log.(add|rm)_capture_stream(): Add functions

Add functions log.(add|rm)_capture_stream(). The functions are meant
to capture everything passed to syslog into the stream objects
installed by it. Not sure about future semantics changes:
add_capture_stream() takes a currently unused flags argument, and it
suppresses everything else logged until the stream is removed again.

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

tools/python/jwutils/log.py

@@ -1,11 +1,11 @@
 from __future__ import print_function
-import syslog
-import sys
-import inspect
-import re
+
+from typing import List, Tuple, Optional, Any
+
+import sys, re, io, syslog, inspect
+
 from os.path import basename
 from datetime import datetime
-from typing import List, Tuple, Optional, Any
 from . import misc
 
 # --- python 2 / 3 compatibility stuff
@@ -90,6 +90,23 @@ _prio_colors         = {
     EMERG            : [ CONSOLE_FONT_BOLD + CONSOLE_FONT_MAGENTA, CONSOLE_FONT_OFF ],
 }
 
+class Stream:
+    def __init__(self, stream, flags):
+        self.stream = stream
+        self.flags = flags
+
+_streams: dict[int, io.IOBase] = dict()
+_stream_descriptors = [reversed(range(1, 16))]
+
+def add_capture_stream(stream, flags=0x0):
+    ret = _stream_descriptors.pop()
+    _streams[ret] = Stream(stream=stream, flags=flags)
+    return ret
+
+def rm_capture_stream(sd):
+    del _streams[sd]
+    _stream_descriptors.append(sd)
+
 def prio_gets_logged(prio: int) -> bool: # export
     if prio > _level:
         return False
@@ -172,6 +189,11 @@ def slog(prio: int, *args, only_printable: bool=False, **kwargs) -> None: # expo
         return
 
     files = []
+    if 'capture' in kwargs:
+        files.append(kwargs['capture'])
+    elif _streams:
+        files = [s.stream for s in _streams.values()]
+    else:
         if f_stdout in _flags:
             files.append(sys.stdout)