read_nonblock

Reads at most maxlen bytes in the non-blocking manner.

When no data can be read without blocking it raises OpenSSL::SSL::SSLError extended by IO::WaitReadable or IO::WaitWritable.

IO::WaitReadable means SSL needs to read internally so #read_nonblock should be called again when the underlying IO is readable.

IO::WaitWritable means SSL needs to write internally so #read_nonblock should be called again after the underlying IO is writable.

#read_nonblock needs two rescue clause as follows:

# emulates blocking read (readpartial).
begin
  result = ssl.read_nonblock(maxlen)
rescue IO::WaitReadable
  IO.select([io])
  retry
rescue IO::WaitWritable
  IO.select(nil, [io])
  retry
end

Note that one reason that #read_nonblock writes to the underlying IO is when the peer requests a new TLS/SSL handshake. See openssl the FAQ for more details. www.openssl.org/support/faq.html