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 after underlying IO is readable.

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

So OpenSSL::Buffering#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 write to a underlying IO is the peer requests a new TLS/SSL handshake. See openssl FAQ for more details. http://www.openssl.org/support/faq.html

# File ext/openssl/lib/openssl/buffering.rb, line 135
  def read_nonblock(maxlen, buf=nil)
    if maxlen == 0
      if buf
        buf.clear
        return buf
      else
        return ""
      end
    end
    if @rbuffer.empty?
      return sysread_nonblock(maxlen, buf)
    end
    ret = consume_rbuff(maxlen)
    if buf
      buf.replace(ret)
      ret = buf
    end
    raise EOFError if ret.empty?
    ret
  end