5. Driver/server socket protocol

Here’s a brief explanation of the text-based protocol which is used between the drivers and server.

The drivers may send things on the socket at any time. They will send out changes to their local storage immediately, without any sort of prompting from the server. As a result, the server must always check on any driver sockets for activity.

5.1. Formatting

All parsing on either side of the socket is done by parseconf, so the same rules about escaping characters and "quoting multi-word elements" apply here. Values which may contain odd characters are typically sent through pconf_encode to apply \ characters where necessary.

The "" construct is used throughout to force a multi-word value to stay together on its way to the other end.

5.2. Commands used by the drivers

SETINFO

SETINFO <varname> "<value>"
SETINFO ups.status "OB LB"

There is no "ADDINFO" - if a given variable does not exist, it is created upon receiving the first SETINFO command.

DELINFO

DELINFO <varname>
DELINFO ups.temperature

ADDENUM

ADDENUM <varname> "<value>"
ADDENUM input.transfer.low "95"

DELENUM

DELENUM <varname> "<value>"
DELENUM input.transfer.low "98"

ADDRANGE

ADDRANGE <varname> <minvalue> <maxvalue>
ADDRANGE input.transfer.low 95 100

DELRANGE

DELRANGE <varname> <minvalue> <maxvalue>
DELRANGE input.transfer.low 95 100

SETAUX

SETAUX <varname> <numeric value>
SETAUX ups.id 8

This overrides any previous value. The auxiliary value is presently used as a length byte for read-write variables that are strings.

SETFLAGS

SETFLAGS <varname> <flag>...
SETFLAGS ups.id RW STRING

Note that this command takes a variable number of arguments, as multiple flags are supported. Also note that they are not crammed together in "", since "RW STRING" would mean something completely different.

This also replaces any previous flags for a given variable.

ADDCMD

ADDCMD <cmdname>
ADDCMD load.off

DELCMD

DELCMD <cmdname>
DELCMD load.on

DUMPDONE

DUMPDONE

This is only used to tell the server that every possible item has been transmitted in response to its DUMPALL request. Once this has been received by the server, it can be sure that it knows everything that the driver does.

PONG

PONG

This is sent in response to a PING from the server. It is only used as a sanity check to make sure that the driver has not gotten stuck somewhere.

DATAOK

DATAOK

This means that the driver is able to communicate with the UPS, and the data should be treated as usable. It is always sent at the end of the dump if the data is not stale. It may also be sent at other times.

DATASTALE

DATASTALE

This is sent by the driver to inform any listeners that the data is no longer usable. This usually means that the driver is unable to get any sort of meaningful response from the UPS. You must not rely on any status information once this has been sent.

This will be sent in the beginning of a dump if the data is stale, and may be repeated. It is cleared by DATAOK.

5.3. Commands sent by the server

PING

PING

This is sent to check on the health of a driver. The server should only send this when it hasn’t heard anything valid from a driver recently. Some drivers have very little to say in terms of updates, and this may be the only communications they have with the server on a normal basis.

If a driver does not respond with the PONG within a few seconds at the most, it should be treated as dead/unavailable. Data stored in the server must not be passed on to the clients when this happens.

INSTCMD

INSTCMD <cmdname>
INSTCMD panel.test.start

SET

SET <varname> "<value>"
SET ups.id "Data room"

DUMPALL

DUMPALL

The server uses this to request a complete copy of everything the driver knows. This is returned in the form of the same commands (SETINFO, etc.) that would be used if they were being updated normally. As a result, the same parsing happens either way.

The server can tell when it has a full copy of the data by waiting for DUMPDONE. That special response from the driver is sent once the entire set has been transmitted.

5.4. Design notes

Requests

There is no way to request just one variable. This was done on purpose to limit the complexity of the drivers. Their job is to send out updates and handle a few simple requests. DUMPALL is provided to give the server a known foundation.

To track a limited set of variables, a server just needs to do DUMPALL, then only have handlers that remember values for the variables that matter. Anything else should be ignored.

Access/Security

There are no access controls in the drivers. Anything that can connect to their sockets can make requests, including SET and INSTCMD if supported by the driver and hardware. These sockets must be kept secure. If your operating system does not honor permissions or modes on sockets, then you must store them in a directory with suitable permissions to limit access.

Command limitations

As parseconf is used to handle decoding and chunking of the data, there are some limits on what may be used. These default to 32 arguments of 512 characters each, which should be more than enough for everything which is currently needed by the software.

These limits are strictly for sanity purposes, and may be raised if necessary. parseconf itself can handle vast numbers of arguments and characters, with some speed penalty as things get really big.

Re-establishing communications

If the server loses its connection to the driver and later reconnects, it must flush any local storage and start again with DUMPALL. The driver may have changed the internal state considerably during that time, and anything other approach could leave old elements behind.