Rule Engine

Rules let you block, modify, or redirect traffic without writing code.

Rule structure

{
  "id": 1,
  "name": "Block ads",
  "enabled": true,
  "priority": 10,
  "conditions": [
    { "field": "host", "op": "contains", "value": "ads.example.com" }
  ],
  "action": "block"
}

Actions

Action	Effect
passthrough	Allow without change (useful for whitelisting over a broader rule)
block	Return HTTP 403 to the client
modify	Apply modifications to the request and/or response
redirect	Return HTTP 302 to redirect_url

Conditions

All conditions in a rule must match (AND logic). Use multiple rules if you need OR logic.

Fields

Field	Evaluated against
host	Host header
path	URL path
method	HTTP method
header	Any header value (format: Header-Name: value)
body	Request body as a string

Operators

Op	Description
equals	Exact match
contains	Substring match
prefix	Starts with
regex	Python re-compatible regular expression

Set "negate": true to invert any condition.

Modifications

Used with action: modify.

{
  "action": "modify",
  "modifications": [
    {
      "target": "req_header",
      "key": "X-Debug",
      "value": "1",
      "operation": "set"
    },
    {
      "target": "resp_body",
      "operation": "find_replace",
      "find": "production",
      "replace": "staging"
    }
  ]
}

Targets

Target	Description
req_header	Request header
resp_header	Response header
req_body	Request body
resp_body	Response body

Operations

Operation	Description
set	Set header key to value (overwrites)
delete	Delete header key
append	Append value to header
replace	Replace entire body with value
find_replace	Replace find with replace in body

Priority

Higher priority = evaluated first. When multiple rules match, only the highest-priority rule fires.

Managing rules via API

# Create
curl -X POST http://localhost:8081/api/rules \
  -H 'Content-Type: application/json' \
  -d '{
    "name": "Add debug header",
    "enabled": true,
    "priority": 5,
    "conditions": [{"field": "host", "op": "contains", "value": "api.example.com"}],
    "action": "modify",
    "modifications": [{"target": "req_header", "key": "X-Debug", "value": "true", "operation": "set"}]
  }'

# List
curl http://localhost:8081/api/rules

# Update rule 1
curl -X PUT http://localhost:8081/api/rules/1 \
  -H 'Content-Type: application/json' \
  -d '{"enabled": false, ...}'

# Delete rule 1
curl -X DELETE http://localhost:8081/api/rules/1