Inherited Conditions

# Inherited Chain Conditions
#
# A named filter chain declares one `conditions:` block that every filter in the
# chain inherits. The condition is written once at the chain level instead of
# being repeated on each filter, and it composes with any filter-local
# conditions using AND semantics: the chain condition is evaluated first, then
# the filter's own conditions (effective = chain AND filter).
#
# A request-phase condition skips request and response hooks for non-matching
# traffic, including request-body promotion and response tagging. Body mode is
# listener-wide: json_body_field still pre-reads and size-limits every request
# body on this listener (including /health) to end of stream before forwarding.
# A compression filter in a gated chain would also affect every eligible response.
#
# Here the `api-enrichment` chain applies only to `/api/` requests:
#   - `json_body_field` promotes the JSON body's `model` field to an `X-Model`
#     request header (a request-body hook), but only for POST requests: its
#     effective condition is `path_prefix: /api/` AND `methods: [POST]`.
#   - `headers` tags every `/api/` response with `X-Enriched` (a response hook),
#     inheriting the chain condition alone.
# Requests outside `/api/` skip the whole chain: no `X-Model`, no `X-Enriched`.
#
# Usage:
#   cargo run -p praxis-proxy -- -c examples/configs/pipeline/inherited-conditions.yaml
#   curl -i -X POST http://localhost:8080/api/chat -d '{"model":"gpt-4"}'  # X-Model forwarded, X-Enriched on response
#   curl -i -X PUT http://localhost:8080/api/chat -d '{"model":"gpt-4"}'   # only X-Enriched (POST-only body promotion skipped)
#   curl -i -X POST http://localhost:8080/health -d '{"model":"gpt-4"}'    # neither header (outside /api/)

listeners:
  - name: default
    address: "127.0.0.1:8080"
    filter_chains:
      - routing
      - api-enrichment
      - upstream

filter_chains:
  # Route every request to the single backend.
  - name: routing
    filters:
      - filter: router
        routes:
          - path_prefix: "/"
            cluster: backend

  # Every filter in this chain inherits the chain-level condition. The condition
  # is declared once and ANDed with each filter's own conditions.
  - name: api-enrichment
    conditions:
      - when:
          path_prefix: "/api/"
    filters:
      # Effective condition: path_prefix /api/ AND methods POST. Promotes the
      # body's `model` field to a request header the backend can read.
      - filter: json_body_field
        field: model
        header: X-Model
        conditions:
          - when:
              methods: ["POST"]

      # Effective condition: path_prefix /api/ (inherited, no local condition).
      # Tags the response so clients can tell enriched traffic apart.
      - filter: headers
        response_set:
          - name: "X-Enriched"
            value: "true"

  # Declare the backend the router binds.
  - name: upstream
    filters:
      - filter: load_balancer
        clusters:
          - name: backend
            endpoints:
              - "127.0.0.1:3000"

insecure_options:
  allow_private_endpoints: true # example proxies to a local backend