I ported a bunch of frontends to C++ and now I'm occasionally getting this RPC 
error message:

http error: readyState: 4, HTTP status: 502 (Proxy Error), batch request: method: 
"db_get_values", params: [object Object], id: 1583456958869 method: "get_alarms", 
params: null, id: 1583456958869 method: "cm_msg_retrieve", params: [object 
Object], id: 1583456958869 method: "cm_msg_retrieve", params: [object Object], 
id: 1583456958869

I'm assuming I'm doing wrong something somewhere, but does this message contain 
information where to look? Does the ID mean something?

I am on branch develop and use the tmfe frontends. I found that a bool vector 
gets bigger every time I read it from the ODB.

Turns out in midasodb.cxx (as of commit 813f696, lines 478ff) the output vector 
"value" gets appended to without resizing.

Since after line 474 xvalue.size()==value.size() it would make sense to simply 
replace value->push_back() with value[i]= .

The most recent commit (b43aef648c2f8a7e710a327d0b322751ae44afea) throws this 
compiler error:
src/tmfe_main.cxx:39:11: error: 'SIGPIPE' was not declared in this scope
    signal(SIGPIPE, SIG_IGN);

It's fixed by adding #include <signal.h> to that file.

Am I right in thinking that the TMFE HandlePoll function is calle once per 
PollMidas()? And what is the difference to HandleRead()?

> BTW, for production use I recommend midas from the "release" branches, unless one 
> needs a bug fix or new feature from the development branch.

Fair point. I would suggest adding that recommendation to the wiki instructions. I 
forget to add that step otherwise.

Version: release/midas-2020-12

I'm exporting the history data shown in elog:2132/1 to CSV, but when I look at the 
CSV data, the step no longer occurs at the same time in both data sets (elog:2132/2)

History is from two separate equipments/frontends, but both have "Log history" set to 1.

Tried with export of two different time ranges, and the shift appears to remain the same, 
about 4040 rows.

I think from my perspective the separate files are fine. I personally don't really like the format 
with the gaps, so don't see an advantage in putting in the extra work.
I'm surprised the shift is this big, though, it was more than a whole hour in my case, is it the 
time difference between when the frontends were started?

Version: release/midas-2020-12

In the new history display, the checkbox "Change all time axes together" works 
well with the mouse-based zoom, but does not apply to the +- buttons.

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 documentation fro the Elog ODB tree here:
https://midas.triumf.ca/MidasWiki/index.php//Elog_ODB_tree#Url

says:

The Built-in elog will ignore this key.

If using an Built-in Elog, this key must NOT be present.

I assume this is an artifact from amending the documentation, but it's unclear if 
the key has to be removed or not. I.e. if the key exists and is empty, will the 
built-in elog work? In what way will it break?

The documentation for the sequencer loop says:

<quote>
LOOP [name ,] n ... ENDLOOP	To execute a loop n times. For infinite loops, "infinite" 
can be specified as n. Optionally, the loop variable running from 0...(n-1) can be accessed 
inside the loop via $name.
</quote>

In fact the loop variable runs from 1...n, as can be seen by running this exciting 
sequencer code:

1 COMMENT "Figuring out MSL"
2 
3 LOOP n,4
4   MESSAGE $n,1
5 ENDLOOP

Maybe this is already possible, I have a hard time understanding the mhttpd source code.

I would like to use a function defined in the <script> block of my custom page as an onchange callback.

Specific example:
I have an modbthermo that I would like to change to three different colours for "too cold", "just right", and "too hot" (measuring porridge, presumably). The examples only show the explicit (condition)?(val1):(val2) syntax, which doesn't allow more than two values, so I had hoped to replace

onchange="this.dataset.color=this.value > 40?'red':'blue';"

with something like

onchange="this.dataset.color=check_Temp(this.value);"

or

onchange="check_Temp(this.value, this.dataset.color);"

if that's easier somehow. The function itself would then return the colour string, or set the color argument to that string (I'm not sure if JS passes references or just values.)

Is this a possibility?

I figured I wasn't the first to have this idea.
Works great, thanks!

I really like the concept of the odbxx interface.
I think it would be a nice feature if one could have a read_only connection, e.g. by declaring a "const midas::odb".
Just for fun I tried if this already works, but the compiler doesn't allow const midas::odb for e.g. the [] operator. I'm guessing this would be non-trivial to implement, but I like the idea of certain Midas clients being able to read the odb without risking corruption.

Actually, now that I look again, there is a mistake in the instructions:
you say

onchange="this.dataset.color=check_therm(this)"

but check_therm doesn't return anything and instead changes the color itself. So you either want the function to return the string and use the above assignment, or use the function you provide and use

onchange="check_therm(this)"

> Having a "const midas::odb" probably does not work (at least I would not know how to implement that).
> 
> But I could make an internal flag analog to the auto refresh flags. So you would have
> 
>     o.set_write_protect(true);
> 
> to turn on write protection. Would that work for you?

Absolutely. Looking at the underlying code I was also at a loss how const would work.
I'm mostly just interested in having small clients that only read from the odb (for whatever reason) without risking corrupting it by messing something 
up in the code, especially since such small clients are almost by definition hacked together quickly on the fly.

I'm constructing a TMFeEquipment with this constructor:

MagnetFe(const char *eqname, const char *eqfilename) // ctor
        : TMFeEquipment(eqname, eqfilename)
    {
        fEqConfEventID = 3;
        fEqConfBuffer = "SYSTEM";
        fEqConfPeriodMilliSec = 1000; // in milliseconds
        fEqConfLogHistory = 1;
        fEqConfReadOn = RO_ALWAYS;
    }


When I start with a fresh ODB, the directories are created correctly, and e.g. the 
event ID is set correctly, but "Read on" is set to 1 (i.e. RO_RUNNING) instead of 
0xFF.
Now when I set it to 0xFF manually and restart, it gets overwritten to 7 
(RO_NONTRANS), which I guess is a relatively recent change and doesn't affect me 
negatively.

This is not a bug per se, but I find it a little odd that the MVOdb functions RS, 
RSA, RSAI, and WSA use std::string as their type, while WS ans WSAI use const 
char*

Seems to me like simple overloading a la
void WS(const char* varname, const std::string v, MVOdbError* error = NULL){
    WS(varname, v.c_str(), v.size(), error);
}

should be all that's needed, right?