Dear fellows,
I'm happy to finally be able to provide a RFC for this long awaited feature!
(esp. @clepple , @zykh , @jimklimov)

From docs/net-protocol.txt, Future ideas -> Command status:

After sending an INSTCMD or SET, a client will eventually be able to poll to see whether it was completed successfully by the driver.

Proposal:

• Add a new "CMDSET_STATUS" command in the network protocol to enable/disable
  the feature and provide status tracking information upon request:

  • docs/net-protocol.txt additions

    SET CMDSET_STATUS

    
    Form:
    
        SET CMDSET_STATUS "<value>"
        SET CMDSET_STATUS ON
        SET CMDSET_STATUS OFF
    
    Response:
    
        OK
        ERR INVALID-ARGUMENT (if "value" is not "ON" or "OFF")
        ERR USERNAME-REQUIRED (if not yet authenticated)
        ERR PASSWORD-REQUIRED (if not yet authenticated)
    
    
    GET CMDSET_STATUS
    

    Form:

    GET CMDSET_STATUS               (activation status of CMDSET_STATUS)
    GET CMDSET_STATUS [<status_id>] (execution status of a command / setvar) 
    GET CMDSET_STATUS 1bd31808-cb49-4aec-9d75-d056e6f018d2
    

    Response:

    PENDING              (command execution is pending)
    SUCCESS              (command was successfully executed)
    ERR UNKNOWN          (command execution failed with unknown error)
    ERR INVALID-ARGUMENT (command execution failed due to missing or invalid argument)
    ERR FAILED           (command execution failed)
    

• whenever CMDSET_STATUS is enabled, and a valid command / setvar is received by upsd,
  upsd will allocate an ID (UUID v4 random, see below notes) and forward to driver
  the request with the additional STATUS_ID tag and ID parameter

  • docs/sock-protocol.txt additions

    Commands sent by the server

    INSTCMD

    
        INSTCMD <cmdname> [cmdparam] [STATUS_ID <ID>]
    
        INSTCMD panel.test.start
        INSTCMD load.off 10 
        INSTCMD load.on 10 STATUS_ID 1bd31808-cb49-4aec-9d75-d056e6f018d2
    
    

  • NOTE:

    • cmdparam is an additional and optional parameter for the command,
    • "STATUS_ID " can be provided to track commands execution status, if
      CMDSET_STATUS was set to ON on upsd. In this case, driver will later return
      the execution status, using STATUS_ID

• driver receives the cmd / setvar request from upsd. Then, upon completion of
  this action, driver sends back the status with the ID (using CMDSET_STATUS) and
  forgets about it (managed at the dstate level and not provided to upshandlers)

  • docs/sock-protocol.txt additions

    Commands used by the drivers

    CMDSET_STATUS

    
        CMDSET_STATUS <ID> <value>
    
    This is sent in response to an INSTCMD or SET VAR that includes a STATUS_ID,
    upon completion of request execution by the driver. <value> is the integer
    return value from the driver handlers instcmd and setvar (see
    drivers/upshandler.h). The server is in charge of translating these codes into
    strings, as per docs/net-protocol.txt GET CMDSET_STATUS.
    
    
    

• upsd receives the status of the command / settings and updates the matching
  status tracking entry

• upsd deletes tracked IDs upon time based (execution timestamp + CMDSETSTATUSDELAY in upsd.conf)

Notes:

• A working implementation is available as https://github.com/networkupstools/nut/tree/cmdset_status

• This work is sponsored by Eaton

• I'm not fan of the CMDSET_STATUS name, but had no better idea apart from
  STATUS_TRACKING / STATUS_ID. Comments and proposal welcome!

• the modifications are:

  • non regressive: if CMDSET_STATUS is not enabled, the protocol will behave as
    usual. Hence, existing implementation will not be altered
  • not impacting other clients: though the tracking structure is global (to
    avoid loss of info when clients disconnect), only client that enabled
    CMDSET_STATUS will receive the ID and be able to query the status info
  • mainly supported by upsd, its sstate and netcmds layer
  • limited to dstate for drivers. No other modification are
    needed in the drivers or elsewhere

• ID generation: I've selected UUID v4 (random) to ensure uniqueness of the
  generated ID. For now, I've added a basic implementation in the code, but it's
  limited in OS scope, which I plan to address more cleanly. My requirements are:

  • support all our OS scope (Linux, Windows, Mac, Unix inc. BSD and Solaris,
    HP-UX, AIX, ...)
  • no external dependency (embedded / homebrew implementation)
  • Possible UUID approaches:
    • https://github.com/spc476/SPCUUID
    • https://github.com/rxi/uuid4 (tiny, embeddable, MIT license, Linux/Mac/FreeBSD/Win support)
    • http://www.ossp.org/pkg/lib/uuid/
    • libuuid (from e2fsprogs) (Linux only)
    • homebrew implem (using /dev/urandom, fallback on random/rand/...)

• There are other remainders to be addressed for a full completion, but which can be separe work):

  • Augeas completion for CMDSETSTATUSDELAY
  • upscmd
  • upsrw
  • libnutclient (@boricj will very probably handle this)
  • Python
  • Perl
  • jNUT (@EmilienKia)
  • anything I missed?

Testing procedure:

• retrieve and compile the branch https://github.com/networkupstools/nut/tree/cmdset_status
• configure a device in ups.conf and a user in upsd.users
• launch the driver and upsd
• open a telnet using

telnet localhost 3493

• authenticate using

USERNAME "username from upsd.users"
PASSWORD "password from upsd.users"

• check if status tracking is enabled:

GET CMDSET_STATUS

will return:

OFF

• enable status tracking using:

SET CMDSET_STATUS ON

• issue an instant command or variable setting. For example:

INSTCMD myups load.off

You will receive back an "OK" answer with a status ID:

OK d6470a8e-4521-411c-beef-69cc9b33a94b

• Ask for the status of this command using:

GET CMDSET_STATUS d6470a8e-4521-411c-beef-69cc9b33a94b

• You will receive an answer like:

SUCCESS