I have a more subtle point about the new ODB key for using an external elog I mentioned in [1].  I was very confused after changing the ODB "External Elog" because mhttpd still wasn't using my external elog URL.  I started trying to debug mhttpd.cxx, but found a lot of bits of mhttpd didn't seem to be getting called.  I eventually realized that my browser had been caching the responses for some (though not all) of the MIDAS navigation buttons.  Clearing my browser cache fixed the problem and allowed me to use the MIDAS button to the external ELOG.  This caching happens on my macbook for both Firefox 84.0.2 and Safari 13.1.

Many of the requests to mhttpd end up going to send_fp(), where we explicitly set the cache time to 24 hours.

   // send HTTP cache control headers                                                                                               
   time_t now = time(NULL);
   now += (int) (3600 * 24);
   struct tm* gmt = gmtime(&now);
   const char* format = "%A, %d-%b-%y %H:%M:%S GMT";
   char str[256];
   strftime(str, sizeof(str), format, gmt);
   r->rsprintf("Expires: %s\r\n", str);

Some other MIDAS buttons don't seem to be cached by the browser; for instance the response for the 'OldHistory' button doesn't get cached.

Should we remove the cache instruction for at least some of the buttons?  At least for the elog button where we want the link direction to get switched by an ODB key the caching seems a bad idea.

[1] https://midas.triumf.ca/elog/Midas/2078

Let me first explain a bit why caching is there. Once we had the case that someone from 
TRIUMF opened a midas custom page at T2K. It took about one minute (!) to load the page. 

When we looked at it, we found that the custom page pulled about 100 items with individual
HTTP requests from Japan, each taking about one second for the roundtrip. Then we redesigned
the custom page communication so that many ODB entries could be retrieved in one operation,
which improved the loading time from 100s to about 2s.

With the buttons we will have to make the same compromise. If we do not cache anything,
loading the midas status page over the Pacific takes many seconds. If we cache all, any
change on the midas side will not be reflected on the web page. So there is a compromise
to be made. I thought I designed it such that the side menu is cached locally, but when
the user presses "reload", then the full menu is fetched from the server. Of course one
has to remember this, so changing the ELOG URL or other things on the menu require a
reload (or wait a certain time for the cache to expire). So try again if that's working
for you. If not, I can visit it again and check if there is any bug.

If we go the route to disable the cache, better try this to T2K and see what you get before
we commit ourselves to that. Last time TRIUMF people were complaining a lot about long
load times.

Best,
Stefan

I tried reloading the pages.  If I reloaded the actual elog page 

https://server.triumf.ca/?cmd=Elog

then it bypassed the cache and got the correct updated page from mhttpd.

However, if when I reloaded the status page

https://server.triumf.ca/?cmd=Status

and then clicked the Elog button then I just got the cached (old) page.  Admittedly reloading the status page doesn't make so much sense (once I thought about it), but it is what I tried first (I'm good at modelling unexpected user behaviour); so there is some risk that the user will try reloading the wrong page and will be stuck not getting the external elog page (until 24 hours runs out).

Anyway, I will update the documentation to note that you need to reload the elog page after changing this variable.  That's probably an adequate solution.

I certainly don't suggest getting rid of caching entirely.  I was trying to think whether there was a set of pages where it would make sense to disable the cache (like the elog page).  But maybe that will just cause more problems.


> Let me first explain a bit why caching is there. Once we had the case that someone from 
> TRIUMF opened a midas custom page at T2K. It took about one minute (!) to load the page. 
> 
> When we looked at it, we found that the custom page pulled about 100 items with individual
> HTTP requests from Japan, each taking about one second for the roundtrip. Then we redesigned
> the custom page communication so that many ODB entries could be retrieved in one operation,
> which improved the loading time from 100s to about 2s.
> 
> With the buttons we will have to make the same compromise. If we do not cache anything,
> loading the midas status page over the Pacific takes many seconds. If we cache all, any
> change on the midas side will not be reflected on the web page. So there is a compromise
> to be made. I thought I designed it such that the side menu is cached locally, but when
> the user presses "reload", then the full menu is fetched from the server. Of course one
> has to remember this, so changing the ELOG URL or other things on the menu require a
> reload (or wait a certain time for the cache to expire). So try again if that's working
> for you. If not, I can visit it again and check if there is any bug.
> 
> If we go the route to disable the cache, better try this to T2K and see what you get before
> we commit ourselves to that. Last time TRIUMF people were complaining a lot about long
> load times.
> 
> Best,
> Stefan

>    r->rsprintf("Expires: %s\r\n", str);

The best I can tell, none of this works in current browsers. with google-chrome,
I see it cache pretty much everything regardless of "expires", "no cache", etc
and anything else I tried.

Things like shift-<reload>, etc used to work to refresh the cache, but not any more.

So, I too, see confusing side-effects of caching, where I change something in ODB,
but "nothing happens". Then I scratch my head for 30 minutes until I remember
to open the javascript debugger where shift-<reload> (or is it ctrl-<reload>) actually works.

