Plugin: yanlr

• infos = Information about the yanlr plugin is in keys below
• infos/author = René Schwaiger sanss.nosp@m.ecou.nosp@m.rs@me.nosp@m..com
• infos/licence = BSD
• infos/needs = directoryvalue yamlsmith
• infos/provides = storage/yaml
• infos/recommends =
• infos/placements = getstorage
• infos/status = maintained unittest preview experimental unfinished nodoc concept discouraged
• infos/metadata =
• infos/description = This storage plugin use a parser generated by ANTLR to read YAML files

Yan LR

Introduction

This plugin uses ANTLR to generate a parser for the YAML serialization format. Apart from the hand written lexer, all other parts of the plugin use standard ANTLR tools, such as

• an ANTLR parser grammar,
• a listener, that reacts to matches in the grammar building a key set, and
• an error listener that reacts to syntax errors

Dependencies

The plugin requires

• ANTLR 4.6 or later, and
• ANTLR 4’s C++ runtime.

If packages for those libraries are not available for your system, you can install them manually. For more information about that please take a look at ANTLR’s homepage and at the ReadMe of the ANTLR C++ runtime.

Please note that we only tested the plugin with ANTLR 4.7.1 (and later versions of ANTLR).

Arch Linux

In Arch Linux the required packages are called antlr4 and antlr4-runtime.

pacman -Sy --noconfirm antlr4 antlr4-runtime

Debian Linux

In Debian Linux you need the packages antlr4 and libantlr4-runtime-dev.

apt-get -y install antlr4 libantlr4-runtime-dev

macOS

To install the dependencies of the plugin using Homebrew, please use the command below.

brew install antlr antlr4-cpp-runtime

Examples

Mappings

`` @section autotoc_md963 Mount plugin touser/tests/yanlr` sudo kdb mount config.yaml user/tests/yanlr yanlr

Manually add some mappings to the configuration file

printf 'all : circles presuppose
' > kdb file user/tests/yanlr printf 'hello : world
' >> kdb file user/tests/yanlr

kdb ls /tests/yanlr #> user/tests/yanlr/all #> user/tests/yanlr/hello

kdb get user/tests/yanlr/all #> circles presuppose

Store value at root of mountpoint

kdb set user/tests/yanlr 'Mount Eerie' kdb get user/tests/yanlr #> Mount Eerie

Add new key-value pairs

Yan LR actually uses the YAML Smith plugin to write data

kdb set user/tests/yanlr/brand new kdb set user/tests/yanlr/brand/new eyes kdb set user/tests/yanlr/dance/gavin 'Dance!'

kdb ls /tests/yanlr #> user/tests/yanlr #> user/tests/yanlr/all #> user/tests/yanlr/brand #> user/tests/yanlr/brand/new #> user/tests/yanlr/dance/gavin #> user/tests/yanlr/hello

kdb get /tests/yanlr/hello #> world kdb get user/tests/yanlr/brand #> new kdb get /tests/yanlr/dance/gavin #> Dance!

Undo modifications to the key database

kdb rm -r user/tests/yanlr sudo kdb umount user/tests/yanlr

### Arrays

Mount plugin to `/tests/yanlr`

sudo kdb mount config.yaml user/tests/yanlr yanlr

Manually add a sequences to the configuration file

printf 'primes:
' > kdb file user/tests/yanlr printf ' - two
' >> kdb file user/tests/yanlr printf ' - three
' >> kdb file user/tests/yanlr printf ' - five
' >> kdb file user/tests/yanlr

kdb ls user/tests/yanlr #> user/tests/yanlr/primes #> user/tests/yanlr/primes/#0 #> user/tests/yanlr/primes/#1 #> user/tests/yanlr/primes/#2

