This project shows a bug in the java.net.HttpURLConnection class.
The HttpURLConnection class caps and mess up the body of a big HTTP POST.
If you send a HTTP POST with a small body, it works, but if you send a HTTP POST with, for instance, 10k bytes on its body, it does not work.
Just do the command ./gradlew test and wait for the test results.
If you run it today (19/July/2021) in macOS, it will not work. The server will not receive correctly the bytes sent. If you do the same tests in Linux, it works.
Apparently, the problem happens exactly when BODY content has more than 65839 characters.
It happens in all the java versions I tested (8, 9, 10, 14, 16) under macOS, although, the same code works in Linux. I think it's a bug on it's core libs, written in C for macOS.
Dear Java Developer, We have finished evaluating your report and have assigned it a Bug ID: JDK-8271187. The issue is visible on bugs.java.com at the following url JDK-8271187. To provide more information about this issue, click here.