Re: PV Access Protocol Specification

[Michael Davidsaver via Core-talk <core-talk@aps.anl.gov>]

On 4/10/19 10:11 AM, Kasemir, Kay wrote:
>> In the interest of not enabling us to kick this can down the road indefinitely.
>> https://github.com/epics-base/pvAccessCPP/wiki/protocol
>> This wiki is editable by anyone with a github account.
>    
> 
> Thanks!
> 
> I've updated the size encoding.
> 
> I'm unclear where "-1" (byte 255) as Null indicator is used.
> Wouldn't that be the same as size 0, no elements?

You are not alone in wondering about this.

There are some places in the c++ code where -1 isn't handled,
and will result in a decode error.  cf. my earlier link to
CMD_SEARCH message handling.

However, there are some places where it is:

https://github.com/epics-base/pvDataCPP/blob/8f0111e482aa139f4311378f2b0bc831c46420b2/src/misc/serializeHelper.cpp#L106

And hey, our first TODO of the thread.

>  if(size!=(size_t)-1) // TODO null strings check, to be removed in the future