Create channel, subscribe and start watching

Motivation

As a client, I want to create a channel, subscribe and receive notifications about changes.

Terms

Functional Design

• The client initiates an SSE connection by making POST /api/v2/apps/{owner}/{app}/notifications with the payload containing the list of subscriptions.
• The connection is then kept open, allowing the server to stream events continuously.
• Client receives events, see Result

Request headers

Key	Value
Content-Type	application/json
Accept	text/event-stream
Authorization	Bearer {PrincipalToken}

Parameters

Parameter	Type	Description
Path
owner	string	name of a user who owns the application
app	string	name of an application
wsid	int64	the ID of workspace
Headers
PrincipalToken	string	Token returned by login

Authorization

• In order to create a channel, the client must provide a valid, non-expired PrincipalToken for the specified application in the Authorization header
• For every specified view in the subscription, the client must have read permission for that view in the specified workspace.

Request body

JSON object:

{
  "subscriptions": [
    {
      "entity": "sys.Heartbeat30",
      "wsid": 0
    },
    {
      "entity": "pkg.SalesView",
      "wsid": 100341234143
    }
    // more subscriptions can be added here
  ],
  "expiresInSeconds": 100, // optional, in seconds, default is 86400 (24h)
}

Heartbeat

When sys.Heartbeat30 is specified as the name of the subscription item, the server will send heartbeat events every 30 seconds. Event for the heartbeat contains "." as the name, and zero as the workspace ID.

Result

When the connection is established, the server responds with:

Content-Type: text/event-stream
Cache-Control: no-cache
Connection: keep-alive

Then it starts sending events to the client. Each event is formatted as follows:

event: {event-name}
data: {event-data}

The first event is always a channel ID (uuid), which is used to identify the connection, example:

event: channelID
data: 123e4567-e89b-12d3-a456-426614174000

The subsequent events contain updates for the subscription items, where {event-name} is update, and {event-data} is the JSON object containing the details of the update. Example view update event:

event: update
data: {"app":"myapp", "item":"pkg.SalesView", "wsid":0, "offset": 0}

event: update
data: {"app":"myapp", "item":".", "wsid":100341234143, "offset": 1234567890}

The {event-data} is an UTF-8 encoded text. Each event ends with a double newline (\n\n)

In case of an error, the server responds with an HTTP error:

Code	Description	Body
400	Bad Request	error object
401	Unauthorized	error object
403	Forbidden, client has no permissions to read from view	error object
429	Too may requests, rate limiting	error object
500+	Server errors / service unavailable	error object

Technical design

Components

• ~cmp.routerCreateChannelHandler~covrd¹✅ function to handle the request in router
  • ~err.routerCreateChannelInvalidToken~covrd²✅ if the token is invalid or expired
  • ~err.routerCreateChannelNoPermissions~uncvrd³❓ if the client has no permissions to read from the specified view

Integration tests

• ~it.CreateChannelSubscribeAndWatch~covrd⁴✅

Footnotes

1. [~server.n10n/cmp.routerCreateChannelHandler~impl] pkg/router/impl_apiv2.go:156:impl ↩

2. [~server.n10n/err.routerCreateChannelInvalidToken~impl] pkg/router/impl_apiv2.go:280:impl ↩

3. [~server.n10n/err.routerCreateChannelNoPermissions~impl] ↩

4. [~server.n10n/it.CreateChannelSubscribeAndWatch~impl] pkg/sys/it/impl_n10n_test.go:49:impl ↩