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POaccept socket from local client on ALL interfaces; rejcct remote client
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  1. POaccept socket from local client on ALL interfaces; rejcct remote client
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    copied!<p>I need to write a small socket server proxy application that accepts connections from local applications on ALL interfaces (socket should bind to 0.0.0.0).</p> <p>I'm not aware of way to achieve this (I have additional requirements that prevent binding to the 127.0.0.1).</p> <p>A first attempt at this does the following:</p> <p>bind(0.0.0.0) ... s = accept() ... // reject remote connection if (s.src_addr is not in local_interfaces) close() ... //proceed normally with local conenction</p> <p>This implementation has a side effect on remote applications - they see an accept/close combination. The system is required to behave such that remote application perceive that "nothing is there": -->SYN &lt;--RST/ACK</p> <p>To implement this behavior I used winsock API combination of SO_CONDITIONAL_ACCEPT and a WSAAccept callback (LPCONDITIONPROC lpfnCondition),to accept / reject a connection based on its origin interface (i.e. is it one of the local addresses or not).</p> <p>This results in the desired functional behavior: local apps work; remote apps get the required WSAECONNREFUSED error.</p> <p>This comes with a certain prices: SO_CONDITIONAL_ACCEPT has certain side effects (see MSDN), but more importantly, we need a LINUX implementation and may later have to port this to other UNIXs.</p> <p>My first priority is a LINUX solution. Note that I'm willing to go beyond the socket API if that's what it takes.</p>
 

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