os.Connection.read(): Support ReadOnlyPrintable

Add flag ReadOnlyPrintable and support it in read(). This omits all
characters not in string.printable from read()'s result.

This comes in handy if systemd spits out bouncing start-job-running
asterisks which find their way back to the reader but close the shell
on him.

Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/devtest/os/Connection.py

@@ -4,6 +4,7 @@ from abc import ABC, abstractmethod
 from enum import Enum, IntFlag
 import asyncio
 import types
+import string
 from jwutils.log import *
 from .TestPhases import TestPhases
 
@@ -21,6 +22,7 @@ class Connection(ABC): # export
         FailOnTimeout      = 0x01
         ReadStripNewline   = 0x02
         ReadDecodeToString = 0x04
+        ReadOnlyPrintable  = 0x08
 
     class Info:
 
@@ -124,10 +126,12 @@ class Connection(ABC): # export
                     r = r.decode('utf-8', errors='replace')
                 except Exception as e:
                     slog(WARNING, 'Failed to decode string, returning undecoded ({}): "{}"'.format(e, r))
-                    return str(r)
+                    r = str(r)
             if flags & self.Flags.ReadStripNewline:
                 if len(r) and r[-1] == '\n':
                     r = r[0:-1]
+            if flags & self.Flags.ReadOnlyPrintable:
+                r = ''.join(filter(lambda x: x in string.printable, r))
         return r
 
     async def readline(self, timeout=None):