Add brotli mime type detection to file and libmagic #259

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claunia · 2026-01-29T20:40:57Z

claunia commented

2026-01-29 20:40:57 +00:00

Originally created by @stokito on GitHub (Oct 27, 2018).

The Linux file utility doesn't recognize brotli MIME type:

$ file -i some_archive.br
some_archive.br: application/octet-stream; charset=binary

I know, this is not related for the brotli itself but could you send a PR to file and libmagic so they start to recognize brotli mime type?

https://github.com/file/file/blob/master/src/compress.c
https://github.com/file/file/blob/master/magic/Magdir/archive

Also please confirm the correct brotli mime type #724

Originally created by @stokito on GitHub (Oct 27, 2018). The Linux `file` utility doesn't recognize brotli MIME type: ``` $ file -i some_archive.br some_archive.br: application/octet-stream; charset=binary ``` I know, this is not related for the brotli itself but could you send a PR to file and libmagic so they start to recognize brotli mime type? https://github.com/file/file/blob/master/src/compress.c https://github.com/file/file/blob/master/magic/Magdir/archive Also please confirm the correct brotli mime type #724

claunia commented

2026-01-29 20:40:58 +00:00

@eustas commented on GitHub (Nov 1, 2018):

There is a little problem. Most utilities scan first file bytes and compare them against "magic" bytes.
Well,... for brotli 254 of 256 byte values are valid as the first file byte.

Brotli was designed to be "stream" format rather than file format. There is a "brotli-framing-format" project that adds tons of features (including "magic header bytes")... but it is not public yet.

@eustas commented on GitHub (Nov 1, 2018): There is a little problem. Most utilities scan first file bytes and compare them against "magic" bytes. Well,... for brotli 254 of 256 byte values are valid as the first file byte. Brotli was designed to be "stream" format rather than file format. There is a "brotli-framing-format" project that adds tons of features (including "magic header bytes")... but it is not public yet.

claunia commented

2026-01-29 20:40:59 +00:00

@stokito commented on GitHub (Nov 1, 2018):

If I understood correctly gzip is also can be named as stream format but this is not a problem for them to add few magic bytes.
I already used \xce\xb2\xcf\x81 as brotli magic bytes and application/x-brotli as mime type but asked here #724 to confirm.

Where can I read at least something about this framing format? Will we still be able to use regular .br files?

@stokito commented on GitHub (Nov 1, 2018): If I understood correctly gzip is also can be named as stream format but this is not a problem for them to add few magic bytes. I [already used](https://github.com/mate-desktop/engrampa/blob/master/src/fr-archive.c#L555) `\xce\xb2\xcf\x81` as brotli magic bytes and `application/x-brotli` as mime type but asked here #724 to confirm. Where can I read at least something about this framing format? Will we still be able to use regular .br files?

claunia commented

2026-01-29 20:40:59 +00:00

@eustas commented on GitHub (Nov 1, 2018):

gzip is a wrapper for deflate streams

@eustas commented on GitHub (Nov 1, 2018): `gzip` is a wrapper for `deflate` streams

claunia commented

2026-01-29 20:41:00 +00:00

@stokito commented on GitHub (Nov 10, 2018):

So, the magic bytes which I used are actually from another framing format from #462

@stokito commented on GitHub (Nov 10, 2018): So, the magic bytes which I used are actually from another framing format from #462

claunia commented

2026-01-29 20:41:01 +00:00

@doronbehar commented on GitHub (Oct 6, 2019):

I've opened an issue about this in file's bug tracker:

https://bugs.astron.com/view.php?id=111

So @eustas, the issue is that this implementation doesn't include magic bytes when it creates files and not streams?

@doronbehar commented on GitHub (Oct 6, 2019): I've opened an issue about this in `file`'s bug tracker: https://bugs.astron.com/view.php?id=111 So @eustas, the issue is that this implementation doesn't include magic bytes when it creates files and not streams?

claunia commented

2026-01-29 20:41:01 +00:00

@unphased commented on GitHub (Aug 4, 2024):

What is the state of this? Most (but not all! which is not looking promising) of the brotli files i looked at start with the byte 5b...

@unphased commented on GitHub (Aug 4, 2024): What is the state of this? Most (but not all! which is not looking promising) of the brotli files i looked at start with the byte `5b`...

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Reference: starred/brotli#259