mirror of
https://github.com/QuasarApp/openssl.git
synced 2025-05-05 05:59:38 +00:00
5626f634c3
Commit 02f0274e8c0596dcf7e2d104250232a42c650b96 moved ALPN processing into an extension finalization function, as the only documented ordering requirement from previous commits was that ALPN processing occur after SNI processing, and SNI processing is performed before the extension finalization step. However, it is useful for applications' alpn_select callbacks to run after ciphersuite selection as well -- at least one application protocol specification (HTTP/2) imposes restrictions on which ciphersuites are usable with that protocol. Since it is generally more preferrable to have a successful TLS connection with a default application protocol than to fail the TLS connection and not be able to have the preferred application protocol, it is good to give the alpn_select callback information about the ciphersuite to be used, so that appropriate restrctions can be enforced in application code. Accordingly, split the ALPN handling out into a separate tls_handl_alpn() function akin to tls_handle_status_request(), called from tls_post_process_client_hello(). This is an alternative to resuscitating ssl_check_clienthello_tlsext_late(), something of an awkwward name itself. Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/4070)
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 |
|_____________________________| |_______________________________|