Text 348, 373 rader
Skriven 2005-05-30 21:40:53 av Michiel Broek (2:280/2802)
Ärende: FSP-1018 rev 2 part 2
=============================
e.g. M_SKIP "config.sys 125 2476327846"
Implementation note: when receive M_SKIP mailer should wait
some time after session end before next poll to that link
to prevent continuous poll.
5.6 Example of Frame Exchange in a Simple Binkp Session
-------------------------------------------------------
Originating side (1:1/1.1@fidonet) has file1 for answering side
(2:2/2.2@fidonet) and answering side has file2 for originating side
+----------------------------------------------------------------+
| Originating side | Answering side |
|--------------------------------+-------------------------------|
| M_NUL "SYS ..." | M_NUL "SYS ..." |
| M_NUL "ZYZ ..." | M_NUL "ZYZ ..." |
| M_NUL "LOC ..." | M_NUL "LOC ..." |
| M_NUL "VER ..." | M_NUL "VER ..." |
| M_NUL "OPT ..." | M_NUL "OPT ..." |
| M_ADR "1:1/1.1@fidonet" | M_ADR "2:2/2.2@fidonet" |
| M_PWD "password" | (waiting for a password from |
| | remote) |
|--------------------------------+-------------------------------|
| (waiting for password | M_OK "secure" |
| acknowledgement) | |
|--------------------------------+-------------------------------|
| (got M_OK) | M_FILE "file2 200 42342434 0" |
|--------------------------------+-------------------------------|
| M_FILE "file1 100 423424244 0" | data |
|--------------------------------+-------------------------------|
| data | data |
|--------------------------------+-------------------------------|
| data | data |
|--------------------------------+-------------------------------|
| M_EOB | (got file1, acknowledging it) |
|--------------------------------+-------------------------------|
| (got file2, acknowledging it) | M_GOT "file1 100 423424244" |
|--------------------------------+-------------------------------|
| M_GOT "file2 200 42342434" | data |
|--------------------------------+-------------------------------|
| | M_EOB |
+----------------------------------------------------------------+
6. Protocol States
------------------
The protocol has two major stages: session setup (different for
originating side and answering side) and file transfer (where state
machined for both sides are the same). Methods for initiating
connection as well as numerical values for particular timeouts are
dependent on the underlying layer's protocol suite and are not
considered here. Mailer MAY allow configuration of timeouts in
reasonably wide range to cover all supported transport protocols.
The Finite State Machine notation is used throughout this section
as defined by [FTS-0001].
6.1 Session Setup Stage
-----------------------
Originating side should initiate a binkp session according to Table
1. Answering side should be able to act according to Table 2. Any
optional extensions of the handshake procedure MUST NOT confuse the
other side, which may choose at it's discretion to follow this
minimal implementation. Upon successful handshake, both sides
follow Table 3 (file transfer stage). That's why terms Answering
side and Originating side were chosen for this specification
instead of Client and Server - both sides play the same roles, and
their state machines differ in session setup stage only.
Session setup stage has the following roles
* Authentication (REQUIRED). Answering side, upon reception of a
password (common secret word) from Originating side, decides
whether the password really matches the list of presented
addresses, and either acknowledges it by sending M_OK frame or
rejects by sending M_ERR frame. This mechanism is called Basic
Authentication Scheme and MUST be supported by all Mailers.
Basic Authentication Scheme has the following limitations:
* If Originating side presented multiple addresses, the
password for all of the addresses must be the same to
prevent security bugs. (May be solved by "hide aka
mechanism" usage, don't described in this text.)
* Cleartext reusable passwords are passed over a network
(may be solved by CRAM extension).
* Verification is made on Answering side only, thus
Originating side has no way to verify Answering side.
(May be solved by 'IP address restriction' extension).
* Indicating protocol options (OPTIONAL). Sides may exchange
specially formatted M_NUL messages to indicate supported
extensions. Sides MAY use another technique to indicate
extensions, but using M_NUL "OPT ..." frame is recommended
for compatibility.
6.1.1 Originating Side
----------------------
Originating side sends M_ADR and M_PWD frames, waits for successful
authentication acknowledgement from the Answering side (M_OK frame)
and goes to file transfer stage; or receive M_ERR frame and close
connection. Originating side MUST NOT wait before sending M_ADR
frame, i.e. this frame should be send just after setting up a
connection on underlying layer. Originating side MUST NOT wait
before sending M_PWD except after reception of M_ADR frame. The
term wait in this paragraph means do not send anything while
expecting data from remote.
