Multi part reverse lookup

[NebularNerd]

Closes #57

While digging through files for PR #58 I discovered that we could do with a footer style reverse lookup on the multi part match to help boost confidence scores (especially if the footer is small as well). This modifies the multiple match to allow reverse looksup.

To behave like the normal forward match, we aggregate the matched.byte_match and magic_row.byte_match to provide a longer match to the _confidence function. One downside of the is that in the match data it will report the two matches smooshed together, e.g.:

• .mlt is 0x3c6d6c74 / <mlt (0.4) and 3c2f6d6c743e0a / </mlt>\n (0,7), combined confidence of 0.8 but you'll see <mlt</mlt>\n in the data which looks untidy (could there be a better way to address this)

Also, some unexpected results:

• .pt2 cannot score above 0.8 when combined, I imagine it's because both are long matches which score 0.8 individually
• .ct gets 0.4 for CREM and 0.8 for DONE but the combined will not go above 0.8

Sample files.zip

Any improvements/comments are welcome, it works but there might be a better, nicer looking way to handle this.

New entries for magic_data.json:

• Shotcut .mlt opensource video editor
• Creamtracker .ct: Tracker format from the creator of BeRo Tracker BeRo's Blog, under Audio software
• Picatune 2 .pt2: Another music format from the creator of BeRo Tracker Picatune 2

[NebularNerd]

Not sure why checks are failing, still a bit of a GitHub noob when it comes to certain aspects.

EDIT:
Fixed it, ran the code block I modified through Black Playground and all is well. Will have to look more into that later for debugging/prettifying my own code.

[cdgriffith]

Suggested change

	if "-" in str(magic_row.offset):
	start = magic_row.offset
	end = magic_row.offset + len(magic_row.byte_match)
	match_area = footer[start:end] if end != 0 else footer[start:]
	if match_area == magic_row.byte_match:
	new_matches.add(
	PureMagic(
	byte_match=matched.byte_match + magic_row.byte_match,
	offset=magic_row.offset,
	extension=magic_row.extension,
	mime_type=magic_row.mime_type,
	name=magic_row.name,
	)
	)
	else:
	start = magic_row.offset
	end = magic_row.offset + len(magic_row.byte_match)
	if end > len(header):
	start = magic_row.offset
	end = magic_row.offset + len(magic_row.byte_match)
	if magic_row.offset < 0:
	match_area = footer[start:end] if end != 0 else footer[start:]
	if match_area == magic_row.byte_match:
	new_matches.add(
	PureMagic(
	byte_match=matched.byte_match + magic_row.byte_match,
	offset=magic_row.offset,
	extension=magic_row.extension,
	mime_type=magic_row.mime_type,
	name=magic_row.name,
	)
	)
	else:
	if end > len(header):

Haven't verified the logic / tested myself but just wanted to provide a bit of python specific cleanup. Moving the start and end outside the if statements as they are the same, and check magic_row.offset < 0 instead of against a string (if that's a problem for some reason let me know.)

[NebularNerd]

@cdgriffith, Tested and no issues, I have merged it into the PR. Thanks for the suggestions, my coding skills are ok but I know there's always room for improvement. 🙂

I used a str() as I had brain fog and skipped past the correct < 0 method, both achieve the same goal, just mine was the long way round. 🤣

[NebularNerd]

Conflicts resolved 🙂