kdb set user/tests/yanlr/primes/#3 seven

Retrieve index of last array element

kdb meta-get user/tests/yanlr/primes array #> #3

Undo modifications to the key database

kdb rm -r user/tests/yanlr sudo kdb umount user/tests/yanlr

### Boolean Values

Mount plugin to `/tests/yanlr`

sudo kdb mount config.yaml user/tests/yanlr yanlr

Manually add a boolean value to the database

printf 'boolean: true' > kdb file user/tests/yanlr

Elektra stores boolean values as `0` and `1`

kdb get user/tests/yanlr/boolean #> 1

Undo modifications to the key database

kdb rm -r user/tests/yanlr sudo kdb umount user/tests/yanlr

### Null Values

Mount plugin to `/tests/yanlr`

sudo kdb mount config.yaml user/tests/yanlr yanlr

Manually add a null value to the database

printf '"null":' > kdb file user/tests/yanlr

Elektra adds the metakey `binary` for empty keys

kdb meta-ls user/tests/yanlr/null #> binary

Undo modifications to the key database

kdb rm -r user/tests/yanlr sudo kdb umount user/tests/yanlr

### Error Messages

Mount plugin

sudo kdb mount config.yaml user/tests/yanlr yanlr

Manually add syntactically incorrect data

printf – 'key: - element 1
' > kdb file user/tests/yanlr printf – '- element 2 # Incorrect Indentation!' >> kdb file user/tests/yanlr

The plugin reports the location of the error

kdb ls user/tests/yanlr

RET: 5

STDERR: .*/config.yaml:2:1: mismatched input '- ' expecting end of map.*

Let us look at the error message more closely.

Since the location of `config.yaml` depends on the current user and OS,

we store the text before `config.yaml` as `user/tests/error/prefix`.

kdb set user/tests/error "$(2>&1 kdb ls user/tests/yanlr)" kdb set user/tests/error/prefix "$(kdb get user/tests/error | grep 'config.yaml' | head -1 | sed -E 's/(.*)config.yaml.*/\1/')"

We also store the length of the prefix, so we can remove it from every

line of the error message.

kdb set user/tests/error/prefix/length "$(kdb get user/tests/error/prefix | wc -c | sed 's/[ ]*//g')"

Since we only want to look at the “reason” of the error, we

remove the other part of the error message with `head` and `tail`.

kdb get user/tests/error | tail -n6 | cut -c"$(kdb get user/tests/error/prefix/length | tr -d '\n')"- #> config.yaml:2:1: mismatched input '- ' expecting end of map #> - element 2 # Incorrect Indentation! #> ^^ #> config.yaml:2:37: extraneous input 'end of map' expecting end of document #> - element 2 # Incorrect Indentation! #> ^

Fix syntax error

printf – 'key: - element 1
' > kdb file user/tests/yanlr printf – ' - element 2 # Fixed!' >> kdb file user/tests/yanlr

kdb ls user/tests/yanlr #> user/tests/yanlr/key #> user/tests/yanlr/key/#0 #> user/tests/yanlr/key/#1

Undo modifications

kdb rm -r user/tests/error kdb rm -r user/tests/yanlr sudo kdb umount user/tests/yanlr

## Limitations

- The plugin does **not support**

  - plain scalars that span **multiple lines**,
  - **special characters** inside double quoted scalars,
  - other **line endings** than `\n` (Unix line endings),
  - **block scalars**,
  - **flow collections**,
  - **tags**,
  - **anchors & aliases**,
  - **multiple documents**, and
  - document **start and end markers**

  .

- Yan LR does not provide write support for data. Please use the [YAML Smith](@ref src_plugins_yamlsmith_README_md) plugin for that purpose.

### Input Restrictions

The plugin should, but does not, limit the amount

- of **nesting levels**,
- the **length of numbers**, and
- the **length of scalars**

. These restrictions would make it less easy to crash the parser, by feeding it unrestricted data.

### Duplicate Keys

Currently the plugin parses the input

```yaml
duplicate: one
duplicate: two

storing the value two. According to the YAML specification the parser should not allow duplicated keys, and instead fail with an error, for the input above.