action.yml

name: 'Slack Post Message Action'
description: 'GitHub Action that posts a message to a Slack channel'
inputs:
  token:
    description: "The Slack auth token.  This is only required if environment variable SLACK_BOT_TOKEN is not set."
    required: false
  channel:
    description: "The channel name to post to"
    required: true
  thread_ts:
    description: "The timestamp ID of the parent message to reply to"
    required: false
  text:
    description: "The message text to post"
    required: true
  unfurl_links:
    description: "Whether links in the message should be unfurled"
    type: boolean
    default: true
outputs:
  ts:
    description: "The timestamp ID of the message that was just posted"
    value: ${{steps.slack-post-message.outputs.ts}}
branding:
  icon: 'tag'
  color: 'blue'
runs:
  using: 'composite'
  steps:
    - name: Validate required inputs
      shell: bash
      run: |
        [[ "${{ inputs.channel }}" ]] || { echo "required input 'channel' not specified" ; exit 1; }
        [[ "${{ inputs.text }}" ]] || { echo "required input 'text' not specified" ; exit 1; }
    - name: POST to chat.postMessage API
      id: slack-post-message
      shell: bash
      run: |
        response=$(curl --fail-with-body --silent --show-error \
          --request POST \
          --header "Authorization: Bearer ${{ env.SLACK_BOT_TOKEN || inputs.token }}" \
          --header "Content-Type: application/json; charset=utf-8" \
          --url https://slack.com/api/chat.postMessage \
          --data $'{"channel": "${{ inputs.channel }}", "thread_ts": "${{ inputs.thread_ts }}", "unfurl_links": ${{ inputs.unfurl_links }}, "text": "${{ inputs.text }}"}' \
        )
        echo "Slack message API response:\n$response"
        ts=$(echo "$response" | jq --raw-output '.ts')
        echo "Setting ts output to $ts"
        echo "ts=$ts" >> $GITHUB_OUTPUT