I've been there before on IRIS zlib compression library....

The problem is explained in Compress(), from Class Reference %SYSTEM.Util, Compress() method (emphasis mine):

Returns the compressed form of a given string.
When Type is specified, it is the compress algorithm used to compress the data. Its value can be "zlib", "zstd" or "lz4". If Type is not specified then the "zlib" compression algorithm is used. A compressed string is a compressed data block with a customized wrapper. Use Decompress() to decompress it.

So, after Compress() you need to remove the "customized wrapper":

set compressed=$e(compressed,4,*-5)

Unfortunately Decompress() needs the custom wrapper, and I don't know how to make it up, however, as in your sample, I/O can be used, using file in your sample.

Regarding the file I/O, note that form Open command documentation:

"zlib" — Use the zlib compression library. /COMPRESS="zlib" is equivalent to /GZIP=1

So, if you change:

open tmpFile:("WNS":::/COMPRESS="zlib":/GZIP=0):0

With:

open tmpFile:("WNS":::/GZIP=0):0

It will then work just fine.

I fully agree that it's a pity to have zilib compress/uncompress utility "custimized" with proprietary wrapper that makes it unusable for any "standard use". However in that case you can use I/O, file or other devices. Personally I use XDEV for compress/decompress and leave the silly %SYSTEM.Util.Compress()/Decompress() alone.

First I'd suggest to test the DSN from linux, assumung you are using unixODBC ODBC driver manager:

isql -v HL7Interface2 myusername mypassword

What do you mean by "I concatenated them into one file, all.gz."?
How did you do that?

You may have already fond this in this community, maybe not: 

Caché ObjectScript Quick Reference  (aka "the Cheat Sheet")

You can use/reference %SYS.Journal.Record class and method from Python to work with journal files, what's your problem with that?

What do you need to achieve?

I don't think that implementing %SYS.Journal.Record functionality in Python from scratch would be easy and I miss a good reason why anyone would want to do that.

To work with journal files IRIS provide an API implemented in %SYS.Journal.Record class and that's what we are supposed to use.

If the target of your transformation is an HL7 message you should not unescape HL7 content, if you do it your HL7 message will be invalid.

In your example \T\ is the escape of the "&" character that is a field separator.

If the target of your transformation is not an HL7 message then you do need to unescape your fields.

Instead of using $translate or $replace I suggest using the Unescape() method in the EnsLib.HL7.Segment class, this assure you are unescaping all possible escaped character.
The Unescape() method is in the segment class, so first you need to reference a segment (any segment), then the Unescape() method. I'd use the MSH segment, so your method call will be:
source.GetSegmentAt("MSH").Unescape()

Then all you need is to pass the field reference, for exaple:

source.GetSegmentAt("MSH").Unescape(source.{AIS:UniversalServiceIdentifier.Identifier})
or/and:
source.GetSegmentAt("MSH").Unescape(source.{AIS:UniversalServiceIdentifier.Text})

Almost impossible to help without details on the .NET code you are using to connect and call Caché.

I think examples use very old version of Visual Studio

You are using an old version/product too, Caché 2018.1.

Congratulation Robert! 🏆🎖

Definitely deserved recognition.

The prerequisites for the InterSystems HL7 Interface Specialist certification include the training course and "At least 6 months - 1 year designing, building, and performing basic troubleshooting of HL7 interfaces with InterSystems products version 2019.1 or higher."

Actual/real experience will definitely help in passing the certification, theoretical study and some exercise may not be enough to gain the knowledge required.

In the exam description page you can find a list of "Exam Topics and Content". All questions in the exam belong to those topics.

Last but not least, everything is contained in the documentation.

Where/when do you want to know it?

Usually you get this information looking at the trace of the session/message.

Or you need to know the sender from within your BO code/method?

I don't think there is a callback method available.

One option could be to subclass %CSP.REST and use your subclass instead of %CSP.REST.

