Experimental Physics and
Industrial Control System

Andrew Johnson via Core-talk <core-talk at aps.anl.gov> · Sat, 05 Aug 2023 22:20:35 -0000

The version of yajl that comes with Base 7.0.6.1 and later can generate
JSON5 which handles infinities and NaN values, but it looks like the
pvAccess code in pvget isn't enabling that option in the print
formatter. Applying the following patch to modules/pvData should fix it:

diff --git a/src/factory/printer.cpp b/src/factory/printer.cpp
index 928fc4f..31f7116 100644
--- a/src/factory/printer.cpp
+++ b/src/factory/printer.cpp
@@ -404,6 +404,9 @@ std::ostream& operator<<(std::ostream& strm, const PVStructure::Formatter& forma
     if(format.xfmt==PVStructure::Formatter::JSON) {
         JSONPrintOptions opts;
         opts.multiLine = false;
+#if EPICS_VERSION_INT>=VERSION_INT(7,0,6,1)
+        opts.json5 = true;
+#endif
         printJSON(strm, format.xtop, format.xshow ? *format.xshow : BitSet().set(0), opts);
         strm<<'\n';
         return strm;

Given that this is actually a bug against pvDataCPP I have filed an
issue against that module on GitHub referring to this bug report:
https://github.com/epics-base/pvDataCPP/issues/92

** Bug watch added: github.com/epics-base/pvDataCPP/issues #92
   https://github.com/epics-base/pvDataCPP/issues/92

** Changed in: epics-base
       Status: New => Triaged

** Changed in: epics-base
   Importance: Undecided => Medium

** Also affects: epics-base/7.0
   Importance: Medium
       Status: Triaged

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https://bugs.launchpad.net/bugs/2029482

Title:
  pvget json error

Status in EPICS Base:
  Triaged
Status in EPICS Base 7.0 series:
  Triaged

Bug description:
  I’ve been using `pvget -M json` and have noticed a problem with it
  when the PV has the alarm fields set like so:

  double lowAlarmLimit nan
  double lowWarningLimit nan
  double highWarningLimit nan
  double highAlarmLimit nan

  When I run pvget I get the following:

  > pvget -M json IOC:m1.RBV
  IOC:m1.RBV {"value":88.129999999999995,"alarm":{"severity":0,"status":0,"message":"NO_ALARM"},"timeStamp":{"secondsPastEpoch":1691063460,"nanoseconds":182366000,"userTag":0},"display":{"limitLow":-100.0,"limitHigh":100.0,"description":"motor 1","units":"degrees","precision":5,"form":{"index":0,"choices":["Default","String","Binary","Decimal","Hex","Exponential","Engineering"]}},"control":{"limitLow":-100.0,"limitHigh":100.0,"minStep":0.0},"valueAlarm":{"active":false,"lowAlarmLimit"Error in monitor handler : yajl_gen_invalid_number

  It looks like YAJL doesn’t like the nan values. If I set them to non-
  nan values then the error goes away.

  This is with base 7.0.7.

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System