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Subject: [Bug 1902560] [NEW] Read info items using a filter
From: Andrew Johnson via Core-talk <core-talk at aps.anl.gov>
To: core-talk at aps.anl.gov
Date: Mon, 02 Nov 2020 18:12:00 -0000
Public bug reported:

Info items are currently only accessible from inside the IOC, but a few
people have asked if they could be fetched over the network. The
simplest way to implement that is probably with a server-side filter,
which makes this functionality optional and decouples the code from the
internals of the IOC.

The filter could accept parameters to control what it returns, such as:

1. A list of all the info item names attached to this record or alias.
2. A list of info item names attached that match a particular pattern.
3. Number of info items attached.
4. Value of a specific info item, selected by index number or item name.
5. All info item names and values, formatted as a JSON object (beware that item values can now themselves be JSON objects, don't assume they are just a string).

It would be reasonable to limit item names to 39 characters so #1 and #2
above could return an array of DBF_STRINGs, and #3 could return a
DBF_SHORT or DBF_LONG, but item values can be much longer so the return
types of #4 and #5 would need to be an array of DBF_CHAR with some
chosen maximum length.

CAUTION: Record aliases have their own info item namespace, separate
from the record they alias:

record(ai, ai1) {
  info(tag1, "record")
  alias(al1)
}
record("*", al1) {
  info(tag2, "alias")
}

epics> dbli
ai1 info(tag1, "record")
al1 info(tag2, "alias")

** Affects: epics-base
     Importance: Wishlist
         Status: Confirmed


** Tags: codeathon

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https://bugs.launchpad.net/bugs/1902560

Title:
  Read info items using a filter

Status in EPICS Base:
  Confirmed

Bug description:
  Info items are currently only accessible from inside the IOC, but a
  few people have asked if they could be fetched over the network. The
  simplest way to implement that is probably with a server-side filter,
  which makes this functionality optional and decouples the code from
  the internals of the IOC.

  The filter could accept parameters to control what it returns, such
  as:

  1. A list of all the info item names attached to this record or alias.
  2. A list of info item names attached that match a particular pattern.
  3. Number of info items attached.
  4. Value of a specific info item, selected by index number or item name.
  5. All info item names and values, formatted as a JSON object (beware that item values can now themselves be JSON objects, don't assume they are just a string).

  It would be reasonable to limit item names to 39 characters so #1 and
  #2 above could return an array of DBF_STRINGs, and #3 could return a
  DBF_SHORT or DBF_LONG, but item values can be much longer so the
  return types of #4 and #5 would need to be an array of DBF_CHAR with
  some chosen maximum length.

  CAUTION: Record aliases have their own info item namespace, separate
  from the record they alias:

  record(ai, ai1) {
    info(tag1, "record")
    alias(al1)
  }
  record("*", al1) {
    info(tag2, "alias")
  }

  epics> dbli
  ai1 info(tag1, "record")
  al1 info(tag2, "alias")

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