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openssl/ssl/statem
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Matt Caswell 1f359471f9 Provide an SSLfatal() macro 
Typically if a fatal error occurs three things need to happen:

- Put an error on the error queue
- Send an alert
- Put the state machine into the error state

Although all 3 of these things need to be done every time we hit a fatal
error the responsibilities for doing this are distributed throughout the
code. The place where the error goes on the queue, where the alert gets
sent and where the state machine goes into the error state are almost
invariably different. It has been a common pattern to pass alert codes up
and down the stack to get the alert information from the point in the code
where the error is detected to the point in the code where the alert gets
sent.

This commit provides an SSLfatal() macro (backed by an ossl_statem_fatal
function) that does all 3 of the above error tasks. This is largely a drop
in replacement for SSLerr, but takes a couple of extra parameters (the SSL
object, and an alert code).

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4778)
2017-12-04 13:31:48 +00:00
..
extensions.c If a server is not acknowledging SNI then don't reject early_data 2017-11-21 17:46:22 +00:00
extensions_clnt.c Allow a client to send early_data with SNI if the session has no SNI 2017-11-21 17:46:22 +00:00
extensions_cust.c Implement Maximum Fragment Length TLS extension. 2017-11-05 17:46:48 +01:00
extensions_srvr.c Implement Maximum Fragment Length TLS extension. 2017-11-05 17:46:48 +01:00
README
statem.c Provide an SSLfatal() macro 2017-12-04 13:31:48 +00:00
statem.h Provide an SSLfatal() macro 2017-12-04 13:31:48 +00:00
statem_clnt.c Normalize on session_ctx for stats where possible 2017-10-30 10:21:10 -05:00
statem_dtls.c Move ossl_assert 2017-08-03 10:48:00 +01:00
statem_lib.c Resolve warnings in VC-WIN32 build, which allows to add /WX. 2017-11-13 10:58:57 +01:00
statem_locl.h Implement Maximum Fragment Length TLS extension. 2017-11-05 17:46:48 +01:00
statem_srvr.c Replace tls1_ec_curve_id2nid. 2017-09-26 13:00:26 +01:00

README 

State Machine Design
====================

This file provides some guidance on the thinking behind the design of the
state machine code to aid future maintenance.

The state machine code replaces an older state machine present in OpenSSL
versions 1.0.2 and below. The new state machine 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 the state machine component

The message flow state machine is divided into a reading sub-state machine and a
writing sub-state machine. See the source comments in statem.c for a more
detailed description of the various states and transitions possible.

Conceptually the state machine component is designed as follows:

                        libssl
                           |
---------------------------|-----statem.h--------------------------------------
                           |
                    _______V____________________
                   |                            |
                   |    statem.c                |
                   |                            |
                   |    Core state machine code |
                   |____________________________|
        statem_locl.h     ^          ^
                 _________|          |_______
                |                            |
   _____________|____________   _____________|____________
  |                          | |                          |
  | statem_clnt.c            | | statem_srvr.c            |
  |                          | |                          |
  | TLS/DTLS client specific | | TLS/DTLS server specific |
  | state machine code       | | state machine code       |
  |__________________________| |__________________________|
               |        |_______________|__       |
               |        ________________|  |      |
               |       |                   |      |
   ____________V_______V________   ________V______V_______________
  |                             | |                               |
  | statem_both.c               | | statem_dtls.c                 |
  |                             | |                               |
  | Non core functions common   | | Non core functions common to  |
  | to both servers and clients | | both DTLS servers and clients |
  |_____________________________| |_______________________________|