remote/client: fallback to telnet when microcom is not available

microcom is generally not available on rpm based distributions[1],
making it hard to setup labgrid client on them.

[1] https://repology.org/project/microcom/versions

Signed-off-by: Nick Cao <nickcao@nichi.co>
[r.czerwinski@pengutronix.de: rebased, added CHANGES.rst entry]
Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>

Author: NickCao

CHANGES.rst

@@ -47,6 +47,7 @@ New Features in 24.0
   switches running OpenWrt using the ubus interface.
 - The pyproject.toml gained a config for `ruff <https://github.com/astral-sh/ruff>`_.
 - ``setuptools_scm`` is now used to generate a version file.
+- labgrid-client console will fallback to telnet if microcom is not available.
 
 
 Bug fixes in 24.0

doc/getting_started.rst

@@ -349,8 +349,8 @@ Now we can connect to the serial console:
 
     labgrid-venv $ labgrid-client -p example-place console
 
-.. note:: Using remote connection requires ``microcom`` installed on the host
-   where the labgrid-client is called.
+.. note:: Using remote connection requires ``microcom`` or ``telnet`` installed
+   on the host where the labgrid-client is called.
 
 See :ref:`remote-usage` for some more advanced features.
 For a complete reference have a look at the :doc:`labgrid-client(1) <man/client>`

labgrid/remote/client.py

@@ -13,6 +13,7 @@
 import signal
 import sys
 import shlex
+import shutil
 import json
 from textwrap import indent
 from socket import gethostname
@@ -826,18 +827,32 @@ async def _console(self, place, target, timeout, *, logfile=None, loop=False, li
         # check for valid resources
         assert port is not None, "Port is not set"
 
-        call = ["microcom", "-s", str(resource.speed), "-t", f"{host}:{port}"]
+        microcom_bin = shutil.which("microcom")
 
-        if listen_only:
-            call.append("--listenonly")
+        if microcom_bin is not None:
+            call = [microcom_bin, "-s", str(resource.speed), "-t", f"{host}:{port}"]
+
+            if listen_only:
+                call.append("--listenonly")
+
+            if logfile:
+                call.append(f"--logfile={logfile}")
+        else:
+            call = ["telnet", host, str(port)]
+
+            logging.info("microcom not available, using telnet instead")
+
+            if listen_only:
+                logging.warning("--listenonly option not supported by telnet, ignoring")
+
+            if logfile:
+                logging.warning("--logfile option not supported by telnet, ignoring")
 
-        if logfile:
-            call.append(f"--logfile={logfile}")
         print(f"connecting to {resource} calling {' '.join(call)}")
         try:
             p = await asyncio.create_subprocess_exec(*call)
         except FileNotFoundError as e:
-            raise ServerError(f"failed to execute microcom: {e}")
+            raise ServerError(f"failed to execute remote console command: {e}")
         while p.returncode is None:
             try:
                 await asyncio.wait_for(p.wait(), 1.0)