I have a strange problem with perl clients to web service at work.

The service serves large files to windows clients running on many windows versions. The perl client under windows downloads the files using LWP. For historical reasons there are lots of different Perl versions. The server is either Perl + Mason + Apache2 or Python Tornado without a web server, in both cases inside a Docker container.

I have discovered that on recent windows versions, if the client is running Perl 5.24.0 or older, then on some occasions data sent from the Python server is lost, while apparently identical data from the Perl + Mason server arrives correctly. It looks like the http request is sent correctly, the server sends the reply, but the client does not receive it. I suspect that there is some sort of buggy interaction between Perl and the windows TCP/IP stack, but I don’t really know.

If I upgrade Perl to 5.24.1, then the bug disappears. I have observed this with both the Strawberry and Active State distributions of Perl.

So I am trying to work out what changed in the windows networking between the 5.24.0 and 5.24.1 versions of Perl. Naturally I have read the relevant perldelta, but I can’t see any changes that look likely, I have also looked at the source code diff in git, but there are too many changes to read easily, and as far as I can tell, no windows specific changes. I can’t find a list of bugs closed in 5.24.1.

Any ideas what the significant change is? If you could point me to a bug that was closed in 5.24.1 then that would be great.