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?

Answer 1

Unless your application is actually responding to and generating its own IP packets (which would be incredibly silly), you probably don’t need to do testing at that layer. Simply testing at the TCP layer (e.g, connect(), send(), recv(), shutdown()) will probably be sufficient, as those events are the only ones which your server will be aware of.