File Transfers Broken with newer versions of Visual C++

[davidrg]

This is known to affect Visual C++ 14.x (2015, 2017, 2019, 2022) but likely affects all versions going back to 9.0 (2008) - see #1.

This needs fixing This needs fixing before switching over to a newer version of Visual C++ is possible.

[davidrg]

This was caused by calling _setmode to set a file caching hint (_O_SEQUENTIAL). As far as I can tell this has never been valid - in Visual C++ 4.2-6 the docs only mention _O_BINARY and _O_TEXT as valid options (the older docs don't seem to mention _O_SEQUENTIAL at all though its present in the headers). In Visual C++ 2022 (and probably all versions going back to 2008) this results in a failed assertion.

Instead the correct method seems to be to supply the 'S' file mode to fopen.