Avoid reading the frame unless there's enough data

This is a sanity check to avoid issues when the tag ends with padding that is not declared in the extended header.
Fixes #69.

src/ID3v2FrameReader.js

@@ -205,9 +205,12 @@ class ID3v2FrameReader {
     tags: ?Array<string>
   ): TagFrames {
     var frames = {};
-
-    while (offset < end) {
+    var frameHeaderSize = this._getFrameHeaderSize(id3header);
     // console.log('header', id3header);
+    while (
+      // we should be able to read at least the frame header
+      offset < (end - frameHeaderSize)
+    ) {
       var header = this._readFrameHeader(data, offset, id3header);
       var frameId = header.id;
 
@@ -280,31 +283,41 @@ class ID3v2FrameReader {
     return frames;
   }
 
+  static _getFrameHeaderSize(id3header: TagHeader): number {
+    var major = id3header.major;
+
+    if (major == 2) {
+      return 6;
+    } else if (major == 3 || major == 4) {
+      return 10;
+    } else {
+      return 0;
+    }
+  }
+
   static _readFrameHeader(
     data: MediaFileReader,
     offset: number,
     id3header: TagHeader
   ): TagFrameHeader {
     var major = id3header.major;
     var flags = null;
+    var frameHeaderSize = this._getFrameHeaderSize(id3header);
 
     switch (major) {
       case 2:
       var frameId = data.getStringAt(offset, 3);
       var frameSize = data.getInteger24At(offset+3, true);
-      var frameHeaderSize = 6;
       break;
 
       case 3:
       var frameId = data.getStringAt(offset, 4);
       var frameSize = data.getLongAt(offset+4, true);
-      var frameHeaderSize = 10;
       break;
 
       case 4:
       var frameId = data.getStringAt(offset, 4);
       var frameSize = data.getSynchsafeInteger32At(offset+4);
-      var frameHeaderSize = 10;
       break;
     }
 

src/__tests__/ID3v2FrameReader-test.js

@@ -413,4 +413,28 @@ describe("ID3v2FrameReader", function() {
     );
     expect(tags.MP3e).not.toBeDefined();
   });
+
+  // Some tags were found to have padding but no extended header declaring the
+  // padding size (https://github.com/aadsm/jsmediatags/issues/69).
+  it("should ignore undeclared padding", function() {
+    var artistName = bin("Lead Artist");
+    var fileData = [].concat(
+      bin("TPE1"),
+      [0x00, 0x00, 0x00, 1 + artistName.length], // size
+      [0x00, 0x00], // flags
+      [0x00], // text encoding
+      artistName, // content
+      // undeclared padding
+      [0x00, 0x00]
+    );
+    var fileReader = new ArrayFileReader(fileData);
+    var id3header = {major: 4};
+
+    var tags = ID3v2FrameReader.readFrames(
+      0,
+      fileData.length,
+      fileReader,
+      id3header
+    );
+  });
 });