Reusable constants in yaml schema

[Sebitosh]

Objective

Add a feature to define constant variables to be replaced in values of parameters when parsing MRTS yaml files. Two types of constants could be defined, global constants and per-file constants. They could then be replaced when parsing.

Proposition

For global constants, a default_constants section would be added as a subsection of global sections:

global:
  version: MRTS/0.1
  baseid: 100000
  default_operator: "@rx"
  default_constants:
    - constant:
        name: ONE
        value: 1
    - constant:  
        name: TWO
        value: "two"
    - constant:
        name: THREE
        value: 'three'

  templates:
  - name: "SecRule for TARGETS"
    template: |
      SecRule $TARGET "$OPERATOR $OPARG" \
          "id:$CURRID,\
          phase:$PHASE,\
          deny,\
          t:none,\
          log,\
          msg:'%{MATCHED_VAR_NAME} was caught in phase:$PHASE',\
          ver:'$VERSION'"
  default_tests_phase_methods:
  - 1: get
  - 2: post
  - 3: post
  - 4: post
  - 5: post

For per-file constants, a constants section would be located as a root section:

target: null
rulefile: MRTS_001_INIT.conf
testfile: null
constants:
  - constant:
    - name: ONE
    - value: 1
objects:
- object: ...

The constants would then be accessible inside other sections, using @{ as prefix and }@ as suffix around it's name, to instruct the parser that it is a constant to be substituted. In case @{ }@ symbols are parsed but no corresponding constant is found, no substition takes place to avoid modifying possibly legitimate rule configurations.

testdata:
  phase_methods:
    2: post
    3: post
    4: post
  targets:
    - target: '/*'
      test:
        input:
        headers:
          - name: Content-Type
            value: @{XML}@
          - name: Content-Length
            value: @{ONE}@

As specified in the MRTS documentation, any global section parsed later than an other global section is overwritten, including for default_constants. If constant names are used multiple times, the latest occurence defines the value. Implementation would be based on a constant dictionnary, like the variables of templates.

[airween]

Closing as completed via #17.