Use Control Char / Tag as Watermarking Start

[mhellmeier]

🚀 Feature Request

Current Problem

The watermarker library is able to add a watermark with or without compression. When analyzing a watermarked text or file, the library needs to know which type of watermark is used (compressed, uncompressed, specific format, etc.). This is currently not possible. There might be specific use cases that have specific requirements towards the style, compression, linting or format of the watermark.

Proposed Solution

Every watermark should start with a 2-digit control character (like a number) that identifies the type of watermark. Using a 2-digit control char instead of a 1-digit allows to have a bigger namespace for future formats.

Example: Instead of adding Test as a watermark, 00Test will be watermarked if the watermark is uncompressed, 01Test will be added as a watermark if the watermark is compressed. The first control char must be inserted without compression to get it working.

Additional Context

The other components, like the CLI tool and the webinterface, need to be updated after the issue is implemented since it is a breaking change.

Further, a table in the documentation is needed to document the control char and its meaning, for example:	Control Char	Meaning
00	Uncompressed Watermark
01	Compressed Watermark using X compression technique
02	Specialized compression for use case Y
03	...
...	...

[mhellmeier]

After discussion, the following decision could be good for a first implementation:

• Usage of one Byte as a control char (--> called "tag") to have 255 possible specific implementations
• If checksums are needed, they could be integrated into the tags, like 00 for uncompressed watermark without checksum and 10 for uncompressed watermark with checksum
• If the length of the watermark should be included inside the watermark, another tag could be created for it, like 11 for uncompressed watermark with checksum and with length-indicator