Thank you for reporting this problem:

a) ODB key *names* are restricted to 31 characters (32 bytes, last byte is a NUL), not 256 characters.
b) ODB string length is unlimited (32-bit length field)
c) ODB C API "db_get_value" & co require fixed length buffer and most users of this API provide a 256-byte fixed buffer for strings, some of them also do not 
check the status code, resulting in silent truncation. (I think the ODB functions themselves report truncation to midas.log, so not completely silent).

We try to fix this where we must - but it is cumbersome with the current ODB API - as in your fix on has to:
- get the ODB key, extract size
- allocate buffer
- call db_get_value() & co
- use the data
- remember to free the buffer on each and every return path

The first three steps could become one if we had an ODB "get_data" function that automatically allocated the data buffer.

But the main source of bugs will be the last step - remember to free the buffer, always.

P.S.

We are not alone in pondering how to do this best. If you want to see it "done right",
read the fresh-off-the-presses book "Go Programming Language" by Alan Donovan and Brian Kernighan,
http://www.gopl.io/

Brian Kernighan is the "K" in K&R "C programming language", still around and kicking, now at Google.
Sadly the "R" passed away in 2011 - http://www.nytimes.com/2011/10/14/technology/dennis-ritchie-programming-trailblazer-dies-at-70.html

K.O.

> Both the /Script and /CustomScript trees in the ODB allow users to trigger a 
> script via Midas - which silently truncates command strings longer than 
> 256 characters.
> 
> I'd prefer that Midas place no limit on string length.  Failing that, it would be
> helpful to have character limits called out in the documentation 
> (https://midas.triumf.ca/MidasWiki/index.php//Script_ODB_tree#.3Cscript-name.3E_key_or_subtree,
> https://midas.triumf.ca/MidasWiki/index.php//Customscript_ODB_tree).
> 
> As far as I can tell, odb.c allows arbitrarily large strings in the ODB data.  
> (Although key *names* are restricted to 256 characters.)  I've submitted one 
> possible version of an arbitrary-length exec_script() as a pull request 
> (https://bitbucket.org/tmidas/midas/pull-requests/).
> 
> Am I misunderstanding any critical pieces?  Does Midas intentionally treat 
> strings in the ODB as limited to 256 characters?