Table 1: Session setup, originating side
+-----------------------------------------------------------------+
| # | Name | Predicate(s) | Action(s) |Next|
|----+------------+-----------------+------------------------+----|
| S0 | ConnInit | | Attempt to | S1 |
| | | | establish | |
| | | | connection | |
|----+------------+-----------------+------------------------+----|
| S1 | WaitConn | Connection | Send M_NUL frames with | S2 |
| | | established | system info (optional) | |
| | | | | |
| | | | Send M_ADR frame with | |
| | | | system addresses | |
| | | | | |
| | | | Set Timer | |
| | | | | |
| | | | See if we have | |
| | | | password for the | |
| | | | remote | |
| | |-----------------+------------------------+----|
| | | Connection | Report no |exit|
| | | refused | connection | |
|----+------------+-----------------+------------------------+----|
| S2 | SendPasswd | Yes, we have a | Send M_PWD "password" | S3 |
| | | password | frame | |
| | | | Reset Timer | |
| | |-----------------+------------------------+----|
| | | No, there's no | Send M_PWD "-" | S3 |
| | | password | frame | |
| | | | Reset timer | |
|----+------------+-----------------+------------------------+----|
| S3 | WaitAddr | M_ADR frame | See if answering side | S4 |
| | | received | presented the address | |
| | | | we've called | |
| | |-----------------+------------------------+----|
| | | M_BSY frame | Report remote is busy |exit|
| | | received | | |
| | |-----------------+------------------------+----|
| | | M_ERR frame | Report error |exit|
| | | received | | |
| | |-----------------+------------------------+----|
| | | M_NUL frame | Ignore or parse | S3 |
| | | received | | |
| | |-----------------+------------------------+----|
| | | Other known | Report about unexpected|exit|
| | | frame received | frame, send M_ERR frame| |
| | |-----------------+------------------------+----|
| | | Unknown frame | Ignore | S3 |
| | | received | | |
| | |-----------------+------------------------+----|
| | | Nothing happens | Wait | S3 |
| | |-----------------+------------------------+----|
| | | Timer Expired | Report timeout |exit|
|----+------------+-----------------+------------------------+----|
| S4 | AuthRemote | Yes, the address| See if we've sent a | S5 |
| | | was presented | password for this | |
| | | | address | |
| | |-----------------+------------------------+----|
| | | No, the address | Report we call(ed) the |exit|
| | | was not | wrong system; send | |
| | | presented | M_ERR frame | |
|----+------------+-----------------+------------------------+----|
| S5 | IfSecure | Yes, we've sent | Wait for M_OK frame | S6 |
| | | a M_PWD frame | | |
|----+------------+-----------------+------------------------+----|
| S6 | WaitOk | M_OK frame | report secure or | S7 |
| | | received | non-secure session | |
| | | | (depends on sent pwd) | |
| | |-----------------+------------------------+----|
| | | M_BSY frame | Report remote is busy |exit|
| | | received | (Anwering side MAY | |
| | | | report busy after | |
| | | | reception of caller's | |
| | | | addess) | |
| | |-----------------+------------------------+----|
| | | M_ERR frame | Report error |exit|
| | | received | | |
| | |-----------------+------------------------+----|
| | | M_NUL frame | Ignore or parse, may | S6 |
| | | received | log arguments | |
| | |-----------------+------------------------+----|
| | | Other known | Report unexpected |exit|
| | | frame received | frame; send M_ERR frame| |
| | |-----------------+------------------------+----|
| | | Unknown frame | Ignore | S6 |
| | | received | | |
| | |-----------------+------------------------+----|
| | | Nothing happens | Wait | S6 |
| | |-----------------+------------------------+----|
| | | Timer Expired | Report timeout |exit|
+----+------------+-----------------+------------------------+----|
| S7 | Opts | We have more | Send frames to | T0 |
| | | protocol | negotiate protocol | |
| | | extensions | extensions | |
+-----------------------------------------------------------------+
6.1.2 Answering Side
--------------------
Originating side sends M_ADR and waits for M_ADR and M_PWD frames
from remote. Upon receptions of these frames, it decides whether
the password really matches the list of presented addresses, and
either acknowledges it by sending M_OK frame (and goes to file
transfer stage) or rejects by sending M_ERR frame (and
disconnects). The term wait in this paragraph means do not send
anything while expecting data from remote.
