Resumable Uploads

Serving a market with less than reliable connections? Why let faulty connections frustrate your users when with a little dose of BrowserPlus and a sprinkle of server side logic you can offer resumable, fault-tolerant uploads.

For resumable uploads, a file is sliced into chunks with FileAccess. The file's contents are finger printed with MD5 so we can know once the file is reassembled on the server, that every bit made the journey. And to send those bits, FileTransfer is pressed into service yet again.

Discussion

API

To keep track of what's been uploaded, the typical upload script has been modified to provide a little bit of a web services api. Four JSON encoded results may be returned.

Status	Value	Description
new	" "	Initial response before file is uploaded, empty string.
partial	1,2,3	A comma separated string containing previously uploaded chunk numbers
complete	url	The url pointing to the uploaded file. Because this is a demo, the actual file is never stored on disk.
error	msg	The error message.

For example, when a file is partially uploaded, this response is returned:

{
    "status" : "partial",
    "value"  : "0,1,2,3,4"
}

Farther

This demo artificially limits the user to uploading a single file, one chunk at a time. With a few adjustments, the code could be extended to upload multiple chunks at once, as well as handle multiple files. And as Uploadr shows, files could easily be archived or compressed before uploading to save users with slow links.

While the demo does MD5 checksumming on the entire contents of the file, each individual chunk could be finger printed with the client and then checked upon arrival at the server.

Happy hacking.

Note: Source on GitHub.