Getting Production Data Out of Google App Engine And Into your iOS App

This following post is probably going to be useful to an extremely niche audience: anyone developing a multi-user iOS app that has a GAE backend. I’m currently working on Outwitters and debugging turn-based games on the local dev server (dev_appserver.py) is really quick and painless. The problem arises from the nature the game. It’s a multiplayer game, and as such, requires multiple users to function. You can only go so far with creating ‘mock user’ accounts, and fake data populating your local server. With each build I always find some sort of issue that the alpha testers stumble across that may not be server-related but the gamestate that the “production” server is holding is something I want to grab and debug with locally. Wouldn’t that be nice?

So when you run a local dev server the command is pretty simple:

[code]

dev_appserver.py pathToCode

[/code]

Not bad. Now if you want to access it on your machine you simply do an http request to localhost:8080. The problem comes in when you’re developing for a mobile device. The dev server is no longer at localhost but on some local LAN IP. That’s a pretty easy fix too:

[code]

dev_appserver.py –address 192.168.1.x pathToCode
[/code]

Now in your iOS app you can send requests to a local server. We’re in business, awesome! So you want to download the data from your hosted application over at appengine.google.com? Pretty simple. Uploading it is pretty straightforward to if you use the –url option with “appcfg.py upload_data”.

Now this is where I ran into problems, and I couldn’t find a clear cut answer as to why uploading data to my local dev server was simply not working. It would ask for credentials, and no matter what I put, it would fail. Hopeless. I used all sorts of combinations of my local address and ports for the –url flag for appcfg.py and tried countless combinations of any of my known logins for both appengine and my local dev machine. I then decided to go back to basics, and follow their instructions exactly. I downloaded the production data as documented. Then I launched a clean dev server with no command line options. It worked as advertised! I had all the data frolicking about inside my dev server, but I couldn’t access it with any of my iOS devices. Without the address option, the dev server would launch with localhost as being it’s address, and no other device could connect to it.

So after banging my head on the keyboard for a couple hours, and not being able to find any answers as to why upload_data only works to a local dev server if you’re running on localhost, I found a round-about way of getting production data into my own iOS friendly dev server:

  1. Download the data as per the documentation
  2. Now launch  dev_appserver.py, but this time declare a datastore path as a command line argument. This is the –datastore_path= option. Also run it with a –default_partition of “” (empty string), to mirror production’s data.
  3. Now that you have a dev server running on localhost with a defined datastore file, upload your data to your dev server with appcfg.py (by using the –url option pointed to localhost).
  4. Once uploaded you can now shut down that server.
  5. Now run a dev_appserver with the commands that you usually run with (the –address flag), but add a –datastore_path pointing to the datastore file you used in step 2.
  6. W0ot!
A lot more cumbersome than just doing a simple download/upload routine to test stuff locally. Of course, I may be missing something entirely as I’m still relatively new to GAE, and there may be a way to do this with a local dev server that is running on an actual LAN ip instead of localhost, but I haven’t been able to find it. Hopefully this will prove useful to those using GAE for their iOS apps as well, or they’ve found a better way to do this and can leave a comment :).

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