ssl:send gets stuck

I have some tests in Ranch that get stuck when trying to send data using an ssl socket:

https://builds.ninenines.eu/logs/ranch/121/archlinux/ct_run.ct_ranch@archlinux0.2019-05-07_09.30.18/ninenines.ranch.sendfile_SUITE.logs/run.2019-05-07_09.30.53/suite.log.html

These tests send a 20MB file containing random data, emulating the file:sendfile function with normal sends.

What I can see from an initial look is that:

• The test itself gets stuck when trying to send via ssl:send -> tls_sender:send_data
• The tls_sender process gets stuck with the following stacktrace:

[{prim_inet,send_recv_reply,2,[]},
 {tls_sender,send_application_data,4,
     [{file,"tls_sender.erl"},{line,432}]},
 {gen_statem,call_state_function,5,
     [{file,"gen_statem.erl"},{line,1586}]},
 {gen_statem,loop_event_state_function,6,
     [{file,"gen_statem.erl"},{line,967}]},
 {proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,249}]}]

I can see this issue on Arch Linux (local and server), Ubuntu and macOS at the moment, so it's probably not platform-specific.

There was no such problems with OTP-21.3.7, for example: https://builds.ninenines.eu/logs/ranch/120/archlinux/

To reproduce you can do the following:

$ git clone https://github.com/ninenines/ranch
$ cd ranch
$ make ct-sendfile t=ssl:filename ERLANG_OTP=OTP-21.3.8

This will build OTP-21.3.8. If you already have it in the path don't include the ERLANG_OTP variable.