====== Detecting MegaZeux files ======

===== Detecting MegaZeux worlds with magic bytes =====

The MegaZeux world file header (for all versions) is documented [[https://www.digitalmzx.com/fileform.html#world|here]]. From there, we can see that the following logic is sufficient:

  * The file extension is always `MZX` (world file),
  * If byte 25 is zero, the bytes 26-28 (magic) are either `MZX`, `MZ2`, `MZA`, or `M\x02?`, where ? is any byte;
  * If byte 25 is non-zero, the bytes 41-43 (magic) are either `MZX`, `MZ2`, `MZA`, or `M\x02?`, where ? is any byte;

Bytes 0-24 can then be used to parse the world title (codepage 437, null-terminated).

===== Detecting MegaZeux boards with magic bytes =====

Like the instructions above:

  * The file extension is always `MZB` (board file),
  * Byte 0 is always 0xFF,
  * Bytes 1-3 (magic) are either `MB2` or `M\x02?`, where ? is any byte;

Bytes 0-24 can then be used to parse the world title.

===== Detecting MegaZeux save files with magic bytes =====

Like the instructions above:

  * The file extension is always `SAV`,
  * The bytes 0-4 (magic) are either `MZSV2`, `MZXSA`, or `MZS\x02?`, where ? is any byte.

===== Detecting MegaZeux 2.00+ worlds with checkres =====

The most comprehensive to detect a MegaZeux 2.00+ file is to use `checkres`, a tool built as part of the MegaZeux distribution ([[https://github.com/AliceLR/megazeux|source code]], directory src/utils):

  ./checkres -AV [file]

If the error code is 1, the file is not a valid MegaZeux 2.00+ file. If the error code is 0, the file is a valid MegaZeux 2.00+ file - additionally, a CSV will be output containing the file's dependencies and whether or not they have been located, for example:

  Required by,Expected file,Status,Found in
  CAVERNS.MZX,CV_BALON.MOD,FOUND,.
  CAVERNS.MZX,CV_BOSS.MOD,FOUND,.
  CAVERNS.MZX,CV_HEVEN.MOD,FOUND,.
  CAVERNS.MZX,CV_MAGIC.MOD,FOUND,.
  CAVERNS.MZX,CV_STORY.MOD,FOUND,.
  CAVERNS.MZX,CV_TECH.MOD,FOUND,.
  CAVERNS.MZX,CV_TITLE.MOD,FOUND,.

Notice that I mentioned "2.00+" (this is also important, as for very modern files - we're talking the last few years - the format changed significantly, being effectively a ZIP file with a special file layout). For MegaZeux 1.xx worlds (the only MegaZeux worlds currently on DiscMaster), the output will be as follows:

  ERROR: Worlds from MegaZeux 1.xx are not supported by this utility.

As with ZZT/Super ZZT, I am open to working on a dedicated tool to handle these (though PNG screenshot exports would be a little trickier).