[ruby-core:76893] [Ruby trunk Bug#12678] No way to set a timeout for TLS handshake when using Net::SMTP

Issue #12678 has been reported by Ben Weintraub.

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Bug #12678: No way to set a timeout for TLS handshake when using Net::SMTP
https://bugs.ruby-lang.org/issues/12678

* Author: Ben Weintraub
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin15]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
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When establishing a connection to an SMTP server, Net::SMTP doesn't offer a way to specify a timeout for how long the TLS handshake should take.

In our production environment, this means we routinely see hangs under this callstack:

.../lib/ruby/2.1.0/net/smtp.rb:586:in `connect'
.../lib/ruby/2.1.0/net/smtp.rb:586:in `tlsconnect'
.../lib/ruby/2.1.0/net/smtp.rb:563:in `do_start'
.../lib/ruby/2.1.0/net/smtp.rb:520:in `start'
.../shared/bundle/ruby/2.1.0/gems/mail-2.5.4/lib/mail/network/delivery_methods/smtp.rb:112:in `deliver!'

The C-level backtrace here looks like this:

Thread 1 (Thread 0x7f7709587700 (LWP 30870)):
#0  0x00007f77085ea4b7 in ppoll () from /lib64/libc.so.6
#1  0x00007f7709719cd9 in rb_wait_for_single_fd (fd=<value optimized out>, events=<value optimized out>, tv=0x0) at thread.c:3675
#2  0x00007f7709719e32 in rb_thread_wait_fd_rw (fd=<value optimized out>) at thread.c:3514
#3  rb_thread_wait_fd (fd=<value optimized out>) at thread.c:3525
#4  0x00007f77095f08bf in rb_io_wait_readable (f=34) at io.c:1094
#5  0x00007f77009aa894 in ossl_start_ssl (self=140149417009120, func=0x7f7700755570 <SSL_connect>, funcname=0x7f77009c3ba7 "SSL_connect", nonblock=<value optimized out>) at ossl_ssl.c:1282
#6  0x00007f77096f522a in vm_call_cfunc_with_frame (th=0x7f770a9585b0, reg_cfp=0x7f7709583530, ci=<value optimized out>) at vm_insnhelper.c:1510
#7  0x00007f7709708e11 in vm_call_cfunc (th=0x7f770a9585b0, cfp=0x7f7709583530, 

You can replicate this behavior by starting a dummy server using 'nc' (netcat), and then running the attached ruby script to connect to it.

Steps to reproduce:

1. Start a netcat process listening on port 8888 ('nc -l 8888')
2. Run the attached net-smtp-connect-timeout.rb
3. Wait

Expected results:

The call to smtp.start should eventually time out.

Actual results:

The call to smtp.start hangs forever.

Notes:

Net::HTTP addresses this same issue by using a loop around SSLSocket.connect_nonblock:
https://github.com/ruby/ruby/blob/trunk/lib/net/http.rb#L934-L943

... seems like Net::SMTP should do the same.

We're hitting this issue using Ruby 2.1.7 in production, but I've also verified that it happens on 2.3.1.



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