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Entry  19 Jun 2017, Thomas Lindner, Bug Report, mhttpd ODB editor changes string length, breaks  
    Reply  21 Jun 2017, Thomas Lindner, Bug Report, mhttpd ODB editor changes string length, breaks  
Message ID: 1303     Entry time: 21 Jun 2017     In reply to: 1301
Author: Thomas Lindner 
Topic: Bug Report 
Subject: mhttpd ODB editor changes string length, breaks  
To follow up; with some help from Konstantin and Stefan, we realized that this
particular problem should already be fixed.  While I was using the most recent version
of MIDAS, I hadn't rebuild the EPICS frontend programs when I was doing this test.  Once
I did that the error no longer occurred.  This is because the most recent version of
MIDAS includes a check that will resize these particular string variables before using
them (technically, this is included in db_get_record1()); this resizing only happens for
these couple strings that must have a fixed size.

We are still having a separate discussion about whether this treatment of string lengths
that need to have a fixed size can be further improved.  Will update once discussion

> I guess this might be related to the changes in the last elog conversation; but
> I'll break it out as a separate problem.
> The new mhttpd ODB editor seems to resize all strings (not just strings that are
> greater than 256 characters).  So, when I change some string with the mhttpd ODB
> editor to 'ffffff', then I find that the string size is now ~7 characters.
> This might be fine in general; but it seems to cause a problem when dealing with
> alarms.  In particular, I find that if I try to set (through mhttpd) the
> "execute command" for an alarm class or the "condition" for an alarm, then I get
> into lots of trouble.  For instance, I changed the "execute command" for my
> alarm class through mhttpd; when associated alarms were triggered, I got errors
> 21:58:12 [feSourceEpics,ERROR] [odb.c:9133:db_get_record,ERROR] struct size
> mismatch for "/Alarms/Classes/Alarm" (expected size: 348, size in ODB: 100)
> 21:58:12 [feSourceEpics,ERROR] [alarm.c:379:al_trigger_class,ERROR] Cannot get
> alarm class record
> This makes sense, since ALARM_CLASS has a fixed size
> typedef struct {
>    BOOL write_system_message;
>    ...
>    char execute_command[256];
>    ...
>    char display_fgcolor[32];
> so problems will clearly occur when I change the size and try to grab it:
>    ALARM_CLASS ac;
>    status = db_get_record1(hDB, hkeyclass, &ac, &size, 0, strcomb(alarm_class_str));
> I guess that similar problems also occur if you edit the string for ALARM or
> PROGRAM_INFO instances.  These problems do not occur when I change my strings
> with odbedit, which doesn't resize strings below 256.
> I'm not sure what the proper solution is.  A temporary solution is that the
> mhttpd ODB editor shouldn't resize strings if the new size is less than 256
> characters; in that case the size should be left as 256 characters.
> This test was done with MIDAS git repository as of today:
> commit 45a90dc329554f528485da121501daf6ecde100d
ELOG V3.1.4-2e1708b5