How does this iOS app communicate over the USB port?

ios external-accessory
user2629998 picture user2629998 · Jan 24, 2015 · Viewed 19.6k times · Source

This app promises to turn your iOS device into a second monitor and uses the standard USB cable to connect to the computer, as opposed to the network which all other similar apps use.

Back when I heard about it, it wasn't yet available so I thought it was a scam. To my surprise, they released the app and it actually works as described.

How does it work ? As far as I know there are no APIs to drive the USB port in iOS, and the computer connected via USB through the standard charging/syncing cable doesn't count as an MFI accessory.

Note that they provide the server software (the one that installs on the Mac and streams the desktop to the device) on their download page for free, reverse-engineering it could shed some light on this but I unfortunately don't have the skills for that.

Answer

Huy Le picture Huy Le · Feb 25, 2015

Dean told about it on his blog.

Duet uses Peertalk, an open source library allowing to pass TCP connections through the USB connection without being part of the MFI program.

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