Can't connect to 0.0.0.0 under Windows in GAE development mode

Question

We have a java application serving images thru Image Service from GAE. Testing it with eclipse under a Linux machine works perfect. But testing exactly the same code in a Windows machine (Vista) fails when bringing the images. The images url are like:

http://0.0.0.0:8888/_ah/img/encoded_gs_key:cHJvZmlsZXBpY3R1cmVzLzVVTkhjc1IybjktQTlrckdiZWZfTkE

I think it has to do with the 0.0.0.0 address, since Linux resolves it to 127.0.0.1 but Windows fails even pinging to it. Is there any way to make 0.0.0.0 works under Windows? Is there any way to change the 0.0.0.0 address that GAE development mode uses to resolve images?

Answer 1

Short answer: I agree with Eight-Bit Guru. The fact that it works on Linux is probably just luck. (Although I'm sure the Linux networking guys would claim that Windows has it all wrong, but I digress).

I hit a similar issue porting some code from Linux to Windows once. My main thread would send an empty UDP packet to the listening address of the socket blocked on a recvfrom call on another thread. The thread waking up on the blocking recvfrom() call would notice the exit condition and promptly return.

The code on Linux worked. The main thread would call getsockname to get the local listen address of the socket and send a packet to it. And it just kind of worked when the socket was binded on INADDR_ANY (which means "all adapters", but is encoded as 0.0.0.0). Sending to 0.0.0.0 would reach the listening socket.

But this code path bombed on the port to Windows. The fix was to just detect when the listen address was 0.0.0.0 and switch it to send to 127.0.0.1 (localhost). And all was well.

So if fixing the code that generates the URL doesn't work, here's two solutions I thought about:

1. Add a route to the routing table (doesn't work)

Now I got to thinking if it was possible to just add a route to the route table. From the cmd line:

route add 0.0.0.0 MASK 255.255.255.255 10.120.30.194

That actually successfully adds a route to the table...

But alas, it didn't seem to work like I thought it would....

2. Run a proxy server

I think this might work for local debugging. You could run Fiddler along with your code. Implement a script/rule in Fiddler that will convert 0.0.0.0 to 127.0.0.1.

You didn't say what was doing the download. If it's a browser, then something like GreaseMonkey might be your friend.

Answer 2

I think in this case, Linux is doing it wrong - I assume it's trying to be helpful by routing 0.0.0.0 to 127.0.0.1 in an attempt to help things work, but actually 0.0.0.0 is intended to be a non-routable address and Windows is correctly not routing it.

See here: http://en.wikipedia.org/wiki/0.0.0.0