This file contains documentation related to the FLOM client/server protocol
The protocol is based on XML messages exchange.
No validation is performed against XML.
XML parsing is "static": only expected tags/attributes are searched and
retrieved.
XML generation is "static": from a composite struct, a serialization function
is able to understand the struct, generates the resulting XML document.
The usage of XML is possibly not strictly compliant with standards; it's used
as a serialization/deserialization tool to avoid portability nightmares and
cross platform issues (server is big endian, client is little endian or server
is ASCII, client is EBCDIC...).
Every message must have two distinctive fields in the header:
- level: the level of implemented protocol
- verb: the operation correlated to the data contained in the XML document
- step: the progress inside the operation
This documentations contains: state tables for transitions of client/server
messages and some message samples.
***************************************************************************
verb=1 (lock)
level: message level, version
verb: lock -> 1
step: 8, 16, 24
type: 0 = NL null lock
1 = CR concurrent read
2 = CW concurrent write
3 = PR/SH (protected read/shared lock)
4 = PW/UP (protected write/update lock)
5 = EX exclusive lock
wait: 0 = no wait
1 = wait if the resource can not be locked
client->server message (ask for a lock)
<msg level="0" verb="1" step="8">
<resource name="_RESOURCE" type="5" wait="1">
</msg>
server->client message (answer: lock obtained/not obtained/wait)
<msg level="0" verb="1" step="16">
<answer rc="0/..."/>
</msg>
server->client message (answer: lock obtained)
<msg level="0" verb="1" step="24">
<answer rc="0/..."/>
</msg>
client server description
verb=1,step=8 --> ask for a lock
<-- verb=1,step=16 the lock can be aquired, not acquired
or queued
<-- verb=1,step=24 the lock can be aquired or not acquired
if there was a previous queued answer
***************************************************************************
verb=2 (unlock)
level: message level, version
verb: unlock -> 2
step: 8
client->server message (async assertion)
<msg verb="2" step="8">
<resource name="_RESOURCE">
</msg>
client server description
verb=2,step=8 --> send the unlocked resource
***************************************************************************
verb=3 (ping)
level: message level, version
verb: ping -> 3
step: 8, 16
server->client message (are you alive?)
<msg level="0" verb="3" step="8">
</msg>
client->server message (I'am alive)
<msg level="0" verb="3" step="16">
</msg>
***************************************************************************