it is too abstract to say for sure, but send might just block until the request is handled off to the next layer (for example succesfully written to the OS network socket buffer), so unless the server carefully closes its recv window until it is done handling the request[1] , no, I wouldn't expect send to block until the server is done handling the request.

[1] i.e. backpressure, which would actually be the ideal way for the server to implement whatever rate limiting it wants, but we are assuming here that the server has a less than ideal interface.