ASIHTTPRequest Problem

Why do I always get the “A connection failure occurred” on the 1st attempt, but success on the next?

This issue I had a lot of hard time to figure out why. The problem resides in ASIHTTPRequest itself (iOS), not the rails code.
To make a long story short, the problem is specific to the use of persistent connection for every request sent by ASIHTTPRequest.
While this is good for GET requests, most server implementation does not allow persistent connection to be used with POST request.
I didn't really have time to investigate it deeply on the server side of things but I think that the problem resides with the 100-Continue header that should be sent (and which isn't) with request that has body attached to it (hence PUT/POST). If you want to have a deeper look at what I'm talking about go have a read at the spec sheet: http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html
So the persistent connection used by ASIHTTPRequest wait for a 100 response to be sent, which is never sent. so it ends up being timed out.
A fix is to set persistentConnection to NO with your post requests like the following:

ASIHTTPRequest *req                     = [ASIHTTPRequest requestWithURL:url];
req.shouldAttemptPersistentConnection   = NO;