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AudioDownloader Class

Author: Tom Byrne

The AudioDownloader class simplifies the task of "chunking" a large remote (audio) file down to the device. The server hosting the remote file must support byte-ranged GET requests. Note that some very convenient places to publicly host a file (Dropbox, Google Drive, Box) all use chunked transfer encoding, which this class does not yet support.

Usage

The AudioDownloader communicates with the device via two events, push and pull.

On instantiation, the downloader configures a callback handler for pull events from the device. During a download, pull events will trigger the downloader to fetch the next chunk of data from the remote URL and send that chunk to the device with a push event.

The pull event allows the device to apply some back pressure during a download. At the start of a download, the AudioDownloader will push a pre-set number of chunks to the device (this number is set by QUEUE_DEPTH inside the class). After this, a new chunk will only be fetched and sent on a pull event; the device can be configured to send this event only after consuming a complete buffer.

Steps to performing a chunked download:

  1. Instantiate the AudioDownloader
  2. Set the URL to download from
  3. Call the start method to begin the download. The download will complete automatically when the full file is fetched.

Example

downloader <- AudioDownloader();

http.onrequest(function(req, res) {
    downloader.setDownloadURL(req.body);
    res.send(200, "OK\n");
    downloader.start();
});

For a more complete example, see the examples folder for the VS10XX Audio Codec IC.