It seems that the only reliable way to bypass the browser cache is to add
a tag with a random number to the URL ("&ts=currenttime").

This is for HTTP GET requests. HTTP POST does not seem to be cached, so I do not worry
about this nonsense for json-rpc requests.

Perhaps we should do this random number trick for all user actions. User can
press buttons only so fast, we should be able to sustain the rate. Anything
loaded automatically or from a timer, we should allow caching.

BTW, things like midas.js are also cached, and it is common to see problems
after updating midas, where status.html is newly loaded, but midas.js is an old
stale version from cache.

Messy.

K.O.

> It seems that the only reliable way to bypass the browser cache is to add
> a tag with a random number to the URL ("&ts=currenttime").

Indeed that's the only reliable way to avoid caching across browsers. An alternative is

("&r=" + Math.random())

to add a random number.


> BTW, things like midas.js are also cached, and it is common to see problems
> after updating midas, where status.html is newly loaded, but midas.js is an old
> stale version from cache.

Reloading JavaScript file NOT from the cache is really tricky these days. I added a
special Google Chrome extension to clear my browser cache, which works reliably:

https://chrome.google.com/webstore/detail/clear-cache/cppjkneekbjaeellbfkmgnhonkkjfpdn

Stefan

Is it possible to embed modbvalue in an SVG for use within a custom page?

thanks.

You can't really embed it, but you can overlay it. You tag the SVG with a 
"relative" position and then move the modbvalue with an "absolute" position over 
it:

<svg style="position:relative" width="400" height="100">
  <rect width="300" height="100" style="fill:rgb(255,0,0);stroke-width:3;stroke:rgb(0,0,0)" />
  <div class="modbvalue" style="position:absolute;top:50px;left:50px" data-odb-path="/Runinfo/Run number"></div>
</svg>

The new history as well as the clock in the web page header show the local time 
of the user's computer running the browser.
Would it be possible to make it either always use the time zone of the Midas 
server, or make it selectable from the config page?
It's not ideal trying to relate error messages from the midas.log to history 
plots if the time stamps don't match.

> The new history as well as the clock in the web page header show the local time 
> of the user's computer running the browser.
> Would it be possible to make it either always use the time zone of the Midas 
> server, or make it selectable from the config page?
> It's not ideal trying to relate error messages from the midas.log to history 
> plots if the time stamps don't match.

I implemented a new row in the config page to select the time zone. 

"Local": Time zone where the browser runs
"Server": Time zone where the midas server runs (you have to update mhttpd for that)
"UTC+X": Any other time zone

The setting affects both the status header and the history display.

I spent quite some time with "named" time zones like "PST" "EST" "CEST", but the 
support for that is not that great in JavaScript, so I decided to go with simple 
UTC+X. Hope that's ok.

Please give it a try and let me know if it's working for you.

Best,
Stefan

I found a way to embed modbvalue into a SVG:

<text x="100" y="100" font-size="30rem">
Run=<tspan class="modbvalue" data-odb-path="/Runinfo/Run number"></tspan>
</text>

This seems to behave better that the suggestion below.

> You can't really embed it, but you can overlay it. You tag the SVG with a 
> "relative" position and then move the modbvalue with an "absolute" position over 
> it:
> 
> <svg style="position:relative" width="400" height="100">
>   <rect width="300" height="100" style="fill:rgb(255,0,0);stroke-width:3;stroke:rgb(0,0,0)" />
>   <div class="modbvalue" style="position:absolute;top:50px;left:50px" data-odb-path="/Runinfo/Run number"></div>
> </svg>

> > The new history as well as the clock in the web page header show the local time 
> > of the user's computer running the browser.
> > Would it be possible to make it either always use the time zone of the Midas 
> > server, or make it selectable from the config page?
> > It's not ideal trying to relate error messages from the midas.log to history 
> > plots if the time stamps don't match.
> 
> I implemented a new row in the config page to select the time zone. 
> 
> "Local": Time zone where the browser runs
> "Server": Time zone where the midas server runs (you have to update mhttpd for that)
> "UTC+X": Any other time zone
> 
> The setting affects both the status header and the history display.
> 
> I spent quite some time with "named" time zones like "PST" "EST" "CEST", but the 
> support for that is not that great in JavaScript, so I decided to go with simple 
> UTC+X. Hope that's ok.
> 
> Please give it a try and let me know if it's working for you.
> 
> Best,
> Stefan

Hi Stefan,

This is great, the UTC+x is perfect, thank you.
PAA

Dear all,
      I'm trying to use the logging on a mysql DB. Following the instructions on 
the Wiki, I recompiled MIDAS after installing mysql, and cmake with NEED_MYSQL=1 
can find it:

-- MIDAS: Found MySQL version 8.0.23

Then, I compiled my frontend (cmake with no options + make) and run it, but in the 
ODB I cannot find the tree for mySQL. I have only:

Logger/Runlog/ASCII

while I would expect also:

Logger/Runlog/SQL

What could be missing? Maybe should I add something in the CMakeList file or run 
cmake with some option?

