This is the first part to removing the buffer BIO. The eventual end
state is the SSL_PROTOCOL_METHOD is responsible for maintaining one
flight's worth of messages. In TLS, it will just be a buffer containing
the flight's ciphertext. In DTLS, it's the existing structure for
retransmit purposes. There will be hooks:
- add_message (synchronous)
- add_change_cipher_spec (synchronous)
- add_warning_alert (synchronous; needed until we lose SSLv3 client auth
and TLS 1.3 draft 18; draft 19 will switch end_of_early_data to a
handshake message)
- write_flight (BIO; flush_flight will be renamed to this)
This also preserves the exact return value of BIO_flush. Eventually all
the BIO_write calls will be hidden behind BIO_flush to, to be consistent
with other BIO-based calls, preserve the return value.
BUG=72
Change-Id: I74cd23759a17356aab3bb475a8ea42bd2cd115c9
Reviewed-on: https://boringssl-review.googlesource.com/13222
Reviewed-by: Adam Langley <agl@google.com>
8d5f9da2e3