Capture

The Capture filter's job is to find a series of bytes within a packet, and capture it into Filter Dynamic Metadata, so that it can be utilised by filters further down the chain.

This is often used as a way of retrieving authentication tokens from a packet, and used in combination with Concatenate and TokenRouter filter to provide common packet routing utilities.

Capture strategies

There are multiple strategies for capturing bytes from the packet.

Suffix

Captures bytes from the end of the packet.

Prefix

Captures bytes from the start of the packet.

Regex

Captures bytes using a regular expression. Unlike other capture strategies, the regular expression can return one or many values if there are multiple matches.

Filter name

quilkin.filters.capture.v1alpha1.Capture

Configuration Examples

#![allow(unused)]
fn main() {
let yaml = "
version: v1alpha1
filters:
  - name: quilkin.filters.capture.v1alpha1.Capture
    config:
      metadataKey: myapp.com/myownkey
      prefix:
        size: 3
        remove: false
clusters:
  - endpoints:
      - address: 127.0.0.1:7001
";
let config = quilkin::config::Config::from_reader(yaml.as_bytes()).unwrap();
assert_eq!(config.filters.load().len(), 1);
}

Configuration Options (Rust Doc)

$schema: http://json-schema.org/draft-07/schema#
title: Config
type: object
required:
- metadata_key
- strategy
properties:
  metadata_key:
    description: The key to use when storing the captured value in the filter context. If a match was found it is available under `{{metadata_key}}/is_present`.
    allOf:
    - $ref: '#/definitions/Key'
  strategy:
    description: The capture strategy.
    allOf:
    - $ref: '#/definitions/Strategy'
definitions:
  Key:
    description: A key in the metadata table.
    type: string
  Strategy:
    description: Strategy to apply for acquiring a set of bytes in the UDP packet
    oneOf:
    - description: Looks for the set of bytes at the beginning of the packet
      type: object
      required:
      - kind
      - size
      properties:
        kind:
          type: string
          enum:
          - PREFIX
        remove:
          description: Whether captured bytes are removed from the original packet.
          default: false
          type: boolean
        size:
          description: The number of bytes to capture.
          type: integer
          format: uint32
          minimum: 0.0
    - description: Look for the set of bytes at the end of the packet
      type: object
      required:
      - kind
      - size
      properties:
        kind:
          type: string
          enum:
          - SUFFIX
        remove:
          description: The number of bytes to capture.
          default: false
          type: boolean
        size:
          description: Whether captured bytes are removed from the original packet.
          type: integer
          format: uint32
          minimum: 0.0
    - description: Look for the set of bytes at the end of the packet
      type: object
      required:
      - kind
      - pattern
      properties:
        kind:
          type: string
          enum:
          - REGEX
        pattern:
          description: The regular expression to use for capture.
          type: string

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