Apache HttpClient 4.x behaving strange when uploading larger files?

Most likely it is a combination of several factors that leads to this situation

(1) Most likely your client does not use the 'expect-continue' handshake when sending large request entity with a request that does not include an authentication header.

(2) The server detects early that the request fails its expectations and instead of reading and discarding full request body it responds early with 401 status and closes connection on its end. In my opinion, this is an HTTP protocol violation on the part of the server.

(3) While some HTTP agents can deal with early responses, Apache HttpClient cannot due to the limitation of the Java blocking I/O (a thread of execution can either read or write from a blocking socket, but not both).

There are multiple ways of addressing the issue, the 'expect-continue' handshake being the easiest and most natural one. Alternatively one can execute a simple HEAD or a GET request to force HTTP authentication prior to executing a large POST or PUT request. HttpClient is capable of re-using authentication data for subsequent requests in the same logical HTTP session.