes called Intel-style. */
   setLittleEndian() {
     this.littleEndian_ = true;
   }
@@ -292,6 +294,27 @@ export class ByteStream {
     return strToReturn;
   }
 
+  /**
+   * Skips n bytes in the stream.
+   * @param {number} n The number of bytes to skip. Must be a positive integer.
+   */
+  skip(n) {
+    const num = parseInt(n, 10);
+    if (n !== num || num < 0) {
+      throw 'Error!  Called skip() with a non-positive integer';
+    } else if (num === 0) {
+      return;
+    }
+
+    const totalBytesLeft = this.getNumBytesLeft();
+    if (num > totalBytesLeft) {
+      throw 'Error!  Overflowed the byte stream while skip()! n=' + num +
+      ', ptr=' + this.ptr + ', bytes.length=' + this.getNumBytesLeft();
+    }
+
+    this.movePointer_(n);
+  }
+
   /**
    * Feeds more bytes into the back of the stream.
    * @param {ArrayBuffer} ab

tests/io-bytestream.spec.js

@@ -202,6 +202,51 @@ describe('bitjs.io.ByteStream', () => {
     expect(str).equals('ABCDEFGHIJKL');
   });
 
+  describe('skip()', () => {
+    /** @type {ByteStream} */
+    let stream;
+
+    beforeEach(() => {
+      for (let i = 0; i < 4; ++i) array[i] = i;
+      stream = new ByteStream(array.buffer);  
+    });
+
+    it('skips bytes', () => {
+      stream.skip(2);
+      expect(stream.getNumBytesRead()).equals(2);
+      expect(stream.getNumBytesLeft()).equals(2);
+      expect(stream.readNumber(1)).equals(2);
+      expect(stream.readNumber(1)).equals(3);
+    });
+
+    it('skip(0) has no effect', () => {
+      stream.skip(0);
+      expect(stream.getNumBytesRead()).equals(0);
+      expect(stream.getNumBytesLeft()).equals(4);
+      expect(stream.readNumber(1)).equals(0);
+    });
+
+    it('skip() with negative throws an error', () => {
+      expect(() => stream.skip(-1)).throws();
+      expect(stream.getNumBytesLeft()).equals(4);
+    });
+
+    it('skip() past the end throws an error', () => {
+      expect(() => stream.skip(4)).does.not.throw();
+      expect(stream.getNumBytesLeft()).equals(0);
+      expect(() => stream.skip(1)).throws();
+    });
+
+    it('skip() works correct across pages of bytes', () => {
+      const extraArr = new Uint8Array(4);
+      for (let i = 0; i < 4; ++i) extraArr[i] = i + 4;
+      stream.push(extraArr.buffer);
+      expect(stream.readNumber(1)).equals(0);
+      stream.skip(5);
+      expect(stream.readNumber(1)).equals(6);
+    });
+  });
+
   it('Tee', () => {
     for (let i = 0; i < 4; ++i) array[i] = 65 + i;
     const stream = new ByteStream(array.buffer);