~/Downloads/gun-master$ rebar3 compile
===> Verifying dependencies...
===> Fetching cowlib ({git,"https://github.com/ninenines/cowlib",
"master"})
===> WARNING: It is recommended to use {branch, Name}, {tag, Tag} or {ref, Ref}, otherwise updating the dep may not work as expected.
===> Fetching ranch ({git,"https://github.com/ninenines/ranch",
"master"})
===> WARNING: It is recommended to use {branch, Name}, {tag, Tag} or {ref, Ref}, otherwise updating the dep may not work as expected.
===> Compiling cowlib
===> Compiling ranch
===> Compiling gun
/Users/7stud/Downloads/gun-master/_build/default/lib/gun/src/gun_sse.erl:16: Warning: behaviour gun_content_handler undefined
/Users/7stud/Downloads/gun-master/_build/default/lib/gun/src/gun_data.erl:16: Warning: behaviour gun_content_handler undefined
OSX 10.10.5 Erlang 19.2