There is a bug in the Flash player that makes it impossible to implement a RESTful architecture with a Flex or Flash backend. In essence, it is a buggy implementation of an http client - the client cannot get to the response body unless the reponse code is 200.. This is really bad. But what is an embarrassment for Adobe is that: That bug was opened more than a year ago It is marked as priority C only It was closed and had to be reopened after the community complained Adobe engineers suggested as a workaround to purchase LCDS Server So, lessons learned (actually: lessons that proof in practice what was clear beforehand ): It does not matter too much if Flex is open-sourced as long as the Flash player is not It does not matter at all if Flex or Flash are open-sourced if the community cannot apply patches and get them into the deployed player Flex being open source is completely irrelevant.
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