probe_mtu doesn't work on Alpine Linux

[zonescape]

I think this is because of ping command on Alpine Linux has different options than e.g. on Debian.

# docker container run -it --rm python:3.13.1-alpine3.21 sh

/ # ping -c 1 -s 1072 -W 4 -i 1 -M do -4 192.168.1.1
ping: unrecognized option: M
BusyBox v1.37.0 (2024-12-13 21:18:49 UTC) multi-call binary.

Usage: ping [OPTIONS] HOST

Send ICMP ECHO_REQUESTs to HOST

	-4,-6		Force IP or IPv6 name resolution
	-c CNT		Send only CNT pings
	-s SIZE		Send SIZE data bytes in packets (default 56)
	-i SECS		Interval
	-A		Ping as soon as reply is received
	-t TTL		Set TTL
	-I IFACE/IP	Source interface or IP address
	-W SEC		Seconds to wait for the first response (default 10)
			(after all -c CNT packets are sent)
	-w SEC		Seconds until ping exits (default:infinite)
			(can exit earlier with -c CNT)
	-q		Quiet, only display output at start/finish
	-p HEXBYTE	Payload pattern

Here is the steps to reproduce the bug:

# docker container run -it --rm python:3.13.1-alpine3.21 sh

/ # python --version
Python 3.13.1

/ # pip --version
pip 24.3.1 from /usr/local/lib/python3.13/site-packages/pip (python 3.13)

/ # apk add gcc python3-dev musl-dev linux-headers
fetch https://dl-cdn.alpinelinux.org/alpine/v3.21/main/x86_64/APKINDEX.tar.gz
fetch https://dl-cdn.alpinelinux.org/alpine/v3.21/community/x86_64/APKINDEX.tar.gz
(1/22) Installing libgcc (14.2.0-r4)
(2/22) Installing jansson (2.14-r4)
(3/22) Installing libstdc++ (14.2.0-r4)
(4/22) Installing zstd-libs (1.5.6-r2)
(5/22) Installing binutils (2.43.1-r1)
(6/22) Installing libgomp (14.2.0-r4)
(7/22) Installing libatomic (14.2.0-r4)
(8/22) Installing gmp (6.3.0-r2)
(9/22) Installing isl26 (0.26-r1)
(10/22) Installing mpfr4 (4.2.1-r0)
(11/22) Installing mpc1 (1.3.1-r1)
(12/22) Installing gcc (14.2.0-r4)
(13/22) Installing linux-headers (6.6-r1)
(14/22) Installing musl-dev (1.2.5-r8)
(15/22) Installing pkgconf (2.3.0-r0)
(16/22) Installing libexpat (2.6.4-r0)
(17/22) Installing mpdecimal (4.0.0-r0)
(18/22) Installing python3 (3.12.8-r1)
(19/22) Installing python3-pycache-pyc0 (3.12.8-r1)
(20/22) Installing pyc (3.12.8-r1)
(21/22) Installing python3-pyc (3.12.8-r1)
(22/22) Installing python3-dev (3.12.8-r1)
Executing busybox-1.37.0-r9.trigger
OK: 305 MiB in 50 packages

