Middleware actions

  1. 'connect'
  2. 'receive'
  3. 'reply'
  4. 'receivePresence'
  5. 'sendPresence'
  6. 'query'
  7. 'readSnapshots'
  8. 'op'
  9. 'submit'
  10. 'apply'
  11. 'commit'
  12. 'afterWrite'

The actions represent different stages of information flow through the server. These hooks are also available on backend.MIDDLEWARE_ACTIONS.

All of the actions will have these context properties:

action – string

The triggered middleware action

agent – Agent

The Agent communicating with the client

backend – Backend

The Backend handling the request

'connect'

A new client connected to the server.

This action has these additional context properties:

stream – Stream

The Stream that connected

req – Object

The request argument provided to backend.listen()

'receive'

The server received a message from a client.

This action has these additional context properties:

data – Object

The received data

'reply'

The server is about to send a non-error reply to a client message.

This action has these additional context properties:

request – Object

The client’s received request

reply – Object

The reply about to be sent

'receivePresence'

Presence information has just been received from a client. The presence has not yet been transformed against any ops it has missed.

This action has these additional context properties:

collection – string

The collection the presence is associated with

presence – Object

The presence object that was received. Its shape depends on its type

'sendPresence'

Presence information is about to be sent to a client.

This action has these additional context properties:

collection – string

The collection the presence is associated with

presence – Object

The presence object being sent. Its shape depends on its type

'query'

A new query request is about to be submitted to the database

This action has these additional context properties:

index – string

The name of the query’s collection or projection

collection – string

The name of the query’s target collection

projection – string

The name of the query’s projection

fields – Object

The query’s projection fields

channel – string (deprecated)

This property is deprecated use channels instead. The Pub/Sub channels the query will subscribe to. Defaults to its collection channel.

channels – string[]

The Pub/Sub channels the query will subscribe to. Defaults to its collection channel.

query – Object

The query being submitted to the database adapter

options – Object

The query options

db – DB

The database the query will be run against

'readSnapshots'

One or more snapshots were loaded from the database for a fetch or subscribe.

This action has these additional context properties:

collection – string

The collection the snapshots belong to

snapshots – Snapshot[]

The Snapshots being read

snapshotType – string

One of:

  • current – the snapshots are the latest version
  • byVersion – the snapshots are being fetched by version
  • byTimestamp – the snapshots are being fetched by timestamp

'op'

An operation was loaded from the database.

This action has these additional context properties:

collection – string

The collection of the op

id – string

The document ID

op – Object

The op being read

'submit'

An operation has been submitted to the server.

This action has these additional context properties:

collection – string

The collection of the op

id – string

The document ID

op – Object

The submitted op

snapshot – Snapshot

The snapshot

extra – Object

extra.source – Object

The submitted source when doc.submitSource is set to true

saveMilestoneSnapshot – boolean

Flag to control saving a milestone snapshot

suppressPublish – boolean

Flag to prevent broadcasting over pub/sub

retries – number

The number of times the op has attempted to submit

maxRetries – number

The maximum number of times to retry submitting the op

channels – string[]

The pub/sub channels the op will publish to

'apply'

An operation is about to be applied to a snapshot, before committing.

This action has the same additional context properties as 'submit'.

'commit'

An operation was applied to a snapshot, and is about to be committed to the database.

This action has the same additional context properties as 'submit'.

'afterWrite'

An operation and its updated snapshot were successfully written to the database.

This action has the same additional context properties as 'submit'.