[ruby/net-http] Use nonblocking IO to detect eof

The call to `@socket.eof?` can block when attempting to reuse a
persistent connection and there are SSL Handshake messages ready to be
read, but no Application Data, such as when the server sends an updated
NewSessionTicket in TLS 1.3.

Instead call `OpenSSL::SSL::SSLSocket#read_nonblocking`, which will read
and process the SSL Handshake message, but return `nil` on EOF or an empty
string if no data is available. It may also return `:wait_readable` or
`:wait_writable` which indicates the socket is reusable.

Author: joshcooper

lib/net/http.rb

@@ -2467,7 +2467,7 @@ def begin_transport(req)
           debug 'Conn close because of keep_alive_timeout'
           @socket.close
           connect
-        elsif @socket.io.to_io.wait_readable(0) && @socket.eof?
+        elsif eof?
           debug "Conn close because of EOF"
           @socket.close
           connect
@@ -2482,6 +2482,14 @@ def begin_transport(req)
       req['host'] ||= addr_port()
     end
 
+    def eof?
+      if defined?(OpenSSL::SSL) && @socket.io.is_a?(OpenSSL::SSL::SSLSocket)
+        @socket.io.read_nonblock(0, exception: false).nil?
+      else
+        @socket.io.to_io.wait_readable(0) && @socket.eof?
+      end
+    end
+
     def end_transport(req, res)
       @curr_http_version = res.http_version
       @last_communicated = nil