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WebSocket Validator

By Kong Inc.

Validate individual WebSocket messages against to a user-specified schema before proxying them.

Message schema can be configured by type (text or binary) and sender (client or upstream).

When an incoming message is invalid according to the schema, a close frame is sent to the sender (status: 1007) and the peer before closing the connection.

At least one of the following complete message validation configurations must be defined:

  • config.client.text.type and config.client.text.schema
  • config.client.binary.type and config.client.binary.schema
  • config.upstream.text.type and config.upstream.text.schema
  • config.upstream.binary.type and config.upstream.binary.schema

Usage

Note: Currently, the only supported validation type is JSON schema draft4, so all examples will use this.

Validate client text frames

This example validates that client text frames:

  • Are valid JSON
  • Are a JSON object ({})
  • Have a name attribute (of any type)
curl -i -X POST http://HOSTNAME:8001/services/SERVICE/plugins \
  --data "name=websocket-validator" \
  --data "config.client.text.type=draft4" \
  --data 'config.client.text.schema={ "type": "object", "required": ["name"] }'

Add the following entry to the plugins: section in the declarative configuration file:

plugins:
- name: websocket-validator
  service: SERVICENAME
  config:
    client:
      text:
        schema: '{ "type": "object", "required": ["name"] }'
        type: draft4

Here’s an example sequence for this configuration:

 .------.                               .----.                          .--------.
 |Client|                               |Kong|                          |Upstream|
 '------'                               '----'                          '--------'
    |                                     |                                 |
    |     text(`{ "name": "Alex" }`)      |                                 |
    |>----------------------------------->|                                 |
    |                                     |                                 |
    |                                     |    text(`{ "name": "Alex" }`)   |
    |                                     |>------------------------------->|
    |                                     |                                 |
    |     text(`{ "name": "Kiran" }`)     |                                 |
    |>----------------------------------->|                                 |
    |                                     |                                 |
    |                                     |   text(`{ "name": "Kiran" }`)   |
    |                                     |>------------------------------->|
    |                                     |                                 |
    |  text(`{ "missing_name": true }`)   |                                 |
    |>----------------------------------->|                                 |
    |                                     |                                 |
    |         close(status=1007)          |                                 |
    |<-----------------------------------<|                                 |
    |                                     |                                 |
    |                                     |             close()             |
    |                                     |>------------------------------->|
 .------.                               .----.                          .--------.
 |Client|                               |Kong|                          |Upstream|
 '------'                               '----'                          '--------'