iPhone: Strategies for uploading large files from phone to server

We're running into issues uploading hires images from the iPhone to our backend (cloud) service. The call is a simple HTTP file upload, and the issue appears to be the connection breaking before the upload is complete - on the server side we're getting IOError: Client read error (Timeout?).

This happens sporadically: most of the time it works, sometimes it fails. When a good connection is present (ie. wifi) it always works.

We've tuned various timeout parameters on the client library to make sure we're not hitting any of them. The issue actually seems to be unreliable mobile connectivity.

I'm thinking about strategies for making the upload reliable even when faced with poor connectivity.

The first thing that came to mind was to break th开发者_StackOverflowe file into smaller chunks and transfer it in pieces, increasing the likelihood of each piece getting there. But that introduces a fair bit of complexity on both the client and server side.

Do you have a cleverer approach? How would you tackle this?

I would use the ASIHTTPRequest library. It's have some great features like bandwidth throttling. It can upload files directly from the system instead of loading the file into memory first. Also I would break the photo into like 10 parts. So for a 5 meg photo, it would be like 500k each. You would just create each upload using a queue. Then when the app goes into background, it can complete the part it's currently uploading. If you cannot finish uploading all the parts in the allocated time, just post a local notification reminding the user it's not completed. Then after all the parts have been sent to your server, you would call a final request that would combine all the parts back into your photo on the server-side.

Yeah, timeouts are tricky in general, and get more complex when dealing with mobile connections.

Here are a couple ideas:

1. Attempt to upload to your cloud service as you are doing. After a few failures (timeouts), mark the file, and ask the user to connect their phone to a wifi network, or wait till they connect to the computer and have them manually upload via the web. This isn't ideal however, as it pushes more work to your users. The upside is that implementationwise, it's pretty straight forward.

2. Instead of doing an HTTP upload, do a raw socket send instead. Using raw socket, you can send binary data in chunks pretty easily, and if any chunk-send times out, resend it until the entire image file is sent. This is "more complex" as you have to manage binary socket transfer but I think it's easier than trying to chunk files through an HTTP upload.

Anyway that's how I would approach it.