Go bindings for exiv2 (http://www.exiv2.org)
Those bindings are at the moment (very) incomplete, but already allow you to read the metadata of a file, get the EXIF fields out of it, and add EXIF/IPTC string fields. Binding coverage will be extended as I start needing more methods (or receiving more pull requests :) ).
You need to have libexiv2 installed at version 0.27 at least.
sudo apt install libexiv2-devNote: Because Exiv2 is a C++ library, you probably need Go 1.2 to benefit from the improved C++ support in CGO.