Save persistent file in NaCl and read inside app JavaScript code

Question

In my chrome app, I would like to save a persistent file in NaCl module (using Pepper API or nacl_io), then open and read it with JavaScript code inside the app.

The NaCl part is implemented by using nacl_io and works fine (with html5fs and PERSISTENT type).

How can I do the other part in JS code?

Answer 1

You can access the files in JavaScript using the Filesystem API.

Here is an example of reading a file from that page:

function onInitFs(fs) {

  fs.root.getFile('log.txt', {}, function(fileEntry) {

    // Get a File object representing the file,
    // then use FileReader to read its contents.
    fileEntry.file(function(file) {
       var reader = new FileReader();

       reader.onloadend = function(e) {
         var txtArea = document.createElement('textarea');
         txtArea.value = this.result;
         document.body.appendChild(txtArea);
       };

       reader.readAsText(file);
    }, errorHandler);

  }, errorHandler);

}

window.requestFileSystem(window.TEMPORARY, 1024*1024, onInitFs, errorHandler);

In your case, you'll want to read from the PERSISTENT filesystem instead of the TEMPORARY filesystem.

Please note that this API is prefixed in Chrome as window.webkitRequestFileSystem.