58 lines
1.9 KiB
Markdown
58 lines
1.9 KiB
Markdown
---
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title: Use Messages for Workflow Notifications
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impact: MEDIUM
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impactDescription: Enables reliable inter-workflow and external-to-workflow communication
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tags: communication, messages, send, recv, notification
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---
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## Use Messages for Workflow Notifications
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Use `dbos.Send` to send messages to a workflow and `dbos.Recv` to receive them. Messages are queued per topic and persisted for reliable delivery.
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**Incorrect (using external messaging for workflow communication):**
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```go
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// External message queue is not integrated with workflow recovery
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ch := make(chan string) // Not durable!
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```
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**Correct (using DBOS messages):**
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```go
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func checkoutWorkflow(ctx dbos.DBOSContext, orderID string) (string, error) {
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// Wait for payment notification (timeout 120 seconds)
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notification, err := dbos.Recvstring
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if err != nil {
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return "", err
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}
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if notification == "paid" {
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_, err = dbos.RunAsStep(ctx, func(ctx context.Context) (string, error) {
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return fulfillOrder(orderID)
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}, dbos.WithStepName("fulfillOrder"))
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return "fulfilled", err
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}
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_, err = dbos.RunAsStep(ctx, func(ctx context.Context) (string, error) {
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return cancelOrder(orderID)
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}, dbos.WithStepName("cancelOrder"))
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return "cancelled", err
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}
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// Send a message from a webhook handler
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func paymentWebhook(ctx dbos.DBOSContext, workflowID, status string) error {
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return dbos.Send(ctx, workflowID, status, "payment_status")
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}
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```
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Key behaviors:
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- `Recv` waits for and consumes the next message for the specified topic
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- Returns the zero value if the wait times out, with a `DBOSError` with code `TimeoutError`
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- Messages without a topic can only be received by `Recv` without a topic
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- Messages are queued per-topic (FIFO)
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**Reliability guarantees:**
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- All messages are persisted to the database
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- Messages sent from workflows are delivered exactly-once
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Reference: [Workflow Messaging and Notifications](https://docs.dbos.dev/golang/tutorials/workflow-communication#workflow-messaging-and-notifications)
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