Tests have proven that 20K is a very bad buffer size for uploads on
Windows, while 16K for some odd reason performed a lot better.
We do the ifndef check to allow this value to easier be changed at build
time for those who feel adventurous. The practical minimum is about
400 bytes since libcurl uses a buffer of this size as a scratch area
(unrelated to network send operations).
Tests have proven that 20K is a very bad buffer size for uploads on Windows, while 16K for some odd reason performed a lot better. We do the ifndef check to allow this value to easier be changed at build time for those who feel adventurous. The practical minimum is about 400 bytes since libcurl uses a buffer of this size as a scratch area (unrelated to network send operations).