You subclass can be something like:

Class MyCustomCSP.REST Extends %CSP.REST
{

ClassMethod DispatchRequest(url As %String, method As %String, forwarded As %Boolean = 0, args...) As %Status
{
	Set sc=##super(url,method,forwarded,.args)
	
	; your "onPostDispatch" code here 
	Quit sc
}

}

Just in case, try adding a "code" action BEFORE your actions with:

  Do source.Stream.Rewind()
  Do target.Stream.Clear()

How big (Size) is the stream? If it's larger then the maximum string supported string length (~3.5MB), then you have a problem with your code.

When it does not work, do you get an error?

In the DTL, how do you set the "Create" option/parameter? (copy or new?)

Is there any other reference/set referencing the Stream in the DTL?

What product? If it's HealthShare then you should use the class HS.Local.ZAUTHENTICATE in HSCUSTOM namespace.

In fact, for simple XML export (no namespace and other amenities) you can just use XMLExport*() methods.

ClassMethod test()
{
	Set message=##class(Mensajes.Response.Radiologia.NumeroOrdenAcodigoSERAMResponse).%New()
	Set message.resultado.codigo="06050301"
	Set message.resultado.error=##class(EsquemasDatos.Seguridad.Error).%New()
	Set message.resultado.error.codigo=0
	Set message.resultado.error.descripcion="Proceso realizado correctamente"
	
	Set sc=message.resultado.XMLExportToString(.string)
    ; handle sc error here

	Write string,!!
	
	; convert XML string back to object
    Set reader = ##class(%XML.Reader).%New()
    Set sc=reader.OpenString(string)
    ; handle sc error here
    Do reader.Correlate("resultado","EsquemasDatos.Radiologia.Resultado")
    Do reader.Next(.ReturnObject,.sc)
    ; handle sc error here
    Write "ReturnObject is of type ",ReturnObject.%ClassName(1),!
    do ReturnObject.XMLExport(,",indent")
	
	Quit
}

Result:

Do ##class(Mensajes.Response.Radiologia.NumeroOrdenAcodigoSERAMResponse).test()
<resultado><error><codigo>0</codigo><descripcion>Proceso realizado correctamente</descripcion></error><codigo>06050301</codigo></resultado>
 
ReturnObject is of type EsquemasDatos.Radiologia.Resultado
<resultado>
  <error>
    <codigo>0</codigo>
    <descripcion>Proceso realizado correctamente</descripcion>
  </error>
  <codigo>06050301</codigo>
</resultado>

OK, you asked XML string to object 😊

ClassMethod test()
{
	Set message=##class(Mensajes.Response.Radiologia.NumeroOrdenAcodigoSERAMResponse).%New()
	Set message.resultado.codigo="06050301"
	Set message.resultado.error=##class(EsquemasDatos.Seguridad.Error).%New()
	Set message.resultado.error.codigo=0
	Set message.resultado.error.descripcion="Proceso realizado correctamente"
	
	Set writer=##class(%XML.Writer).%New()
	Set writer.Indent=1

	Set sc=writer.OutputToString()
	; handle sc error here
	Set sc=writer.RootObject(message.resultado)
	; handle sc error here
	Set string=writer.GetXMLString()
	Write string,!
	
	; convert XML string back to object
    Set reader = ##class(%XML.Reader).%New()
    Set sc=reader.OpenString(string)
    ; handle sc error here
    Do reader.Correlate("resultado","EsquemasDatos.Radiologia.Resultado")
    Do reader.Next(.ReturnObject,.sc)
    ; handle sc error here
    Write "ReturnObject is of type ",ReturnObject.%ClassName(1),!
    do ReturnObject.XMLExport(,",indent")
	
	Quit
}

Result:

Do ##class(Mensajes.Response.Radiologia.NumeroOrdenAcodigoSERAMResponse).test()
<resultado>
  <error>
    <codigo>0</codigo>
    <descripcion>Proceso realizado correctamente</descripcion>
  </error>
  <codigo>06050301</codigo>
</resultado>
 
ReturnObject is of type EsquemasDatos.Radiologia.Resultado
<resultado>
  <error>
    <codigo>0</codigo>
    <descripcion>Proceso realizado correctamente</descripcion>
  </error>
  <codigo>06050301</codigo>
</resultado>