On Wednesday, 31 May 2017 at 13:04:52 UTC, Steven Schveighoffer
wrote:
I have discovered an annoyance in using vibe.d instead of
another web framework. Simple errors in indexing crash the
entire application.
Since I wrote/run a bunch of websites/network services written in
D, here's my experience/advice:
First, this is not something specific to array indexing, but an
entire class of logic errors which are sometimes recoverable.
Other examples are associative array indexing, division by zero,
and out-of-memory errors resulting from underflows. All of these
are due to bugs in the program, but could hypothetically be
handled without compromising the integrity of the process.
My advice:
1. Let the program crash. Make sure it's restarted afterwards,
either via a looping script, or a watchdog.
2. Make sure you are notified of the error. I don't mean just
recorded in a log file somewhere, but set it up so you receive an
email any time it happens, with the stack trace. I run all my D
network services from a cronjob, which automatically sends output
by email. If you have the stack trace, most of these bugs take
only a few minutes to fix - at the very least, turning the error
into an exception is a trivial modification if you don't have
time for a full root cause analysis at that moment.
3. Design your program so that it can be terminated at any point
without resulting in data corruption. I don't know if Vibe.d can
satisfy this constraint, but e.g. the ae.net.http.server workflow
is to build/send the entire response atomically, meaning that the
Content-Length will always be populated. Wrap your database
updates in transactions. Use the "write to temporary file then
rename over the original file" pattern when updating files. Etc.
