Add initial state machine rewrite code
This is the first drop of the new state machine code. The rewrite has the following objectives: - Remove duplication of state code between client and server - Remove duplication of state code between TLS and DTLS - Simplify transitions and bring the logic together in a single location so that it is easier to validate - Remove duplication of code between each of the message handling functions - Receive a message first and then work out whether that is a valid transition - not the other way around (the other way causes lots of issues where we are expecting one type of message next but actually get something else) - Separate message flow state from handshake state (in order to better understand each) - message flow state = when to flush buffers; handling restarts in the event of NBIO events; handling the common flow of steps for reading a message and the common flow of steps for writing a message etc - handshake state = what handshake message are we working on now - Control complexity: only the state machine can change state: keep all the state changes local to a file This builds on previous state machine related work: - Surface CCS processing in the state machine - Version negotiation rewrite Reviewed-by: Tim Hudson <tjh@openssl.org> Reviewed-by: Richard Levitte <levitte@openssl.org>
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