# Mattress: a command line tool for working with Linux extended attributes (xattrs)

The comfiest way to work with Linux extended attributes (xattrs) written in pure Rust
and made of delicious, fibrous Open Source code.

Mattress provides tools for manipulating xattrs on individual files as well as for working with the filesystem as a document database
where the filesystem paths act as primary keys and extended attributes provide non-indexed fields.

## History

Mattress was developed in conjunction with the [Audiotater](https://git.disroot.org/joshhansen/audiotater) audio annotation tool.

## License

This software is licensed under GPL version 3 only.

## Examples

Mattress operates through a set of subcommands, each with a primary function.

### Move

Moves xattr values from one path to another.

* `mtr mv path1.txt path2.txt`: move all xattrs from path1.txt to path2.txt
* `mtr mv -f id path1.txt path2.txt`: move xattr `id` from path1.txt to path2.txt
* `mtr mv -f id -f url path1.txt path2.txt`: move xattrs `id` and `url` from path1.txt to path2.txt

### Copy

Copies xattr values from one path to another.

* `mtr cp path1.txt path2.txt`: copy all xattrs from path1.txt to path2.txt
* `mtr cp -f id path1.txt path2.txt`: copy xattr `id` from path1.txt to path2.txt
* `mtr cp -f id -f url path1.txt path2.txt`: copy xattrs `id` and `url` from path1.txt to path2.txt

### Remove

Removes xattr values.

* `mtr rm path.txt`: remove all xattrs on path.txt
* `mtr rm -f id path.txt`: remove xattr `id` from path.txt
* `mtr rm -f id -f url path1.txt path2.txt path3.txt`: remove xattrs `id` and `url` from path1.txt, path2.txt, and path3.txt

### Set

Sets xattr values.

* `mtr set -s id=123 path1.txt`: set xattr `id` to value `123` on path1.txt
* `mtr set -s id=123 -s url=http://example.com path1.txt path2.txt path3.txt`: set xattr `id` to value `123` and xattr `url` to value `http://example.com` on path1.txt, path2.txt, and path3.txt

### Get

Get and print xattr values for one or more paths.

By default, the `get` subcommand outputs a tab-separated table with a column order of `path`, `field`, `value`. The value bytes are written to stdout as-is without decoding.

By contrast, when outputting JSON, Mattress attempts to decode values as UTF-8, filling in a default codepoint when the decoding fails.

* `mtr get path1.txt`: print all xattrs associated with path1.txt as raw (undecoded) TSV
* `mtr get -f id path1.txt`: print xattr `id` and its value on path1.txt as raw (undecoded) TSV
* `mtr get -f id -f url path1.txt path2.txt path3.txt`: print xattrs `id` and `url` and their respective values on path1.txt, path2.txt, and path3.txt as raw (undecoded) TSV

The `get` command can also output JSON:

* `mtr get -j path1.txt`: print all xattrs associated with path1.txt as UTF-8 decoded JSON
* `mtr get -j -f id path1.txt`: print xattr `id` and its value on path1.txt as UTF-8 decoded JSON
* `mtr get -j -f id -f url path1.txt path2.txt path3.txt`: print xattrs `id` and `url` and their respective values on path1.txt, path2.txt, and path3.txt as JSON

TODO Recursive `get` that benefits from "table" structure / indexing.

### Index

Indexes a "table".

When Mattress acts on a directory as if it were a database table, each file acts as a relational "record" with the primary key coming from the
subpath under the table directory.

Each file's extended attributes act as the relational attributes, with an overloadable virtual attribute `id` that represents the primary key.
For each subcomponent $i of the primary key, there is also a virtual attribute `id$i`.

Table directories created by Mattress also contain a special xattr `user.mattress.keyname` which gives a user-friendly name for the primary key
component represented by that directory.

Examples:

* `mtr idx -k name ./people ./people-by-name`: recursively reindex the contents of `./people` into a new directory `./people-by-name` with primary key
  coming from xattr `name` and files hardlinked to the corresponding files in `./people`.

  That means the `./people-by-name` directory's files will have filenames taken from the names of the people as defined in xattr `name`.

  The new directory `./people-by-name` will have xattr `user.mattress.keyname=name` so later commands can do efficient index lookups using
  user-friendly field names.

* `mtr idx -k region -k name -s ./people-by-name ./people-by-region-and-name`: recursively reindex the contents of `./people-by-name` into a new directory
  `./people-by-region-and-name` with primary key being the compound of xattr `region` and xattr `name` (in that order) and files hardlinked to the
  corresponding files in `./people`, resolved via the hardlinks in `./people-by-name`.

  The output directory `./people-by-region-and-name` will have xattr `user.mattress.keyname=region` and each region-named subdirectory will have
  xattr `user.mattress.keyname=name`.