Added support for using a fifo on windows with a Named Pipe.

[bobjoe400]

I attempted to write this patch with as little change to your written code as possible.

Implemented a simple wrapper for the pipe and serial objects as well as implementing a windows-based, non-file, select.select() method.

Usage on windows will look like:

python serial-pcap --fifo mypipename COM#

This differs from the linux fifio because you are not declaring a "file" in a directory. You're just declaring a name. This is due to how Named Pipes work and how they have to be in the Named Pipe directory.

This will produce a pipe in the named pipe directory, \\.\pipe\ that can be used in the Windows version of pipe just like the Linux fifo. So, you would put into the "pipe" section \\.\pipe\mypipename.

The ability to use select() with a fifo on windows comes from the fact that the I have switched to a selectors-based I/O Multiplexor instead of the previously used select-based.

I've done some quick tests to make sure that this works on both linux and windows, and it seems too still function as it did previously.

[matthijskooijman]

Thanks for your contribution. I haven't touched this code in a long time, but I'm happy to merge support for Windows :-)

I've left some inline comments, but overall I wonder about the selectors approach you've used. Am I understanding correctly that you've used the selectors package to get a consistent API between Windows and Linux, but on Windows you are essentially just busy-waiting by polling the pipe and serial port for their output? That seems inefficient (and without some sleep/delay to throttle, would also max out CPU usage?). Does that mean that Windows does not have a way to actually use select or something similar to wait for input and a closed output pipe in a blocking way?

[bobjoe400]

So actually, in your original code, the script doesn't even work at all on Windows.

Windows doesn't have a way to really do select with non-sockets.

From the select documentation, select.poll() is only supported on Unix systems. Windows doesn't have a built-in or even abstracted version of polling files. selectors.PollSelector() isn't even exposed to a Windows machine as seen in their source code for selectors.py.

I've looked into the WSAPoll() call as part of the Winsock api, but that only supports sockets.

I've looked at this version of a simple poll abstraction for Windows, but it really just appears to do what selectors.SelectSelector().select() does, and doesn't do any actual "polling".

It seems like the only way to get the "poll" functionality that you're looking for on Windows would be to rewrite this with threads and some kind of asyncio implementation.

What do you think is the best way forward on this? It's clear that's there may be another way to do what I've done. My goal was to do this with as little of change to the original code as possible.