How to test server behavior under network loss at every possible packet

Question

I'm working with mobile, so I expect network loss to be common. I'm doing payments, so each request matters.

I would like to be able to test my server to see precisely how it will behave with client network loss at different points in the request cycle -- specifically between any given packet send/receive during the entire network communication.

I suspect that the server will behave slightly differently if the communication is lost while sending the response vs. while waiting for a FIN-ACK, and I want to know which timings of disconnections I can distinguish.

I tried simulating an http request using scapy, and stopping communication between each TCP packet. (I.e.: first send SYN then disappear; then send SYN and receive SYN-ACK and then disappear; then send SYN and receive SYN-ACK and send ACK and then disappear; etc.) However, I quickly got bogged down in the details of trying to reproduce a functional TCP stack.

Is there a good existing tool to automate/enable this kind of testing?