Thank you,
      Francesco

I solved this, it was a failed "make clean" before recompiling. Now it works.

Sorry for the noise.

Francesco

> Dear all,
>       I'm trying to use the logging on a mysql DB. Following the instructions on 
> the Wiki, I recompiled MIDAS after installing mysql, and cmake with NEED_MYSQL=1 
> can find it:
> 
> -- MIDAS: Found MySQL version 8.0.23
> 
> Then, I compiled my frontend (cmake with no options + make) and run it, but in the 
> ODB I cannot find the tree for mySQL. I have only:
> 
> Logger/Runlog/ASCII
> 
> while I would expect also:
> 
> Logger/Runlog/SQL
> 
> What could be missing? Maybe should I add something in the CMakeList file or run 
> cmake with some option?
> 
> Thank you,
>       Francesco

There have been times in ALPHA that an alarm is triggered and the shift crew 
are unclear who to contact if they aren't trained to fix the specific 
failure mode.

I wish to add the property 'Users responsible' to the ODB for Alarms and 
Programs.

I have drafted what this might look like in a new pull request:
https://bitbucket.org/tmidas/midas/pull-requests/22/add-users-responsible-
field-for-specific

It requires changing of several data structures, I think I have found all 
instances of the definitions so the ODB should 'repair' any of the old 
structures adding in users responsible.

If 'Users responsible' is set, MIDAS messages append them after the message 
in brackets '()'. If used in conjunction with the MIDAS messenger 
(mmessenger), the users responsible can be 'tagged' directly.

I.e, for slack, simply set the 'users responsible' to <@UserID|Nickname>, 
for mattermost '@username', for discord '<@userid>'. Note that discord 
doesn't allow you to tag by username, but numeric userid



I have expanded char array in 'al_trigger_class' to handle the potentially 
longer MIDAS messages. Perhaps since I'm touching these lines I should 
change these temporary containers to std::string (line 383 and 386 of 
alarm.cxx)?

I have tested this quite a bit for my system, I am not sure how I can test 
mjsonrpc.

I think this is a good idea and I support it. We have a similar problem in MEG and 
we solved that with external (bash) scripts called in case of alarms. One feature 
there we have is that for some alarms, several people want to get notified. So 
people can "subscribe" to certain alarms. The subscription are now handled inside 
Slack which I like better, but maybe it would be good to have more than one "user 
responsible". Like if one person is sleeping/traveling, it's good to have a 
substitute. Can you make an array out of that? Or a comma-separated list?

Best,
Stefan

> I think this is a good idea and I support it. We have a similar problem in MEG and 
> we solved that with external (bash) scripts called in case of alarms. One feature 
> there we have is that for some alarms, several people want to get notified. So 
> people can "subscribe" to certain alarms. The subscription are now handled inside 
> Slack which I like better, but maybe it would be good to have more than one "user 
> responsible". Like if one person is sleeping/traveling, it's good to have a 
> substitute. Can you make an array out of that? Or a comma-separated list?
> 
> Best,
> Stefan

Presently there are 256 characters in the 'users responsible' field, so you can just 
list many users (no space, space or comma whatever). Discord, slack and mattermost 
don't care, they just parse the user tags.

I can still make this an array and pass a std::vector<std::string> into 
al_trigger_class function?

> I can still make this an array and pass a std::vector<std::string> into 
> al_trigger_class function?

Maybe 256 chars are enough at the moment. If other people complain in the future, we can 
re-visit.

Stefan

> > I can still make this an array and pass a std::vector<std::string> into 
> > al_trigger_class function?
> 
> Maybe 256 chars are enough at the moment. If other people complain in the future, we can 
> re-visit.
> 
> Stefan

Thinking about it, an array of maybe 80 character would give enough space for a name, a tag 
and phone number. Do I need to budget memory very strictly? Would 32 entries of 80 
characters be too much? 

> > > I can still make this an array and pass a std::vector<std::string> into 
> > > al_trigger_class function?
> > 
> > Maybe 256 chars are enough at the moment. If other people complain in the future, we can 
> > re-visit.
> > 
> > Stefan
> 
> Thinking about it, an array of maybe 80 character would give enough space for a name, a tag 
> and phone number. Do I need to budget memory very strictly? Would 32 entries of 80 
> characters be too much? 

On that level memory is cheap.

Stefan

I've updated the branch / pull request to use an array of 10 entries (80 chars each). 32 felt a 
little overkill when I saw it on screen, but absolutely happy to set it to any number you 
recommend.

The array gets flattened out when an alarm is triggered, currently the formatting produces

AlarmClass : AlarmMessage (Flattened List Of Users Responsible Array With Space Separators)

If experiments want to use Discord / Slack / Mattermost tags and or add phone numbers, that 
should fit in 80 characters