Moved to Forum: Original Link
First-time poster, long-time lurker. Totally free, detailed ebook on the internals of Android. A little old - does not include v7 stuff - but pretty darn good, and excellent at a cost of free. Author has been screwed by the #Vault7 leaks including a copy of his book, so he's releasing it for free from his website to hopefully reduce the number of people who are back-doored with a dodgy PDF. I'm in no way affiliated, but I like free and I like people doing nice things so if you like the book as well, try to swing the guy a few bucks (I will be).
vault7 contained thousands of documents, nobody would've noticed.