[Slack] no_text error with Slack integration

Recently I had a task to integrate Slack notification in Github Action workflow. Thanks to the repository slack-github-action, the work becomes much easier.

The Slack integration works well when the payload only contains text and block. However, an error popped up while I changed the payload only with attachments. (We can add color to attachments which will highlight the message in Slack channel)

The error was

axios post failed, double check the payload being sent includes the keys Slack expects\n Error: no_text

The first reaction after seeing the error is that I should add a text into the payload. But it turned out that the Slack message will only show the text content and ignore the attachment.

The solution is when we want to display attachments, we also need to add a basic blocks field instead of text field. Something like

{
	"blocks": [
		{
			"type": "section",
			"text": {
				"type": "mrkdwn",
				"text": "bar"
			}
		}
	],
	"attachments": [
		{
			"color": "#FF0000",
			"blocks": [
				{
					"type": "section",
					"text": {
						"type": "mrkdwn",
						"text": "foo"
					}
				}
			]
		}
	]
}

If putting the above payload into the Slack build kit, it will be a misleading. That’s also why I stuck with the issue.

I would recommend to use chat.postMessage test to debug the payload. It works like a charm.

If with the above payload and env SLACK_WEBHOOK_URL still do not work in Github Action integration, I would suggest to try to add another env SLACK_WEBHOOK_TYPE like below

  env:
    SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
    SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK

The completed Github Action step job looks like:

- name: Send custom JSON data to Slack workflow
  id: slack
  uses: slackapi/slack-github-action@v1.18.0
  with:
    # For posting a rich message using Block Kit
    payload: |
	  {
		"blocks": [
		  {
			"type": "section",
			"text": {
			  "type": "mrkdwn",
			  "text": "bar"
			}
	 	  }
		],
		"attachments": [
		  {
			"color": "#FF0000",
			"blocks": [
			  {
				"type": "section",
				"text": {
				  "type": "mrkdwn",
				  "text": "foo"
			    }
			  }
		    ]
		  }
		]
	  }
  env:
    SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
    SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK