I wrote the windows code "blind" based on this documentation.

So 4 Windows builds fail, the others work!? The test 1560 error output is awesomely weird and hard to detect. in Circle CI it looks like this:

 URL: -
 in: https://xn--rksmrgs-5wao1o.se
 wanted: https | [11] | [12] | [13] | räksmörgås.se | [15] | / | [16] | [17]
 got:    https | [11] | [12] | [13] | räksmörgås.se | [15] | / | [16] | [17]

But when I copy and pasted it here, it shows:

 URL: -
 in: https://xn--rksmrgs-5wao1o.se
 wanted: https | [11] | [12] | [13] | räksmörgås.se | [15] | / | [16] | [17]
 got:    https | [11] | [12] | [13] | räksmörgås.se� | [15] | / | [16] | [17]

Assuming I get the correct trailing byte, it is 0x16.

got: https | [11] | [12] | [13] | räksmörgås.se� | [15] | / | [16] | [17]

I think you should have passed the length of in_w + 1. it says pass the count of characters of param lpASCIICharStr (which is in wide characters) and +1 is needed because of this: "The retrieved string is null-terminated only if the input string is null-terminated."

i don't know where -1 comes from maybe that was in earlier versions of the doc i will check

I just guessed on the -1 since it seems to work for the conversion in the other direction...

I just guessed on the -1 since it seems to work for the conversion in the other direction...

I just checked an old Windows SDK offline documentation from Windows 7 2009 and I do not see it documented there either so I don't know why we did it that way. I will change it.

awesome @jay, that seems to have done it!