--- type: docs title: "Pub/sub API reference" linkTitle: "Pub/Sub API" description: "Detailed documentation on the pub/sub API" weight: 300 --- ## Publish a message to a given topic This endpoint lets you publish data to multiple consumers who are listening on a `topic`. Dapr guarantees At-Least-Once semantics for this endpoint. ### HTTP Request ``` POST http://localhost:/v1.0/publish//[?] ``` ### HTTP Response codes Code | Description ---- | ----------- 204 | Message delivered 403 | Message forbidden by access controls 404 | No pubsub name or topic given 500 | Delivery failed ### URL Parameters Parameter | Description --------- | ----------- `daprPort` | The Dapr port `pubsubname` | The name of pubsub component `topic` | The name of the topic `metadata` | Query parameters for metadata as described below > Note, all URL parameters are case-sensitive. ```shell curl -X POST http://localhost:3500/v1.0/publish/pubsubName/deathStarStatus \ -H "Content-Type: application/json" \ -d '{ "status": "completed" }' ``` ### Headers The `Content-Type` header tells Dapr which content type your data adheres to when constructing a CloudEvent envelope. The `Content-Type` header value populates the `datacontenttype` field in the CloudEvent. Unless specified, Dapr assumes `text/plain`. If your content type is JSON, use a `Content-Type` header with the value of `application/json`. If you want to send your own custom CloudEvent, use the `application/cloudevents+json` value for the `Content-Type` header. #### Metadata Metadata can be sent via query parameters in the request's URL. It must be prefixed with `metadata.`, as shown below. Parameter | Description --------- | ----------- `metadata.ttlInSeconds` | The number of seconds for the message to expire, as [described here]({{< ref pubsub-message-ttl.md >}}) `metadata.rawPayload` | Boolean to determine if Dapr should publish the event without wrapping it as CloudEvent, as [described here]({{< ref pubsub-raw.md >}}) > Additional metadata parameters are available based on each pubsub component. ## Optional Application (User Code) Routes ### Provide a route for Dapr to discover topic subscriptions Dapr will invoke the following endpoint on user code to discover topic subscriptions: #### HTTP Request ``` GET http://localhost:/dapr/subscribe ``` #### URL Parameters Parameter | Description --------- | ----------- `appPort` | The application port #### HTTP Response body A JSON-encoded array of strings. Example: ```json [ { "pubsubname": "pubsub", "topic": "newOrder", "route": "/orders", "metadata": { "rawPayload": "true", } } ] ``` > Note, all subscription parameters are case-sensitive. #### Metadata Optionally, metadata can be sent via the request body. Parameter | Description --------- | ----------- `rawPayload` | boolean to subscribe to events that do not comply with CloudEvent specification, as [described here]({{< ref pubsub-raw.md >}}) ### Provide route(s) for Dapr to deliver topic events In order to deliver topic events, a `POST` call will be made to user code with the route specified in the subscription response. The following example illustrates this point, considering a subscription for topic `newOrder` with route `orders` on port 3000: `POST http://localhost:3000/orders` #### HTTP Request ``` POST http://localhost:/ ``` > Note, all URL parameters are case-sensitive. #### URL Parameters Parameter | Description --------- | ----------- `appPort` | The application port `path` | Route path from the subscription configuration #### Expected HTTP Response An HTTP 2xx response denotes successful processing of message. For richer response handling, a JSON-encoded payload body with the processing status can be sent: ```json { "status": "" } ``` Status | Description --------- | ----------- `SUCCESS` | Message is processed successfully `RETRY` | Message to be retried by Dapr `DROP` | Warning is logged and message is dropped Others | Error, message to be retried by Dapr Dapr assumes that a JSON-encoded payload response without `status` field or an empty payload responses with HTTP 2xx is a `SUCCESS`. The HTTP response might be different from HTTP 2xx. The following are Dapr's behavior in different HTTP statuses: HTTP Status | Description --------- | ----------- 2xx | message is processed as per status in payload (`SUCCESS` if empty; ignored if invalid payload). 404 | error is logged and message is dropped other | warning is logged and message to be retried ## Message envelope Dapr pub/sub adheres to version 1.0 of CloudEvents. ## Related links * [How to publish to and consume topics]({{< ref howto-publish-subscribe.md >}}) * [Sample for pub/sub](https://github.com/dapr/quickstarts/tree/master/tutorials/pub-sub)