it’s a blog about async, and especially cancelation. parse presumably doesn’t do any I/O. read/send are the interesting bits because they hit the network, where latency is practically unbounded. a first approach at cancelation might be to make precisely those I/O routines cancelable via (say) error injection, in such a way that none of the non-I/O code ever needs to care specifically about cancelation. so read/send is where the “interesting” cancelation logic lives or hooks into.