Problem to read/write TAP driver in Windows 10

[Mariano Gentile]

Good Morning,

In the last days we were facing some errors in Windows 10,
connected with the TAP driver, taken from the OpenVPN web site
(we tested both versions, but normally we use the newest one
tap-windows-9.21.2.exe).

We faced three types of error.

The first one I suppose it is just a simple mistake, since we see the
error message:
"Failed to read the TAP device: The operation completed successfully."
Reading the code of "tun-win32.c" file, the "os_read_tun()" function
returns an error
if the "ReadFile()" function returns FALSE, but I suppose
in that case it is not really an error, since the reported error is
ERROR_SUCCESS.
Even if the Microsoft documentation says that "ReadFile()" should return
TRUE,
I think we could easily catch this special error and just go on, do you
agree?

The second and third errors that we are facing are a bit more difficult
to understand:
“Failed to read from TAP device: A device attached to the system is not
functioning.” -> ERROR_GEN_FAILURE
"Failed to write the TAP device. The data area passed to a system call
is too small" -> ERROR_INSUFFICIENT_BUFFER
respectively from the function "ReadFile()" and "WriteFile()", both in
the tun-win32.c file.
I saw the last commits of OpenConnect and that part of code did not
changed recently.
I was trying to understand what is going wrong, but reading the
Microsoft documentation,
it seems that the two functions are indeed called in a proper way, so I
have no clue at the moment.

I would be glad to find a solution and help fixing this problem, but I
am out of ideas.
Do you have some hint about what could be wrong?

Thanks
Best regards
Mariano Gentile

-- 
Mariano Gentile
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eMail: mag at schaeuffelhut-berger.de

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