/ # pip install ofunctions.network
Collecting ofunctions.network
  Downloading ofunctions.network-1.6.0-py3-none-any.whl.metadata (18 kB)
Collecting requests>=2.22.0 (from ofunctions.network)
  Downloading requests-2.32.3-py3-none-any.whl.metadata (4.6 kB)
Collecting command-runner>=1.3.1 (from ofunctions.network)
  Downloading command_runner-1.7.0-py3-none-any.whl.metadata (26 kB)
Collecting ofunctions.bisection>=0.2.1 (from ofunctions.network)
  Downloading ofunctions.bisection-1.0.0-py3-none-any.whl.metadata (9.0 kB)
Collecting ofunctions.threading>=2.3.0 (from ofunctions.network)
  Downloading ofunctions.threading-2.3.0-py3-none-any.whl.metadata (17 kB)
Collecting ofunctions.misc>=1.5.2 (from ofunctions.network)
  Downloading ofunctions.misc-1.8.0-py3-none-any.whl.metadata (18 kB)
Collecting psutil>=5.3.0 (from ofunctions.network)
  Downloading psutil-6.1.1.tar.gz (508 kB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Preparing metadata (pyproject.toml) ... done
Collecting typing>=3.5.0 (from ofunctions.network)
  Downloading typing-3.7.4.3.tar.gz (78 kB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Preparing metadata (pyproject.toml) ... done
Collecting ipaddress (from ofunctions.network)
  Downloading ipaddress-1.0.23-py2.py3-none-any.whl.metadata (923 bytes)
Collecting charset-normalizer<4,>=2 (from requests>=2.22.0->ofunctions.network)
  Downloading charset_normalizer-3.4.1-cp313-cp313-musllinux_1_2_x86_64.whl.metadata (35 kB)
Collecting idna<4,>=2.5 (from requests>=2.22.0->ofunctions.network)
  Downloading idna-3.10-py3-none-any.whl.metadata (10 kB)
Collecting urllib3<3,>=1.21.1 (from requests>=2.22.0->ofunctions.network)
  Downloading urllib3-2.3.0-py3-none-any.whl.metadata (6.5 kB)
Collecting certifi>=2017.4.17 (from requests>=2.22.0->ofunctions.network)
  Downloading certifi-2024.12.14-py3-none-any.whl.metadata (2.3 kB)
Downloading ofunctions.network-1.6.0-py3-none-any.whl (15 kB)
Downloading command_runner-1.7.0-py3-none-any.whl (25 kB)
Downloading ofunctions.bisection-1.0.0-py3-none-any.whl (8.0 kB)
Downloading ofunctions.misc-1.8.0-py3-none-any.whl (13 kB)
Downloading ofunctions.threading-2.3.0-py3-none-any.whl (11 kB)
Downloading requests-2.32.3-py3-none-any.whl (64 kB)
Downloading ipaddress-1.0.23-py2.py3-none-any.whl (18 kB)
Downloading certifi-2024.12.14-py3-none-any.whl (164 kB)
Downloading charset_normalizer-3.4.1-cp313-cp313-musllinux_1_2_x86_64.whl (145 kB)
Downloading idna-3.10-py3-none-any.whl (70 kB)
Downloading urllib3-2.3.0-py3-none-any.whl (128 kB)
Building wheels for collected packages: psutil, typing
  Building wheel for psutil (pyproject.toml) ... done
  Created wheel for psutil: filename=psutil-6.1.1-cp36-abi3-linux_x86_64.whl size=283373 sha256=d61e3ac7210bd39db4ae1a86bf5ad080b773196ed92a5d8ef003bbcbcaec391d
  Stored in directory: /root/.cache/pip/wheels/ff/fe/eb/59cac25690b1a9600e50b007a414ddabb88c04e3ca5df008d9
  Building wheel for typing (pyproject.toml) ... done
  Created wheel for typing: filename=typing-3.7.4.3-py3-none-any.whl size=26365 sha256=16cbc3570112ac826109cd4b73dbef1eca6ddde996f868f080f433bf544bbb09
  Stored in directory: /root/.cache/pip/wheels/5d/1b/f4/fbdc2bc618f0ba7aec7295d67f62d40e6027a6ce14df9ec3c8
Successfully built psutil typing
Installing collected packages: ipaddress, urllib3, typing, psutil, ofunctions.threading, idna, charset-normalizer, certifi, requests, ofunctions.misc, ofunctions.bisection, command-runner, ofunctions.network
Successfully installed certifi-2024.12.14 charset-normalizer-3.4.1 command-runner-1.7.0 idna-3.10 ipaddress-1.0.23 ofunctions.bisection-1.0.0 ofunctions.misc-1.8.0 ofunctions.network-1.6.0 ofunctions.threading-2.3.0 psutil-6.1.1 requests-2.32.3 typing-3.7.4.3 urllib3-2.3.0
WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager, possibly rendering your system unusable.It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv. Use the --root-user-action option if you know what you are doing and want to suppress this warning.

