This book appeared very shortly after Go hit 1.0. It was an invaluable resource at the time. Now, maybe not so much, but thanks to Jan for putting in the work when it was dearly needed by the community.
Agreed, I was looking through the examples in the HTTP chapter and they're not very idiomatic Go code by today's standards. For HTTP at least, you're better off following the examples from the official Go documentation than following this book.
I can't speak to the rest of the book, which seems like a pretty ambitious effort, but the crypto content needs to be burned out of it with a scorching torch.
"Security" is a big topic. For cryptography, a good (but inadequate) starting point is _Cryptography Engineering_. If you write cryptography the way this book suggests you should, you will implement egregious vulnerabilities.
We thought the book had some good parts. If you want to see more examples, Russ Whites' blog http://ntwrk.guru/ actually dissects a network protocol stack written in go. He goes fairly deep as the protocols are open sourced and written in go. He mainly focuses on BGP in GO. Fun read. Very insightful.
For martini specifically, there are a couple libs found under martini-contrib community [1], but nothing on the maturity level of django/rails. It's still fairly wild-west unless you're content using http basic auth.
