Experimental Physics and
Industrial Control System

Eric Norum <[email protected]> · Tue, 13 Nov 2012 14:54:00 -0800

On Nov 13, 2012, at 1:56 PM, Andrew Johnson <[email protected]> wrote:

> Hi Mark,
> 
> On 2012-11-13 Mark Rivers wrote:
>> 
>> So do we agree with Andrew's recommendation that NORD should including the
>> trailing Nil, or should NORD be the actual number of elements that were
>> read, and clients must be fixed to handle this if they want to use long
>> string support?
> 
> Passing around long strings that don't have (or count) a terminating Nil byte 
> is inherently risky, although the danger is more likely to be annoying 
> (appending garbage or old text to the current text) than to induce crashes in 
> the IOC.
> 
> An aSub record subroutine is a client, and it's very easy for the subroutine's 
> author to not realize that the long string in their record's input field may 
> not be Nil-terminated.  The code that reads the input link into that field is 
> generic and can't add the Nil.  If the code calls strlen() on the buffer or 
> passes it into sprintf() without doing the termination dance it's going to 
> count the garbage.
> 
> I understand Eric's desire to not add zero bytes to data that Asyn reads in 
> through a serial or network port and that is obviously essential, but that's 
> not what you're proposing to do anyway.  If I've read your message correctly 
> asynPortDriver parameter strings are coming from internal sources, they are 
> not providing raw data from the port.  By counting the Nil when it is already 
> present you are reducing the work that the author of a 1-off aSub subroutine 
> has to do, and making the IOC code more robust.

So how does the author of a client (aSub subroutine or anything else) determine the meaning of NORD with the proposed change in place?
How does the author determine whether the the source of a an array of characters is something that appends a nil or something like a serial/network port that does not?   Maybe the source might even change at run time.
Mucking with the semantics of NORD is a BadIdea (™, IMHO).

-- 
Eric Norum
[email protected]

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System