Merge standalone webapp and GAE in Go

I'm working on a very simple web app, written in Go language. I have a standalone version and now port it to GAE. It seems like there is very small changes, mainly concerning datastore API (in the standalone version I need just files). I also need to include appengine packages and use init() instead of main().

Is there any simple way to merge both versions? As there is no preprocessor in Go, it seems like I must write a GAE-compatible API for the standalone version and use this mock module for standalone build and use real API for GAE version. But it sounds like an overkill to me.

Another problem is that GAE might be using older Go version (e.g. now recent Go release uses new template package, but GAE uses older one, and they are incompatible). So, is there any change to handle such differences at build time or on runtime?

Thanks, Serge

UPD: Now GAE uses the same Go version (r60), as the stable standalone compiler, so the abstr开发者_运维百科action level is really simple now.

In broad terms, use abstraction. Provide interfaces for persistence, and write two implementations for that, one based on the datastore, and one based on local files. Then, write a separate main/init module for each platform, which instantiates the appropriate persistence interface, and passes it to your main application to use.

My immediate answer would be (if you want to maintain both GAE and non-GAE versions) that you use a reliable VCS which is good at merging (probably git or hg), and maintain separate branches for each version. The GAE API fits in reasonably well with Go, so there shouldn't be too many changes.

As for the issue of different versions, you should probably maintain code in the GAE version and use gofix (which is unfortunately one-way) to make a release-compatible version. The only place where this is likely to cause trouble is if you use the template package, which is in the process of being deprecated; if necessary you could include the new template package in your GAE bundle.

If you end up with GAE code which you don't want to run on Google's servers, you can also look into AppScale.