@chris-derrell yvervoort gave me the final hint/tip how to solve it. It was all about the right upload-format, which i was asking right from the beginning of my post. The BEST-ANSWER was very close to be the endsolution. Only problem was? → Exactly → the right upload-format.
To solve this i took a HTML-Component which includes an FILE-SELECTOR. The FILE-SELECTOR generates the base64-code which has a prefix. And this is the important point. The question was —> what to put into the BUFFER (which format).
For those, who want to solve this mystery → inspect the base-64 code and think about my tip—> prefix!
And with some testings (different formats), at the end i could generate the right binary-code and bring it to work.
But one question is still open.
Would this be possible without using a HTML-Component including a FILE-SELECTOR?
…to be continued, when my M-Uploader is completely ready 