Experimental Physics and
Industrial Control System

Andrew Johnson via Core-talk <core-talk at aps.anl.gov> · Sun, 02 Aug 2020 06:12:54 -0000

I've changed my mind about octal escapes.

The JSON5 spec says "\012" should decode as a <nil> byte followed by
"12", whereas C and dbTranslateEscape() decode it as a line-feed
character "\n". We probably don't want to get different values for the
VAL and DESC fields as would happen here if we don't do something:

record(stringin, s1) {
  field(DESC, "\041")           # "!" - dbTranslateEscape()
  field(INP, {const:"\041"})    # "" - yajl
}

I now think the best solution is to drop support for octal character
escapes completely, and require strings to use \xXX hex escapes if they
can't use literal characters directly. I suspect octal escapes are very
rarely used now, and removing them would resolve this difference,
leaving just \a and \uXXXX to be decoded differently.

I will implement and document this change on my json5 branch.

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https://bugs.launchpad.net/bugs/1783475

Title:
  const link support can't handle escaped charactors

Status in EPICS Base:
  Triaged
Status in EPICS Base 3.16 series:
  Won't Fix
Status in EPICS Base 7.0 series:
  Triaged

Bug description:
  I think the following should work, but it doesn't.  The culprit seems
  to be the call to dbTranslateEscape() in dbRecordField() and
  dbRecordInfo().  The escaped newline is handled correctly by dbLex,
  but the later dbJLinkParse() errors on the now unescaped newline.

  > record(stringin, "test") {
  >      field(INP, {const:"multi\nline"})
  > }

  > dbJLinkInit: lexical error: invalid character inside string.
  >                          {"const":"multi line"}
  >                      (right here) ------^

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System