Firefox Addon Reading Local XPI, File and Directory Listing

Question

Following a chat in #amo-editors, I was wondering if the following are possible from a Firefox Addon:

1. Opening a local XPI for reading
2. Listing all files in above XPI with their sizes
3. Reading selected files

Answer 1

Absolutely possible.

1 + 2) Have to use nsIZipReader to read the xpi. This gives you all files within it.

3) To read contents you have to use zip readers getInputStream function and then wrap it in stream instance, then read it with argument of entry.realSize as read on stream takes characters to read.

MDN :: nsIZipWriter

MDN :: nsIZipReader

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edit: i was curious. i think i got it. heres example of how to make it dump contents of a zip (list all files within). see the console.log(entryPointer) that spits out the "zip path". it also reads the contents of the files.

var zr = Cc["@mozilla.org/libjar/zip-reader;1"].createInstance(Ci.nsIZipReader);
Cu.import('resource://gre/modules/osfile.jsm');
Cu.import('resource://gre/modules/FileUtils.jsm');

var reusableStreamInstance = Cc['@mozilla.org/scriptableinputstream;1'].createInstance(Ci.nsIScriptableInputStream);

//var pathExtFolder = OS.Path.join(OS.Constants.Path.profileDir, 'extensions');
var pathToXpiToRead = OS.Path.join(OS.Constants.Path.profileDir, 'extensions', 'PortableTester@jetpack.xpi');
var nsiFileXpi = new FileUtils.File(pathToXpiToRead);

//Services.ww.activeWindow.alert(pathToXpiToRead);

try {
  zr.open(nsiFileXpi); //if file dne it throws here
  var entries = zr.findEntries('*');
  while (entries.hasMore()) {
    var entryPointer = entries.getNext(); //just a string of "zip path" (this means path to file in zip, and it uses forward slashes remember)
    var entry = zr.getEntry(entryPointer); // should return true on `entry instanceof Ci.nsIZipEntry`
    console.log('entryPointer', entryPointer);
    /* CONSOLE OUTPUT
     * "entryPointer" "bootstrap.js" Scratchpad/1:18
     */
    console.info('entry', entry);
    /* CONSOLE OUTPUT
     * "entry" XPCWrappedNative_NoHelper { QueryInterface: QueryInterface(), compression: Getter, size: Getter, realSize: Getter, CRC32: Getter, isDirectory: Getter, lastModifiedTime: Getter, isSynthetic: Getter, permissions: Getter, compression: 8 } Scratchpad/1:19
     */
    if (!entry.isDirectory) {
        var inputStream = zr.getInputStream(entryPointer);
        reusableStreamInstance.init(inputStream);
        var fileContents = reusableStreamInstance.read(entry.realSize);
        console.log('contenst of file=', fileContents);
    } else {
        console.log('is directory, no stream to read');
    }
  }
} catch (ex) {
  console.warn('exception occured = ', ex);
  if (ex.name == 'NS_ERROR_FILE_NOT_FOUND') {
    Services.ww.activeWindow.alert('XPI at path does not exist!\n\nPath = ' + pathToXpiToRead);
  }
} finally {
  zr.close();
  console.log('zr closed');
  //Cu.forceGC(); //im not sure shoud i do this here?
}

I'm not sure if I should do a Cu.forceGC() in the finally, maybe @nmaier can advise us on that.

I'm also not sure if I handled reading the input stream properly, it works, but i dont know memory wise. I did .read(entry.realSize) first time doing this.

variable viewer on entry: