Added variables for nuclei + refactor variable handling

[Ice3man543]

Proposed changes

Added variables support for HTTP, DNS, Network and Headless templates.

id: variables

info:
  name: variable example
  author: pdteam
  severity: info

variables:
  a1: "{{to_lower(rand_base(5))}}"

requests:
  - raw:
      - |
        POST /search.php?test=query HTTP/1.1
        Host: {{Hostname}}
        Origin: http://testphp.vulnweb.com
        Content-Type: application/x-www-form-urlencoded

        searchFor={{a1}}&goButton=go

    matchers-condition: and
    matchers:
      - type: word
        words:
          - "{{a1}}"

      - type: dsl
        dsl:
          - "contains(body, a1)"

    extractors:
      - type: kval
        kval:
          - "a1"

echo http://testphp.vulnweb.com | ./nuclei -t tt.yaml -duc

                     __     _
   ____  __  _______/ /__  (_)
  / __ \/ / / / ___/ / _ \/ /
 / / / / /_/ / /__/ /  __/ /
/_/ /_/\__,_/\___/_/\___/_/   2.6.5

		projectdiscovery.io

[WRN] Use with caution. You are responsible for your actions.
[WRN] Developers assume no liability and are not responsible for any misuse or damage.
[INF] Using Nuclei Engine 2.6.5 (outdated)
[INF] Using Nuclei Templates 8.9.6 (latest)
[INF] Templates added in last update: 9
[INF] Templates loaded for scan: 1
[variables] [http] [info] http://testphp.vulnweb.com/search.php?test=query [d0imr] [a1=d0imr]

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[ehsandeep]

merge conflict

outdated

[ehsandeep]

We can add variables.md under https://github.com/projectdiscovery/nuclei-docs/tree/master/docs/templating-guide to include relevant information in docs.

[Ice3man543]

projectdiscovery/nuclei-docs#35 - done here