Latency toxic is not bidirectional (and this is undocumented) #655
Description
I'm using toxiproxy to test an networked game that uses Cristian's Algorithm to synchronize a client clock with a server clock. On a typical TCP connection, latency will be symmetric after the first few messages are exchanged.
Based on my testing, the latency toxic is unidirectional, applying only to host-to-client communications. This asymmetric delay breaks the assumptions underlying this clock sync method. When running client and server on the same PC with a toxiproxy between them, a clock sync request dispatched at T=475218ms reaches the server at T=475218ms (ie, immediately) and the reply is received at T=475278ms (with the 60ms latency I configured).
TRACE time sync_receive: Roundtrip 60ms (client real time 180475218~180475278)
Host's real time: 180475218
Furthermore, the unidirectional latency is undocumented: indeed, the README implies otherwise:
latency
Add a delay to all data going through the proxy. The delay is equal tolatency+/-jitter.
If latency were indeed applied to all data going through the proxy, I would expect a latency toxic valued at 25ms to produce 50ms of roundtrip delay. But this is not the case (and this project seems much too mature to change the default behavior).
So, I recommend updating the documentation to reflect the "one-way" nature of the latency toxic.
In the future, a bidirectional mode for the latency toxic would be very useful for applications like mine. Symmetric latency allows for a much better simulation of real-world network conditions than the current toxic.