Usually I do this:

set sc = ..method()
/// finalization
quit:$$$ISERR(sc) sc

I always use %Status and try to wrap calls in this macro:

#define qoe(%expr) $$$QuitOnError(%expr)

For example:

$$$qoe(..computeDigest(canonicalized))

$$$ERROR($$$SQLError, SQLCODE, %msg)

You can use PythonGateway to call Python code from InterSystems IRIS directly.

Example:

set sc = ##class(isc.py.Main).SimpleString("x='HELLO'", "x", , .x)
write x
>HELLO

You can start with

set %gw = createJavaGateway()

Where createJavaGateway is

ClassMethod createJavaGateway()
{
  quit:$d(%gw) %gw
  /// init connection
}

And remove disconnect part. This way %gw variable would stay alive betwee the calls.

Is the response actually compressed?

I thought automatic decompression is happening a few layers down on the stack.

Use session id to track data between calls.

In general I would suggest moving to REST stateless architecture.

I prefer

johndoe.test.lib.class

As long as storage aligns, you can use this approach.

Calling @Anton Umnikov 
 

How are you planning to determine to which service the message should go?

Probably 3,641,144.

Calling @Dan Pasco 
 

Here's how you can add your ObjectScript snippents to VSCode.

Which version are you on?

Update to 2016.1+.

Check dformat 18-21.

Pleas port relevant parts of ExecuteResult class.

If the user does not have W access on routines db he will not be able to edit it.

Also the  whole DB might be marked as RO.