LZ4 Legacy support?

[Caesurus]

I noticed that the package doesn't have legacy support
There is this legacy magic value here: https://github.com/lz4/lz4/blob/dev/programs/lz4io.c#L80

Is there any plan to support this?

[pierrec]

There is no plan to support the legacy format at this moment.
Feel free to research it and send a PR if you need it though :).

[Caesurus]

Thanks :) I'm trying to use this project to extract a compressed linux kernel. Turns out that various samples I have are compressed with legacy LZ4.

$ hexdump -n 32 vmlinux_LZ4_19377.lz4
0000000 02 21 4c 18 2d 80 39 00 84 7f 45 4c 46 02 01 01
0000010 00 01 00 43 02 00 3e 00 0e 00 01 07 00 13 40 18

Not knowing anything about lz4 I started digging and it seems that even the lz4 repo has support for it in a standalone application but not in the library itself. https://github.com/lz4/lz4/blob/dev/doc/lz4_Frame_format.md#legacy-frame

If I do get some spare cycles I may try to figure out how to add support and provide a PR.
Thanks again.

[Caesurus]

Sorry for commenting/reopening a closed issue.

Had some time this morning to hack away at some stuff. Got it implemented here:
https://github.com/Caesurus/lz4/blob/master/reader_legacy.go
at the moment there is still a unit test failing (partial read after seek): https://github.com/Caesurus/lz4/blob/master/reader_legacy_test.go#L118

It's extracting my legacy sample kernel correctly. I'll do clean up and do some more testing, then I'll send a PR your way (if you're still interested).

I decided against trying to integrate it into the reader as is, I didn't want to impact performance with unneeded operations and making the code more complex. I also don't have a writer for it since I'm not interested in creating legacy lz4 compressed files. Any comments or recommendations are always welcome

[pierrec]

Thanks. Definitely interested. Once you are done, I will add it to the v4 branch as well, this time using a functional option for it.

[Caesurus]

Yay, I have the PR open. I love go... but don't love what I need to do to correct imports when merging back from a forked project :(

Thanks for the excellent work on this project BTW, and making it available! Much much appreciated 👍

[pierrec]

PR merged and legacy support also added on v4.

[anatol]

And I am trying to write an initramfs in lz4 format anatol/booster#34

As it was mentioned earlier kernel need the legacy format. Does anybody have a plan to implement the legacy writer?