A visual trace URL takes the form of:

EnsPortal.VisualTrace.zen?SESSIONID=12818

You'll need to run some queries (once in the router namespace and once in the edge namespace) to find the session ID that corresponds to your control ID.

You can find messages with that control id by querying the search table.

First you need to get the search table property ID for the MSHControlID. Change the value of ClassExtent to match whatever your local search table class is if you're not using the default:

SELECT PropId from Ens_Config.SearchTableProp WHERE ClassExtent='EnsLib.HL7.SearchTable' AND Name='MSHControlID'

Let's say that returns a PropId of 1

You can then query the search table for the control ID you're looking for where PropValue is the control id. If you have a custom search table you'll need to use your custom table name here instead of the default EnsLib_HL7.SearchTable:

SELECT DocId FROM EnsLib_HL7.SearchTable WHERE PropId=1 AND PropValue='123456789'

This gives you the ID for the message body. Let's say it returned a DocId of 98765. You can then query the message header table to get the session ID that that message body belongs to:

SELECT DISTINCT(SessionId)
FROM Ens.MessageHeader WHERE MessageBodyID = 98765

Keep in mind that the URL for the Visual Trace could change in future versions, so you're doing this at your own risk.

Currently the most common approach for creating a web application/page which sources data from IRIS is to use one of the popular client side web application frameworks such as Angular, React, or vue.js. In IRIS you would build a web service which your app would call to get data.

Creating REST Services
https://docs.intersystems.com/irislatest/csp/docbook/Doc.View.cls?KEY=GREST

The following sample works for me. HTML rendering capabilities are limited by what Apache FOP can handle.

Class test.ZenReportItemHtml Extends %ZEN.Report.reportPage
{

Parameter DEFAULTMODE = "pdf";

Parameter MYMARKUP = "<div style='font-weight:bold'>bold</div><br/><div>not-bold</div>";

XData ReportDefinition [ XMLNamespace = "http://www.intersystems.com/zen/report/definition" ]
{
<report xmlns="http://www.intersystems.com/zen/report/definition" name="Test" runonce="true">
     <element name="MyMarkup" escape="html" expression="..#MYMARKUP" />
</report>
}

XData ReportDisplay [ XMLNamespace = "http://www.intersystems.com/zen/report/display" ]
{
<report xmlns="http://www.intersystems.com/zen/report/display" name="Test">     
    <document width="8.5in" height="11in" marginLeft="1.25in"
      marginRight="1.25in" marginTop="1.0in" marginBottom="1.0in">
    </document>
    <body>
        <item field="MyMarkup" copyhtml="true" />
     </body>
 </report>
}

}

I suspect that some of the binary bytes are getting converted to UTF-8, and this is what the "u" option in the sixth argument of %WriteJSONStreamFromObject specifies.

You can try removing the "u" and see if that helps, but even if it does I believe you will find other problems because JSON isn't meant to carry raw binary data. Generally binary data is base 64 encoded when putting it in JSON.

One example of the problem with binary data is that the value of binario needs to be enclosed in quotes "". But the binary data could include a byte which is the same code as a quote, which would cause the JSON recipient to think that the value of binario has ended.

My suggestion is to base 64 encode the binary data.

You were on the right track with %WriteJSONFromObject(), but you'll want to use %WriteJSONStreamFromObject() instead. I don't see what purpose the Body property in your request class serves. You can just create a stream object variable instead.

set myTempStream=##class(%Stream.GlobalCharacter).%New()
set tSC=##class("%ZEN.Auxiliary.altJSONProvider").%WriteJSONStreamFromObject(.myTempStream, pRequest)
if $$$ISERR(tSC) {
    quit tSC
}

...then later:

Set tSC=..Adapter.PostURL(tURL,.tHttpResponse, , myTempStream)

A pool size of 1 is the recommendation when you need to maintain FIFO (process all messages strictly in the sequence that they arrived). Going above 1 is fine if FIFO isn't required.

Each additional pool job will result in an additional OS-level process, which adds a little bit of memory usage. How much CPU is used by each process depends on how much work the operation is doing. Essentially, changing pool size from 1 to 2 has the same resource impact as adding another identical business operation.

The max possible pool size depends on lots of factors. I would suggest starting small (2? 4?), see how that affects the queue, and increase accordingly. Having a pool size of 10, for instance, isn't likely to cause performance or resource problems unless your operation is doing something crazy. If you start getting into a pool size of dozens you might want to take a closer look with the WRC. One of your main limitations might be how many concurrent connections System A allows you to make.