Update topic SMTs

This document explains how to update a Single Message Transform (SMT) for a Pub/Sub topic. Changes to SMTs take effect within a few minutes. For topic SMTs, the changes apply to new messages published after the SMT is updated.

To update topic SMTs, you can use the Google Cloud console, the Google Cloud CLI, the client library, or the Pub/Sub API.

Required roles and permissions

To get the permissions that you need to update topic SMTs, ask your administrator to grant you the Pub/Sub Editor (roles/pubsub.editor) IAM role on your project. For more information about granting roles, see Manage access to projects, folders, and organizations.

This predefined role contains the permissions required to update topic SMTs. To see the exact permissions that are required, expand the Required permissions section:

Required permissions

The following permissions are required to update topic SMTs:

  • Grant the update a topic permission on the topic: projects.topics.patch
  • Grant the view a topic permission on the project. This permission is only required if you are using the Google Cloud console: pubsub.topics.view

You might also be able to get these permissions with custom roles or other predefined roles.

You can configure access control at the project level and at the individual resource level.

Update topic SMTs

To update topic SMTs, follow these steps:

Console

  1. In the Google Cloud console, go to the Pub/Sub Topics page.

    Go to Topics

  2. Click the topic for which you want to edit SMTs.

  3. In the topic details page, click Edit.

    The Transforms tab lists all the SMTs that are attached to the topic.

  4. In the Edit topic page, you can do the following tasks:

    1. Add a new SMT. Click Add a transform.

    2. Edit an existing SMT. Expand any SMT to edit the SMT.

    3. Rearrange the SMTs. Use the up and down arrows.

    4. Delete an SMT. Click the delete button.

  5. Click Update.

gcloud

  1. In the Google Cloud console, activate Cloud Shell.

    Activate Cloud Shell

    At the bottom of the Google Cloud console, a Cloud Shell session starts and displays a command-line prompt. Cloud Shell is a shell environment with the Google Cloud CLI already installed and with values already set for your current project. It can take a few seconds for the session to initialize.

  2. Run the gcloud pubsub topics updatecommand:

    gcloud pubsub topics update TOPIC_ID \
    --message-transforms-file=TRANSFORMS_FILE

    Replace the following:

    • TOPIC_ID: The ID or name of the topic you want to update.

    • TRANSFORMS_FILE: The path to the YAML or JSON file containing the updated SMTs.

      The following is an example of a YAML transforms file:

      - javascriptUdf:
    code: >
        function redactSSN(message, metadata) {
          const data = JSON.parse(message.data);
          delete data['ssn'];
          message.data = JSON.stringify(data);
          return message;
        }
    functionName: redactSSN
- javascriptUdf:
    code: >
        function filterHighAmount(message, metadata) {
          const data = JSON.parse(message.data);
          if (data['amount'] > 100 ) { return null; }
          return message;
        }
    functionName: filterHighAmount

    To clear all the SMTs from the topic, use the following command:

    gcloud pubsub topics update TOPIC_ID --clear-message-transforms

    Replace TOPIC_ID with the ID or name of the topic you want to update.

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