Publishing JSON message to Pub/Sub topic fails with 400 bad request error

Problem

Publishing a message to a Cloud Pub/Sub topic through an API call with cURL fails with the following error:

error code: 400 Bad Request

error message: Invalid JSON payload received... Cannot bind query parameter... Field  could not be found in request message

status: INVALID_ARGUMENT

 

Environment

  • Cloud Pub/Sub

Solution

  1. The message data has to be passed as a base64 encoded string. Use the following commands to base64 encode a message and pass it with the --data field in the cURL command: 
    message='demo message'
     
    encoded_message='echo $message | base64'
     
    curl -s -X POST -H 'content-type: application/json' -H "Authorization: Bearer $TOKEN" 'https://pubsub.googleapis.com/v1/projects/<project name>/topics/<topic name>:publish' --data "{\"messages\" : [{\"data\": \"$encoded_message\"}]}"

Cause

To publish a message using REST API or cURL commands, a POST request is sent. In the request, the body includes:

  • KEY: the key of a message attribute
  • VALUE: the value for the key of the message attribute
  • MESSAGE_DATA: a base64-encoded string with the message data

The message must contain either a non-empty data field or at least one attribute, and must be a base64-encoded string.