]>
Commit | Line | Data |
---|---|---|
f0de3959 MC |
1 | State Machine Design |
2 | ==================== | |
3 | ||
4 | This file provides some guidance on the thinking behind the design of the | |
5 | state machine code to aid future maintenance. | |
6 | ||
7 | The state machine code replaces an older state machine present in OpenSSL | |
8 | versions 1.0.2 and below. The new state machine has the following objectives: | |
9 | - Remove duplication of state code between client and server | |
10 | - Remove duplication of state code between TLS and DTLS | |
11 | - Simplify transitions and bring the logic together in a single location | |
12 | so that it is easier to validate | |
13 | - Remove duplication of code between each of the message handling functions | |
14 | - Receive a message first and then work out whether that is a valid | |
15 | transition - not the other way around (the other way causes lots of issues | |
16 | where we are expecting one type of message next but actually get something | |
17 | else) | |
18 | - Separate message flow state from handshake state (in order to better | |
19 | understand each) | |
20 | - message flow state = when to flush buffers; handling restarts in the | |
21 | event of NBIO events; handling the common flow of steps for reading a | |
22 | message and the common flow of steps for writing a message etc | |
23 | - handshake state = what handshake message are we working on now | |
24 | - Control complexity: only the state machine can change state: keep all | |
25 | the state changes local to the state machine component | |
26 | ||
27 | The message flow state machine is divided into a reading sub-state machine and a | |
28 | writing sub-state machine. See the source comments in statem.c for a more | |
29 | detailed description of the various states and transitions possible. | |
30 | ||
31 | Conceptually the state machine component is designed as follows: | |
32 | ||
33 | libssl | |
34 | | | |
35 | ---------------------------|-----statem.h-------------------------------------- | |
36 | | | |
37 | _______V____________________ | |
38 | | | | |
39 | | statem.c | | |
40 | | | | |
41 | | Core state machine code | | |
42 | |____________________________| | |
b5acbf91 | 43 | statem_local.h ^ ^ |
f0de3959 MC |
44 | _________| |_______ |
45 | | | | |
46 | _____________|____________ _____________|____________ | |
47 | | | | | | |
48 | | statem_clnt.c | | statem_srvr.c | | |
49 | | | | | | |
50 | | TLS/DTLS client specific | | TLS/DTLS server specific | | |
51 | | state machine code | | state machine code | | |
52 | |__________________________| |__________________________| | |
53 | | |_______________|__ | | |
54 | | ________________| | | | |
55 | | | | | | |
56 | ____________V_______V________ ________V______V_______________ | |
57 | | | | | | |
58 | | statem_both.c | | statem_dtls.c | | |
59 | | | | | | |
60 | | Non core functions common | | Non core functions common to | | |
61 | | to both servers and clients | | both DTLS servers and clients | | |
62 | |_____________________________| |_______________________________| | |
63 |