add logging capability

README.md

@@ -49,6 +49,12 @@ CTRL-A is the escape character. CTRL-A + Q quits megacom. CTRL-A + CTRL-A sends
 
 there will be more keyboard shortcuts later, hopefully
 
+### non-tty mode
+
+megacom can be run even if stdin is not a tty. in this mode, keyboard shortcuts (CTRL-A) are
+disabled and input is passed through verbatim. this can be useful to pipe input and output out of a
+UART device with programs that are not tty-aware
+
 ### baud
 
 any standard baud rate (as an integer) which is supported by pyserial can be used. usually you want

megacom/__init__.py

@@ -2,6 +2,8 @@ import argparse
 import asyncio
 import contextlib
 import errno
+import fcntl
+import os
 import re
 import signal
 import sys
@@ -31,29 +33,39 @@ MODE_LOOKUP = {
 
 
 class TtyRaw:
-    __slots__ = ["isatty", "fd", "settings"]
+    __slots__ = ["isatty", "infd", "outfd", "settings"]
     isatty: bool
-    fd: int
+    infd: int
+    outfd: int
     settings: List[Any]
 
     def __init__(self) -> None:
         self.isatty = False
-        self.fd = 0
+        self.infd = 0
+        self.outfd = 0
         self.settings = []
 
-    def __enter__(self) -> None:
+    def __enter__(self) -> 'TtyRaw':
         if sys.stdin.isatty():
             self.isatty = True
-            self.fd = sys.stdin.fileno()
-            self.settings = termios.tcgetattr(self.fd)
-            tty.setraw(self.fd)
-        return None
+            self.infd = sys.stdin.fileno()
+            self.outfd = sys.stdout.fileno()
+            self.settings = termios.tcgetattr(self.infd)
+            tty.setraw(self.infd)
+        return self
 
     def __exit__(self, exc_type: Optional[Type[BaseException]],
                  exc_value: Optional[BaseException],
                  exc_traceback: Optional[TracebackType]) -> Literal[False]:
         if self.isatty:
-            termios.tcsetattr(self.fd, termios.TCSADRAIN, self.settings)
+            termios.tcsetattr(self.infd, termios.TCSADRAIN, self.settings)
+        # unset nonblocking modes
+        flags = fcntl.fcntl(self.infd, fcntl.F_GETFL)
+        flags = flags & (~os.O_NONBLOCK)
+        fcntl.fcntl(self.infd, fcntl.F_SETFL, flags)
+        flags = fcntl.fcntl(self.outfd, fcntl.F_GETFL)
+        flags = flags & (~os.O_NONBLOCK)
+        fcntl.fcntl(self.outfd, fcntl.F_SETFL, flags)
         return False
 
 
@@ -74,15 +86,21 @@ ESC_CHAR = b"\x01"
 
 
 class KeycodeHandler:
-    __slots__ = ["exit_flag", "esc"]
+    __slots__ = ["exit_flag", "esc", "isatty"]
     exit_flag: asyncio.Event
     esc: bool
+    isatty: bool
 
-    def __init__(self) -> None:
+    def __init__(self, isatty: bool) -> None:
         self.exit_flag = asyncio.Event()
         self.esc = False
+        self.isatty = isatty
 
     def process(self, byte: bytes) -> bytes:
+        # only translate or eat input if stdin is actually a tty
+        if not self.isatty:
+            return byte
+
         if self.esc:
             self.esc = False
             if byte == b"q":
@@ -104,7 +122,7 @@ class KeycodeHandler:
         return byte
 
 
-async def megacom(tty: str, baud: int, mode: str, logfile: Optional[str]) -> None:
+async def megacom(ttyraw: TtyRaw, tty: str, baud: int, mode: str, logfile: Optional[str]) -> None:
     (stdin, stdout) = await setup_async()
 
     m = MODE_RE.match(mode)
@@ -124,7 +142,7 @@ async def megacom(tty: str, baud: int, mode: str, logfile: Optional[str]) -> Non
             sys.exit(1)
 
     loop = asyncio.get_event_loop()
-    keycodes = KeycodeHandler()
+    keycodes = KeycodeHandler(ttyraw.isatty)
 
     loop.add_signal_handler(signal.SIGINT, lambda: keycodes.exit_flag.set())
 
@@ -268,6 +286,6 @@ def main() -> None:
     parser.add_argument("-l", "--logfile", type=str, default="", help="file to log to")
     args = parser.parse_args()
 
-    with TtyRaw():
-        asyncio.run(megacom(args.tty, args.baud, args.mode,
+    with TtyRaw() as ttyraw:
+        asyncio.run(megacom(ttyraw, args.tty, args.baud, args.mode,
                             args.logfile if args.logfile != "" else None))