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yajl

README.md

  • infos = Information about YAJL plugin is in keys below
  • infos/author = Markus Raab elektra@libelektra.org
  • infos/licence = BSD
  • infos/provides = storage/json
  • infos/needs = directoryvalue
  • infos/recommends = rebase comment type
  • infos/placements = getstorage setstorage
  • infos/status = maintained coverage unittest
  • infos/description = JSON using YAJL

Introduction

This is a plugin reading and writing JSON files using the library yail

The plugin was tested with yajl version 1.0.8-1 from Debian 6 and yajl version 2.0.4-2 from Debian 7.

Examples of files which are used for testing can be found below the folder in "src/plugins/yajl/yajl".

The JSON grammar can be found here.

A validator can be found here.

Supports every KeySet except when arrays are intermixed with other keys. Has only limited support for metadata.

Dependencies

  • libyajl-dev (version 1 and 2 should work)

Types

The type of the data is available via the metadata type:

  • string: The JSON string type.
  • boolean: The JSON boolean type (true or false)
  • double: For JSON numbers.

If no metadata type is given, the type is either:

  • null on binary null-key
  • string otherwise

Any other type/value will still be treated as string, but the warning #78 will be added because of the potential data loss.

Special values

In JSON it is possible to have empty arrays and objects. In Elektra this is mapped using the special names

###empty_array

and

___empty_map

Arrays are mapped to Elektra’s array convention #0, #1,..

Restrictions

  • Only UTF-8 is supported. Use the iconv plugin if your locale are not UTF-8. When using non-UTF-8 the plugin will be able to write the file, but cannot parse it back again. You will error #77, invalid bytes in UTF8 string.
  • Everything is string if not tagged by metakey "type" Only valid JSON types can be used in type, otherwise there are some fall backs to string but warnings are produced.
  • Arrays will be normalized (to #0, #1, ..)
  • Comments of various JSON-dialects are discarded.
  • Mixing of arrays and maps is not detected and leads to corrupted JSON files. Please specify arrays to avoid such situations.

Because of these potential problems a type checker and comments filter are highly recommended.

Usage

The following example shows you how you can read and write data using this plugin.

# Mount the plugin to the cascading namespace `/tests/yajl`
sudo kdb mount config.json /tests/yajl yajl

# Manually add a key-value pair to the database
printf '{ "number": 1337 }' > `kdb file /tests/yajl`

# Retrieve the new value
kdb get /tests/yajl/number
#> 1337

# Determine the data type of the value
kdb getmeta /tests/yajl/number type
#> double

# Add another key-value pair
kdb set /tests/yajl/key value
#> Using name user/tests/yajl/key
#> Create a new key user/tests/yajl/key with string "value"

# Retrieve the new value
kdb get /tests/yajl/key
#> value

# Check the format of the configuration file
kdb file user/tests/yajl/ | xargs cat
#> {
#>     "key": "value",
#>     "number": 1337
#> }

# Add an array
kdb set user/tests/yajl/piggy/#0 straw
kdb set user/tests/yajl/piggy/#1 sticks
kdb set user/tests/yajl/piggy/#2 bricks

# Retrieve an array key
kdb get user/tests/yajl/piggy/#2
#> bricks

# Check the format of the configuration file
kdb file user/tests/yajl | xargs cat
#> {
#>     "key": "value",
#>     "number": 1337,
#>     "piggy": [
#>         "straw",
#>         "sticks",
#>         "bricks"
#>     ]
#> }

# Undo modifications to the database
kdb rm -r /tests/yajl
sudo kdb umount /tests/yajl

Directory Values

The YAJL plugin support values in directory keys via the Directory Value plugin.

# Mount the plugin to the cascading namespace `/tests/yajl`
sudo kdb mount config.json /tests/yajl yajl

# Add two directory keys and one leaf key
kdb set /tests/yajl/roots 'Things Fall Apart'
kdb set /tests/yajl/roots/bloody 'Radical Face'
kdb set /tests/yajl/roots/bloody/roots 'No Roots'

# Add an array containing two elements
kdb set /tests/yajl/now ', Now'
kdb set /tests/yajl/now/#0 'Neighbors'
kdb set /tests/yajl/now/#1 'Threads'

kdb ls /tests/yajl
#> user/tests/yajl
#> user/tests/yajl/now
#> user/tests/yajl/now/#0
#> user/tests/yajl/now/#1
#> user/tests/yajl/roots
#> user/tests/yajl/roots/bloody
#> user/tests/yajl/roots/bloody/roots

# Retrieve directory values
kdb get /tests/yajl/roots
#> Things Fall Apart
kdb get /tests/yajl/roots/bloody
#> Radical Face

# Retrieve leaf value
kdb get /tests/yajl/roots/bloody/roots
#> No Roots

# Check array
kdb get /tests/yajl/now
#> , Now
kdb getmeta /tests/yajl/now array
#> #1
kdb get /tests/yajl/now/#0
#> Neighbors
kdb get /tests/yajl/now/#1
#> Threads

# Undo modifications to the database
kdb rm -r /tests/yajl
sudo kdb umount /tests/yajl

OpenICC Device Config

This plugin was specifically designed and tested for the OpenICC_device_config_DB although it is of course not limited to it.

Mount the plugin:

kdb mount --resolver=resolver_fm_xhp_x color/settings/openicc-devices.json /org/freedesktop/openicc yajl rename cut=org/freedesktop/openicc

or:

kdb mount-openicc

Then you can copy the OpenICC_device_config_DB.json to systemwide or user config, e.g.

cp src/plugins/yajl/examples/OpenICC_device_config_DB.json /etc/xdg
cp src/plugins/yajl/examples/OpenICC_device_config_DB.json ~/.config

kdb ls system/org/freedesktop/openicc

prints out then all device entries available in the config

kdb get system/org/freedesktop/openicc/device/camera/0/EXIF_manufacturer

prints out "Glasshuette" with the example config in source

You can export the whole system openicc config to ini with:

kdb export system/org/freedesktop/openicc simpleini > dump.ini

or import it:

kdb import system/org/freedesktop/openicc ini < dump.ini