On windows, the flp_errno routine does not print the error codes of the errors that actually happen.

For example: in dlb_io.c:255, net_io_write_async can return, because FLB_WOULDBLOCK detected the socket would block by looking at WSAGetLastError. The caller (flb_http_client.c:1161) notices the error and tries to do error reporting with flb_errno. However, flb_errno only checks errno, not WSAGetLastError, which contains the appropriate error code windows. Consequently, the error messages look like this:

[2021/03/02 12:29:00] [error] [O:\fluent-bit\src\flb_http_client.c:1161 errno=0] No error

Not very helpful. I expect the error routine to output the actual error from WSAGetLastError.

To reproduce, tail a file to an elasticsearch output where the host is unreachable on windows.