Apps Suggestions for Library for Android based Chat App

[rscl.mumbai]

Hi,

Has anyone developed a Web Sockets based Chat app?
I'm wondering what Libraries / APIs to use.
Some of my requirements are:

• Async send/recv of messages
• Send-Recv files (images, pdf etc)
• Maintain chat sessions when switching between Mobile data - Wifi - No Connectivity
• Prevent message loss during low or no connectivity
• Concurrent messaging from multiple devices

Please share your choices & reasons. I'd also like to know how your experience was?

Suggestions & advices welcome!

Thanks in advance
Sans