Platform Events Developer Guide
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Subscribe to Platform Event Notifications with CometD
Salesforce sends platform events to CometD clients sequentially in the order they’re received. The order of event notifications is based on the replay ID of events. A CometD client can receive a batch of events at once. The number of event messages in a batch can vary. If the client uses a buffer for the received events, ensure that the buffer size is large enough to hold all event messages in the batch. The buffer size needed depends on the publishing rate and the event message size. At a minimum, set the buffer size to 10 MB, and adjust it higher if needed.
The process of subscribing to platform event notifications through CometD is similar to subscribing to PushTopics or generic events. The only difference is the channel name. The platform event channel name is case-sensitive and is in the following format.
1/event/Event_Name__eTo subscribe to a custom channel, use this format.
1/event/Channel_Name__chnUse this CometD endpoint with the API version appended to it.
1/cometd/66.0Example
If you have a platform event named Low Ink, provide this channel name when subscribing.
1/event/Low_Ink__eThe message of a delivered platform event looks similar to the following example for Low Ink events.
1{
2 "data": {
3 "schema": "dffQ2QLzDNHqwB8_sHMxdA",
4 "payload": {
5 "CreatedDate": "2017-04-09T18:31:40.517Z",
6 "CreatedById": "005D0000001cSZs",
7 "Printer_Model__c": "XZO-5",
8 "Serial_Number__c": "12345",
9 "Ink_Percentage__c": 0.2
10 },
11 "event": {
12 "EventUuid": "2ec0e371-1395-457f-9275-be1b527a72f7",
13 "replayId": 2
14 }
15 },
16 "channel": "/event/Low_Ink__e"
17}The schema field in the event message contains the ID of the platform event schema. The schema is versioned—when the schema changes, the schema ID changes as well. For more information about retrieving the event schema, see Get the Event Schema.
Add custom logic to your client to perform some operations after a platform event notification is received. For example, the client can create a request to order a new cartridge for this printer model.