Table 2: Session setup, answering side
+-----------------------------------------------------------------+
| # | Name | Predicate(s) | Action(s) |Next|
|----+----------+---------------------+----------------------+----|
| R0 | WaitConn | Incoming connection | Send M_NUL frames | R1 |
| | | established | with system info and | |
| | | | capabilities | |
| | | | (optional). | |
| | | | Send M_ADR frame | |
| | | | with system addresses| |
| | | | Set Timer | |
| | |---------------------+----------------------+----|
| | | Nothing happens | Wait | R0 |
|----+----------+---------------------+----------------------+----|
| R1 | WaitAddr | M_ADR frame | See if we have a | R2 |
| | | received | password for each | |
| | | | of the remote | |
| | | | addresses | |
| | |---------------------+----------------------+----|
| | | M_ERR frame | Report error |exit|
| | | received | | |
| | |---------------------+----------------------+----|
| | | M_NUL frame | Ignore or parse, | R1 |
| | | received | optionally log. | |
| | |---------------------+----------------------+----|
| | | Other known frame | Report unexpected |exit|
| | | received | frame; send M_ERR | |
| | | | frame | |
| | |---------------------+----------------------+----|
| | | Unknown frame | Ignore | R1 |
| | | received | | |
| | |---------------------+----------------------+----|
| | | Nothing happens | Wait | R1 |
| | |---------------------+----------------------+----|
| | | Timer expired | Report timeout |exit|
|----+----------+---------------------+----------------------+----|
| R2 | IsPasswd | Yes, we have a | Set Timer | R3 |
| | | password | | |
| | |---------------------+----------------------+----|
| | | Yes, but we have | Send M_ERR frame |exit|
| | | several different | Report | |
| | | passwords for | inconsistent | |
| | | different addresses | password settings | |
| | | of the remote | | |
| | |---------------------+----------------------+----|
| | | No, there's no | Set Timer | R3 |
| | | password | | |
|----+----------+---------------------+----------------------+----|
| R3 | WaitPwd | M_PWD frame | See if the | R4 |
| | | received | password matches | |
| | | | or if no password and| |
| | | | no password received | |
| | |---------------------+----------------------+----|
| | | M_ERR frame | Report error |exit|
| | | received | | |
| | |---------------------+----------------------+----|
| | | M_NUL frame | Ignore or parse, | R1 |
| | | received | optionally log. | |
| | |---------------------+----------------------+----|
| | | Other known frame | Report unexpected |exit|
| | | received | frame; send M_ERR | |
| | | | frame | |
| | |---------------------+----------------------+----|
| | | Unknown frame | Ignore | R3 |
| | | received | | |
| | |---------------------+----------------------+----|
| | | Nothing happens | Wait | R3 |
| | |---------------------+----------------------+----|
| | | Timer Expired | Report timeout |exit|
|----+----------+---------------------+----------------------+----|
| R4 | PwdAck | Yes, the password | Send M_OK frame | R5 |
| | | matches | Report secure | |
| | | | session | |
| | |---------------------+----------------------+----+
| | | No password and got | Send M_OK frame | R5 |
| | | M_PWD "-" frame | Report unsecure | |
| | | | session | |
| | |---------------------+----------------------+----|
| | | No, password does | Report password error|exit|
| | | not match | Send M_ERR | |
+-----------------------------------------------------------------+
| R5 | Opts | We have more | Send frames to | T0 |
| | | protocol extensions | negotiate protocol | |
| | | | extensions | |
+-----------------------------------------------------------------+
6.2 File Transfer Stage
-----------------------
File transfer stage is based on two major routines. We call them
Receive Routine and Transmit Routine. These routines perform some
actions depending on their state variables. State variables are
RxState for Receive Routine and TxState for Transmit Routine.
RxState := { RxWaitF | RxAccF | RxReceD | RxWriteD | RxEOB |
RxDone }
TxState := { TxGNF | TxTryR | TxReadS | TxWLA | TxDone }
Table 3: File Transfer
+-----------------------------------------------------------------+
| # | Name | Predicate(s) | Action(s) | Next |
|----+--------------+---------------------+----------------+------|
| T0 | InitTransfer | none | Set Timer | T1 |
| | | | Set RxState to | |
| | | | RxWaitF | |
| | | | Set TxState to | |
| | | | TxGNF | |
|----+--------------+---------------------+----------------+------|
| T1 | Switch | RxState is RxDone | Report session | exit |
| | | and TxState is | complete | |
| | | TxDone | | |
| | |---------------------+----------------+------|
| | | Data Available in | call Receive | T2 |
| | | Input Buffer | routine | |
| | |---------------------+----------------+------|
| | | Free space exists | call Transmit | T3 |
| | | in output buffer | routine | |
| | |---------------------+----------------+------|
| | | Nothing happens | Wait | T1 |
| | |---------------------+----------------+------|
| | | Timer Expired | Report Timeout | exit |
|----+--------------+---------------------+----------------+------|
| T2 | Receive | Receive routine | Set Timer | T1 |
| | | returned OK | | |
| | |---------------------+----------------+------|
| | | Receive routine | Close all | exit |
| | | returned Failure | opened files | |
| | |---------------------+----------------+------|
| | | Receive routine | Call Receive | T2 |
| | | returned Continue | routine again | |
|----+--------------+---------------------+----------------+------|
| T3 | Transmit | Transmit routine | Set Timer | T1 |
| | | returned OK | | |
| | |---------------------+----------------+------|
| | | Transmit routine | Close all | exit |
| | | returned Failure | opened files | |
| | |---------------------+----------------+------|
| | | Transmit routine | Call Transmit | T3 |
| | | returned Continue | routine again | |
+-----------------------------------------------------------------+
Tables 4-6 are not actually state machines, but routines called
during file transfer stage
Greetings, Michiel Broek
Email: mbse@mbse.dds.nl
Fidonet: Michiel Broek at 2:280/2802
... You're not drunk if you can lie on the floor without hanging on.
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