/ # python
Python 3.13.1 (main, Jan  8 2025, 18:18:10) [GCC 14.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

>>> from ofunctions.network import probe_mtu

>>> print(probe_mtu("192.168.1.1"))
Traceback (most recent call last):
  File "/usr/local/lib/python3.13/site-packages/ofunctions/network/__init__.py", line 451, in probe_mtu
    return bisection.bisect(ping, ping_args, allow_all_expected=True)[1]
           ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/ofunctions/bisection/__init__.py", line 79, in bisect
    raise ValueError("Both sides of the argument list are unexpected results")
ValueError: Both sides of the argument list are unexpected results

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    print(probe_mtu("192.168.1.1"))
          ~~~~~~~~~^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/ofunctions/network/__init__.py", line 462, in probe_mtu
    raise ValueError(
        "Unable to determine MTU via defined method: {}".format(exc)
    )
ValueError: Unable to determine MTU via defined method: Both sides of the argument list are unexpected results

It should be noted that the same error ("ValueError: Both sides of the argument list are unexpected results") happens if ping command is not installed. This is confusing.

[deajan]

Thank you for your report.
Unfortunately, the ping command you're showing doesn't seem to have any fragmentation commands, since it's a minimal implementation on busybox, so there's nothing I can do.

[zonescape]

If this can't be fixed, then probably the best thing to do is to provide a clear error message. Not just "ValueError".

[deajan]

Not as simple as you might think.

Determining MTU via ping requires bisection of multiple ping commands with various MTU values.
As ping exit code is handled as an error if not 0, having all ping commands fail will tell bisection that "Both sides of the argument list are unexpected results", in this case that translates to "whatever MTU we tried, we always got a bad result".

Now checking for ping availability is not hard, but getting various error messages depending on exit codes that might change between ping implementations / shell implementations is a programming nightmare.

Example: running ping -c bad <dest> and ping <dest> where dest is unreachable produce the same exit code.

For instance, what are alpine Linux exit codes when running ping in following scenarios:

• Executed okay
• Failed to reach destination
• Reached the destination only 50% of time
• Executed with a non existing argument
• Executed with an existing but bad argument
• Binary missing

So yes, it's more trivial than just having a clear error message.

[zonescape]

I don't think it's as difficult as you describe:

• command existence can be checked by shutil.which("ping")
• GNU & BSD ping variants can be separated using special call of the command (see below)

I found this question about date command. It can be adapted to ping command by using -V (show version) flag.

#!/bin/sh

if ping -V >/dev/null 2>&1 ; then
    echo GNU ping
else
    echo BSD ping
fi

I did a little research regarding ping command:

OS	-M option present	option to detect MTU for IPv4	-V option present
Linux	✓	✓(-M)	✓
Alpine	✗	✗	✗
macOS	✓ (has different meaning)	✗	✗
FreeBSD	✓ (has different meaning)	✗	✗
OpenBSD	✗	✗	✓(has different meaning & must have value)
NetBSD	✗	✓(has different name: -D)	✗

Conclusions:

• probe_mtu must not work by default on Alpine, macOS and xBSD
• ping -V call can be used to detect GNU ping variant

[deajan]

I don't think it's as difficult as you describe

Happy for you that you find the task easy.
I have developped software than ran on Linux/*BSD/MacOS and MSYS Windows in the past. Getting the right command syntax is okayish, but getting the right exit codes is a raw nightmare.

I'm actually much more in favor for a full python implementation of the ping command, which would render the whole code highly portable and less error prone.

I've eyed this one which still lacks DF implementation (but has PMTUD capabilities), and this one that needs some love to add DF implementation too.