DASP trace: sent lines yellow, received green on a console

Plain text when stdout is a pipe or file. Also remembers localhost as the last device.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dasp.py

@@ -98,7 +98,43 @@ def _trace(direction, msg, datagram=None):
     hexdump = ""
     if datagram:
         hexdump = " [" + datagram.hex(" ") + "]"
-    _trace_out(f"[DASP] {ts} {direction} {name}{seq}{ack} payload={plen}{hexdump}")
+    line = f"[DASP] {ts} {direction} {name}{seq}{ack} payload={plen}{hexdump}"
+    color = _TRACE_COLORS.get(direction)
+    if color and _console_colors():
+        line = f"{color}{line}\033[0m"
+    _trace_out(line)
+
+
+# Sent lines yellow, received lines green, so the two directions read apart at a glance.
+_TRACE_COLORS = {"S": "\033[93m", "R": "\033[92m"}
+_colors_ok = None
+
+
+def _console_colors():
+    """True when stdout is a console that understands ANSI colour codes.
+
+    Windows consoles need virtual-terminal processing switched on first; a pipe or
+    file gets plain text so captured logs stay free of escape codes.
+    """
+    global _colors_ok
+    if _colors_ok is None:
+        import sys
+        stream = sys.__stdout__
+        try:
+            _colors_ok = stream is not None and stream.isatty()
+        except (OSError, ValueError):
+            _colors_ok = False
+        if _colors_ok and os.name == "nt":
+            try:
+                import ctypes
+                kernel32 = ctypes.windll.kernel32
+                handle = kernel32.GetStdHandle(-11)          # STD_OUTPUT_HANDLE
+                mode = ctypes.c_uint32()
+                _colors_ok = bool(kernel32.GetConsoleMode(handle, ctypes.byref(mode))
+                                  and kernel32.SetConsoleMode(handle, mode.value | 0x0004))
+            except (OSError, AttributeError):
+                _colors_ok = False
+    return _colors_ok
 
 
 # Trace lines are printed by a thread of their own. The send and receive threads must